S. Thomas Purucker

• PhD Ecology & Evolutionary Biology
• Research Ecologist at United States Environmental Protection Agency

Evaluating biomarkers of stress in amphibians is critical to conservation, yet current techniques are often destructive and/or time‐consuming, which limits ease of use. In the present study, we validate the use of dermal swabs in spotted salamanders ( Ambystoma maculatum ) for biochemical profiling, as well as glutathione (GSH) stress response foll...

Controlled laboratory experiments are often performed on amphibians to establish causality between stressor presence and an adverse outcome. However, in the field, identification of lab-generated biomarkers from single stressors and the interactions of multiple impacts are difficult to discern in an ecological context. The ubiquity of some pesticid...

A growing list of chemicals are approved for production and use in the United States and elsewhere, and new approaches are needed to rapidly assess the potential exposure and health hazard posed by these substances. Here, we present a high-throughput, data-driven approach that will aid in estimating occupational exposure using a database of over 1....

Hummingbirds are charismatic fauna that provide important pollination services, including in the continental US, where 15 species regularly breed. Compared to other birds in North America, hummingbirds (family Trochilidae) have a unique exposure route to pesticides because they forage on nectar. Therefore, hummingbirds may be exposed to systemic pe...

Spatially explicit ecological risk assessment (ERA) requires estimating the overlap between chemical and receptor distribution to evaluate the potential impacts of exposure on nontarget organisms. Pesticide use estimation at field level is prone to error due to inconsistencies between ground-reporting and geospatial data coverage; attempts to recti...

Vernal pool fairy shrimp, Branchinecta lynchi, is a freshwater crustacean endemic to California and Oregon, including California’s Central Valley. B. lynchi is listed as a Federally Threatened species under the US Endangered Species Act, and as a vulnerable species on the IUCN Red List. Threats that may negatively impact vernal pool fairy shrimp po...

The US Environmental Protection Agency (USEPA) employs a tiered process for assessing risks of pesticides to bees. The model discussed in this paper focuses on honey bees (Apis mellifera L.). If risks to honey bees are identified at the first tier based on exposure and toxicity data for individual adult and larval honey bees, then effects are evalu...

Non-targeted analysis (NTA) methods are widely used for chemical discovery but seldom employed for quantitation due to a lack of robust methods to estimate chemical concentrations with confidence limits. Herein, we present and evaluate new statistical methods for quantitative NTA (qNTA) using high-resolution mass spectrometry (HRMS) data from EPA’s...

Background Environmental health research has recently undergone a dramatic shift, with ongoing technological advancements allowing for broader coverage of exposure and molecular biology signatures. Approaches to integrate such measures are still needed to increase understanding between systems-level exposure and biology. Objectives We address this...

One of the biggest challenges in ecological risk assessment is determining the impact of multiple stressors on individual organisms and populations in real world scenarios. Frequently, data derived from laboratory studies of single stressors are used to estimate risk parameters and do not adequately address scenarios where other stressors exist. Em...

Chemical exposure estimation through the dermal route is an underemphasized area of ecological risk assessment for terrestrial animals. Currently, there are efforts to create exposure models to estimate doses from this pathway for use in ecological risk assessment. One significant limitation has been insufficient published data to characterize expo...

The U.S. EPA frequently uses avian or fish toxicity data to set protective standards for amphibians in ecological risk assessments. However, this approach does not always adequately represent aquatic-dwelling and terrestrial-phase amphibian exposure data. For instance, it is accepted that early life stage tests for fish are typically sensitive enou...

Reservoirs are dominant features of the modern hydrologic landscape and provide vital services. However, the unique morphology of reservoirs can create suitable conditions for excessive algae growth and associated cyanobacteria blooms in shallow in-flow reservoir locations by providing warm water environments with relatively high nutrient inputs, d...

The increasing use of agrochemicals, alone and in combination, has been implicated as a potential causative factor in the decline of amphibians worldwide. Fertilizers and pesticides are frequently combined into single-use tank mixtures for agricultural applications to decrease costs while meeting the food demands of a growing human population. Limi...

Honey bees are crucial pollinators for agricultural crops but are threatened by a multitude of stressors including exposure to pesticides. Linking our understanding of how pesticides affect individual bees to colony‐level responses is challenging because colonies show emergent properties based on complex internal processes and interactions among in...

Pesticides are being applied at a greater extent than in the past. Once pesticides enter the ecosystem, many environmental factors can influence their residence time. These interactions can result in processes such as translocation, environmental degradation, and metabolic activation facilitating exposure to target and non-target species. Most anur...

