Category Archives: Earth Science

IRIS Toxicological Review of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (RDX) (External Review Draft)

The IRIS Toxicological Review of Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was released for external peer review in September 2016. The EPA’s Science Advisory Board’s (SAB) Chemical Assessment Advisory Committee (CAAC) will conduct a peer review of the scientific basis supporting the RDX assessment and release a final report of their review. Information regarding the peer review can be found on the SAB website.

IRIS Toxicological Review of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (RDX) (Interagency Science Consultation Draft)

On March 10, 2016, the public comment draft Toxicological Review of Hexahydro-1,3,5-trinitro-1,3,5-triazine and the draft charge to external peer reviewers were released for public review and comment. The Toxicological Review and charge were reviewed internally by EPA and by other federal agencies and White House Offices before public release. Consistent with the May 2009 IRIS assessment development process, all written comments on IRIS assessments submitted by other federal agencies and White House Offices are made publicly available. Accordingly, interagency comments and the interagency science consultation materials provided to other agencies, including interagency review drafts of the IRIS Toxicological Review of Hexahydro-1,3,5-trinitro-1,3,5-triazine and the charge to external peer reviewers, are posted on this site.

IRIS Toxicological Review of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (RDX) (Preliminary Assessment Materials)

In August 2013, EPA released the draft literature searches and associated search strategies, evidence tables, and exposure response arrays for RDX to obtain input from stakeholders and the public prior to developing the draft IRIS assessment. Specifically, EPA was interested in comments on the following:

  • Draft literature search strategies
    • The approach for identifying studies
    • The screening process for selecting pertinent studies
    • The resulting list of pertinent studies
  • Preliminary evidence tables
    • The process for selecting studies to include in evidence tables
    • The quality of the studies in the evidence tables

The literature search strategy, which describes the processes for identifying scientific literature, contains the studies that EPA considered and selected to include in the evidence tables. The preliminary evidence tables and exposure-response arrays present the key study data in a standardized format. The evidence tables summarize the available critical scientific literature. The exposure-response figures provide a graphical representation of the responses at different levels of exposure for each study in the evidence table.

Comprehensive trends assessment of nitrogen sources and loads to estuaries of the coterminous United States

Sources of nitrogen and phosphorus to estuaries and estuarine watersheds of the coterminous United States have been compiled from a variety of publically available data sources (1985 – 2015). Atmospheric loading was obtained from two sources. Modelled and interpolated measurements of atmospheric nitrogen deposition to watersheds was obtained from the National Atmospheric Deposition Program (NADP). Nitrogen deposition to both watersheds and estuaries was also obtained from recently updated Community Multiscale Atmospheric Quality (CMAQ) models, which now incorporate bi-directional ammonia fluxes. Measured and modelled watershed nutrient point sources have been compiled from the Environmental Protection Agency’s Discharge Monitoring Report (DMR) Pollutant Loading Tool and Enforcement and Compliance History Online (ECHO) database. Nonpoint sources from urban and agricultural sources have been estimated based on trends in developed lands from the National Land Cover Dataset (NLCD) and fertilizer, and manure applications, the latter derived from the Nutrient Use GIS (NuGIS) database and National Agricultural Statistics Service (NASS) crop layers. These sources were translated to cumulative estimated estuarine loads using updated land-to-water delivery ratios and the fraction delivered to river mouth obtained from regional and national US Geological Survey Spatially Referenced Regressions On Watershed Attributes (SPARROW) models. The SPARROW models were used to estimate both historic and potential future trends in annual loading (2002-2012/2014, 2025). Nutrient source and loading estimates are made available through EPA’s Estuary Data Mapper application (EDM; Spatial and temporal trends in loading and source apportionment will be discussed.

