Development of a mechanistic model for analyzing avian reproduction data for pesticide risk assessment

Mechanistic effect models are increasingly recommended as tools for refining evaluations of risk from exposure to pesticides. In the context of bird and mammal risk assessments, DEB-TKTD models have been recommended for characterizing sublethal effects at lower tiers. However, there are currently no such models. Currently, chronic, multi-generational studies are performed to characterize potential effects of pesticides on avian reproduction, but it is has not been established to what extent results from these studies can inform effect models. Here, a standard Dynamic Energy Budget (DEB) model was extended to account for the avian toxicity endpoints observed in regulatory studies. We linked this new implementation to a toxicological module to capture observed pesticide effects on reproduction via a decreased efficiency of egg production. We analysed ten reproduction studies with five different pesticides conducted with the mallard (Anas platyrhynchos) and the northern bobwhite (Colinus virginianus). The new model implementation accurately distinguished between effects on egg production from direct mechanism of toxicity and from food avoidance. Due to the specific nature of regulatory studies, model applicability for risk refinement is currently limited. We provide suggestions for next steps in model development.

Applying a hybrid model to support management of the endangered Topeka shiner in oxbow habitats

Introduction

Habitat restoration aims at reinstating abiotic and biotic habitat conditions to support long-term species persistence and viability. This management practice is commonly part of recovery plans developed for species listed as threatened or endangered under the Endangered Species Act. The endangered Topeka shiner (Notropis topeka) inhabits off-channel habitats, such as oxbow lakes which are increasingly the focus of restoration, but the exact abiotic conditions conducive to its persistence in this habitat are not fully understood. In this study, a hybrid model consisting of an individual-based model of the Topeka shiner and an aquatic ecosystem model representing the oxbow habitat was applied to identify optimal environmental conditions for the persistence of Topeka shiner populations.

Materials and methods

Environmental conditions that correlated with Topeka shiner presence were gathered from published studies and included water temperature, turbidity, oxbow depth, light intensity (as a function of riparian vegetation presence), dissolved nitrogen, and dissolved phosphorus. Selected conditions were systematically varied in simulations and results were analyzed with a partial rank correlation method that quantifies the relative influence on model output from multiple factors.

Results

Conducted simulations identified water temperature, depth, and dissolved inorganic nitrogen to be the most influential for Topeka shiner population biomass and additional simulations were conducted exploring the magnitudes and directions of effects of these three factors. Water temperature had the largest positive impact on population biomass followed by oxbow depth and nitrogen reduction.

Discussion

We recommend that the three identified factors be further explored in a combination of empirical and modeling approaches to advise management for the endangered Topeka shiner. This study demonstrated how ecological models could inform recovery plans by identifying factors that enhance species persistence. Ultimately, models should support management practices that result in long-term population viability of listed species and could facilitate their timely delisting.

Using life-history trait variation to inform ecological risk assessments for threatened and endangered plant species

Developing population models for assessing risks to terrestrial plant species listed as threatened or endangered under the Endangered Species Act (ESA) is challenging given a paucity of data on their life histories. The purpose of this study was to develop a novel approach for identifying relatively data-rich nonlisted species that could serve as representatives for species listed under the ESA in the development of population models to inform risk assessments. We used the USDA PLANTS Database, which provides data on plants present in the US territories, to create a list of herbaceous plants. A total of 8742 species was obtained, of which 344 were listed under the ESA. Using the most up-to-date phylogeny for vascular plants in combination with a database of matrix population models for plants (COMPADRE) and cluster analyses, we investigated how listed species were distributed across the plant phylogeny, grouped listed and nonlisted species according to their life history, and identified the traits distinguishing the clusters. We performed elasticity analyses to determine the relative sensitivity of population growth rate to perturbations of species' survival, growth, and reproduction and compared these across clusters and between listed and nonlisted species. We found that listed species were distributed widely across the plant phylogeny as well as clusters, suggesting that listed species do not share a common evolution or life-history characteristics that would make them uniquely vulnerable. Lifespan and age at maturity were more important for distinguishing clusters than were reproductive traits. For clusters that were intermediate in their lifespan, listed and nonlisted species responded similarly to perturbations of their life histories. However, for clusters at either extreme of lifespan, the response to survival perturbations varied depending on conservation status. These results can be used to guide the choice of representative species for population model development in the context of ecological risk assessment. Integr Environ Assess Manag 2023;19:213-223. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Atrazine and estradiol effects on development of Acris blanchardi (Blanchard's cricket frog) exposed in outdoor enclosures

BACKGROUND

The herbicide atrazine has been proposed as a potential endocrine disrupting compound (EDC) for amphibians. Using atrazine concentrations below or at those typically found in surface waters (0.5, 5.0, 50 μg/L), we exposed Acris blanchardi (Blanchard's cricket frog) larvae throughout development until metamorphosis (i.e. Gosner stages 26-45). An additional 50 μg/L treatment (50s μg/L) was utilized where supplemented algae was added to control for indirect atrazine effects from reduced food sources. In addition to atrazine, experimental groups also included a negative control and two positive controls, 17β-estradiol (E2) at 2.3 and 25 μg/L. At 60 days post-metamorphosis, A. blanchardi metamorphs were euthanized for analysis of gross and histopathological development.

