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Preview: Recent EPA Catalog Records.

Recent Science Inventory records from the EPA

Up to 100 Science Inventory records released or updated since midnight 07/27/2017

Published: Thu, 27 Jul 2017 20:48:10 GMT

Copyright: Public Domain

Alternative Test Methods for Developmental Neurotoxicity: A History and Path Forward (OECD EFSA workshop)

Thu, 27 Jul 2017 18:12:06 GMT

Exposure to environmental contaminants is well documented to adversely impact the development of the nervous system. However, the time, animal and resource intensive EPA and OECD testing guideline methods for developmental neurotoxicity (DNT) are not a viable solution to characterizing potential chemical hazards for the thousands of untested chemicals currently in commerce. Thus, research efforts over the past decade have endeavored to develop cost-effective alternative DNT testing methods. These efforts have begun to generate data that can inform regulatory decisions. Yet there are major challenges to both the acceptance and use of this data. Major scientific challenges for DNT include development of new methods and models that are “fit for purpose”, development of a decision-use framework, and regulatory acceptance of the methods. It is critical to understand that use of data from these methods will be driven mainly by the regulatory problems being addressed. Some problems may be addressed with limited datasets, while others may require data for large numbers of chemicals, or require the development and use of new biological and computational models. For example mechanistic information derived from in vitro DNT assays can be used to inform weight of evidence (WoE) or integrated approaches to testing and assessment (IATA) approaches for chemical-specific assessments. Alternatively, in vitro data can be used to prioritize (for further testing) the thousands of chemicals used in commerce for which there is no data at all on their potential to cause DNT. The focus of this problem-dictated strategy is that testing is driven by decision-making needs, and the amount of resource utilization is adjusted to provide efficient and timely data to address the needs. As the health and environmental impacts of the decision increase, data needs increase, resource use increases, and the need increases for reduced scientific uncertainty in estimates of risk. Recent advances in testing methods and models hold great promise for the development and use of efficient testing strategies for DNT that are capable of initial prioritization and screening, hazard characterization, and hazard prediction. This abstract does not necessarily reflect U.S. EPA policy.

Shrinking cities examined from a shrinking scale – the impact of household and neighborhood heterogeneity on changes in material and energy consumption, ecosystem services and environmental impact

Thu, 27 Jul 2017 14:52:49 GMT

Urban populations continue to increase globally and cities have become the dominant human habitat. However, the growth of cities is not universal. Shrinking cities face decreased income, reduced property values, and decreased tax revenue. Fewer people per unit area creates inefficiencies and higher costs for infrastructure maintenance and the provision of public amenities. However, population losses and economic distress are not equal in all neighborhoods, and in fact are quite heterogeneously distributed across the landscape. Broader statements about the trajectory of a shrinking city may mask underlying differences in economic, cultural, and environmental impacts as well as the ability of some neighborhoods to be resilient and adaptive to economic changes as well as climate change and other environmental stressors. This paper examines the recent impact of population loss in neighborhoods in the Río Piedras watershed in San Juan, Puerto Rico, on the provision of ecosystem services, material and energy flows, and ecological impacts, using public data and data collected previously in two household surveys. Using scenarios, we estimate future population changes and their potential positive and negative impacts on the environment and human well-being in these neighborhoods.

Carbon storage and greenhouse gas fluxes in the San Juan Bay Estuary: Current trends and likely future states.

Thu, 27 Jul 2017 14:39:28 GMT

Mangrove systems are known carbon (C) and greenhouse gas (GHG) sinks, but this function may be affected by global change drivers that include (but are not limited to) eutrophication, climate change, species composition shifts, and hydrological changes. In Puerto Rico’s San Juan Bay Estuary, mangrove wetlands are characterized by anthropogenic impacts, particularly tidal restriction due to infilling of the Martin Pena Canal and eutrophication. The objective of our research is to measure carbon sequestration and carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes in the San Juan Bay Estuary to understand the sustainability and role in global climate of this urban mangrove ecosystem. Cores for C sequestration measurements were collected and GHG fluxes were measured during rainy and dry seasons at 5 sites along a gradient of development and nitrogen loading in the San Juan Bay Estuary. At each site, paired GHG flux measurements were performed for mangrove wetland soil and estuarine water using static and floating chambers. Our results suggest a positive relationship between urban development and CH4 and N2O emissions, and demonstrate that in this system, estuarine waters are a major methane source. In addition to providing characterization of GHG fluxes in an urban subtropical estuary, these data provide a baseline against which future states of the estuary (after planned hydrological restoration has been implemented) may be compared.