Climate, Clams, and a Changing Watershed: A time series analysis to quantify the impact of management and climate on water quality in the Potomac Estuary

The Potomac River is the largest tributary of the Chesapeake Bay and has been a key study site in water quality research, beginning with work to address public health concerns such as safe drinking water and waterborne disease during periods of population growth and urbanization at the turn of the 19th century. An updated analysis of the Potomac is timely because a number of management actions have taken place since the early 2000s. These include upgrades at the Blue Plain Wastewater Treatment Plant to biological nitrogen reduction practices that have greatly reduced point sources from this large facility, dramatic declines in NOx emissions over the Potomac airshed, changes in agricultural practices in the watershed, and shifts in climate. Here we present our approach of applying General Additive Models to unravel the complex impacts of nutrient and freshwater inputs from the watershed, as well as within-estuary processes driven by climatic conditions, as they relate to two key water quality criteria. The results of this analysis permit us to present a narrative that connects dynamics in the watershed to ecological processes within the tidal Potomac in an effort to assess how management actions related to nutrient loadings impact chlorophyll-a and dissolved oxygen concentrations.

Helminths, in Infectious Diseases 4th Edition

Helminths are the most common parasites infecting humans. While the world population numbers approximately 6 billion, there are probably a similar number of helminthes infections occurring in humans. Helminths are transmitted to humans through food, water, soil, and by arthropod and molluscan vectors. The helminths infect every organ and organ system. They are prevalent in the intestines, but are also found in the liver, lungs, blood and occasionally in the brain and other organs. This chapter describes some of the human parasitic worms, their biology, epidemiology, pathogenicity, clinical aspects of helminthic infection, diagnosis and prevention.

ToxRefDB – Release user-friendly web-based tool for mining ToxRefDB

ACToR links to a chemical toxicity reference database called ToxRefDB ( which allows scientists and the interested public to search and download thousands of toxicity testing results on hundreds of chemicals. ToxRefDB provides detailed chemical toxicity data in a publically accessible searchable format.
ToxRefDB contains mammal toxicity information that when combined with other sources of information, such as exposure and metabolism, form the basis for pesticide risk assessments.

A resilience framework for chronic exposures: water quality and ecosystem services in coastal social-ecological systems

We outline a tailored resilience framework that applies ecosystem service concepts to coastal social-ecological systems (SES) affected by water quality degradation. Unlike acute coastal disturbances such as hurricanes or oil spills, water quality issues, particularly those related to nutrients, exist as more constant, slow-moving and frustratingly chronic problems. Because of their slow onset time, these problems should provide the opportunity for communities to mitigate and or adapt in a way which maintains the system’s structure and function, although experience shows this does not necessarily mean mitigation or adaptation will happen or has happened. Our intent is to provide a lens through which to conduct research to inform long-term community planning decisions pertaining to chronic water quality issues in coastal systems. We apply the resilience framework to Cape Cod’s (Barnstable County, Massachusetts, USA) coastal waters and communities and impacts from nitrogen over-enrichment. By working under a unified framework, research can be more appropriately directed to fill knowledge gaps to inform and facilitate management decisions that may lead to enhanced SES resilience. This entails investigating system feedbacks and improving our understanding of adaptive capacity, thereby enhancing the ability for self-correcting mechanisms within the SES.

Marsh soil responses to tidal water nitrogen additions contribute to creek bank fracturing and slumping

Large-scale dissolved nutrient enrichment can cause a reduction in belowground biomass, increased water content of soils, and increased microbial decomposition, which has been linked with slumping of low marsh Spartina vegetation into creeks, and ultimately marsh loss. Our study was part of a whole-ecosystem, nutrient-enrichment experiment which was conducted in four first-order tidal creeks (reference creeks: West and Nelson; fertilized creeks: Sweeney and Clubhead) in the Plum Island Sound Estuary (MA) in the northeast USA. We report significantly increased soil % organic matter (P reference creeks). The fertilized organic soils had noticeably more benthic algae and appeared more decomposed and watery. The continuity in horizontal soil shear strength, measured across the adjacent low and high marsh in the fertilized Sweeney, was significantly reduced (P < 0.0001) compared with the reference creek. We identified the reduced continuity of soil shear strength across the marsh landscape as a possible mechanism contributing to the reported fracturing and creek-bank collapse in the fertilized creek systems. In addition, in the face of accelerated sea level rise in recent years in the northeast USA, an increase in flooding exposure by low marsh vegetation apparently caused increases in soil wet bulk density, reductions in Spartina belowground biomass, and increases in Distichlis spicata cover among both reference and nitrogen enriched creeks, which may exacerbate marsh responses (e.g., creek-bank fracturing and slumping) to coastal eutrophication.