RESULTS

Atrazine did not significantly influence mortality (mean recovery of 54% across treatments), sex ratio, body mass (BM), snout-vent length (SVL), gonad size, nor gonad development of A. blanchardi. Females exposed to 50s μg/L atrazine had 29% less mass, were 10% shorter, and had a 29% lower mean ovary area (mm² ) as compared to negative controls, suggesting algae enrichment had a significant negative effect. Males exposed to estradiol (25 μg/L) showed an increased level of oviduct development. Ovary area was also significantly influenced by estradiol treatment at 2.3 and 25 μg/L.

CONCLUSION

Overall, estradiol had much less effect than predicted based on other model species (e.g. Xenopus laevis). Development of A. blanchardi, overall, was not affected by long-term exposure to environmentally relevant concentrations of atrazine. However, this species also was largely insensitive to exogenous estradiol in this test system. © 2022 Society of Chemical Industry.

Coupling field-scale and watershed models for regulatory modeling of pesticide aquatic exposures in streams

Estimating exposure in receiving waterbodies is a key step in the regulatory process to evaluate potential ecological risks posed by the use of agricultural pesticides. The United States Environmental Protection Agency (USEPA) currently uses the Variable Volume Water Model (VVWM) to predict environmental concentrations of pesticides in static waterbodies (ponds) that receive edge-of-field runoff inputs from the Pesticide Root Zone Model (PRZM). This regulatory model, however, does not adequately characterize potential pesticide concentrations in flowing water systems (streams and rivers) drained from watershed areas. This study aims at addressing this gap by coupling the regulatory PRZM model with a watershed-level hydrological model, the Soil and Water Assessment Tool (SWAT), to predict pesticide concentrations in flowing water habitats for aquatic organisms. This coupled PRZM-SWAT model was applied in a test watershed (~HUC12), a headwater watershed of Goodwater Creek in Missouri, and simulation results at the outlet of this watershed were compared to daily and near-daily measured streamflow and atrazine concentration data from a decade-long sampling campaign. Overall, the PRZM-SWAT model captured (1) the general magnitude and temporal trend of daily atrazine concentrations, (2) the observed high-end of exposure levels (>3 ppb) of atrazine concentrations, and (3) the 90^th centile annual maximum for various exposure durations (1-, 4-, 7-, 21-, and 60-day rolling average), which are important exposure metrics used in assessing the potential ecological risks posed by the application of pesticides. The PRZM-SWAT model is expected to expand the utility of the field-scale regulatory model to include pesticide exposure prediction capability in flowing waterbodies from agricultural watersheds. Integr Environ Assess Manag 2022;18:1678-1693. © 2022 SETAC.

A data accuracy evaluation strategy to improve the representation of potential pesticide use areas for endangered species assessments

The use of "best available data" is a fundamental requirement for all scientific forms of analysis. This paper discusses ways to improve the accuracy of data used to evaluate the potential impacts of pesticides on species that are listed as threatened or endangered under the Endangered Species Act (ESA) by ensuring the best available spatial data representing pesticide use sites are applied correctly. A decision matrix is presented that uses accuracy information from metadata contained in the US Department of Agriculture's (USDA's) Cropland Data Layer (CDL) and the Census of Agriculture (CoA) to improve how labeled pesticide use sites are spatially delineated. We suggest recommendations for the current pesticide evaluation process used by the US Environmental Protection Agency (USEPA) and subsequently by the US Fish and Wildlife Services and National Marine Fisheries Service (collectively known as the Services) in Section 7 consultation activities. The decision matrix is applied to each cultivated land layer in the USDA's CDL with recommendations for how best to use each layer in the evaluation process. Application of this decision matrix will lead to improved representation of labeled uses and more accurate overlap calculations used in the assessment of potential impacts of pesticides on endangered species. Integr Environ Assess Manag 2022;18:1655-1666. © 2022 SETAC.

Probabilistic co-occurrence assessment for suites of listed species

Section 7 of the Endangered Species Act requires the US Environmental Protection Agency (US EPA) to consult with the Services (US Fish and Wildlife Service and National Marine Fisheries Service) over potential pesticide impacts on federally listed species. Consultation is complicated by the large number of pesticide products and listed species, as well as by lack of consensus on best practices for conducting co-occurrence analyses. Previous work demonstrates that probabilistic estimates of species' ranges and pesticide use patterns improve these analyses. Here we demonstrate that such estimates can be made for suites of sympatric listed species. Focusing on two watersheds, one in Iowa and the other in Mississippi, we obtained distribution records for 13 species of terrestrial and aquatic listed plants and animals occurring therein. We used maximum entropy modeling and bioclimatic, topographic, hydrographic, and land cover variables to predict species' ranges at high spatial resolution. We constructed probabilistic spatial models of use areas for two pesticides based on the US Department of Agriculture Cropland Data Layer and reduced classification errors by incorporating information on the relationships between individual pixels and their neighbors using object-based images analysis. We then combined species distribution and crop footprint models to derive overall probability of co-occurrence of listed species and pesticide use. For aquatic species, we also integrated an estimate of downstream residue transport. We report each separate species-by-use-area co-occurrence estimate and also combine these modeled co-occurrence probabilities across species within watersheds to produce an overall metric of potential pesticide exposure risk for these listed species at the watershed level. We propose that the consultation process between US EPA and the Services be based on such batched estimation of probabilistic co-occurrence for multiple listed species at a regional scale. Integr Environ Assess Manag 2022;18:1088-1100. © 2021 SETAC.