Comparing rat and rabbit embryo-fetal developmental toxicity studies for 379 pharmaceuticals: On systemic dose and developmental effects (Critical Reviews in Toxicology)

Thu, 27 Jul 2017 14:37:28 GMT

A database of embryo-fetal developmental toxicity (EFDT) studies of 379 pharmaceutical compounds in rat and rabbit was analyzed for species differences based on toxicokinetic parameters of area under the curve (AUC) and maximum concentration (Cmax) at the developmental adverse effect level (dLOAEL). For the vast majority of cases (83% based on AUC of n=283), dLOAELs in rats and rabbits were within the same order of magnitude (less than 10-fold different) when compared based on available data on AUC and Cmax exposures. For 13.5% of the compounds the rabbit was more sensitive and for 3.5% of compounds the rat was more sensitive when compared based on AUC exposures. For 12% of the compounds the rabbit was more sensitive and for 1.3% of compounds the rat was more sensitive based on Cmax exposures. When evaluated based on human equivalent dose (HED) conversion using standard factors, the rat and rabbit were equally sensitive. The relative extent of embryo-fetal toxicity in the presence of maternal toxicity was not different between species. Overall effect severity incidences were distributed similarly in rat and rabbit studies. Individual rat and rabbit strains did not show a different general distribution of systemic exposure LOAELs as compared to all strains combined for each species. There were no apparent species differences in the occurrence of embryo-fetal variations. Based on power of detection and given differences in the nature of developmental effects between rat and rabbit study outcomes for individual compounds, EFDT studies in two species have added value over single studies.

Assessment of the urban water system with an open, reproducible process applied to Chicago

Thu, 27 Jul 2017 14:21:17 GMT

Urban water systems convey complex environmental and man-made flows. The relationships among water flows and networked storages remains difficult to comprehensively evaluate. Such evaluation is important, however, as interventions are designed (e.g, conservation measures, green infrastructure) to modify specific flows of urban water (e.g. drinking water, stormwater) that may have systemic effects. We have developed a general model that specifies the relationships among urban water system components, and a set of tools for evaluating the model for any city as the R package CityWaterBalance. CityWaterBalance provides a reproducible workflow for assessing urban water system(s) by facilitating the retrieval of open data, largely via web services, and analysis of these data using open-source R functions. It allows the user to 1) quickly assemble a quantitative, unified picture of flows thorough an urban area, and 2) easily change the spatial and temporal boundaries of analysis to match scales relevant to local decision-making. We used CityWaterBalance to evaluate the water system in the Chicago metropolitan area on a monthly basis for water years 2001-2010. Results, including the relative magnitudes and temporal variability of major water flows in greater Chicago, are used to consider 1) trade-offs associated with management alternatives for stormwater and combined sewer overflows and 2) the significance of future changes in precipitation, which is the largest term in the Chicago water balance.

Variability within Systemic In Vivo Toxicity Studies (ASCCT)

Thu, 27 Jul 2017 14:18:17 GMT

In vivo studies have long been considered the gold standard for toxicology screening. Often time models developed in silico and/or using in vitro data to estimate points of departures (POD) are compared to the in vivo data to benchmark and evaluate quality and goodness of fit. However, it is not certain what a good model is and how well is well before it turns into overfitting. Here we estimate the amount of variance that can be expected within systemic in vivo data. The present study was done using the US EPA’s Toxicity Reference Database (ToxRefDB). The database incorporates over 5,000 in vivo toxicity studies from the Office of Pesticide Programs (registrant-submitted studies), National Toxicology Program, pharmaceutical industries, and publically available literature covering over 1,000 chemicals. Using multilinear regression to calculate the residual sum or squares, we accounted for known variability in study conditions to quantify the unexplained variance of the log10(POD) to be about 0.35. The leave one out method was used to assess the amount of variance explained by each study condition and chemicals were found to be the biggest contributor. Stratifying the dataset by species and administration methods showed similar results, indicating stability of the unexplained variance. Considering and quantifying the unexplained variance will provide a benchmark and lower bounds on the mean-square-error for predictive toxicity model development.

Exploring the effects of temperature and resource limitation on mercury bioaccumulation in Fundulus heteroclitus using dynamic energy budget modeling and behavioral assessment

