Monthly Archives: July 2015

IC3 Issues Alert on DDoS Extortion Campaigns

Original release date: July 31, 2015

The Internet Crime Complaint Center (IC3) has issued an alert to U.S. businesses about a rise in extortion campaigns. In a typical incident, a business receives an e-mail threatening a Distributed Denial of Service (DDoS) attack to its website unless it pays a ransom. Businesses are warned against communicating directly with attackers and advised to use DDoS mitigation techniques instead.

Users and administrators are encouraged to review the IC3 Alert for details and US-CERT Security Tip ST04-015 for more information on DDoS attacks.

This product is provided subject to this Notification and this Privacy & Use policy.

Innovative Research Helps Emergency Responders Better Communicate While Indoors

July 31, 2015

Diagram of signal strength along a walk route

These diagrams illustrate the results of measurements of signal strength along one walk route. On the left are the results of when signals are being transmitted only by the cell tower located two km from the test site. On the right are the results of when transmissions are supplemented by in-building systems. The benefits of supplemental cells are easily seen by comparing the colors between the left and right diagrams with red showing poor coverage and blue showing good coverage.


Nearly everyone is familiar with the need to step outside a building to complete a wireless call. Modern building materials, such as aluminum, steel and even specially-coated window glass, significantly reduce or even block wireless signals

While it might be inconvenient for your average mobile device user, it could become a matter of life or death for an emergency first responder. Police officers and firefighters cannot stop what they are doing to leave a building in order to communicate during a time of crisis.

As part of its mission to improve communications for public safety, the First Responder Network Authority (FirstNet), an independent entity within the Commerce Department’s National Telecommunications and Information Administration (NTIA),identified improved in-building communications as a critical need for first responders and a required component of the nationwide public safety broadband network it’s been tasked with deploying.

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USAID Provides Additional $65 million for Critical Food Assistance to Syrians

Friday, July 31, 2015

The United States Agency for International Development announced today a $65 million contribution through the UN World Food Program (WFP) to allow the organization to continue to reach an estimated 4 million Syrians inside the country and approximately 1.6 million refugees in Jordan, Lebanon, Turkey, and Egypt. This contribution will help keep WFP programs operating through November and avert an imminent shutdown.

USAID Provides Additional $65 million for Critical Food Assistance to Syrians

Friday, July 31, 2015

The United States Agency for International Development announced today a $65 million contribution through the UN World Food Program (WFP) to allow the organization to continue to reach an estimated 4 million Syrians inside the country and approximately 1.6 million refugees in Jordan, Lebanon, Turkey, and Egypt. This contribution will help keep WFP programs operating through November and avert an imminent shutdown.

Performance of two quantitative PCR methods for microbial source tracking of human sewage and implications for microbial risk assessment in recreational waters

Before new, rapid quantitative PCR (qPCR) methods for recreational water quality assessment and microbial source tracking (MST) can be useful in a regulatory context, an understanding of the ability of the method to detect a DNA target (marker) when the contaminant soure has been diluted in environmental waters is needed. This study determined the limtis of detection and quantification of the human-associated Bacteroides sp. (HF183) and human polyomaviruses (HPyVs) qPCR methods for sewage diluted in buffer and in five ambient, Florida water types (estuarine, marine, tannic, lake and river).

Traffic-Related Air Pollution and Dementia Incidence in Northern Sweden: A Longitudinal Study

Author Affiliations open
1Occupational and Environmental Medicine, Public Health and Clinical Medicine, Umeå University, 901 87 Umeå, Sweden; 2Division of Psychiatry, Department of Clinical Sciences, Umeå University, 901 87 Umeå, Sweden; 3Department of Psychology, Umeå University, 901 87 Umeå, Sweden; 4ARC, Karolinska Institutet, Gävlegatan 16, 113 30 Stockholm, Sweden; 5Umeå Center for Functional Brain Imaging, Umeå University, 901 87 Umeå, Sweden

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  • Background: Exposure to ambient air pollution is suspected to cause cognitive effects, but a prospective cohort is needed to study exposure to air pollution at the home address and the incidence of dementia.

    Objectives: We aimed to assess the association between long-term exposure to traffic-related air pollution and dementia incidence in a major city in northern Sweden.

    Methods: Data on dementia incidence over a 15-year period were obtained from the longitudinal Betula study. Traffic air pollution exposure was assessed with a Land Use Regression Model with a spatial resolution of 50 m x 50 m. Annual mean nitrogen oxide levels at the residential address of the participants at baseline (the start of follow-up) was used as a marker for long-term exposure to air pollution.

    Results: Out of 1806 participants at baseline, 191 were diagnosed with Alzheimer’s disease during follow-up, and 111 were diagnosed with vascular dementia. Participants in the highest exposure group were more likely to be diagnosed with dementia (Alzheimer’s disease or vascular dementia), with a Hazard Ratio (HR) of 1.43 (95% Confidence Interval (CI): 0.998, 2.05 for the highest versus lowest quartile). The estimates were similar for Alzheimer’s disease (HR 1.38) and vascular dementia (HR 1.47). The HR for dementia associated for the third quartile versus the lowest quartile was 1.48 (95% CI: 1.03, 2.11). A sub-analysis that excluded a younger sample that had been re-tested after only 5 years of follow-up suggested stronger associations with exposure than in the full cohort (HR = 1.71; 95% CI: 1.08, 2.73 for the highest versus lowest quartile).

    Conclusions: If the associations we observed are causal, then air pollution from traffic might be an important risk factor for vascular dementia and Alzheimer’s disease.

  • This EHP Advance Publication article has been peer-reviewed, revised, and accepted for publication. EHP Advance Publication articles are completely citable using the DOI number assigned to the article. This document will be replaced with the copyedited and formatted version as soon as it is available. Through the DOI number used in the citation, you will be able to access this document at each stage of the publication process.

    Citation: Oudin A, Forsberg B, Nordin Adolfsson A, Lind N, Modig L, Nordin M, Nordin S, Adolfsson R, Nilsson LG. Traffic-Related Air Pollution and Dementia Incidence in Northern Sweden: A Longitudinal Study. Environ Health Perspect;

    Received: 24 February 2014
    Accepted: 28 July 2015
    Advance Publication: 31 July 2015

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Phase 1 Final Report: Titan Submarine

Abstract: The conceptual design of a submarine for Saturn’s moon Titan was a funded NASA Innovative Advanced Concepts (NIAC) Phase 1 for 2014. The proposal stated the desire to investigate what science a submarine for Titan’s liquid hydrocarbon seas might accomplish and what that submarine might look like. Focusing on a flagship class science system (100 kg), it was found that a submersible platform can accomplish extensive science both above and below the surface of the Kraken Mare. Submerged science …

Pollinator Power: Benefits of an Ecosystem Service

Wendee Nicole has written for Discover, Scientific American, and other publications.

Background image: © lightpoet/Shutterstock

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Citation: Nicole W. 2015. Pollinator power: nutrition security benefits of an ecosystem service. Environ Health Perspect 123:A210–A215;

News Topics: Agriculture and Farming, Diet and Nutrition, Ecology and Wildlife, Food Security, Health Disparities, International Environmental Health

Published: 1 August 2015

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Honey bee covered with pumpkin pollen It’s well known that pollinators affect crop yields and thus market prices. New studies are showing they can affect the nutritional value of foods, too.

© Konrad Wothe/Minden Pictures/Corbis

The world has been abuzz with the dramatic losses of cultivated honey bees due to colony collapse disorder1 as well as declines of native pollinator species across the globe.2,3,4 Scientists have recently begun calculating the extent to which food crops depend on animal pollinators including bees, butterflies, and bats,5 with one study assigning an economic value to the “ecosystem service” provided by pollinators at approximately $167 billion.6 Even more recently, several other new studies have offered evidence that pollinators may also have a beneficial impact on nutrition security—the availability of essential macro- and micronutrients in the human diet.7,8,9

“It’s really well known that pollination changes the yields of crops and the economics of farming,” says Taylor Ricketts, director of the Gund Institute for Ecological Economics at the University of Vermont. It’s becoming better known, he says, that pollination also affects the nutritional value of foods.

Lack of the three macronutrients (fats, protein, and carbohydrates) and numerous essential micronutrients (vitamins and minerals) can cause specific nutrient-deficiency conditions as well as weaken the immune system, stunt development, and greatly increase mortality from other diseases.10,11 Already, about 795 million people worldwide chronically lack adequate calories and protein,12 and 2 billion suffer from micronutrient deficiencies (so-called hidden hunger).11 According to new estimates, a reduction in pollination services could worsen these problems in certain areas already struggling to overcome them.

The Value of Bees

“Ecosystem services” are the seemingly free benefits provided by nature—provisions such as food and drinking water, life-sustaining processes such as water purification by wetland plants and nutrient cycling in soils, and more.13 The authors of the 2005 Millennium Ecosystem Assessment concluded that “any progress achieved in addressing the Millennium Development Goals of poverty and hunger eradication, improved health, and environmental sustainability is unlikely to be sustained if most of the ecosystem services on which humanity relies continue to be degraded.”13

Perhaps counterintuitively in some cases, human alteration of the natural world has coincided with improvements in many global health indices.14 At the same time, negative impacts of ecosystem changes also have become apparent and may become more so in the future.14 For many ecosystem services, there simply is not enough research to fully understand the associated human health impacts.

In one of the first attempts to assign value to pollination services, Alexandra-Maria Klein, an agroecologist at the University of Freiburg, and colleagues reviewed data on the extent to which global crop production relies on pollinators.15 For their analysis, Klein and colleagues selected 124 fruit, vegetable, and seed crops representing the top 99% of global food production, based on data from the Food and Agriculture Organization of the United Nations (FAO).

“We reviewed all the literature for each crop to find out how dependent it is on pollinators,” Klein says. “When you have the production value for each country, and you know how dependent each country is on pollinators, you can calculate what you lose [if pollinators disappear].”

Some degree of animal pollination was found to be necessary for 87 of the crops assessed, irrelevant for 28 others, and of unknown significance for the remaining 9. The crops that make up the greatest volume of global production (mainly cereal grains and sugarcane) rely on wind- and self-pollination. However, just over one-third of overall crop output comes from plants whose fruit, vegetable, or seed production increases with animal pollination.15

Klein followed this work with a study that estimated how pollinator declines might affect human nutrition.7 Her team collected FAO data on production of more than 150 crops gathered over the period 1997–2007, data from the U.S. Department of Agriculture on the macro- and micronutrient content of each crop, and Klein’s earlier data on crop pollinator dependence. Based on these data, they estimated that the majority of several micronutrients—vitamin A, vitamin C, and most carotenes and tocopherols—comes from crops that at least partially depend on animal pollinators (see table). For three micronutrients—vitamin A and the carotenes lycopene and β-cryptoxanthin—more than 40% was attributed solely to animal pollination.7

The team also estimated that 58% of calcium and 29% of iron comes from pollinator-dependent crops, with 9% and 6%, respectively, attributed solely to animal pollination.7 Although calcium and iron are absorbed more efficiently from meat and dairy sources, those foods are not available to all people due to high cost.16,17

Table—Estimated Percentages of Human Nutrients Derived from Pollinator-Independent versus Pollinator-Dependent CropsEstimated Percentages of Human Nutrients Derived from Pollinator-Independent versus Pollinator-Dependent Crops

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The authors concluded that jeopardizing animal-dependent pollination “could have a potentially drastic effect on human nutrition.”7 They acknowledged their findings were limited by the use of data generated in the United States, which may not reflect the nutrient content of the same foods grown in other countries. Barbara Herren, a program specialist in sustainable agriculture for the FAO, adds that the study also does not consider the traditional, local, and indigenous foods that many local communities depend on heavily, including wild foods gathered in the forest.