Development of a mixed-source, single pesticide database for use in ecological risk assessment: quality control and data standardization practices

Inclusion of pesticide monitoring data in pesticide risk assessment is important yet challenging for several reasons, including infrequent or irregular data collection, disparate sources procedures and associated monitoring periods, and interpretation of the data itself in a policy context. These challenges alone, left unaddressed, will likely introduce unintentional and unforeseen risk assessment conclusions. While individual water quality monitoring programs report standard operating procedures and quality control practices for their own data, cross-checking data for duplicated data from one database to another does not routinely occur. Consequently, we developed a novel quality control and assurance methodology to identify errors and duplicated records toward creating an aggregated, single pesticide database toward use in ecological risk assessment. This methodology includes (1) standardization and reformatting practices, (2) data error and duplicate record identification protocols, (3) missing or inconsistent limit of detection and quantification reporting, and (4) site metadata scoring and ranking procedures to flag likely duplicate records. We applied this methodology to develop an aggregated (multiple-source), national-scale database for atrazine from a diverse set of surface water monitoring programs. The resultant database resolved and/or removed approximately 31% of the total ~ 385,000 records that were due to duplicated records. Identification of sample replicates was also developed. While the quality control and assurances methodologies developed in this work were applied to atrazine, they generally demonstrate how a properly constructed and aggregated single pesticide database would benefit from the methods described herein before use in subsequent statistical and data analysis or risk assessment.

Applying a Hybrid Modeling Approach to Evaluate Potential Pesticide Effects and Mitigation Effectiveness for an Endangered Fish in Simulated Oxbow Habitats

The occurrence of some species listed under the United States' Endangered Species Act in agricultural landscapes suggests that their habitats could potentially be exposed to pesticides. However, the potential effects from such exposures on populations are difficult to estimate. Mechanistic models can provide an avenue to estimating the potential impacts on populations, considering realistic assumptions about the ecology of the species, the ecosystem it is part of, and the potential exposures within the habitat. In the present study, we applied a hybrid model of the Topeka shiner (Notropis topeka), a small endangered cyprinid fish endemic to the US Midwest, to assess the potential population-level effects of realistic exposures to a fungicide (benzovindiflupyr). The Topeka shiner populations were simulated in the context of the food web found in oxbow habitats that are the focus of ongoing habitat restoration efforts for the species. We applied realistic, time-variable exposure scenarios and represented lethal and sublethal effects to individual Topeka shiners using toxicokinetic-toxicodynamic models. With fish in general showing the highest sensitivity to the compound, direct effects on simulated Topeka shiner populations governed the population-level effects. We characterized the population-level effects of different exposure scenarios with exposure multiplication factors (EMFs) applied. The introduction of a vegetative filter strip (VFS; 15 ft; 4.6 m) between the treated area and the oxbow habitat was shown to be effective as mitigation because EMFs were 2 to 3 times higher than for the exposure scenario without VFS. Environ Toxicol Chem 2021;40:2615-2628. © 2021 SETAC.

Evaluating a developmental endocrine toxicity assay for Blanchard's cricket frog (Acris blanchardi) in outdoor enclosures

A developmental toxicity testing design was evaluated for larval and post-metamorphic Blanchard's cricket frogs (Acris blanchardi) raised in outdoor enclosures. Larvae were chronically exposed to 17β-estradiol (0.0-2.3 μg/L E2) from free swimming (Gosner stage 26) until metamorphosis. Juvenile frogs were allowed to mature within the enclosures for 60 days to assess effects of larval exposure on development, including body mass, snout-vent length (SVL), sex ratio, gonad size, and gonadal histopathology. Forty-eight percent of the initial 600 animals were recovered at the end of the study. Recovery was not influenced by E2 exposure, but larval losses were negatively impacted by unusually high spring rain events that flooded some larval tanks, and heat-related mortality of late stage larvae during summer. All surviving larvae completed metamorphosis within an average of 47 days. Overall, E2 exposure did not influence sex ratio, or the body mass, SVL, or gonad size of either males or females. Development of testes was not influenced by E2 exposure, but oviduct development in males was 4.5-fold greater in the highest treatment. Oviduct and ovary development in females exposed to the two highest E2 treatments were half that of control females. Although not treatment related and despite ad-lib feeding, variation in terminal body mass and SVL within enclosures was pronounced, with minimum - maximum differences ranging from 207 to 1442 mg for body mass and 1 mm to 15 mm for SVL. This design allowed us to assess the effects of larval exposure to a contaminant on post-metamorphic development of a native amphibian in a semirealistic field environment. With modifications to decrease flooding or overheating, this enclosure design and species is a good test system for assessing contaminant effects on development of an amphibian from early larval stages through reproductive maturity.