Thu, 27 Jul 2017 14:12:16 GMT

Global climate change is likely to affect both temperature and resource availability in aquatic ecosystems. While higher temperatures may result in increased food consumption and increased mercury accumulation, they may also lead to increased growth and reduced mercury accumulation through somatic dilution. Dynamic energy budget (DEB) theory provides a broad and generalizable framework based on first principles of energy metabolism that is well suited to understand these interactions, allowing joint acquisition and interpretation of chemical exposure and stressor effect information to be translated into demographic rate changes. In the current study, we conducted growth and bioaccumulation experiments to examine the interaction of temperature and resource availability on mercury accumulation and effects in the estuarine fish Fundulus heteroclitus (mummichog). In the first experiment, juvenile mummichog were fed tuna naturally contaminated with Hg at either 3.3% or 10% of their dry body weight/day and held at either 15 or 27 °C for 28 days. Growth was low in most treatments, except in fish fed 10% body weight held at 27 °C (40% weight and 12% length increase). However, methylmercury bioaccumulation was similar across feeding conditions but increased with temperature (~17-fold increase in methylmercury concentration at 27 °C and ~7-fold increase at 15 °C, regardless of feeding rate). In the second experiment, mummichogs from two wild populations with differing native mercury exposures were fed either a high or low methylmercury diet. Fish were strip-spawned every two weeks during the feeding period. Adults were sampled for total mercury concentration at the start and end of the experiment, and egg methylmercury concentration was measured in unfertilized eggs from each spawning event. Danioscope software was used to assess the heart rate of developing embryos at 10 days post fertilization. A dark:light movement assay determined differences in behavior of larvae between treatments at three and 10 days post hatch using Ethovision software. Tissue analysis indicated successful maternal transfer of mercury to eggs in the high mercury feed treatment. Heart rate and movement assays indicated potential population level differences in baseline behavior. The use of these data in a DEB model may greatly aid in understanding how temperature and resource availability affect mercury bioaccumulation. Overall, this work contributes to the ongoing development of an ecological modeling framework in a fish with an extensive toxicological and genomic background. Ultimately, we are working to connect molecular mechanistic, physiological, reproductive, and behavioral responses to population level fitness.

Integration of different data gap filling techniques to facilitate assessment of polychlorinated biphenyls: A proof of principle case study (ASCCT meeting)

Thu, 27 Jul 2017 13:58:59 GMT

Data gap filling techniques are commonly used to predict hazard in the absence of empirical data. The most established techniques are read-across, trend analysis and quantitative structure-activity relationships (QSARs). Toxic equivalency factors (TEFs) are less frequently used data gap filling techniques which are applied to estimate relative potencies for mixtures of chemicals that contribute to an adverse outcome through a common biological target. For example, The TEF approach has been used for dioxin-like effects comparing individual chemical activity to that of the most toxic dioxin: 2,3,7,8-tetrachlorodibenzo-p-dioxin. The aim of this case study was to determine whether integration of two data gap filling techniques: QSARs and TEFs improved the predictive outcome for the assessment of a set of polychlorinated biphenyl (PCB) congeners and their mixtures. PCBs are associated with many different adverse effects, including their potential for neurotoxicity, which is the endpoint of interest in this study. The dataset comprised 209 PCB congeners, out of which 87 altered in vitro Ca(2+) homeostasis from which neurotoxic equivalency values (NEQs) were derived. The preliminary objective of this case study was to develop a QSAR model to predict NEQ values for the 122 untested PCB congeners. A decision tree model was developed using the number of position specific chlorine substitutions on the biphenyl scaffold as a fingerprint descriptor. Three different positional combinations were explored on the basis of equivalence between ortho, meta and para positions. Five different decision trees were developed on the basis of restrictions on tree growth. The training dataset of 87 tested PCBs was evaluated using 5-fold cross validation and leave-one-out (LOO) internal validation to ultimately predict NEQ values for the 122 untested PCBs. The evaluation statistics of the “best” decision tree model resulted in LOOCV RMSE: 0.29, 5-fold CV test RMSE: 0.34, and R2: 0.79. The results demonstrate the utility of using the TEF approach as an alternative data gap filling technique.

Using ecological models to investigate stressor effects throughout the life cycle of mummichogs

Thu, 27 Jul 2017 13:36:06 GMT

Ecological models of mummichogs (Fundulus heteroclitus) provide valuable tools to link controlled laboratory experiments to field observations. Mummichogs are useful study organisms due to their amenability to laboratory conditions, the availability of well-developed molecular tools, and their rich history in ecology and evolution. To understand the effects of chemicals and other stressors on population persistence, we are developing and testing a mathematical model of fecundity and dynamic energy budget which will ultimately be integrated into individual-based model of population persistence. Utilizing data from laboratory-based pair and small group spawning, an oocyte growth and spawning model developed for fathead minnow (Pimephales promelas) was modified for mummichog. To determine the comparability of laboratory experiments using small numbers of individuals to natural populations, we assessed the reproductive status and energetic reserves of mummichogs held in the lab, and those collected in Succotash Marsh, Jerusalem, RI during breeding season (July 2016). Fish were collected by seine at the same tidal stage on multiple days throughout the lunar cycle, and the abundance of individuals in four size-classes (80 mm) was recorded. Consistent with a resource-rich environment, the laboratory-bred fish were more likely to have mature oocytes than the field-caught 41-60 mm fish, and they had a much greater mass of body fat and greater hepatosomatic indices. These data, along with an ongoing laboratory-based growth and reproduction experiments, are being used to refine the fecundity and bioenergetics models. This combination of laboratory experiments, field study and ecological models provide a testable system to predict the effects of stressors on the tradeoffs throughout the mummichog lifecycle between energy storage, growth, and reproduction.