Most corn (Zea mays) seeds planted in the US in recent years are coated with a seed treatment containing neonicotinoid insecticides. Abrasion of the seed coating generates insecticide‐laden planter dust that disperses through the landscape during corn planting and has resulted in many ‘bee‐kill’ incidents in North America and Europe. We investigate...

The extent of plasma protein binding is an important compound-specific property that influences a compound’s pharmacokinetic behavior and is a critical input parameter for predicting exposure in physiologically based pharmacokinetic (PBPK) modeling. When experimentally determined fraction unbound in plasma (fup) data are not available, quantitative...

Research Impact Statement: Gridded precipitation datasets vary in capturing different extreme events, both dry and wet, and different precipitation data sources usage led to varying parameter calibrations in watershed modeling. ABSTRACT: Gridded precipitation datasets are becoming a convenient substitute for gauge measurements in hydrological model...

Vernal pools are ephemeral wetlands that provide critical habitat to many listed species. Pesticide fate in vernal pools is poorly understood because of uncertainties in the amount of pesticide entering these ecosystems and their bioavailability throughout cycles of wet and dry periods. The Pesticide Water Calculator (PWC), a model used for the reg...

Modeling pesticide concentrations in urban environments is challenging relative to agricultural environments because of uncertainties about use practices in developed areas and infrastructure complexities that challenge existing fate and transport algorithms. We simulate urban runoff and stream water concentrations of bifenthrin, a commonly detecte...

The protection of listed species through the Ecological Risk Assessment (ERA) process is encumbered by the number and diversity of species that need protection and the limited data available to inform assessments. Ecological communities within isolated ecosystems often contain a number of biologically diverse endemic, endangered, and threatened spe...

Environmental simulations of pesticide fate and transport can be complex and highly parameterized with uncertain input values. In the face of this uncertainty, many environmental risk models incorporate conservative assumptions in order to avoid false negative decision errors. We examine a regulatory model, the Pesticide Water Calculator (PWC) with...

Environmental context Metabolomics can be used to provide a snapshot of an organism’s physiology as the organism is exposed to varying environmental conditions. In this study, laboratory-reared amphibians were exposed to multiple pesticides, analogous to field exposures, resulting in an impact to both pesticide body concentrations and the amphibian...

Environmental fate and transport processes are influenced by many factors. Simulation models that mimic these processes often have complex implementations, which can lead to over-parameterization. Sensitivity analyses are subsequently used to identify critical parameters whose uncertainties can be further reduced or better described and prediction...

In this study, the impact of hydration status on dermal uptake of pesticides in two species of amphibians is examined. Absorption of pesticides in anurans occurs primarily through a highly vascularized dermal seat patch; however, pesticides can also enter through the superficial dermis following exposure. Despite the growing body of literature on d...

To study spray drift contributions to non-targeted habitats, pesticide concentrations in stemflow (water flowing down the trunk of a tree during a rain event), throughfall (water from tree canopy only), and surface water in an agriculturally impacted wetland area near Tifton, Georgia, USA were measured (2015-2016). Agricultural fields and sampling...

We employ Monte Carlo simulation and sensitivity analysis techniques to describe the population dynamics of pesticide exposure to a honey bee colony using the VarroaPop + Pesticide model. Simulations are performed of hive population trajectories with and without pesticide exposure to determine the effects of weather, queen strength, foraging activi...

Pesticide use in agricultural areas requires the application of numerous chemicals to control target organisms, leaving non-target organisms at risk. The present study evaluates the hepatic metabolomic profile of one group of non-target organisms, amphibians, after exposure to a single pesticide and pesticide mixtures. Five common-use pesticide act...

Understanding how pesticide exposure to non-target species influences toxicity is necessary to accurately assess the ecological risks these compounds pose. To assess the potential metabolic activation of broad use pesticides in amphibians, in vitro and in vivo metabolic rate constants were derived from toad (Anaxyrus terrestris) livers in experimen...

The objective of the current study was to use a biomarker-based approach to investigate the influence of atrazine exposure on American toad (Anaxyrus americanus) and grey tree frog (Hyla versicolor) tadpoles. Atrazine is one of the most frequently detected herbicides in environmental matrices throughout the United States. In surface waters, it has...

Pesticides have been implicated as a major factor in global amphibian declines and may pose great risk to terrestrial phase amphibians moving to and from breeding ponds on agricultural landscapes. Dermal uptake from soil is known to occur in amphibians, but predicting pesticide availability and bioconcentration across soil types is not well underst...