Strength of methods assessment for aquatic primary producer toxicity data: A critical review of atrazine studies from the peer-reviewed literature

Improving the quality of pesticide toxicity studies is a shared goal in ecotoxicology and a priority for risk assessors. Using the herbicide atrazine and testing on primary producers as a case study, we developed and applied a transparent scoring system for assessing the quality of peer-reviewed studies. The exercise also highlights where data gaps exist for planning future work. We determined that, while a large number of studies (147) present experimental data fitting basic inclusion criteria, only a small proportion provide sufficient information on the test substance, test organism, and test results to be considered of sufficient quality (i.e., a minimum score of >8 out of 16, meaning no critical study weaknesses identified) that would allow recommendation for their use in decision-making. Optimal studies for use in first tier risk assessment were further identified for each taxonomic group as the highest-scoring study scoring >8, that also used the technical grade active ingredient, reported an EC50 for a population-level endpoint (e.g. cell density, dry weight), and an exposure period in line with standard tests (≤96-h for algae, ≤14-d for macrophytes). Ultimately, 22 freshwater studies (four periphyton, ten macrophytes, and eight phytoplankton) achieved scores >8. Only one study with marine phytoplankton scored >8, and no studies met the risk assessment inclusion criteria for marine/estuarine periphyton or macrophytes. This indicates a potential research need with respect to toxicity data for salt-water species. Finally, registrant studies were evaluated, and in many cases, were the most appropriate for risk assessment, with the greatest scores observed for their respective species relative to those reported in the peer-reviewed literature. This exercise highlights the importance of defining and identifying well-performed toxicity tests, illuminating knowledge gaps, and reporting high quality data in support of the risk assessment process outside of the standard regulatory framework.

A Hybrid Individual-Based and Food Web-Ecosystem Modeling Approach for Assessing Ecological Risks to the Topeka Shiner (Notropis topeka): A Case Study with Atrazine

A hybrid model was used to characterize potential ecological risks posed by atrazine to the endangered Topeka shiner. The model linked a Topeka shiner individual-based bioenergetics population model (TS-IBM) to a comprehensive aquatic system model (CASM_TS ) to simulate Topeka shiner population and food web dynamics for an Iowa (USA) headwater pool. Risks were estimated for monitored concentrations in Iowa, Missouri, and Nebraska (USA), and for monitored concentrations multiplied by 2, 4, and 5. Constant daily atrazine concentrations of 10, 50, 100, and 250 µg/L were assessed. Exposure-response functions were developed from published atrazine toxicity data (median effect concentrations [EC50s] and no-observed-effect concentrations). Two toxicity scenarios were developed: the first included sensitive and insensitive species of algae, and the second reduced algal EC50 values to increase atrazine sensitivity. Direct and indirect effects of atrazine on Topeka shiner prey were modeled; direct effects on Topeka shiner were not assessed. Risks were characterized as differences between population biomass values of 365-d baseline and exposure simulations. The results indicated no discernable food web effects for monitored atrazine concentrations or constant exposures of 10 µg/L on Topeka shiner populations for either toxicity scenario. Magnified monitored concentrations and higher constant concentrations produced greater modeled indirect effects on Topeka shiners. The hybrid model transparently combines species-specific and surrogate species data to estimate food web responses to environmental stressors. The model is readily updated by new data and is adaptable to other species and ecosystems. Environ Toxicol Chem 2019;38:2243-2258. © 2019 SETAC.

Comparative Analysis of Plant Demographic Traits Across Species of Different Conservation Concern: Implications for Pesticide Risk Assessment

Pesticide risk assessment for "listed" (threatened and endangered) plant species is hampered by a lack of quantitative demographic information. Demographic information for nonlisted plant species could provide risk-assessment data and inform recovery plans for listed species; however, it is unclear how representative demography of the former would be for the latter. We performed a comparison of plant demographic traits and elasticity metrics to explore how similar these are between listed and nonlisted species. We used transition matrices from the COMPADRE Plant Matrix Database to calculate population growth rate (λ), net reproductive rate (R_o ), generation time (T_g ), damping ratio (ρ), and summed elasticities for survival (stasis), growth, fertility (reproduction), and evenness of elasticity (EE). We compared these across species varying in conservation status and population trend. Phylogenetic generalized least squares (PGLS) models were used to evaluate differences between listed and nonlisted plants. Overall, demographic traits were largely overlapping for listed and nonlisted species. Population trends had a significant impact on most demographic traits and elasticity patterns. The influence of T_g on elasticity metrics was consistent across all data groupings. In contrast, the influence of λ on elasticity metrics was highly variable, and correlated in opposite directions in growing and declining populations. Our results suggested that population models developed for nonlisted plant species may be useful for assessing the risks of pesticides to listed species. Environ Toxicol Chem 2019;38:2043-2052. © 2019 SETAC.