“Forests provide important dietary diversity to local populations, which depend on nontimber forest products to a much larger degree than is well understood,” Herren says. She points to recent research showing that children living in heavily forested areas of Africa tend to have more nutritious diets than children in areas with less tree cover.18 In addition, she says, “the demand for pollinator-dependent crops is increasing far faster in developing countries—where food and nutrition security are an issue—than in developed countries.”19

Pollination and Nutrition Security

Animal pollinators appear to affect fruit condition, nutrient content, and hence market value in complex ways. One experiment found that bee-pollinated strawberries were redder, heavier, and firmer, and had reduced sugar–acid ratios—all leading to longer shelf life and higher market value—compared with wind- and self-pollinated fruits.20 Other studies have found animal pollination is associated with higher calcium content in apples,21 oil content in rapeseed,22 and sugar content in mandarin oranges.23

Klein and colleagues studied nutrient levels in almonds to determine whether they varied according to how the trees were pollinated.24 The researchers found lower levels of vitamin E but a higher ratio of oleic to linoleic acids in almonds from cross-pollinated trees compared with those from self-pollinated trees. There is evidence that almonds have cardioprotective qualities, which is attributed to their content of oleic acid, a monounsaturated fat.25 The researchers suggest that a higher ratio of oleic to linoleic acid (a polyunsaturated fat) would be desired by consumers looking for health benefits.24

In another study led by Klein, researchers found a strong relationship between pollination method and nut size.In an experimental orchard in the Sacramento Valley, they found that self-pollinated almond trees produced fewer and heavier nuts compared with hand-pollinated ones, with bee-pollinated almonds intermediate in size. The following season, the researchers gathered various sizes of nuts under normal orchard conditions, without experimental intervention, and found no association between nut weight and levels of nutrients per unit weight.26

“We thought maybe [the nutrient differences] are an indirect effect of, and triggered by, the size of the nut,” says Klein. “[But] we didn’t find a difference between size, so it needs to be related to pollinators.”

To take the emerging field a step further, Klein next joined forces with scientists from Stanford University’s Woods Institute for the Environment and the University of Minnesota’s Institute on the Environment through the Natural Capital Project, a group that maps and valuates ecosystem services. They wanted to identify regions where agriculture overall, as well as production of specific nutrients, depends most critically on pollination services. This information could help policy makers prioritize areas for pollinator conservation.

Using spatial data on the yield of 115 food crops around the world plus Klein’s data on crop pollinator dependence, they created maps depicting hot spots where production of heavily pollinator-dependent crops overlaps with deficiency in various micronutrients.8 “We ranked all nations by the extent of their pollination dependence for different micronutrients,” explains lead author Rebecca Chaplin-Kramer, a research associate for the Natural Capital Project. The team focused on three of the micronutrients most important for global health: vitamin A, iron, and folate. Vitamin A deficiency causes 800,000 deaths annually, doubling the mortality of several other diseases and quadrupling the rate of maternal mortality during childbirth.27 Iron deficiency is one of the world’s most common micronutrient deficiencies, causing preventable anemia, susceptibility to infection, and cognitive impairment.28 Folate is important in preventing neural tube defects in the developing fetus.29

Of these three micronutrients, vitamin A was estimated to be the most pollinator-dependent, approaching 50% in Thailand and scattered areas in India, Australia, Mexico, the United States, and other countries. Folate and iron reached a maximum of 12–15% pollinator dependence in parts of Asia, Mexico, Africa, and Brazil.8

The authors also mapped crop pollinator dependence against regions suffering from deficiencies of these essential micronutrients. They found that pollinator-dependent hot spots (where micronutrient production was more than 30% pollinator-dependent for vitamin A and more than 15% pollinator-dependent for iron) were three times more likely to occur in regions identified by the World Health Organization as at risk for vitamin A deficiency and iron-deficiency anemia (data to map folate deficiencies were unavailable).8

Chaplin-Kramer and colleagues also compared demand for the three micronutrients against pollinator-dependent supply. They estimated that pollinator-dependent production provides 13 times more folate and 5 times more vitamin A than the global population needs to meet daily intake recommendations, but only one-third of the iron needed.8

Vendor with pumpkins at a Kolkata marketA Kolkata market vendor opens a pumpkin to check its quality. Pumpkins are a rich source of vitamin A, one of the most highly pollinator-dependent micronutrients. Studies of vitamin A and other important nutrients suggest that pollinator declines would affect different areas in different ways, depending on people’s current nutritional status, whether their usual sources of various nutrients depend on animal pollination, and the availability of nonpollinator-dependent alternative foods.

© Rupak De Chowdhuri/Reuters/Corbis

But this supply–demand mismatch varies regionally, and production of vitamin A may be more limited in certain places. In parts of Southeast Asia, for example, Chaplin-Kramer says pollinator-dependent crops produce only 48% of the local demand. “That means there is already not enough vitamin A being produced [by crops] locally in Southeast Asia for people to reach their nutritional requirements,” Chaplin-Kramer says, “but in Central America [pollinator-dependent crops] produce way more than people could locally consume.” Although global trade can supplement local production, the fact that many of these countries are already malnourished suggests that the excess supply of micronutrients at a global level is irrelevant to the nutritional needs in many places.

Chaplin-Kramer says the findings have implications for both policy and science. “For policy, this demonstrates why the public health community should think more broadly about ecosystem services that may support or lead to further risk in nutritional health,” she says. The study also raises concern over whether continued pollinator losses will increase malnourishment and hidden hunger in regions where these conditions overlap with pollinator dependence.

“We need to be studying pollination in different places, based on where people may need it the most,” says Chaplin-Kramer. Such regions could be targeted for further studies, in contrast to the somewhat random nature of ecosystem services research up to this point.14

Incorporating Diet

The next step is for investigators to examine how people in developing nations actually get their nutrition and whether that might change if pollinators were to disappear. In 2015 Ricketts, along with project lead Alicia Ellis of the University of Vermont and coauthor Samuel Myers of Harvard Medical School, reported findings from one such study.9 The study is one of the first projects of HEAL (Health & Ecosystems: Analysis of Linkages), a consortium of research institutions established to quantify the links between conservation, ecosystems, and human health.

“There’s a lot of talk about this, and some case studies, but we’re trying to systematically relate ecosystem change to health outcomes,” Ricketts says. “The focus of HEAL is to be as quantitative and clear and rigorous as we can.”

The researchers estimated how complete removal of pollinators—an unlikely scenario—would affect access to micronutrients of widespread health importance, namely, vitamin A, folate, and iron (as in the work by Chaplin-Kramer) as well as calcium and zinc. Calcium plays a key role in neuromuscular and skeletal development and function, while zinc is essential in numerous biochemical functions throughout the body.29 They used diet surveys from Uganda, Mozambique, Bangladesh, and Zambia to estimate levels of these micronutrients consumed in local diets. They analyzed nutrient intake for various groups but focused on children aged 1–3 years, because these nutrients are particularly important for growth and development.

Based on their analysis, the researchers predicted that pollinator loss would likely affect human health in highly variable ways, depending on local dietary preferences, the availability of alternatives to pollinator-dependent foods, and the state of people’s current nutrition.9 In Zambia, for instance, almost everybody studied was well nourished in vitamin A, to the point that individuals could absorb a loss of pollinator-dependent sources of this nutrient. In Bangladesh people were malnourished, and they had not been consuming pollinator-dependent foods high in vitamin A, so a reduction in pollinators likely would not change their nutritional status, either.

By contrast, in Uganda and Mozambique, many people were on the threshold of vitamin A deficiency. Ellis says these individuals had been getting much of their vitamin A from pollinator-dependent foods, and in those populations, the loss of pollinators would likely push many people below the nutritional threshold.9

“It’s important to note that this occurred mostly just for vitamin A in our study,” Ellis says. “For other nutrients, such as iron, pollinator declines may make no difference. It depends on if individuals are consuming foods that are highly dependent on pollinators and if they are getting most of their nutrients from those foods.”

The apparently negligible impact of pollinator declines on nutrition in countries where people are already very nutrient deficient could change if public health efforts bring the population to better health. “If other factors improved overall nutrition so that populations weren’t so malnourished, then the change from pollination might make a difference,” says Ricketts. Similarly, if the diets of well-nourished populations were to deteriorate for other reasons, then pollination changes might begin to matter for them as well.

Ricketts and his colleagues are continuing studies on how pollination affects human health, incorporating behavioral and dietary choices. For example, if pollinator populations were to decline, people who get their vitamin A from squash, which depends on insect pollination, may be able to switch to vitamin A–rich sweet potatoes, which have similar texture but don’t depend on insects. But would they?

“You can logic your way through it,” Ricketts says, “but we wouldn’t have predicted what we found based on just looking at these big global databases of food. … We’re finding that understanding human behavior is often really critical in figuring out whether nature helps human health.”

“The Ellis paper is a great example of what we need to do more of to understand the real vulnerability in the system,” says Chaplin-Kramer, who has begun a major project modeling how local nutrition might be affected by different agricultural interventions in Ghana and Burkina Faso. “The point is to connect more to the demand for the pollination service based on actual diet, rather than just the supply of the service,” she says.

Herren believes this emerging line of research is quite important. “We have spent far too long looking solely at calories as the answer to food security,” she says, “and not nutrition security.”


1. vanEngelsdorp D, et al. Colony collapse disorder: a descriptive study. PLoS ONE 4(8):e6481 (2009); doi: 10.1371/journal.pone.0006481.

2. Potts SG, et al. Global pollinator declines: trends, impacts and drivers. Trends Ecol Evol 25(6):345–353 (2010); doi: 10.1016/j.tree.2010.01.007.

3. Burkle LA, et al. Plant-pollinator interactions over 120 years: loss of species, co-occurrence, and function. Science 339(6127):1611–1615 (2013); doi: 10.1126/science.1232728.

4. Vanbergen AJ, et al. Threats to an ecosystem service: pressures on pollinators. Frontiers Ecol Environ 11(5):251–259 (2013); doi: 10.1890/120126.

5. Losey JE, Vaughan M. The economic value of ecological services provided by insects. Biosci 56(4):311–323 (2006); doi: 10.1641/0006-3568(2006)56[311:TEVOES]2.0​.CO;2.

6. Gallai N, et al. Economic valuation of the vulnerability of world agriculture confronted with pollinator decline. Ecol Econ 68(3):810–821 (2009); doi: 10.1016/j.ecolecon.2008.06.014.

7. Eilers EJ, et al. Contribution of pollinator-mediated crops to nutrients in the human food supply. PLoS ONE 6(6):e21363 (2011); doi: 10.1371/journal.pone.0021363.

8. Chaplin-Kramer R, et al. Global malnutrition overlaps with pollinator-dependent micronutrient production. Proc Biol Sci 281(1794):20141799 (2014); doi: 10.1098/rspb.2014.1799.

9. Ellis AM, et al. Do pollinators contribute to nutritional health? PLoS ONE 10(1):e114805 (2015); doi: 10.1371/journal.pone.0114805.

10. Tulchinsky TH. Micronutrient deficiency conditions: global health issues. Public Health Rev 32(1):243–255 (2010);

11. IFPRI. 2014 Global Hunger Index. Washington,DC: International Food Policy Research Institute. Available: [accessed 24 June 2015].

12. FAO. The State of Food Insecurity in the World 2015—Key Messages [website]. Rome, Italy:United Nations Food and Agriculture Organization. Available:​n/ [accessed 24 June 2015].

13. Hassan R, et al. Ecosystems and Human Well-Being: Current State and Trends, Volume 1. Millennium Ecosystem Assessment. Washington,DC:Island Press (2005).

14. Myers SS, et al. Human health impacts of ecosystem alteration. Proc Natl Acad Sci USA 110(47):18753–18760 (2013); doi: 10.1073/pnas.1218656110.