The Cyanobacteria Assessment Network – Recent Success in Harmful Algal Bloom Detection

Cyanobacteria blooms, which can become harmful algal blooms (HABs), are a huge environmental problem across the United States. They are capable of producing dangerous toxins that threaten the health of humans and animals, quality of drinking water supplies, and the ecosystem in which they develop. Scientists at EPA are part of a team of specialists working to use remote sensing data to improve cyanobacteria detection methods, so state environmental and health agencies can effectively monitor the abundance of cyanobacteria cells and evaluate, in the context of human health thresholds, the necessity to post public advisories to protect human health.
The Cyanobacteria Assessment Network (CyAN), a multi-agency project involving EPA, NASA, NOAA, and USGS, utilizes historical and current satellite data to create an early warning indicator system for HABs in U.S. freshwater systems. Since the project’s inception in October 2015, CyAN imagery has been used to detect algal blooms in Ohio, Florida, California, Vermont, New Hampshire, Massachusetts, Connecticut, and Rhode Island.
Satellite data products and imagery were recently provided to the Utah Division of Water Quality (UDWQ) to support their cyanobacteria monitoring activities due to the severity of Utah’s cyanobacteria blooms in 2016. Satellite imagery acquired approximately one week after the UDWQ’s routine monthly sampling in mid-June identified that a bloom was developing in Provo Bay. Based on this information, UDWQ scientists returned to the area for follow-up sampling. Days later, on June 29, they issued an advisory about a cyanobacteria bloom detected in Utah Lake, warning the public to keep themselves and their pets out of Provo Bay.
Benjamin M. Holcomb, Coordinator of Biological Assessment and HAB Programs with UDWQ, gave CyAN the following acknowledgement: “The images we’ve been receiving through the CyAN project have been tremendously helpful to UDWQ. The near-daily spatial extent and relative magnitude coverage provides the foundation for a wide range of useful outputs. For HAB response, the most likely useful output of providing near-immediate alerts when cyanobacteria cells are reaching human health thresholds gives UDWQ the opportunity to respond more quickly than relying on public reports. Additionally, it provides UDWQ confidence that our in-situ, bloom-response data are representative of very recent bloom conditions. This allows UDWQ to better target field sampling and more efficiently use our limited resources. Finally, images are easily shared with response agencies as a useful visual communication aid.”
CyAN’s goal is to eventually disseminate satellite-derived imagery and data on the concentration and extent of chl-a and cyanobacteria abundance for the continental U.S. through an Android mobile application and the EnviroAtlas, an interactive resource that allows users to discover, analyze, and download data, maps, and other information, to pr

Using National Coastal Assessment Data to Model Estuarine Water Quality at Large Spatial Scales.

The water quality of the Nation’s estuaries is attracting scrutiny in light of population growth and enhanced nutrient delivery. The USEPA has evaluated water quality in the National Coastal Assessment (NCA) and National Aquatic Resource Surveys (NARS) programs. Here we report on a Random Forest modelling investigation of the survey data to identify the predictor variables affecting surface chlorophyll concentrations in designated regions, paying particular attention to the nutrient measures employed (TN and TP vs DIN and DIP) and regional scale. We also examine model results for indications of change in chlorophyll concentrations over time.
The water quality data used for RF modelling were collected at over 7800 randomly selected sites from 2000 to 2006 (NCA) and in 2010 & 2015 (NARS). The sites were sampled during the summer using consistent collection and assessment methods. Water quality measures included temperature, salinity, pH, Secchi depth, dissolved oxygen, chlorophyll a, dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorous (DIP). Total nitrogen (TN) and total phosphorus (TP) were measured nationwide in 2005 and later. Our work identified 26 sub-regions to investigate the importance of local distinctions. The modelling technique used here is a machine learning algorithm that produces unbiased estimates of error and robust measures of variable importance by bootstrapping predictor variables and employing training/test data subsets.
The model results are robust (model statistics: mean squared error = 0.22 and adjusted R2 = 0.685). Based on the percent mean decrease in accuracy, TN, TP, and TN/TP ratio are important predictor variables for chlorophyll, while DIN and DIP are relatively unimportant. The finer-scale subregions are significant predictors, while the large-scale regions are not. Chlorophyll levels are significantly greater in 2010 and 2015 relative to other years.