Winds of change, developing a non-target plant bioassay employing field-based pesticide drift exposure: A case study with atrazine

A field-scale, spray drift study with atrazine was conducted to simultaneously measure spray drift deposition, airborne interception and corresponding biological effects on two sensitive plant species (cucumber and lettuce). Applications of AAtrex 4L (atrazine) were made using ultra-coarse nozzles (TeeJet TTI11004) under worst-case drift potential conditions of bare soil and high wind speeds (i.e. >10 mph; >16 kph). This study was replicated 4 times, each with two parallel spray swaths (92.5 ft or 28 m per swath) perpendicular to wind direction. Within each replicate application, three sampling lines were used to measure drift deposition (using stainless-steel discs) at distances out to 400 ft (122 m), airborne interception (using stainless-steel rods) at distances out to 75 ft (23 m), and potential direct plant effects at 5, 15, 25, 35, and 45 ft (1.5, 4.6, 7.6, 10.7, and 13.7 m) from the downwind edge of the spray swath. Corresponding upwind control discs and plants were also included in each replicate. Each replicate application targeted steady wind speeds between 10 and 15 mph (16 and 24 kph) within a 30-degree angle of the downwind field orientation. On average, each 10% increase in distance from the spray zone resulted in approximately 14% less ground-deposited atrazine. Between 7 and 41× more atrazine mass was collected from vertical rods (airborne drift), compared to horizontally placed stainless-steel discs (ground deposition). Cucumber and lettuce plants exposed to spray drift were monitored for biological effects over 21 days post-application according to standard protocols. Endpoints of survival, weight (biomass), and shoot length were evaluated by comparing distance groups to up-wind controls. Overall, when trials were combined, the aggregate lowest observable effect distance (LOED) was 5-ft (1.5 m) and the aggregate no observable effects distance (NOED) was 15-ft (4.6 m), with cucumbers affected more than lettuce.

Variability in Nontarget Terrestrial Plant Studies Should Inform Endpoint Selection

Inherent variability in nontarget terrestrial plant (NTTP) testing of pesticides creates challenges for using and interpreting these data for risk assessment. Standardized NTTP testing protocols were initially designed to calculate the application rate causing a 25% effect (ER25, used in the United States) or a 50% effect (ER50, used in Europe) for various measures based on the observed dose-response. More recently, the requirement to generate a no-observed-effect rate (NOER), or, in the absence of an NOER, the rate causing a 5% effect (ER05), has raised questions about the inherent variability in, and statistical detectability of, these tests. Statistically significant differences observed between test and control groups may be a product of this inherent variability and may not represent biological relevance. Attempting to derive an ER05 and the associated risk-assessment conclusions drawn from these values can overestimate risk. To address these concerns, we evaluated historical data from approximately 100 seedling emergence and vegetative vigor guideline studies on pesticides to assess the variability of control results across studies for each plant species, examined potential causes for the variation in control results, and defined the minimum percent effect that can be reliably detected. The results indicate that with current test design and implementation, the ER05 cannot be reliably estimated. Integr Environ Assess Manag 2018;14:639-648. © 2018 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Adapting population models for application in pesticide risk assessment: A case study with Mead's milkweed

Population models can facilitate assessment of potential impacts of pesticides on populations or species rather than individuals and have been identified as important tools for pesticide risk assessment of nontarget species including those listed under the Endangered Species Act. Few examples of population models developed for this specific purpose are available; however, population models are commonly used in conservation science as a tool to project the viability of populations and the long-term outcomes of management actions. We present a population model for Mead's milkweed (Asclepias meadii), a species listed as threatened under the Endangered Species Act throughout its range across the Midwestern United States. We adapted a published population model based on demographic field data for application in pesticide risk assessment. Exposure and effects were modeled as reductions of sets of vital rates in the transition matrices, simulating both lethal and sublethal effects of herbicides. Two herbicides, atrazine and mesotrione, were used as case study examples to evaluate a range of assumptions about potential exposure-effects relationships. In addition, we assessed buffers (i.e., setback distances of herbicide spray applications from the simulated habitat) as hypothetical mitigation scenarios and evaluated their influence on population-level effects in the model. The model results suggest that buffers can be effective at reducing risk from herbicide drift to plant populations. These case studies demonstrate that existing population models can be adopted and integrated with exposure and effects information for use in pesticide risk assessment. Environ Toxicol Chem 2018;37:2235-2245. © 2018 SETAC.

Data quality scoring system for microcosm and mesocosm studies used to derive a level of concern for atrazine

The US Environmental Protection Agency (USEPA) has historically used different methods to derive an aquatic level of concern (LoC) for atrazine, though all have generally relied on an expanding set of mesocosm and microcosm ("cosm") studies for calibration. The database of results from ecological effects studies with atrazine in cosms now includes 108 data points from 39 studies and forms the basis for assessing atrazine's potential to impact aquatic plant communities. Inclusion of the appropriate cosm studies and accurate interpretation of each data point-delineated as binary scores of "effect" (effect score 1) or "no effect" (effect score 0) of a specific atrazine exposure profile on plant communities in a single study-is critical to USEPA's approach to determining the LoC. We reviewed the atrazine cosm studies in detail and carefully interpreted their results in terms of the binary effect scores. The cosm database includes a wide range of experimental systems and study designs, some of which are more relevant to natural plant communities than others. Moreover, the studies vary in the clarity and consistency of their results. We therefore evaluated each study against objective criteria for relevance and reliability to produce a weighting score that can be applied to the effect scores when calculating the LoC. This approach is useful because studies that are more relevant and reliable have greater influence on the LoC than studies with lower weighting scores. When the current iteration of USEPA's LoC approach, referred to as the plant assemblage toxicity index (PATI), was calibrated with the weighted cosm data set, the result was a 60-day LoC of 21.2 μg/L. Integr Environ Assess Manag 2018;14:489-497. © 2018 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Assessing and mitigating simulated population-level effects of 3 herbicides to a threatened plant: Application of a species-specific population model of Boltonia decurrens