15. Klein AM, et al. Importance of pollinators in changing landscapes for world crops. Proc Biol Sci 274(1608):303–313 (2007); doi: 10.1098/rspb.2006.3721.

16. Weaver CM, Plawecki KL. Dietary calcium: adequacy of a vegetarian diet. Am J Clin Nutr 59(5 suppl):1238S–1241S (1994); PMID: [Pubmed].

17. Trumbo P, et al. Dietary reference intakes: vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. J Am Diet Assoc 101(3):294–301 (2001); doi: 10.1016/S0002-8223(01)00078-5.

18. Ickowitz A, et al. Dietary quality and tree cover in Africa. Glob Environ Change 24:287–294 (2014); doi: 10.1016/j.gloenvcha.2013.12.001.

19. Aizen MA, et al. Long-term global trends in crop yield and production reveal no current pollination shortage but increasing pollinator dependency. Curr Biol 18(20):1572–1575 (2008); doi: 10.1016/j.cub.2008.08.066.

20. Klatt BK, et al. Bee pollination improves crop quality, shelf life and commercial value. Proc Biol Sci 281(1775):20132440 (2013); doi: 10.1098/rspb.2013.2440.

21. Garratt MPD, et al. Avoiding a bad apple: insect pollination enhances fruit quality and economic value. Agric Ecosyst Environ 184:34–40 (2014); doi: 10.1016/j.agee.2013.10.032.

22. Bommarco R, et al. Insect pollination enhances seed yield, quality, and market value in oilseed rape. Oecologia 169(4):1025–1032 (2012); doi: 10.1007/s00442-012-2271-6.

23. Wallace HM, Lee LS. Pollen source, fruit set and xenia in mandarins. J Hortic Sci Biotechnol 74(1):82–86 (1999).

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25. Jalali-Khanabadi BA, et al. Effects of almond dietary supplementation on coronary heart disease lipid risk factors and serum lipid oxidation parameters in men with mild hyperlipidemia. J Altern Complement Med 16(12):1279–1283 (2010); doi: 10.1089/acm.2009.0693.

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Delta Subsidence: An Imminent Threat to Coastal Populations

The Ganges–Brahmaputra Delta is one of several delta regions around the world that is sinking as the weight of its cities and industries combines with overextraction of natural resources from soft sedimentary deposits.
© Planet Observer/Getty Images

Along the Ganges–Brahmaputra Delta, earthen and concrete embankments surround low-lying agricultural areas known as polders. These embankments protect the land within, but they also block the deposition of new sediments during the rainy season. Consequently, the polders subside. When Cyclone Aila hit Bangladesh in May 2009, floodwaters crested over the embankments, turning sections of the polders to lakes. These residents are hauling mud to help build up an embankment after the cyclone, which did have one benefit—it left the area inundated with a long-overdue deposition of fresh silt, in some areas reaching 70 cm thick.
© Espen Rasmussen/Panos Pictures

Several interconnected factors contribute to land subsidence in delta regions. Delta plains were built up from thousands of years’ worth of silt deposition, producing richly fertile lands. Populations are skyrocketing in these agricultural areas, with many serious repercussions for the land. Construction of levees, dams, and embankments blocks the natural deposition of fresh silt, depriving the land of replenishment and creating bowls where floodwaters pool with nowhere to go. Extraction of groundwater and the fossil fuels that often underlie deltas allows the land to deflate. The sheer weight of growing urban and industrial infrastructure further compresses the land, and impervious surfaces—roofs and pavements—prevent the replenishment of groundwater. Saltwater intrusion, which occurs naturally in most coastal areas, is exacerbated as the depletion of groundwater reduces water pressure. Growing populations and water-intensive industries such as shrimp farming place a heavy demand on groundwater resources. Wells must be drilled deeper, and the water coming up is saltier, as ancient seawater is pulled up by excessive pumping.
© Daniel Gallant; adapted from materials provided by Deltares Research Institute

In a study of subsidence in the Mekong Delta over the period 1995–2010, Laura Erban and colleagues used well-monitoring data to estimate annual average rates of aquifer drawdown (A) and associated compaction-based subsidence at the well locations (B). These estimates corresponded closely to subsidence rates estimated from satellite imagery (C). Overall, the Mekong Delta is estimated to be subsiding at a rate of 1.6 cm per year.
Source: Erban et al. (2014)9

Data from Deltares compare historical subsidence rates from coastal areas around the world with estimates of absolute global sea-level rise. These are average rates; subsidence can differ considerably within a given city, depending on groundwater levels and subsurface characteristics. In some cities subsidence is accelerating as a result of economic growth. Tokyo, however, has shown that locally based mitigation measures can help stem the trend.
© Erkens et al. (2015)21

Background image: © OttoKrause/iStockphoto

Charles W. Schmidt, MS, an award-winning science writer from Portland, ME, has written for Discover Magazine, Science, and Nature Medicine.

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Citation: Schmidt CW. 2015. Delta subsidence: an imminent threat to coastal populations. Environ Health Perspect 123:A204–A209;

News Topics: Aquaculture, Climate Change, Drinking Water Quality, Infrastructure, International Environmental Health, Land Use, Marine and Coastal Science, Natural Resources Urban Issues,

Published: 1 August 2015

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Sea-level rise from a warming climate threatens to inundate coastlines around the world.1 But some of the world’s most vulnerable coasts—those fringing flat delta plains, mainly in Southeast Asia—face the far more immediate threat of sinking land.2 Induced mainly by human activities on a local rather than global scale, this phenomenon, known as land subsidence, can outpace sea-level rise substantially. Indonesia’s biggest city, Jakarta, is sinking at an average rate of 5–10 cm per year,3 much faster than the global rate of sea-level rise, which clocks in at 3.2 mm per year, according to the recent estimates.1 Should subsidence in Jakarta continue unabated, the city could sink up to 6 m by the end of the century, according to JanJaap Brinkman, a water management specialist with Deltares Research Institute in Delft, the Netherlands.

Roughly half a billion people live in delta regions threatened by subsidence, and concerns for their well-being are mounting.4 For instance, in 2007 Jakarta experienced catastrophic flooding—portions of the city were inundated for weeks, 200,000 people were displaced, and roughly 1,400 were hospitalized for waterborne diarrheal diseases and by dengue fever, which is carried by mosquitoes that thrive in standing water.5 Marc Bierkens, a professor of hydrology at Utrecht University, the Netherlands, says Jakarta sits in a subsiding bowl where “floodwaters pool up with nowhere to go.”

Apart from the increased risk of floods and associated diseases, experts consulted for this article say subsidence threatens health in other ways. It accelerates the contamination of freshwater resources with saltwater, making them unsuitable for drinking and agriculture. Subsidence stresses gas lines, sewage pipes, and other infrastructure, which can crack as the land buckles and heaves, increasing the risk of explosions and contamination of surface and groundwater. Finally, the stress of the threat to drinking water supplies, homes, and livelihoods can adversely affect people’s sense of well-being.

Subsidence has been slowed in cities such as Tokyo6 and Bangkok,7 and the lessons learned there are galvanizing efforts to tackle the problem elsewhere. It’s also a multifaceted problem, and researchers are investigating site-specific causes of subsidence in a search for targeted solutions. But in many deltas, time is running out, warns Gilles Erkens, a senior researcher at Deltares Research Institute and Utrecht University. “In many cases, we simply don’t have ten more years to wait for more data,” he says.

Deltaic Processes

The world’s deltas were built up mostly by aggradation, or the deposition of fertile river sediments over thousands of years.8 As such, they comprise important food-producing areas that attract large populations. The Mekong Delta, for instance, which is now subsiding at an average rate of 1.6 cm per year,9 is one of the world’s major rice exporters10 and home to more than 20 million people.9 Unlike rocky continental coasts, delta plains tend to be soft and easily compressed. They’re often propped up by underlying oil, gas, or fresh groundwater that flows through the pores of sediment deposits. As those resources are extracted, the sediments compress, and the land shrinks like a dried sponge.

Some sediments, especially those rich in organic matter, such as peat, also oxidize when they dry. Oxygen binds with carbon in the soils, creating carbon dioxide that is released to the atmosphere. Deprived of the carbon lost to this reaction, the soils lose mass and compact.11

According to James Syvitski, an oceanographer and professor at the University of Colorado, Boulder, a delta’s elevation above sea level depends on four interrelated factors: the ocean’s global volume, aggradation, sediment compaction, and vertical movements resulting from plate tectonics and other geophysical processes. He says the ocean’s overall volume, and thus its elevation in relation to land surfaces, is increasing partly as a result of human-induced climate change. Warmer water expands, and seas are rising as vast ice sheets near the poles melt away.1

Aggradation has been severely limited by dams, levees, and embankments that trap silt and starve deltas of new sediments. And sediment compaction is increasing both with the extraction of groundwater and hydrocarbons, and with the growing extent of urban infrastructure. The weight of urban infrastructure compacts underlying soils, and its nonporous roofs and pavements prevent surface waters from percolating back down into the earth and recharging groundwater.

In 2009 Syvitski reported that increasing compaction and reduced aggradation had put many of the world’s deltas in danger, more than half of them in Asia. “All trends point to ever-increasing areas of deltas sinking below sea level,” he wrote. “And it remains alarming how often deltas flood, whether from land or from sea, and the trends seem to be worsening.”4

The biggest threat, Syvitski says, is that a delta will tip toward a collapsed state, meaning that it likely will never be restored to anything remotely similar to its natural condition. Pakistan’s Indus River Delta has already collapsed, he reported in 2013.2 Overexploited for agriculture, the Indus River runs dry at its discharge into the Arabian Sea nearly 140 days of the year and could soon run dry nearly year-round. The delta has shrunk to a tenth of its original size, and intruding seawater has contaminated adjacent groundwater reservoirs, submerged coastal villages, and displaced hundreds of thousands of people.

By contrast, another sinking delta in Asia—the Ganges–Brahmaputra, with a population of approximately 170 million people—hasn’t collapsed yet, but it’s getting close. Sediment delivery to the Ganges–Brahmaputra Delta has been heavily impacted by dams and levees. The worse subsidence has occurred among the jigsaw puzzle of river islands in southwest Bangladesh that together measure tens of thousands of square kilometers.12

To hold back the sea and create more land for agriculture, concrete and earthen embankments were built around low-lying plots of land known as polders during the 1960s. The embankments blocked replenishment of the delta with river sediment carried downstream by the annual monsoon floods, and the islands have since lost 1–1.5 m of elevation.13 According to Kimberly Rogers, a research associate at the University of Colorado, Boulder, they’re now far more vulnerable to storm surges that can damage or breach the walls around the polders, effectively creating lakes that can last for years. In 2009 Cyclone Aila struck southwest Bangladesh, and the resultant flooding displaced more than 100,000 people in the worst-hit areas.14 But the storm also inundated the islands with fresh silt, in some places reaching a depth of 70 cm,15 reflecting the system’s ability to replenish itself if allowed.

Drivers of Subsidence

Scientists are improving their understanding of what drives subsidence in the Ganges–Brahmaputra Delta, yet much remains unknown. Satellite coverage over this delta was sparse until a few years ago, and there’s a chronic shortage of monitoring data.

That’s also true of Vietnam’s Mekong Delta, where Dutch and Vietnamese scientists are now collaborating on a five-year research project that could reveal opportunities to slow subsidence and limit its effects. Dubbed the Rise and Fall project, it was launched in March 2015 with $1 million in funding primarily from the Netherlands Science Founation.

Project scientists are collecting data and sampling the subsurface geology of the Mekong Delta. They plan to create a sophisticated hydrogeological model that predicts subsidence and saltwater intrusion rates over varying scenarios of population and economic growth. “What we’re ultimately trying to do is develop more sustainable management strategies for the Mekong Delta,” says team leader Esther Stouthamer, an earth scientist and associate professor at Utrecht University.