Characterization of engineered nanoparticles in commercially available spray disinfectant products advertised to contain colloidal silver

Given the potential for human exposure to silver nanoparticles from spray disinfectants and dietary supplements, we characterized the silver-containing nanoparticles in 22 commercial products that advertised the use of silver or colloidal silver as the active ingredient. Characterization parameters included: total silver, fractionated silver (particulate and dissolved), primary particle size distribution, hydrodynamic diameter, particle number, and plasmon resonance absorbance. A high degree of variability between claimed and measured values for total silver was observed. Only 7 of the products showed total silver concentrations within 20% of their nominally reported values. In addition, significant variations in the relative percentages of particulate vs. soluble silver were also measured in many of these products reporting to be colloidal. Primary silver particle size distributions by transmission electron microscopy (TEM) showed two populations of particles – smaller particles (< 5 nm) and larger particles between 20 and 40 nm. Hydrodynamic diameter measurements using nanoparticle tracking analysis (NTA) correlated well with TEM analysis for the larger particles. Z-average (Z-Avg) values measured using dynamic light scattering (DLS); however, were typically larger than both NTA or TEM particle diameters. Plasmon resonance absorbance signatures (peak absorbance at around 400 nm indicative of metallic silver nanoparticles) were only noted in 4 of the 9 yellow-brown colored suspensions. Although the total silver concentrations were variable among products, ranging from 0.54 mg/L to 960 mg/L, silver containing nanoparticles were identified in all of the product suspensions by TEM.

Assessment of Dry Wells for Stormwater Capture and Aquifer Recharge in the Arid and Semi-Arid Southwest

to evaluate the utility of innovative, distributed, low impact development (LID) infrastructure and best management practices (BMPs) for wet weather capture and drinking water aquifer recharge in the arid and semi-arid southwestern USA
Design, build, monitor the performance of systems of BMPs (capture, storage and settling, infiltration, recharge) for the diversion of wash flow, urban and rooftop runoff, recycled wastewater conveyance, into storage, pre-treatment, and focused recharge through infiltration galleries (wider than deep) and dry wells (deeper than wide)
Utilize a step-wise and progressive computer modeling approach that includes overland, vadose zone, and groundwater flow and water quality, for design and evaluation
Explore scenarios for upscaling recharge system performance to evaluate net zero water and aquifer sustainability and resilience as measured by a sustainable yield without negative impacts
Document experience with the dry well system prototype at Fort Irwin military installation with ambition to transfer technology to the urban metroplex (e.g. Los Angeles)
Combination of field observations and computer simulation modeling

Suspect Screening and Non-Targeted Analysis of Drinking Water Using Point-Of-Use Filters

Monitored contaminants in drinking water represent a small portion of the total compounds present, many of which may be relevant to human health. To understand the totality of human exposure to compounds in drinking water, broader monitoring methods are imperative. In an effort to more fully characterize the drinking water exposome, point-of-use water filtration devices (Brita® filters) were employed to collect time-integrated drinking water samples in a pilot study of nine North Carolina homes. A suspect screening analysis was performed by matching high resolution mass spectra of unknown features to molecular formulas from EPA’s DSSTox database. Candidate compounds with those formulas were retrieved from the EPA’s CompTox Chemistry Dashboard, a recently developed data hub for approximately 720,000 compounds. To prioritize compounds into those most relevant for human health, toxicity data from the US federal collaborative Tox21 program and the EPA ToxCast program, as well as exposure estimates from EPA’s ExpoCast program, were used in conjunction with sample detection frequency and abundance to calculate a “ToxPi” score for each candidate compound. From ∼15,000 molecular features in the raw data, 91 candidate compounds were ultimately grouped into the highest priority class for follow up study. Fifteen of these compounds were confirmed using analytical standards including the highest priority compound, 1,2-Benzisothiazolin-3-one, which appeared in 7 out of 9 samples. The majority of the other high priority compounds are not targets of routine monitoring, highlighting major gaps in our understanding of drinking water exposures. General product-use categories from EPA’s CPCat database revealed that several of the high priority chemicals are used in industrial processes, indicating the drinking water in central North Carolina may be impacted by local industries.