A series of simulated rainfall-runoff experiments with applications of different manure types (cattle solid pats, poultry dry litter, swine slurry) was conducted across four seasons on a field containing 36 plots (0.75 × 2 m each), resulting in 144 rainfall-runoff events. Simulating time-varying release of Escherichia coli, enterococci, and fecal c...

Freshwater shrimps are an important biotic component of tropical ecosystems. However, they can have a low probability of detection when abundances are low. We sampled 3 of the most common freshwater shrimp species, Macrobrachium olfersii, Macrobrachium carcinus, and Macrobrachium heterochirus, and used occupancy modeling and logistic regression mod...

For terrestrial amphibians, accumulation of pesticides through dermal contact is a primary route of exposure in agricultural landscapes and may be contributing to widespread amphibian declines. To show pesticide transfer across the amphibian dermis at permitted label application rates, our study was designed to measure pesticide body burdens after...

Four seasonal rainfall simulations in 2009 and 2010 were applied to a field containing 36 plots (0.75 × 2 m each), resulting in 144 runoff events. In all simulations, a constant rate of rainfall was applied then halted 60 min after initiation of runoff, with plot-scale monitoring of runoff every 5 min during that period. Runoff was simulated with t...

Precipitation is a key control on watershed hydrologic modelling output, with errors in rainfall propagating through subsequent stages of water quantity and quality analysis. Most watershed models incorporate precipitation data from rain gauges; higher-resolution data sources are available, but they are associated with greater computational require...

Understanding the survival of fecal indicator bacteria (FIB) and microbial source tracking (MST) markers is critical to developing pathogen fate and transport models. Although pathogen survival in water microcosms and manure-amended soils is well-documented, little is known about their survival in intact cowpats deposited on pastures. We conducted...

Background/Question/Methods Managed honey bee (Apis mellifera L.) colonies have been declining in numbers in both the U.S. and Europe since the 1940s but the declines have increased in the past two decades. The abundance of bees is influenced by a multitude of factors including pathogens, parasites, habitat loss, and pollutants. Honey bee colony...

Hydrologic models are commonly calibrated by optimizing a single objective function target to compare simulated and observed flows, although individual targets are influenced by specific flow modes. Nash-Sutcliffe efficiency (NSE) emphasizes flood peaks in evaluating simulation fit, while modified Nash-Sutcliffe efficiency (MNS) emphasizes lower fl...

Background/Question/Methods Dermal exposure presents a potentially significant but understudied route for pesticide uptake in terrestrial amphibians. Historically, evaluation of pesticide risk to both amphibians and reptiles has been achieved by comparing ingestion and inhalation estimates to bird and/or mammal toxicity values. Although some toxi...

This study investigates the uncertainty associated with simulating runoff at a field scale based on experimental observations on a plot scale. Thirty-six 0.75-m by 2-m plots were delineated within a farm field, and rainfall simulators were used to control precipitation rates and durations on each plot, resulting in monitored runoff. Rainfall-runoff...

This study investigates the uncertainty associated with simulating runoff at a field scale based on experimental observations on a plot scale. Thirty-six 0.75-m by 2-m plots were delineated within a farm field, and rainfall simulators were used to control precipitation rates and durations on each plot, resulting in monitored runoff. Rainfall-runoff...

Spatial Analysis and Decision Assistance (SADA) is a Windows freeware program that incorporates spatial assessment tools for effective environmental remediation. The software integrates modules for GIS, visualization, geospatial analysis, statistical analysis, human health and ecological risk assessment, cost/benefit analysis, sampling design, and...

This letter details the collective views of a number of independent researchers on the technical assessment and evaluation of environmental models and software. The purpose is to stimulate debate and initiate action that leads to an improved quality of model development and evaluation, so increasing the capacity for models to have positive outcomes...

Watershed hydrologic and fate-and-transport models are widely used to forecast water quanti-ty and quality responses to alternative land use and cli-mate change scenarios. The ability of such tools to fore-cast changes in ecosystem services with reasonable accu-racy depends on calibrating reliable simulations of stream-flow, which in turn require a...

Background/Question/Methods We adapt a source apportionment model from airborne particulate matter applications as a potential substitute/supplement for the current use of water pollution pathogen indicators (e.g., Coliform bacteria) at recreational beaches; the objective is to identify water-borne fecal sources for remediation to reduce exposure...

Regional scale watershed management decisions must be informed by the science-based relationship between anthropogenic activities on the landscape and the change in ecosystem structure, function, and services that occur as a result. We applied process-based models that represent watershed loading, mercury processing, instream water quality, habitat...