Overexploited by domestic, industrial, and agricultural users, groundwater tables in Vietnam are falling dramatically. In the past, rice farmers relied on networks of freshwater canals for irrigation and domestic uses. These canals were the route by which new sediment was added to the land during the rainy season. But after Vietnam’s communist government opened the economy in 1986 and encouraged rice exports, villagers used their growing wealth to drill private wells, which strained groundwater resources and disrupted a centuries-old system that favored resedimentation. More than a million wells have since been drilled into the Mekong Delta, and subsidence has been accelerating ever since.9

Meanwhile, rice farming has given way to a more lucrative shrimp industry with an insatiable need for fresh groundwater. Laura Erban, a hydrogeologist at Stanford University, explains that shrimp are raised in brackish ponds, but their yields decline if the water gets too salty. So shrimp farmers use groundwater to continually dilute the ponds, which now stretch, one after the other, along coastlines stripped of the mangrove forests that once protected these shores.

Overexploitation is especially a problem in Cà Mau province, on the Delta’s southern tip.9 More than 100,000 wells have been drilled in the province, shrimp farms abound, and the urban population soared from approximately 66 million in 1990 to 90 million in 2013.16 Subsidence in Cà Mau now averages about 3 cm per year, according to a recent analysis by Erban.9

Meanwhile, groundwater pumps are drilling deeper to reach groundwater, and the water that comes up is saltier. That’s also the case along a heavily populated coastal stretch from Cà Mau to Ho Chi Minh City, about 250 km to the north.9 At the Rise and Fall kickoff meeting on 11 March 2015, a water official from Sóc Trăng province, located between Cà Mau and Ho Chi Minh City, reported that salt levels in groundwater in the province were climbing steadily and had reached as high as 4.2 g/L in some wells sampled in 2013. Water containing more than 2–3 g/L of total dissolved solids is generally considered too salty to drink.17

Gualbert Oude Essink, a hydrogeologist at Deltares Research Institute and associate professor at Utrecht University, says saltwater is penetrating farther into the Mekong Delta every year. Being heavier than freshwater, saltwater migrates down through sediments into shallow aquifers from above, he explains. That makes the groundwater increasingly nonpotable. Furthermore, he says, salt ions also react chemically with the sediments, making the ground more prone to oxidation, compaction, and therefore subsidence.

Where there’s a lot of pumping, saltwater can also contaminate fresh groundwater resources from below. Oude Essink explains that fresh groundwater typically resides over more ancient seawater that can be pulled upward by excessive pumping. That process usually takes several years. Yet it can take much longer—decades or more—for the salt levels in contaminated freshwater aquifers to decline once extraction has ceased. That’s because compared with the pumping pressure that draws saltwater up, the gravity that pulls it down is a much weaker force, Oude Essink explains.

A newer concern is that excessive pumping also could introduce arsenic into deep groundwater aquifers that would otherwise be free of the contaminant. Erban and colleagues reviewed arsenic measurements from nearly 43,000 deep wells in the Mekong Delta and found that many of them had become contaminated over time. It appears that excessive pumping could force that arsenic into deep groundwater, threatening the health of those who drink it. Erban speculates that pumping-related subsidence effectively squeezes dissolved arsenic from the clay layers as they compact. These findings contradict earlier assumptions that intervening clay layers protect deep aquifers from shallow arsenic contamination.18

Tackling the Problem

Japan was one of the first countries to show that shifting away from groundwater use can slow subsidence. Subsidence was detected in Tokyo in the early twentieth century, when city officials were monitoring a pumping-induced drop in the local water table. After World War II, groundwater pumping fell off in the heavily damaged city, the water table rose, and subsidence slowed noticeably.6

As Japan’s economy came back to life, groundwater use picked back up, and by 1968 subsidence in some places peaked at 24 cm per year. The Tokyo Metropolitan Government imposed strict regulations on groundwater consumption, and by 2006 subsidence once again had been reduced, reaching about 1 cm per year in areas that previously had been most affected.6 Oude Essink points out that, while this is a dramatic reduction, it still adds up to a meter of subsidence per century.

Bangkok, Thailand, is another success story. Located in the Chao Phraya River Delta, Bangkok was subsiding by as much as 12 cm per year in the 1980s, when groundwater consumption averaged an estimated 1.2 million m3 per day.7 In 1985, with foundering infrastructure, worsening floods, and skyrocketing costs of pumping storm water into the sea, the government raised groundwater taxes sharply, according to Oranuj Lorphensri, director of the Bureau of Groundwater Control in Bangkok. She says groundwater use has since fallen to 0.8 million m3 per day, and subsidence has been reduced to 1–2 cm per year. To make up for groundwater declines, Lorphensri says, Bangkok shifted to using treated surface water from the nearby Chao Phraya River.

Jakarta, which Deltares’ Brinkman says currently pumps an estimated 180–250 million m3 of groundwater per day (including both licensed and nonlicensed groundwater uses), now faces similar prospects. According to Brinkman, the extraction of deep groundwater under Jakarta has accelerated the compaction of overlying clays. The trend is especially pronounced in northwest Jakarta, where subsidence can reach 20 cm per year.3 Brinkman adds that shallow groundwater contaminated with surface pollution can remain trapped under the city for weeks or months during the dry season, when there is no water to flush the low-lying northern parts of the system.

Erkens says the city’s high-rise buildings, hotels, and industry prefer deep groundwater over treated surface water because the quality of the latter is poor by comparison. “It’s a chicken-and-the-egg problem,” he says. “Companies that supply treated surface water complain they have few users and not enough money for upgrades, but then they can’t grow the customer base because the water quality is unreliable.”

But Brinkman emphasizes that Jakarta has few alternatives. If city officials cannot curtail deep groundwater use substantially within the next five years, he says, by 2030 either the population of northwest Jakarta—currently 4 million people and counting—will have to be evacuated to higher ground, or the Bay of Jakarta must be closed by a giant seawall planned by the government.19 “That’s the reality,” Brinkman says.

Meanwhile, officials in Vietnam remain hopeful that research will point to remedies other than limits on freely available groundwater, which is an engine for economic growth. At the Rise and Fall project’s kickoff meeting, some officials were skeptical that groundwater exploitation is what drives subsidence in the Mekong Delta. “People just say ‘groundwater is causing this,’ but we have no data to prove it,” says Bui Tran Vuong, deputy director general of the Division of Water Resources, Planning, and Investigation for South Vietnam.

Stouthamer insists accumulated evidence from around the world points to groundwater overuse as the main culprit. But she agrees that other factors are likely involved, such as the compaction that results when urban infrastructure is built on poorly supported clay or peat sediments. Changing codes so that infrastructure is engineered for better support from below and built using lighter-weight materials could help with subsidence, she says.

Another possible option is to pump water back underground to counteract subsidence. Known as managed aquifer recharge (MAR),20,21 this can be a controversial proposition. Syvitski warns it could have unpredictable consequences. “Even if you could do it, roads and buildings would buckle as the land rises.” Oude Essink disagrees, saying that MAR projects around the world show it to be a potentially worthy approach for reducing the groundwater declines, and therefore subsidence.

Diking huge stretches of delta shoreline would likely be problematic, as indicated by Bangladesh’s experience with polders. Dikes allow the land they protect to subside, Syvitski says, and they must be routinely elevated to keep pace with steadily rising seas.

These examples illustrate the challenges of addressing a creeping problem that’s barely perceptible to the population in real time. It’s hard to notice a drop in land elevation of a few centimeters per year until its consequences materialize in a catastrophic event, such as a devastating flood. Yet over time, these declines become significant. Where sea level is rising by an estimated 32 cm per century,1 land subsiding by 10 cm per year will sink that far in just over three years. Although sea-level rise gets most of the attention, for vast numbers of people worldwide, subsidence is by far the more immediate problem. But because subsidence is a local problem, local solutions are needed to keep it bay.


1. IPCC. Climate Change 2013: The Physical Science Basis. Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Stocker TF, et al., eds.). Cambridge, United Kingdom and New York, NY:Cambridge University Press (2014). Available: [accessed 23 June 2015].

2. Renaude FG, et al. Tipping from the Holocene to the Anthropocene: how threatened are major world deltas? Curr Opin Environ Sustain 5(6):644–654 (2013); doi: 10.1016/j.cosust.2013.11.007.

3. Abidin HZ, et al. Environmental Impacts of Land Subsidence in Urban Areas of Indonesia [report]. Presented at: FIG Working Week 2015: From the Wisdom of the Ages to the Challenges of the Modern World, Sofia, Bulgaria, 17–21 May 2015. Available:​s/fig_proceedings/fig2015/papers/ts04i/T​S04I_abidin_andreas_et_al_7568.pdf [accessed 23 June 2015].

4. Syvitski JPM, et al. Sinking deltas due to human activities. Nat Geosci 2(10):681–686 (2009); doi: 10.1038/ngeo629.

5. HOPE Worldwide Indonesia. Jakarta Flood Disaster Relief—Progress Report [press release]. Jakarta, Indonesia:HOPE Worldwide Indonesia (7 March 2007). Available:​9733.html [accessed 23 June 2015].

6. Sato XC, et al. Land subsidence and groundwater management in Tokyo. Internat Rev Environ Strat 6(2):403 (2006)

7. Phien-wej N, et al. Land subsidence in Bangkok, Thailand. Engineer Geol 82(4):187–201 (2006); doi: 10.1016/j.enggeo.2005.10.004.

8. Stanley DJ, Warne AG. Worldwide initiation of Holocene marine deltas by deceleration of sea-level rise. Science 265(5169):228–231 (1994); doi: 10.1126/science.265.5169.228.

9. Erban LE, et al. Groundwater extraction, land subsidence, and sea-level rise in the Mekong Delta, Vietnam. Environ Res Lett 9(8):084010 (2014); doi: 10.1088/1748-9326/9/8/084010.

10. Workman D. Rice Exports by Country [website]. World’s Top Exports (2015). Available:​orts-country/3311 [accessed 23 June 2015].

11. Gambolati G, et al. Peat land oxidation enhances subsidence in the Venice watershed. EOS 86(23):217–220 (2005); doi: 10.1029/2005EO230001.

12. Higgins SA, et al. InSAR measurements of compaction and subsidence in the Ganges–Brahmaputra Delta, Bangladesh. J Geophys Res 119(8):1768–1781 (2014); doi: 10.1002/2014JF003117.

13. Brown S, Nicholls RJ. Subsidence and human influences in mega deltas: the case of the Ganges–Brahmaputra–Meghna. Sci Total Environ 527–528:362–374 (2015); doi: 10.1016/j.scitotenv.2015.04.124.

14. Mehedi H. Climate-Induced Displacement: Case Study of Cyclone Aila in the Southwest Coastal Region of Bangladesh. Boyra, Khulna Division, Bangladesh:Coastal Livelihood and Environmental Action Network (2010). Available:​te-Induced-Displacement-Case-Study-of-Cy​clone-Aila-in-the-Southwest-Coastal-Regi​on-of-Bangladesh#scribd [accessed 23 June 2015].

15. Auerbach LW, et al. Flood risk of natural and embanked landscapes on the Ganges–Brahmaputra tidal delta plain. Nat Clim Change 5(2):153–157 (2015); doi: 10.1038/nclimate2472.

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18. Erban LE, et al. Release of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidence. Proc Natl Acad Sci USA 110(34):13751–13756 (2013); doi: 10.1073/pnas.1300503110.

19. Stedman L. Plan progress for the Great Jakarta Sea Wall. Water21 Magazine (February 2014). Available:​ruary-2014/plan-progress-great-jakarta-s​ea-wall [accessed 23 June 2015].