Extrapolating from organism-level endpoints, as generated from standard pesticide toxicity tests, to populations is an important step in threatened and endangered species risk assessments. We apply a population model for a threatened herbaceous plant species, Boltonia decurrens, to estimate the potential population-level impacts of 3 herbicides. We combine conservative exposure scenarios with dose-response relationships for growth and survival of standard test species and apply those in the species-specific model. Exposure profiles applied in the B. decurrens model were estimated using exposure modeling approaches. Spray buffer zones were simulated by using corresponding exposure profiles, and their effectiveness at mitigating simulated effects on the plant populations was assessed with the model. From simulated exposure effects scenarios that affect plant populations, the present results suggest that B. decurrens populations may be more sensitive to exposures from herbicide spray drift affecting vegetative stages than from runoff affecting early seedling survival and growth. Spray application buffer zones were shown to be effective at reducing effects on simulated populations. Our case study demonstrates how species-specific population models can be applied in pesticide risk assessment to bring organism-level endpoints, exposure assumptions, and species characteristics together in an ecologically relevant context. Environ Toxicol Chem 2018;37:1545-1555. © 2018 SETAC.

Developing population models: A systematic approach for pesticide risk assessment using herbaceous plants as an example

Population models are used as tools in species management and conservation and are increasingly recognized as important tools in pesticide risk assessments. A wide variety of population model applications and resources on modeling techniques, evaluation and documentation can be found in the literature. In this paper, we add to these resources by introducing a systematic, transparent approach to developing population models. The decision guide that we propose is intended to help model developers systematically address data availability for their purpose and the steps that need to be taken in any model development. The resulting conceptual model includes the necessary complexity to address the model purpose on the basis of current understanding and available data. We provide specific guidance for the development of population models for herbaceous plant species in pesticide risk assessment and demonstrate the approach with an example of a conceptual model developed following the decision guide for herbicide risk assessment of Mead's milkweed (Asclepias meadii), a species listed as threatened under the US Endangered Species Act. The decision guide specific to herbaceous plants demonstrates the details, but the general approach can be adapted for other species groups and management objectives. Population models provide a tool to link population-level dynamics, species and habitat characteristics as well as information about stressors in a single approach. Developing such models in a systematic, transparent way will increase their applicability and credibility, reduce development efforts, and result in models that are readily available for use in species management and risk assessments.

Population modeling for pesticide risk assessment of threatened species-A case study of a terrestrial plant, Boltonia decurrens

Although population models are recognized as necessary tools in the ecological risk assessment of pesticides, particularly for species listed under the Endangered Species Act, their application in this context is currently limited to very few cases. The authors developed a detailed, individual-based population model for a threatened plant species, the decurrent false aster (Boltonia decurrens), for application in pesticide risk assessment. Floods and competition with other plant species are known factors that drive the species' population dynamics and were included in the model approach. The authors use the model to compare the population-level effects of 5 toxicity surrogates applied to B. decurrens under varying environmental conditions. The model results suggest that the environmental conditions under which herbicide applications occur may have a higher impact on populations than organism-level sensitivities to an herbicide within a realistic range. Indirect effects may be as important as the direct effects of herbicide applications by shifting competition strength if competing species have different sensitivities to the herbicide. The model approach provides a case study for population-level risk assessments of listed species. Population-level effects of herbicides can be assessed in a realistic and species-specific context, and uncertainties can be addressed explicitly. The authors discuss how their approach can inform the future development and application of modeling for population-level risk assessments of listed species, and ecological risk assessment in general. Environ Toxicol Chem 2017;36:480-491. © 2016 SETAC.

Assessing pesticide risks to threatened and endangered species using population models: Findings and recommendations from a CropLife America Science Forum

This brief communication reports on the main findings and recommendations from the 2014 Science Forum organized by CropLife America. The aim of the Forum was to gain a better understanding of the current status of population models and how they could be used in ecological risk assessments for threatened and endangered species potentially exposed to pesticides in the United States. The Forum panelists' recommendations are intended to assist the relevant government agencies with implementation of population modeling in future endangered species risk assessments for pesticides. The Forum included keynote presentations that provided an overview of current practices, highlighted the findings of a recent National Academy of Sciences report and its implications, reviewed the main categories of existing population models and the types of risk expressions that can be produced as model outputs, and provided examples of how population models are currently being used in different legislative contexts. The panel concluded that models developed for listed species assessments should provide quantitative risk estimates, incorporate realistic variability in environmental and demographic factors, integrate complex patterns of exposure and effects, and use baseline conditions that include present factors that have caused the species to be listed (e.g., habitat loss, invasive species) or have resulted in positive management action. Furthermore, the panel advocates for the formation of a multipartite advisory committee to provide best available knowledge and guidance related to model implementation and use, to address such needs as more systematic collection, digitization, and dissemination of data for listed species; consideration of the newest developments in good modeling practice; comprehensive review of existing population models and their applicability for listed species assessments; and development of case studies using a few well-tested models for particular species to demonstrate proof of concept. To advance our common goals, the panel recommends the following as important areas for further research and development: quantitative analysis of the causes of species listings to guide model development; systematic assessment of the relative role of toxicity versus other factors in driving pesticide risk; additional study of how interactions between density dependence and pesticides influence risk; and development of pragmatic approaches to assessing indirect effects of pesticides on listed species.