This review assesses the usefulness of parasites as bioindicators of environmental impact. Relevant studies published in the past decade were compiled; factorial meta-analysis demonstrated significant effects and interactions between parasite levels and the presence and concentration of various pollutants and/or environmental stressors. These effec...

Fish habitat and biodiversity for fish are valuable ecosystem services provided by rivers. Future land development and climate change will likely alter these services, and an understanding of these responses can guide management and restoration priorities. We used hierarchical models that account for natural differences in ecoregion and river drain...

  Nitrate-nitrogen (NO3-N) concentrations in stream water often respond uniquely to changes in inter-annual conditions (e.g., biological N uptake and precipitation) in individual catchments. In this paper, we assess (1) how the spatial distribution of NO3-N concentrations varies across a dense network of nonnested catchments and (2) how relationshi...

This paper reviews concepts for evaluating integrated environmental models and discusses a list of relevant software-based tools. A simplified taxonomy for sources of uncertainty and a glossary of key terms with “standard” definitions are provided in the context of integrated approaches to environmental assessment. These constructs provide a re...

During the past 12000 years agricultural systems have transitioned from natural habitats to conventional agricultural regions and recently to large areas of genetically engineered (GE) croplands. This GE revolution occurred for cotton in a span of slightly more than a decade during which a switch occurred in major cotton production areas from growi...

Anthropogenic contamination is typically distributed heterogeneously through space. This spatial structure can have different effects on the cumulative doses of wildlife exposed to contamination within the environment. These effects are accentuated when individual organisms pursue different movement strategies, and movement strategies can be affect...

Spatial Analysis and Decision Assistance (SADA) is a Windows freeware program that incorporates tools from environmental assessment into an effective problem-solving environment. SADA was developed by the Institute for Environmental Modeling at the University of Tennessee and includes integrated modules for GIS, visualization, geospatial analysis,...

A remedial investigation was conducted to determine the extent and type of contamination in the floodplain soils of Waste Area Grouping (WAG) 2, in conjunction with environmental restoration activities at the US Department of Energy (DOE) Oak Ridge Reservation (ORR). WAG 2 is located downstream from the main Oak Ridge National Laboratory (ORNL) pla...

This report is one of five reports issued in 1996 that provide follow-up information to the Phase I Remedial Investigation (RI) Report for Waste Area Grouping (WAG) 2 at Oak Ridge National Laboratory (ORNL). The five reports address areas of concern that may present immediate risk to public health at the Clinch River and ecological risk within WAG...

This report is one of five reports issued in 1996 that provide follow- up information to the Phase 1 Remedial Investigation (RI) Report for Waste Area Grouping (WAG) 2 at Oak Ridge National Laboratory (ORNL). The five reports address areas of concern that could cause potential human health risk and ecological risk within WAG2 at ORNL. The purpose o...

The Waste Area Grouping (WAG) 1 Groundwater Operable Unit (OU) at Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee, is undergoing a site characterization to identify environmental contamination that may be present. This document, Site Characterization Report for Groundwater in Waste Area Grouping I at Oak Ridge National Laboratory, Oak...

Quantitative decision methods can be developed during environmental restoration projects that incorporate stakeholder input and can complement current efforts that are undertaken for data collection and alternatives evaluation during the CERCLA process. These decision-making tools can supplement current EPA guidance as well as focus on problems tha...

Cleanup of hazardous waste sites under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) is a complicated and painstaking process, particularly at facilities with a multitude of individual hazardous waste sites, each having a multitude of chemicals and radonuclides. The US Department of Energy-Oak Ridge, Environment...

Spatial Analysis and Decision Assistance (SADA) is freeware that implements terrestrial + criteria were applied to determine a spatially explicit remedial design that reduced shrew exposures to protective levels.

A more streamlined approach is proposed for executing the Remedial Investigation/Feasibility Study Process. This approach recognizes the uncertainties associated with the process, particularly regarding the derivation of human health risk estimates. The approach is tailored for early identification of sites and contaminants of immediate concern, ea...

Geostatistical analysis refers to a collection of statistical methods for addressing data that vary in space. By incorporating spatial information into the analysis, geostatistics has advantages over traditional statistical analysis for problems with a spatial context. Geostatistics has a history of success in earth science applications, and its po...

Methods from formal decision theory provide means of addressing environmental health risk management problems. In this report, we discuss the decision theory concept of the ``value of perfect information.`` We illustrate its application to the quantification of upper bounds on data worth, as well as its use as a means of exploring the sensitivity o...