20. Dillon P.. Future management of aquifer recharge. Hydrogeology J 13(1):313–316 (2005); doi: 10.1007/s10040-004-0413-6.

21. Sanchez F, et al. SWIBANGLA: Managing Salt Water Intrusion Impacts in Bangladesh. Delft, the Netherlands:Deltares (2015). Available:​RESHSALT/SWIBANGLA+Managing+saltwater+in​trusion+impacts+in+Bangladesh [accessed 23 June 2015].

22. Erkens G, et al. Sinking Coastal Cities [abstract]. Submitted to: Ninth International Symposium on Land Subsidence, 15–19 November 2015, Nagoya, Japan.

How Good Is Good Enough? Cookstove Replacement Scenarios to Reach Indoor Air Goals

Julia R. Barrett, MS, ELS, a Madison, WI–based science writer and editor, is a member of the National Association of Science Writers and the Board of Editors in the Life Sciences.

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Citation: Barrett JR. 2015. How good is good enough? Cookstove replacement scenarios to reach indoor air goals. Environ Health Perspect 123:A216;

News Topics: Air Pollution, Combustion Emissions, Indoor Air Quality, International Environmental Health, Particulate Matter (PM), Respiratory Health

Published: 1 August 2015

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Air pollutants emitted by low-performing (i.e., high-polluting) cookstoves are estimated to cause 4 million premature deaths annually worldwide.1 High-performing cookstoves may mitigate health problems, but programs to disseminate these cleaner units have been plagued by incomplete adoption and often result in scenarios where both the old and new stoves are used simultaneously—so-called stove stacking. A new study in this issue of EHP examines just how much compliance is required in order to realize the benefits of cleaner technologies.2

The percentage of the global population using low-performing cookstoves dropped between 1980 and 2010, but absolute numbers have remained stable because of population growth.3 Approximately 3 billion people in the developing world prepare food over traditional cookstoves fueled by wood, coal, crop residues, or animal dung, which emit fine particulate matter (PM2.5), carbon monoxide (CO), and other pollutants during use.3 Exposure to these emissions contributes to the development of respiratory and heart diseases, low birth weight, and premature death.4 Traditional stoves are also estimated to produce 25% of the world’s output of black carbon, a potent climate forcer.5

Zambian women learning about improved cookstovesZambian women receive a demonstration of a high-performing cookstove being distributed by the Clean Development Mechanism, which promotes reduction of greenhouse gas emissions in developing countries.

© Per-Anders Pettersson/Getty Images

Despite the benefits of cleaner cookstoves, users may prefer older cooking technologies due to fuel availability, ease of use, and compatibility with local cooking demands—for instance, how well they work at preparing specific dishes.6 “There are lots of stories of where these alternate technologies work well for some tasks, but work really badly for others,” says Andrew Grieshop, an assistant professor in the Department of Civil, Construction, and Environmental Engineering at North Carolina State University, who was not involved in the study. “They’re not as universal as people would like them to be.”

To reap the benefits of cleaner cookstoves, though, not only is their sustained use required,6 they also need to displace low-performing units.2 “Ideally, of course, we’d love to have one hundred percent displacement with super-clean technologies, but we know it’s a transition that’s going to take quite a bit of time in some places,” says study coauthor Michael Johnson, a senior scientist at the Berkeley Air Monitoring Group.

The modeling framework presented by the authors includes predicted concentrations of PM2.5 and CO in kitchens based on the emissions performance of the stove(s) in use, ventilation room volume, and time spent cooking. The concentrations were predicted for scenarios ranging from 0% to 100% displacement of old stoves with new units, and a full day of cooking was assumed to be three 1-hour sessions.2

According to model estimates, a traditional three-stone fire—essentially, a pot balanced over an open fire on a trio of stones—could be used for only approximately 10 minutes per day before exceeding an interim PM2.5 limit of 35 µg/m3 set by the World Health Organization (WHO), whereas a traditional charcoal stove could be used for up to 25 minutes. Furthermore, a three-stone fire and a charcoal stove would reach CO limits within 75 minutes and 50 minutes, respectively. The only scenario that met WHO limits required the highest-performing cookstoves to nearly completely displace traditional stoves. Nevertheless, the model estimated that more modest reductions in use of traditional stoves could be expected to reduce the risk of adverse health outcomes.2

“[This model] is extremely useful in highlighting a key issue that I think the stove community is really only starting to grapple with now,” says Hisham Zerriffi, an assistant professor at the Liu Institute for Global Issues at the University of British Columbia. “This issue is less about the adoption of new stoves and more about the ‘disadoption’ of old stoves. What this study provides is further evidence of the need to think seriously about the factors that drive the way technologies get used in a household and which mix of technologies get used.” Zerriffi was not involved in the study.

The model is limited by factors such as uncertainty about real-world emissions, variability in ventilation, and assumptions about cooking times.2 “As a planning tool, however, it’s useful,” Grieshop says. “It makes the point that you have to be very aware that if you don’t completely replace the current technology, then you are not going to get the benefits—in some cases, you may not even get close.”

Johnson also notes that good field-testing is essential; the model and estimated impacts provide guidance, not absolutes. “Whatever groups ultimately choose to go forward with—in terms of technology, behavior change programs, finding financing mechanisms, and whatever will help implement their program—certainly verification on the ground is going to be critical to make sure that the intended impact is happening.”


1. Lim SS, et al. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet 380(9859):2224–2260 (2012); doi: 10.1016/S0140-6736(12)61766-8.

2. Johnson MA, Chiang RA. Quantitative guidance for stove usage and performance to achieve health and environmental targets. Environ Health Perspect 123(8):820–826 (2015); doi: 10.1289/ehp.1408681.

3. Bonjour S, et al. Solid fuel use for household cooking: country and regional estimates for 1980–2010. Environ Health Perspect 121(7):784–790 (2013); doi: 10.1289/ehp.1205987.

4. Cordes L. Igniting Change: A Strategy for Universal Adoption of Clean Cookstoves and Fuels. Washington, DC:Global Alliance for Clean Cookstoves (November 2011). Available:​ESOURCE/file/000/000/272-1.pdf [accessed 13 July 2015].

5. Bond TC, et al. Bounding the role of black carbon in the climate system: a scientific assessment. J Geophys Res Atmos 118(11):5380–5552 (2013); doi: 10.1002/jgrd.50171.

6. Ruiz-Mercado I, et al. Adoption and sustained use of improved cookstoves. Energy Policy 39(12):7557–7566 (2011); doi: 10.1016/j.enpol.2011.03.028.

Plumbing Pathogens: A Fixture in Hospitals and Homes

Carol Potera, based in Montana, also writes for Microbe, Genetic Engineering News, and the American Journal of Nursing.

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Citation: Potera C. 2015. Plumbing pathogens: a fixture in hospitals and homes. Environ Health Perspect 123:A217;

News Topics: Drinking Water Quality, Built Environment, Infectious Disease, Microbial Agents

Published: 1 August 2015

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Related EHP Article

Epidemiology and Ecology of Opportunistic Premise Plumbing Pathogens: Legionella pneumophila, Mycobacterium avium, and Pseudomonas aeruginosa

Joseph O. Falkinham III, Elizabeth D. Hilborn, Matthew J. Arduino, Amy Pruden, and Marc A. Edwards

Practicing good hygiene is supposed to make you healthier, not sicker. However, a growing body of research shows that certain bacteria can thrive in household and hospital plumbing systems and may cause life-threatening infections among susceptible individuals after inhalation or ingestion. In this issue of EHP, Joseph Falkinham of Virginia Polytechnic Institute and State University in Blacksburg and colleagues review the epidemiology and ecology of what are known as opportunistic premise plumbing pathogens (OPPPs).1

“Premise plumbing” refers to the pipes and fixtures within a building that transport water to taps after it is delivered by the utility. OPPPs are so ubiquitous in plumbing systems that many experts now consider them normal inhabitants, rather than contaminants, of drinking water distribution systems. The new review focuses on Legionella pneumophila, Mycobacterium avium, and Pseudomonas aeruginosa, three of the best studied OPPPs.

Micrograph of Sharklet materialSharklet’s micropatterned surface deters the formation of biofilms without the use of chemical antimicrobials. Materials such as this may be one way to keep OPPPs from colonizing plumbing systems.

Source: Mann et al. (2014)7

OPPPs are estimated to cause nearly 30,000 cases of human disease yearly at a cost of $850 million.2 Elena Naumova, director of the Tufts University Initiative for the Forecasting and Modeling of Infectious Disease, says this is likely a substantial underestimate, because these pathogens are rarely tested for in clinical settings, even in severely ill patients.

In addition, Naumova says, the clinical manifestations of OPPP-related diseases often include common symptoms such as high fever, chills, and fatigue, making it difficult to distinguish them from other pneumonic infections. “The need for identification and reporting these infections is an important conclusion of the review,” she says. Naumova was not involved with the review.

Other waterborne pathogens, such as poliovirus and Salmonella, are more readily killed by disinfectants, and they generally do not reproduce in plumbing systems. In contrast, OPPPs attach to pipe surfaces and grow as recalcitrant biofilms in low-nutrient, stagnant water. They are killed by neither common disinfectants nor natural predators, such as amoebae. Instead, OPPPs multiply inside amoebae after ingestion. “OPPPs are perfectly adapted to drinking water systems,” says Falkinham.

The three OPPPs reviewed by Falkinham and his colleagues are particularly problematic in premise plumbing, and practices for control of these organisms are not well validated, says Mark LeChevallier, director of innovation and environmental stewardship at the New Jersey–based utility American Water. LeChevallier says the authors’ recommendations on research needs will “improve our understanding of the epidemiology and ecology of these emerging pathogens.”

One proposed control method for OPPPs is simply to raise the temperature of hot water systems. In a small ongoing study of patients infected with M. avium, increasing the set point on home water heaters from the recommended 120°F to 140°F appears helpful in eliminating M. avium in home plumbing systems. However, the unpublished study includes just 10 homes, and it’s too early to issue a general recommendation. “We worry about people scalding themselves, and it counteracts energy company pleas to lower temperatures to conserve energy,” says Falkinham.

Some hospitals use a 0.2-µm microbiological filter, such as those made by Pall Medical, on showerheads and faucets in patient rooms to block OPPPs. Steve Ebersohl, senior director of hospital sales with Pall Medical, says physicians who treat OPPP patients can refer them to that company or other manufacturers to learn how to add these filters to their home plumbing fixtures. However, activated charcoal filters, such as the ones often used to purify home water supplies, do not block and may even increase the growth of OPPPs. M. avium, for instance, flourishes on activated charcoal filters,3 where it is supplemented by the trapped metals and organic matter, Falkinham says.

Another option is to coat pipe interiors with agents that block biofilm growth. Sharklet®, a synthetic material that mimics the rough texture of natural shark skin, resists biofouling and reduces biofilm formation by M. avium.4 Made by Sharklet Technologies in Aurora, Colorado, this novel coating has microscopic ribs that discourage pathogens from settling on it. Sharklet Technologies is currently evaluating the material’s ability to prevent biofilm fouling in surgical and hospital settings.5

The common traits shared by L. pneumophila, M. avium, and P. aeruginosa suggest they could be controlled collectively by a few effective treatments, Falkinham says. He hopes those same solutions also may prevent widespread public health impacts associated with emerging OPPPs, such as multidrug-resistant Acinetobacter, which has infected soldiers who were wounded serving in the Middle East.6


1. Falkinham JO, et al. Epidemiology and ecology of opportunistic premise plumbing pathogens: Legionella pneumophila, Mycobacterium avium, and Pseudomonas aeruginosa. Environ Health Perspect 123(8):749–758 (2015); doi: 10.1289/ehp.1408692.