Optimization of culturing conditions for toxicity testing with the alga Oophila sp. (Chlorophyceae), an amphibian endosymbiont

Eggs of the yellow-spotted salamander (Ambystoma maculatum) have a symbiotic relationship with green algae. It has been suggested that contaminants that are preferentially toxic to algae, such as herbicides, may impair the symbiont and, hence, indirectly affect the development of the salamander embryo. To enable testing under near-standard conditions for first-tier toxicity screening, the authors isolated the alga from field-collected eggs and identified conditions providing exponential growth rates in the apparent asexual phase of the alga. This approach provided a uniform, single-species culture, facilitating assessment of common toxicity end points and comparison of sensitivity relative to other species. Sequencing of the 18s ribosomal DNA indicated that the isolated alga is closely related to the recently described Oophila amblystomatis but is more similar to other known Chlamydomonas species, suggesting possible biogeographical variability in the genetic identity of the algal symbiont. After a tiered approach to culturing method refinement, a modified Bristol's media with 1 mM NH4 (+) as nitrogen source was found to provide suitable conditions for toxicity testing at 18 °C and 200 µmol m(-2) s(-1) photosynthetically active radiation (PAR) on a 24-h light cycle. The validity of the approach was demonstrated with Zn(2+) as a reference toxicant. Overall, the present study shows that screening for direct effects of contaminants on the algal symbiont without the presence of the host salamander is possible under certain laboratory conditions.

Response of the green alga Oophila sp., a salamander endosymbiont, to a PSII-inhibitor under laboratory conditions

In a rare example of autotroph-vertebrate endosymbiosis, eggs of the yellow-spotted salamander (Ambystoma maculatum) are colonized by a green alga (Oophila sp.) that significantly enhances salamander development. Previous studies have demonstrated the potential for impacts to the salamander embryo when growth of the algae is impaired by exposure to herbicides. To further investigate this relationship, the authors characterized the response of the symbiotic algae (Oophila sp.) alone to the photosystem II (PSII) inhibitor atrazine under controlled laboratory conditions. After extraction of the alga from A. maculatum eggs and optimization of culturing conditions, 4 toxicity assays (96 h each) were conducted. Recovery of the algal population was also assessed after a further 96 h in untreated media. Average median effective concentration (EC50) values of 123 µg L(-1) (PSII yield), 169 µg L(-1) (optical density), and 299 µg L(-1) (growth rate) were obtained after the 96-h exposure. Full recovery of exposed algal populations after 96 h in untreated media was observed for all endpoints, except for optical density at the greatest concentration tested (300 µg L(-1) ). Our results show that, under laboratory conditions, Oophila sp. is generally less sensitive to atrazine than standard test species. Although conditions of growth in standard toxicity tests are not identical to those in the natural environment, these results provide an understanding of the tolerance of this alga to PSII inhibitors as compared with other species.

Sensitivity of a green alga to atrazine is not enhanced by previous acute exposure

Exposure to atrazine in small lotic systems can be episodic, with short-term pulses (peaks) followed by lower, decreasing concentrations. Algae and macrophytes recover rapidly from pulsed exposure to atrazine, but reported observations of population response to subsequent exposures are minimal and inconclusive. Consequently, the sensitivity of Pseudokirchneriella subcapitata to atrazine following a pulsed exposure was assessed. Exposure concentrations reflected amplifications of those observed in streams from highly vulnerable watersheds in regions of intense use. Initial pulsed atrazine exposure at 0, 150 or 300 μg/L for 24-h was followed by 72-h exposure to 0, 5, 10, 25, or 50 μg/L. Measured responses were cell density, growth rate, chlorophyll-a, and maximum quantum yield of photosystem II. Algal recovery was rapid and prior pulsed exposure to atrazine did not significantly affect subsequent sensitivity (EC10s, EC25s) for any endpoint, indicating no changes in tolerance at the population level for this species.

Detectability of fifteen aquatic micro/mesocosms

Zooplankton abundance and species richness in 15 untreated 12,000 L outdoor microcosms (n = 15) were monitored over the course of 1 year to document the inherent variability and statistical detectability between replicates. Statistical power analysis were applied to derive the statistically minimal detectable difference (MDD) between replicates with default values set at; alpha = 0.1 and beta = 0.2. Copepod abundance and species richness generally demonstrated the best detectability at 0.31 and 0.16, respectively, (n = 15); 0.59 and 0.33 (n = 3). Total zooplankton abundance and species richness had the lowest detectabilities at 0.19 and 0.14, respectively, (n = 15); 0.35 and 0.3 (n = 3). Rotifers, due to their opportunistic and rapid life traits, had the lowest single-species abundance detectabilities at 0.54 (n = 15); 0.8 (n = 3), whereas macroinvertebrate species richness had the lowest detectability at 0.43 (n = 15); 0.7 (n = 3) over 1 year. We recommend a priori calibration of the study design relative to relevant MDDs. Moreover, it is suggested to consider alternatives to statistical null hypothesis testing.