Evaluating a Space-Based Indicator of Surface Ozone-NOx-VOC Sensitivity Over Midlatitude Source Regions and Application to Decadal Trends

Determining effective strategies for mitigating surface ozone (O3) pollution requires knowledge of the relative ambient concentrations of its precursors, NOx, and VOCs. The space-based tropospheric column ratio of formaldehyde to NO2 (FNR) has been used as an indicator to identify NOx-limited versus NOx-saturated O3 formation regimes. Quantitative use of this indicator ratio is subject to three major uncertainties: (1) the split between NOx-limited and NOx-saturated conditions may shift in space and time, (2) the ratio of the vertically integrated column may not represent the near-surface environment, and (3) satellite products contain errors. We use the GEOS-Chem global chemical transport model to evaluate the quantitative utility of FNR observed from the Ozone Monitoring Instrument over three northern midlatitude source regions. We find that FNR in the model surface layer is a robust predictor of the simulated near-surface O3 production regime. Extending this surface-based predictor to a column-based FNR requires accounting for differences in the HCHO and NO2 vertical profiles. We compare four combinations of two OMI HCHO and NO2 retrievals with modeled FNR. The spatial and temporal correlations between the modeled and satellite-derived FNR vary with the choice of NO2 product, while the mean offset depends on the choice of HCHO product. Space-based FNR indicates that the spring transition to NOx-limited regimes has shifted at least a month earlier over major cities (e.g., New York, London, and Seoul) between 2005 and 2015. This increase in NOx sensitivity implies that NOx emission controls will improve O3 air quality more now than it would have a decade ago.

Barriers and Opportunities for the Use of Alternative Technologies to Reduce Nitrogen in Coastal Estuaries

In coastal New England, many communities wrestling with nitrogen over-enrichment from insufficient wastewater management are considering alternative technologies to supplement traditional sewering technology. In particular, communities on Cape Cod, Massachusetts are actively comparing and piloting a number of different alternative technologies as a part of the Clean Water Act’s 208 planning. A range of technologies are being considered from large-scale shellfish seeding to the use of urine-diverting toilets. The technologies vary widely in social acceptance of use, level of uncertainty for contributing to nitrogen reduction, costs, and more. This makes their use challenging for towns charged with meeting nitrogen reduction goals. To better understand these challenges, we conducted more than 25 interviews with participants from local, state and federal governments, regional planning bodies, and technology contractors to identify barriers and opportunities for the use of alternative technologies. The researched technologies included permeable reactive barriers, aquaculture, rain gardens, wetland restoration, living shorelines, and alternative septic systems. A number of opportunities were identified including the perception of reduced costs of implementation, aesthetic or recreational co-benefits, and possibilities for shorter time frames for implementation. Some barriers were also identified, including uncertainty related to the effectiveness of the technologies in reducing nitrogen and their costs, social acceptance of the “new” technologies, and unclear permitting processes. The participants consistently identified the need for improved information sharing among decision makers and with community members in order to successfully implement alternative technologies within their communities. Overall, there is an increased sense of feasibility and possibility for the use of alternative technologies, but almost always as a supplement to traditional sewering.

Nekton use of oyster occupied habitats in two coastal ponds in Rhode Island

Restoration of oyster habitat aims to expand or preserve ecosystem services including increased secondary production of the community. We compare density, biomass, and average standing stock of nitrogen and carbon in seasonal fish and invertebrate collections in Ninigret and Green Hill Pond, in Rhode Island, USA. In Ninigret Pond, we sampled restored oyster reef and oyster aquaculture sites and associated bare sediment sites. Fish and invertebrate density and biomass was significantly higher at restored oyster reef and oyster aquaculture sites than bare sediment sites, with no distinction between the two oyster habitats. Species diversity and richness was greater at the aquaculture site than restored oyster reef and control sites. Aquaculture gear provides structure to attract nekton and may be functionally equivalent to oyster habitat. In Green Hill Pond, we sampled a native oyster bed, a native oyster bed adjacent to seagrass, and bare sediment site. The bare sediment site produced a higher density, species richness and diversity than either oyster habitat. This counterintuitive finding may be a result of increased benthic algal biomass found at the bare sediment site driving secondary production, and the adjacent salt marsh habitat providing functional redundancy. Coastal zone managers interested in restoring the ecological functionality of a complex oyster reef will benefit from understanding the biophysical properties of the seascape.