2. Collier SA, et al. Direct healthcare costs of selected diseases primarily or partially transmitted by water. Epidemiol Infect 140(11):2003–2013 (2012); doi: 10.1017/S0950268811002858.

3. Rodgers MR, et al. Colonisation of point use water filters by silver resistant non-tuberculous mycobacteria. J Clin Pathol 52(8):629 (1999); doi: 10.1136/jcp.52.8.629a.

4. Kim E, et al. A surface with a biomimetic micropattern reduces colonization of Mycobacterium abscessus. FEMS Microbiol Lett 360(1):17–22 (2014); doi: 10.1111/1574-6968.12587.

5. Sharklet Technologies, Inc. Publications [website]. Aurora, CO:Sharklet Technologies, Inc. (updated 8 April 2015). Available:​tions/ [accessed 23 July 2015].

6. Davis KA, et al. Multidrug-resistant Acinetobacter extremity infections in soldiers. Emerg Infect Dis 11(8):1218–1224 (2005); doi: 10.3201/1108.050103.

7. Mann EE, et al. Surface micropattern limits bacterial contamination. Antimicrob Resist Infect Control 3:28 (2014); doi: 10.1186/2047-2994-3-28.

Arsenic and Blood Pressure: A Long-Term Relationship

Nate Seltenrich covers science and the environment from Petaluma, CA. His work has appeared in High Country News, Sierra, Yale Environment 360, Earth Island Journal, and other regional and national publications.

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Citation: Seltenrich N. 2015. Arsenic and blood pressure: a long-term relationship. Environ Health Perspect 123:A218;

News Topics: Arsenic, Cardiovascular Health, Drinking Water Quality

Published: 1 August 2015

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Association between Arsenic Exposure from Drinking Water and Longitudinal Change in Blood Pressure among HEALS Cohort Participants

Jieying Jiang, Mengling Liu, Faruque Parvez, Binhuan Wang, Fen Wu, Mahbub Eunus, Sripal Bangalore, Jonathan D. Newman, Alauddin Ahmed, Tariqul Islam, Muhammad Rakibuz-Zaman, Rabiul Hasan, Golam Sarwar, Diane Levy, Vesna Slavkovich, Maria Argos, Molly Scannell Bryan, Shohreh F. Farzan, Richard B. Hayes, Joseph H. Graziano, Habibul Ahsan, and Yu Chen

Overexposure to naturally occurring arsenic in groundwater and soil can cause a variety of cancers and has been associated with developmental effects, neurotoxicity, diabetes, and cardiovascular disease.1 In this issue of EHP, researchers provide new evidence of arsenic’s ability to elevate blood pressure, potentially leading to hypertension and more serious clinical outcomes.2

Globally, 200 million people are estimated to drink water exposing them to arsenic at concentrations above the World Health Organization’s recommended limit of 10 µg/L.3 An estimated 35–77 million of these people reside in Bangladesh alone,4,5 where nearly all rural households rely on groundwater for drinking water.6

Bangladeshi women collecting drinking waterWidespread arsenic exposure via drinking water in Bangladesh has been called the “largest mass poisoning of a population in history.”10

© SK Hasan Ali/Demotix/Corbis

To gain insight into the link between arsenic exposure and changes in blood pressure, researchers based at the University of Chicago, Columbia University, and New York Langone Medical Center analyzed data for 10,853 individuals participating in the Health Effects of Arsenic Longitudinal Study (HEALS), a long-term prospective cohort study. These individuals were exposed to low to moderately high levels of arsenic from nearly 6,000 contaminated wells in an area of Bangladesh outside the capital of Dhaka.7 (Senior author Yu Chen, an associate professor of population health at New York University, says the cohort has since been expanded to cover a wider area, including data from 11,000 wells.)

“We are trying to reveal the mechanisms that link arsenic exposure and cardiovascular disease,” says first author Jieying Jiang. “We think that increasing blood pressure level might be one of those mechanisms.” Other potential mechanisms include atherosclerosis, oxidative stress, inflammation, and vascular stiffness, which are interrelated and associated with blood pressure, Chen notes.

“The issue with arsenic and hypertension has always been a little more controversial than other outcomes,” says Ana Navas-Acien, coauthor of a 2012 review of the subject.8 She explains that many earlier studies were cross-sectional in design, meaning arsenic exposure and incidence of hypertension were examined at a single point in time, so observed associations were harder to interpret. “If you look at our systematic review, you can see there was a tendency for saying that yes, there is an association, but it was not a clear yes,” she says. “This study definitely clarifies that [association]. It shows it’s extremely important to have prospective data.”

Working with a field staff of more than 100 people, the authors of the current study analyzed blood pressure readings taken from each cohort member four times between October 2000 and March 2009, with the initial measurements serving as a baseline. To assess arsenic exposure, they tested well water and urine samples collected at each of the four visits.

The results showed positive associations between arsenic exposure, whether measured in well water or urine samples, and annual increases in systolic and diastolic blood pressure. These associations were stronger among participants who were oldest at baseline.2

Even when controlling for age, sex, smoking status, educational status, and diabetes history, the researchers saw an average annual increase in systolic blood pressure of 0.43 mmHg for participants exposed to medium-low levels of arsenic in groundwater (12–62 µg/L), 0.54 mmHg for those exposed to medium-high levels (62–148 µg/L), and 0.48 mmHg for those exposed to high levels (above 148 µg/L), as compared with the control group, which was exposed to levels below 12 µg/L. The authors speculate that baseline blood pressure could have already been affected significantly by past arsenic exposure, such that only a limited increase could be further observed.2

The results thus reveal a nonmonotonic dose response, in which individuals exposed to the highest arsenic levels in the study often had a smaller increase than those exposed to medium-high levels.2 In vitro research has shown arsenic to have a nonlinear effect on blood vessel formation and tumor growth.9

In any case, while the observed increases are moderate enough that they don’t point directly to clinical outcomes at the individual level, Navas-Acien says that across a broadly exposed population such as Bangladesh’s, they could translate to more people with hypertension and cardiovascular disease. “If even a small portion of cardiovascular disease can be due to arsenic,” Chen agrees, “that may mean a lot of numbers.”


1. WHO. Arsenic [fact sheet]. Geneva, Switzerland:World Health Organization (December 2012). Available:​s/fs372/en/ [accessed 14 July 2015].

2. Jiang J, et al. Association between arsenic exposure from drinking water and longitudinal change in blood pressure among HEALS cohort participants. Environ Health Perspect 123(8):806–812 (2015); doi: 10.1289/ehp.1409004.

3. Naujokas MF, et al. The broad scope of health effects from chronic arsenic exposure: update on a worldwide public health problem. Environ Health Perspect 121(3):295–302 (2013); doi: 10.1289/ehp.1205875.

4. Khan AW, et al. Arsenic contamination in groundwater and its effect on human health with particular reference to Bangladesh. J Prev Soc Med 16(1):65–73 (1997).

5. Dhar RK, et al. Groundwater arsenic contamination and sufferings of people in Bangladesh may be the biggest arsenic calamity in the world [abstract]. Presented at: International Conference on Arsenic Pollution of Groundwater in Bangladesh: Causes, Effects and Remedies, Dhaka, Bangladesh, 8–12 February 1998.

6. Shafiquzzaman M, et al. Technical and social evaluation of arsenic mitigation in rural Bangladesh. J Health Popul Nutr 27(5):674–683 (2009); doi: 10.3329/jhpn.v27i5.3779.

7. Ahsan H, et al. Health Effects of Arsenic Longitudinal Study (HEALS): description of a multidisciplinary epidemiologic investigation. J Expo Sci Environ Epidemiol 16(2):191–205 (2006); doi: 10.1038/sj.jea.7500449.

8. Abhyankar LN, et al. Arsenic exposure and hypertension: a systematic review. Environ Health Perspect 120(4):494–500 (2012); doi: 10.1289/ehp.1103988.

9. Soucy NV, et al. Arsenic stimulates angiogenesis and tumorigenesis in vivo. Toxicol Sci 76(2):271–279 (2003); doi: 10.1093/toxsci/kfg231.

10. Smith AH, et al. Contamination of drinking-water by arsenic in Bangladesh: a public health emergency. Bull WHO 78(9):1093–1103 (2000); PMID: [Pubmed].

A Closer Look at Obesogens: Lipid Homeostasis Disruption in Daphnia

Lindsey Konkel is a New Jersey–based journalist who reports on science, health, and the environment.

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Citation: Konkel L. 2015. A closer look at obesogens: lipid homeostasis disruption in Daphnia. Environ Health Perspect 123:A219;

News Topics: Animal Models, Ecology and Wildlife, Endocrine Health, Metabolism, Reproductive Health

Published: 1 August 2015

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Obesogens beyond Vertebrates: Lipid Perturbation by Tributyltin in the Crustacean Daphnia magna

Rita Jordão, Josefina Casas, Gemma Fabrias, Bruno Campos, Benjamín Piña, Marco F.L. Lemos, Amadeu M.V.M. Soares, Romà Tauler, and Carlos Barata

Obesogenic chemicals promote weight gain in mammals by altering lipid metabolism, which results in increased fat accumulation.1 Altered lipid metabolism has been associated with serious health problems, including obesity, diabetes, and an increased risk of cardiovascular disease.2 However, very little is known about how obesogenic chemicals might affect invertebrate species. In this issue of EHP, researchers suggest that altered lipid transport from the maternal organism to the egg by a known obesogen may be responsible for reproductive problems in Daphnia magna, a tiny freshwater crustacean.3

In the study, the researchers exposed Daphnia to 0.1 µg/L or 1.0 µg/L of the organometallic pollutant tributyltin (TBT). Once used widely as a biocide in paints designed to keep marine invertebrates from sticking to the hulls of ships, TBT was later shown to accumulate in the environment and harm the reproduction and development of aquatic organisms.4 In marine snails, TBT causes a condition called imposex, in which females develop male sex organs.5 In mouse studies it also has been shown to increase lipid accumulation and promote weight gain across multiple generations.6 In 2008 the International Maritime Organization severely restricted its use as a biocide.4

Micrograph of Daphnia magnaExperimental exposure to TBT altered the transport of lipids from mother Daphnia to her eggs, an effect that could be problematic if it were to occur in an ecological context

© Hajime Watanabe/doi:10.1371/image.pgen.v07.i03

Daphnia, also known as the water flea, is used widely as a model in ecotoxicology studies.7 Within the last decade, scientists have started to use Daphnia in biomedical research as a surrogate species for genomic responses to environmental stressors.7 “We wanted to test whether Daphnia could be used as an invertebrate model for obesogenic effects,” says senior author Carlos Barata, an ecotoxicologist at the Institute of Environmental Assessment and Water Research in Barcelona, Spain.

Female water fleas typically release a brood of offspring each time they molt (shed their exoskeleton). Between molts, Daphnia stores up triacylglycerols from food as lipid droplets. Fats are allocated to the formation of a new carapace during the molting stage and are transferred into eggs; as this occurs, triacylglycerol levels drop.8

Barata and colleagues observed negative effects on reproduction and survival in Daphnia exposed to TBT. “Our findings suggest that TBT disrupted the normal transfer of lipids from adult to egg,” Barata says. Lipid levels in eggs from TBT-exposed females were lower than those in eggs from nonexposed females. Females exposed to TBT also retained more fat droplets after they molted. As adults, offspring of exposed females were less fit—they showed impaired survival and reduced reproduction.3

“We’ve known for a long time that TBT causes reproductive problems in Daphnia. This could be a mechanistic explanation,” says Gerald LeBlanc, an environmental toxicologist at North Carolina State University. LeBlanc was not involved in the study.

Previous research has suggested that TBT may disrupt certain hormonal signaling pathways in Daphnia.9 In this study, the researchers found evidence that TBT activated signaling pathways related to molting and reproduction, presumably by increasing transcription of the retinoid X receptor (RXR) gene.3 In vertebrates, the nuclear receptor known as peroxisome proliferator-activated receptor γ partners with the RXR to stimulate fat cell differentiation and lipid storage.10 These receptors are known targets for TBT.11

However, LeBlanc says it would be premature to call this a model organism for the study of obesogens. “The molecular pathways that are affected [by TBT] in vertebrates don’t exist in Daphnia,” he says.

Bruce Blumberg, a professor of developmental and cell biology at the University of California, Irvine, agrees it may be premature to call Daphnia a model for the study of obesogens. Obesogens are defined as chemicals that produce weight gain by increasing the number and/or size of adipocytes or by modulating lipid metabolism.12 Although lipid transfer is clearly important for fecundity of the animals, Blumberg points out that “the perturbation of lipid transfer from mother to egg in itself isn’t necessarily an obesogenic effect.” Blumberg was not involved in the current study.

Yet if chemicals that cause mammals to get fatter can also perturb lipid dynamics in an ecological context, there could be implications beyond obesity, says Michele La Merrill, a toxicologist at the University of California, Davis. “Although this study is not evaluating invertebrate obesity, it is showing some changes in lipids, and that might be a problem since lipids are important for a number of cell functions, such as membrane integrity,” she explains. La Merrill was not involved in the study.

Barata hopes the research will spur more scientists to explore the roles of known obesogens and emerging contaminants in invertebrates. He says, “There may be new mechanisms of toxicity that can affect our environment.”


1. Grün F, Blumberg B. Minireview: the case for obesogens. Mol Endocrinol 23(8):1127–1134 (2009); doi: 10.1210/me.2008-0485.

2. Grün F, Blumberg B. Perturbed nuclear receptor signaling by environmental obesogens as emerging factors in the obesity crisis. Rev Endocr Metab Disord 8(2):161–171 (2007); doi: 10.1007/s11154-007-9049-x.

3. Jordão R, et al. Obesogens beyond vertebrates: lipid perturbation by tributyltin in the crustacean Daphnia magna. Environ Health Perspect 123(8):813–819 (2015); doi: 10.1289/ehp.1409163.

4. IMO. International Convention on the Control of Harmful Anti-fouling Systems on Ships [website]. London, United Kingdom:International Maritime Organization (2015). Available:​ListOfConventions/Pages/International-Co​nvention-on-the-Control-of-Harmful-Anti-​fouling-Systems-on-Ships-(AFS).aspx [accessed 14 July 2015].

5. Iguchi T, et al. Developmental effects: oestrogen-induced vaginal changes and organotin-induced adipogenesis. Int J Androl 31(2):263–268 (2008); doi: 10.1111/j.1365-2605.2008.00863.x.

6. Chamorro-García R, et al. Transgenerational inheritance of increased fat depot size, stem cell reprogramming, and hepatic steatosis elicited by prenatal exposure to the obesogen tributyltin in mice. Environ Health Perspect 121(3):359–366 (2013); doi: 10.1289/ehp.1205701.

7. NIH. Model Organisms for Biomedical Research: Daphnia [website]. Bethesda, MD:National Institutes of Health (2015). Available:​a/ [accessed 14 July 2015].

8. Tessier AJ, Goulden CE. Estimating food limitation in cladoceran populations. Limnol Oceanogr 27(4):707–717 (1982).

9. Wang YH, et al. Tributyltin synergizes with 20-hydroxyecdysone to produce endocrine toxicity. Toxicol Sci 123(1):71–79 (2011); doi: 10.1093/toxsci/kfr154.

10. Pagliarani A, et al. Toxicity of organotin compounds: shared and unshared biochemical targets and mechanisms in animal cells. Toxicol in Vitro 27(2):978–990 (2013); doi: 10.1016/j.tiv.2012.12.002.

11. Santos MM, et al. Lipid homeostasis perturbation by organotins: effects on vertebrates and invertebrates. In: Biochemical and Biological Effects of Organotins (Pagliarani A, Trombetti F, Ventrella V, eds.). Bologna, Italy:Bentham Science Publishers (2012).

12. Grün F, Blumberg B. Environmental obesogens: organotins and endocrine disruption via nuclear receptor signaling. Endocrinology 147(6 suppl):S50–S55 (2006); doi: 10.1210/en.2005-1129.

Response to “Comment on ‘Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study’”

1Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland; 2Swiss Tropical and Public Health Institute, Basel, Switzerland; 3University of Basel, Basel, Switzerland

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Citation: Spycher BD, Röösli M, Egger M, Kuehni CE. 2015. Response to “Comment on ‘Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study.’” Environ Health Perspect 123:A200–A201;

Address correspondence to B. Spycher, University of Bern, Institute of Social and Preventive Medicine, Finkenhubelweg 11, CH-3012 Bern, Switzerland. E-mail:

The authors declare they have no actual or potential competing financial interests.

Final Publication: 1 August 2015

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Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study

Ben D. Spycher, Judith E. Lupatsch, Marcel Zwahlen, Martin Röösli, Felix Niggli, Michael A. Grotzer, Johannes Rischewski, Matthias Egger, and Claudia E. Kuehni, for the Swiss Pediatric Oncology Group and the Swiss National Cohort Study Group

Comment on “Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study”

Jeffry A. Siegel, Bill Sacks (retired), Ludwig E. Feinendegen, James S. Welsh, Krzysztof W. Fornalski, Mark Miller, Jeffrey Mahn (retired), Leo Gomez (retired), Michael G. Stabin, Patricia Lewis, Vincent J. Esposito, Andrzej Strupczewski, Charles W. Pennington, Jerry M. Cuttler, Chary Rangacharyulu, Chris Davey, and Shizuyo Sutou

Siegel and colleagues object to our use of the word “risk” on the basis that it implies a causal relationship. This is not so. In epidemiology, risk is simply the probability of developing the disease. Comparing risks across exposure strata is a natural way of assessing associations in a cohort study and does not imply causality. Our conclusions regarding causality are, in fact, very cautious.

The authors correctly point out that we are investigating low doses. The comparison they make with worldwide averages is, however, misleading. The worldwide annual dose of 2 mSv represents total background radiation and includes inhaled radon gas and ingested radionuclides. The appropriate comparison is with cosmic and terrestrial gamma radiation, which together contribute an annual average of 0.9 mSv worldwide (UNSCEAR 2000). This figure is on par with our lowest exposure category. Their comments on the use of a geographic model instead of measurements to estimate exposure reiterate limitations that we discuss in the paper.

Siegel and colleagues argue that the point estimates for the highest exposure category are unreasonably high and contradict literature showing protective effects of radiation on cancer. However, they base their argument mainly on ecological studies (Doss and Little 2014; Luckey 2008), which are prone to bias. Our study results are in line with a recent case–control study of 27,447 childhood cancer cases from the United Kingdom, which also observed a risk increase for gamma radiation (Kendall et al. 2013).

The authors suggest that other factors such as socioeconomic status and degree of urbanization are likely to explain our results. However, when we adjust for these factors, our results remain virtually unchanged. Consider the estimated response to cumulative dose, adjusted for sex and birth year (Table 4): For all childhood cancers we estimated an increase in risk per mSv cumulative dose of 2.8% (95% confidence interval [CI]: 0.8%, 4.8%) for the entire cohort and 4.0% (95% CI: 1.7%, 6.4%) for children with stable residence. After adjusting for socioeconomic status—using the Swiss neighbourhood index of socioeconomic position (Panczak et al. 2012), which is based on the education and occupation of household heads, rent, and crowding—and for degree of urbanization (urban, peri-urban, rural), the corresponding estimates were 2.9% (95% CI: 0.9%, 5.0%) and 4.0% (95% CI: 1.7%, 6.3%), respectively. The authors confuse the effects of socioeconomic status on mortality with those on cancer incidence in children. Only the latter could confound our results, but the evidence for their existence is far from conclusive (Adam et al. 2008).

The public health action proposed, i.e., the relocation of children to areas with lower radiation, is nonsensical. Childhood cancer is rare, and we are not dealing with deaths at “alarming rates.” In the whole of Switzerland, there are about 200 new cases per year, of whom more than 80% survive (SCCR 2015). Only a small proportion of the population is living in highly exposed areas. The attributable fraction, assuming a causal relationship, is therefore small. Public health action is better targeted toward modifiable environmental factors leading to larger numbers of deaths from several causes, such as exposure to radon, air pollution, and secondhand tobacco smoke.

It seems to us that the “Scientists for Accurate Radiation Information” a priori exclude the possibility that low-dose radiation could increase the risk of cancer. They will therefore not accept studies that challenge their foregone conclusion.


Adam M, Rebholz CE, Egger M, Zwahlen M, Kuehni CE. 2008. Childhood leukaemia and socioeconomic status: what is the evidence? Radiat Prot Dosimetry 132(2):246–254; doi: 10.1093/rpd/ncn261.

Doss M, Little MP. 2014. Point/counterpoint: low-dose radiation is beneficial, not harmful. Med Phys 41(7):070601; doi: 10.1118/1.4881095.

Kendall GM, Little MP, Wakeford R, Bunch KJ, Miles JC, Vincent TJ, et al. 2013. A record-based case–control study of natural background radiation and the incidence of childhood leukaemia and other cancers in Great Britain during 1980–2006. Leukemia 27(1):3–9; doi: 10.1038/leu.2012.151.

Luckey TD. 2008. The health effects of low-dose ionizing radiation. J Am Phys Surg 13(2):39–42.

Panczak R, Galobardes B, Voorpostel M, Spoerri A, Zwahlen M, Egger M, et al. 2012. A Swiss neighbourhood index of socioeconomic position: development and association with mortality. J Epidemiol Community Health 66:1129–1136; doi: 10.1136/jech-2011-200699.

SCCR (Swiss Childhood Cancer Registry). 2015. Annual Report 2013–2014. Bern, Switzerland:Swiss Childhood Cancer Registry. Available:​leadmin/KKR08/uploads/pdf/Jahresberichte​/Annual_Report_SCCR_2013_2014.pdf [accessed 11 June 2015].

UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation). 2000. Sources and Effects of Ionizing Radiation. Volume I: Sources. Annex B, Exposures from Natural Radiation Sources. Vienna, Austria:United Nations Scientific Committee on the Effects of Atomic Radiation. Available:​xa.pdf [accessed 20 March 2015].

Comment on “Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study”

1Nuclear Physics Enterprises, Marlton, New Jersey, USA; 2U.S. Food and Drug Administration, Washington, DC, USA; 3Heinrich-Heine-University, Dusseldorf, Germany; 4Stritch School of Medicine, Loyola University, Chicago, Illinois, USA; 5Polish Nuclear Society, Warsaw, Poland; 6Sandia National Laboratories, Albuquerque, New Mexico, USA; 7Vanderbilt University, Nashville, Tennessee, USA; 8Free Enterprise Radon Health Mine, Boulder, Montana, USA; 9University of Pittsburgh, Pittsburgh, Pennsylvania, USA; 10National Centre for Nuclear Research, Warsaw, Poland; 11NAC International, Norcross, Georgia, USA; 12Cuttler & Associates, Mississauga, Ontario, Canada; 13University of Saskatchewan, Saskatoon, Saskatchewan, Canada; 14King Abdullah University of Science and Technology, Thuwal, Jeddah, Saudi Arabia; 15Shujitsu University, Okayama, Japan

About This Article open

Citation: Siegel JA, Sacks B, Feinendegen LE, Welsh JS, Fornalski KW, Miller M, Mahn J, Gomez L, Stabin MG, Lewis P, Esposito VJ, Strupczewski A, Pennington CW, Cuttler JM, Rangacharyuku C, Davey C, Sutou S. 2015. Comment on “Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study.” Environ Health Perspect 123:A200;

Address correspondence to J.A. Siegel, Nuclear Physics Enterprises, 4 Wedgewood Dr., Marlton, NJ 08053 USA. E-mail:

All authors are members or associate members of SARI (Scientists for Accurate Radiation Information, SARI, as an organization, has no expenses and thus no funders. SARI’s aim is to provide empirical evidence and scientific reasoning to counter the linear no-threshold paradigm followed by radiation-related regulatory agencies around the world.

Final Publication: 1 August 2015

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Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study

Ben D. Spycher, Judith E. Lupatsch, Marcel Zwahlen, Martin Röösli, Felix Niggli, Michael A. Grotzer, Johannes Rischewski, Matthias Egger, and Claudia E. Kuehni, for the Swiss Pediatric Oncology Group and the Swiss National Cohort Study Group

Response to “Comment on ‘Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study’”

Ben D. Spycher, Martin Röösli, Matthias Egger, and Claudia E. Kuehni

We read with interest the article by Spycher et al. The authors claim their results suggest an increased risk of cancer among children exposed to external dose rates of background ionizing radiation of ≥ 200 nSv/h, compared with those exposed to < 100 nSv/h. However, all that the data show is a positive correlation rather than a causal result, which the word “risk” implies. Besides, these dose rates correspond to annual exposure levels of approximately 1.8 and 0.9 mSv, respectively. Considering that the average natural background exposure rate in the world is on the order of 2 mSv annually, with regions that range up to as much as 260 mSv (Ghiassi-Nejad et al. 2002), these are very low doses.

Importantly, the background exposure rates were based not on actual measurements at children’s homes but on a geographic model. The authors noted they could not “exclude biases due to inaccurate exposure measurement.” It comes as no surprise, therefore, that the various hazard ratios are for the most part extremely low, and most of the 95% confidence intervals include the value of unity. Essentially, for children putatively exposed to a background dose rate exceeding 200 nSv/h, only the confidence intervals for all cancers, leukemias, and acute lymphoblastic leukemias exclude unity.

This, taken seriously, would suggest a markedly increased cancer risk for these children, based on those exposure rates, but only if one begins by assuming that these levels of radiation contribute to producing cancers. There are numerous studies that show that such levels, in fact, elicit protective biological responses that lower the risk of cancer (Doss and Little 2014; Luckey 2008). Furthermore, given the very low attributed exposure rates and the imprecision in the actual exposure estimates, it is more likely than not that this increased childhood cancer occurrence is due to causes other than the background radiation exposure.

For example, it is of interest that those children experiencing the highest estimated background dose rates are those who live in rural areas and in neighborhoods of lowest socioeconomic status. The authors state that adjustments were made for these two confounding factors, but since not much detail was provided regarding the adjustments made, the adequacy of the removal of these factors as causative contributions cannot be independently verified. Nevertheless, it is far more likely that these two factors are more important causes of childhood disease than the extremely low background exposures involved.

Moreover, if it were true that exposure rates above 200 nSv/h, low though they be, were to somehow result in such a markedly increased cancer risk for children, the only reasonable governmental policy action would be to evacuate those children living in rural areas and poor neighborhoods, and relocate them to areas with lower radiation exposure in order to save lives. Failure to act in this manner would leave the government liable for allowing its younger citizens to die at an alarming rate. Studies like this cannot be taken seriously without such public health policy implications being likewise taken seriously.


Doss M, Little MP. 2014. Point/counterpoint: low-dose radiation is beneficial, not harmful. Med Phys 41(7):070601; doi: 10.1118/1.4881095.

Ghiassi-Nejad M, Mortazavi SM, Cameron JR, Niroomand-rad A, Karam PA. 2002. Very high background radiation areas of Ramsar, Iran: preliminary biological studies. Health Phys 82(1):87–93.

Luckey TD. 2008. The health effects of low-dose ionizing radiation. J Am Phys Surg 13(2):39–42.

Response to “Comment on ‘Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study’”

1Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland; 2Swiss Tropical and Public Health Institute, Basel, Switzerland; 3University of Basel, Basel, Switzerland

About This Article open

Citation: Spycher BD, Röösli M, Egger M, Kuehni CE. 2015. Response to “Comment on ‘Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study.’” Environ Health Perspect 123:A198–A199;

Address correspondence to B. Spycher, University of Bern, Institute of Social and Preventive Medicine, Finkenhubelweg 11, CH-3012 Bern, Switzerland. E-mail:

The authors declare they have no actual or potential competing financial interests.

Final Publication: 1 August 2015

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Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study

Ben D. Spycher, Judith E. Lupatsch, Marcel Zwahlen, Martin Röösli, Felix Niggli, Michael A. Grotzer, Johannes Rischewski, Matthias Egger, and Claudia E. Kuehni, for the Swiss Pediatric Oncology Group and the Swiss National Cohort Study Group

Comment on “Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study”

Bobby R. Scott

We thank Scott for his interest in our study on background ionizing radiation and the risk of childhood cancer. Scott claims that if all random and systematic errors in measurements had been addressed, our study would likely have found no association between levels of background ionizing radiation and childhood cancer risk. We acknowledge that errors often affect estimates of long-term exposures, but there are no obvious reasons why the sum of potential measurement errors in our study, if eliminated, should result in a null finding. In fact, there are reasons to the contrary.

Random error (or “statistical” error, in Scott’s terms) in exposure measurement would result in nondifferential misclassification and, therefore, would typically produce an underestimation, not an overestimation, of any effect (Keogh and White 2014). Differential misclassification of exposure, which could lead to under- or overestimation of the association, is unlikely given the design of the study and the geographical model used to estimate exposure. Confounding factors may not have been measured perfectly, but even imperfect measures should affect estimates of dose–response relationships if the factors are indeed confounders. Our estimates were virtually unchanged when including levels of traffic-related air pollution, electromagnetic fields from radio and TV transmitters or high-voltage power lines, and degree of urbanization and socioeconomic status of neighborhoods in the statistical model.

Scott argues that bias may have been introduced due to omission of some radiation sources, in particular exposure from medical procedures. We agree with Scott that ideally all radiation sources should be included in the study. However, in our study, bias due to omitted covariates is unlikely unless the excluded components of radiation dose were correlated with background radiation. It is difficult to see why exposure to medical radiation sources should correlate with other components of background radiation. Nevertheless, omission biases are not easily tractable in generalized linear models (Neuhaus and Jewell 1993) and certainly merit further investigation in this context.

Scott is mistaken in his assessment of our analyses for cumulative dose. The Cox proportional hazards model and the conditional logistic regression model in our nested sample relate cumulative doses with hazards, not with cumulative incidence. Hazards are instantaneous risks, and during model fitting comparisons are made only between children who are of the same age at the time the cases are diagnosed with cancer. In other words, only comparisons of doses accumulated over the same amount of time contribute to the estimation. In contrast to Scott’s assertion, the models can thus deal with the time-varying nature of the exposure and do not overestimate effects.


Keogh RH, White IR. 2014. A toolkit for measurement error correction, with a focus on nutritional epidemiology. Stat Med 33(12):2137–2155; doi: 10.1002/sim.6095.

Neuhaus JM, Jewell NP. 1993. A geometric approach to assess bias due to omitted covariates in generalized linear models. Biometrika 80(4):807–815; doi: 10.1093/biomet/80.4.807.

Comment on “Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study”

Lovelace Respiratory Research Institute, Albuquerque, New Mexico, USA

About This Article open

Citation: Scott BR. 2015. Comment on “Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study.” Environ Health Perspect 123:A198;

Address correspondence to B.R. Scott, Lovelace Respiratory Research Institute, 2425 Ridgecrest Dr. SE, Albuquerque, NM 87108-5129 USA. E-mail:

The author declares he has no actual or potential competing financial interests.

Final Publication: 1 August 2015

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Related EHP Articles

Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study

Ben D. Spycher, Judith E. Lupatsch, Marcel Zwahlen, Martin Röösli, Felix Niggli, Michael A. Grotzer, Johannes Rischewski, Matthias Egger, and Claudia E. Kuehni, for the Swiss Pediatric Oncology Group and the Swiss National Cohort Study Group

Response to “Comment on ‘Background Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide Cohort Study’”

Ben D. Spycher, Martin Röösli, Matthias Egger, and Claudia E. Kuehni

Spycher et al. conducted a nationwide census-based cohort study to investigate whether the incidence of childhood cancer is associated with external exposure to natural background radiation from terrestrial gamma and cosmic rays. The authors claim their results suggest an increased risk of cancer among children exposed to external dose rates of background ionizing radiation of ≥ 200 nSv/h (1.8 mSv/yr) when compared with those exposed to < 100 nSv/h (0.9 mSv/yr). Furthermore, they claim the hazard ratios for each mSv increase in cumulative dose of external radiation are 1.028 (95% confidence interval [CI]: 1.008, 1.048) for any cancer, 1.036 (95% CI: 0.997, 1.077) for leukemia, 1.007 (95% CI: 0.964, 1.052) for lymphoma, and 1.042 (95% CI: 1.008, 1.084) for central nervous system tumors.

Regarding the claimed increasing hazard ratios for childhood cancer for each mSv increase in cumulative dose of external radiation, this would be expected to be the case irrespective of the cause of childhood cancer. This is because childhood cancer cumulative incidence increases with follow-up time, which is positively correlated with cumulative radiation dose from birth. Had cumulative exposure to air pollution, cumulative food intake, or cumulative water intake been used as the risk factor, a similar outcome would be expected because all are positively correlated with follow-up time.

The authors used in their analyses the doubly weighted (via radiation and tissue weighting factors) hypothetical effective dose rate and effective dose related to total-body irradiation from sources outside the body. They were apparently unaware that tissue weighting factors used are based on detriment rather than solely on cancer and that all significant contributions to radiation absorbed dose need to be accounted for. The authors omitted the very important contributions to radiation dose from radionuclides inside the body and from medical procedures. For example, the internal radiation dose to active bone marrow from radon and thoron can be significant (Richardson et al. 1991). Thus, misclassification of individuals to effective dose and dose rate groups likely occurred more frequently than acknowledged by Spycher et al. In addition, when focusing on a specific type of potential outcome (e.g., leukemia) and its association with radiation exposure of a specific target tissue (e.g., active bone marrow), it is better to use the equivalent dose, which involves only the radiation weighting factor, when a mixture of different radiations are involved (National Research Council 2006). This guards against unnecessary systematic error associated with using both the subjective radiation and tissue weighting factors to get the effective dose that was used by the authors.

The individual-specific radiation doses and dose rates assigned by Spycher et al. likely involved significant errors (statistical and systematic), with the dose error possibly being larger than the effective dose assigned to the individual. Part of the systematic error relates to neglected doses from other sources (e.g., internal radionuclides). Because the focus of the research was on very small radiation dose rates and small cumulative doses, it is important to address dose and dose rate errors when conducting such analyses. It is also important to address uncertainty associated with other confounding factors studied (traffic-related air pollution, electromagnetic fields from radio and TV transmitters and from high-voltage power lines, degree of urbanization of municipality, socioeconomic status, etc.) as well as errors related to the use of probabilistic record linkage between the Swiss Childhood Cancer Registry and the Swiss National Cohort. If such errors and uncertainty had been addressed in the authors’ logistic regression analyses, then it is likely that no association between background radiation and childhood leukemia would have been suggested by the research results obtained.


National Research Council. 2006. Health Risks from Exposure to Low Levels of Ionizing Radiation. BEIR VII Phase 2. Washington, DC:National Academies Press.

Richardson RB, Eatough JP, Henshaw DL. 1991. Dose to red bone marrow from natural radon and thoron exposure. Br J Radiol 64(763):608–624; doi: 10.1259/0007-1285-64-763-608.