Assessment of the environmental fate and effects of ivermectin in aquatic mesocosms

Pharmaceuticals in the environment have been subject to increasing public concern and scientific investigation over the past years. More than 100 active pharmaceutical ingredients have been detected in surface waters worldwide at the ng to microg L(-1) range. At these low levels it is commonly assumed that only chronic and/or mixture toxic effects will be discernible in aquatic ecosystems and that there are orders of magnitude between exposure and effect concentrations. Assessment of potential ecosystem risk of pharmaceuticals are recommended but rarely performed in mesocosms, so for most risk assessments the final tier to reduce extrapolation uncertainty is missing. This paper describes the fate and effects of the anthelmintic drug ivermectin for a 265-day period following treatment (nominal concentration levels of 0, 30, 100, 1000 ng L(-1) (or parts per trillion (ppt)) in fifteen 12,000 L outdoor aquatic mesocosms. Although it is established that ivermectin is highly toxic towards invertebrates, it has been believed that ivermectin does not present notable risks to aquatic systems due to the rapid dissipation of the compound and binding to the sediment. Hence, fate and exchange of ivermectin between water and sediment were evaluated in this study. The ivermectin DT(50aqueous) in water was found to be 3-5 days, but concentrations increased and appeared to be stabile in the sediment at 20-30 ng kg(-1) with no assessable DT(50sed). Acute effects (first week) following ivermectin exposure were identified and cladocerans were particularly sensitive (nom. 100 ppt). Chronic responses (<day 97) were observed for the ecosystem structure and function (nom. 30 ppt). Long-term effects (>229 days) were identified for more sediment-active organisms (e.g. Chydoriae and Ephemeroptera) (nom. 1000 ppt). This is the first study to demonstrate the potential environmental risk of ivermectin at or below the predicted environmental concentration using a standardized test methodology (mesocosm) with minimal extrapolation uncertainty.

Human p53 directs DNA strand reassociation and is photolabelled by 8-azido ATP

p53 is the most frequent known target for mutation in human cancer. Evidence suggests that p53 protein may be involved variously in transcription and cell cycle control, in DNA replication and in G1 checkpoint control following the cellular response to radiation induced DNA damage. p53 blocks DNA replication of the small DNA tumour virus, simian virus 40, by inhibiting unwinding of the viral origin of replication by the DNA helicase activity of the virally encoded large T antigen protein. Here we report the novel observation that human p53 protein can bind ATP and exhibits an intrinsic ATP stimulated DNA strand reassociation activity. Both activities map to the carboxyl terminal 128 amino acids of p53. Thus, in addition to any role in transcription, our results indicate that p53 is potentially capable of inhibiting mammalian replicative DNA synthesis by blocking the DNA strand separation step during replication origin recruitment. However, the ability of p53 to modulate the topological relationship between complementary nucleotide strands is also compatible with a direct role for p53 in other aspects of DNA synthesis, recombination or repair.

The E2 binding sites determine the efficiency of replication for the origin of human papillomavirus type 18

Human papillomaviruses (HPV-s) have been shown to possess transforming and immortalizing activity for many different, mainly keratinocyte cell lines and they have been detected in 90% of anogenital cancer tissues, which suggests a causative role in the induction of anogenital and other tumours. We have exploited a quantitative assay to identify and characterize the origin of replication of the human papillomavirus type 18 (HPV-18), one of the most prevalent types in the high-risk HPV group. Replication of HPV origin fragments was studied transiently by cotransfection with a protein expression vector providing replication proteins E1 and E2. We have localized the HPV-18 origin to nucleotides 7767-119. This region contains three E2 binding sites and an essential A/T rich DNA region (nucleotides 9-35) that is partly homologous to the E1 binding site found in bovine papillomavirus type 1 (BPV-1) genome. At least one of the three E2 binding sites was absolutely required for origin function; addition of other E2 sites had cooperative stimulating effect. This is the first quantitative analysis of the E2 binding sites for papillomavirus replication.

A C-terminal alpha-helix plus basic region motif is the major structural determinant of p53 tetramerization

The p53 gene product has been implicated in both human and animal tumorigenesis. p53 forms heterologous complexes with the transforming proteins encoded by several different DNA tumor viruses. p53 also assembles into stable homo-oligomers. We demonstrate that the major structural determinant for the tetramerization of p53 is an alpha-helical plus basic region motif near the C-terminus of the protein. A monomeric p53 mutant adopts a conformation distinct from both 'wild-type' and 'mutant' form as defined by PAb1620 and PAb240 monoclonal antibody recognition. Nevertheless, monomeric and dimeric mutant p53 proteins retain the ability to suppress SV40 origin-directed DNA replication in vivo. Thus, p53-p53 interaction and expression of the PAb1620 epitope is not a prerequisite for such activity. We present data suggesting that suppression of replication by p53 may occur by a mechanism that is independent of detectable p53-T antigen association.

A human tumour-derived mutant p53 protein induces a p34cdc2 reversible growth arrest in fission yeast

We have expressed wild-type and human tumour-derived mutant p53 cDNA genes in the fission yeast Schizosaccharomyces pombe. In the case of one mutant this resulted in a growth arrest of recipient yeast cells. In contrast, wild-type p53 and three other mutant proteins tested did not block outgrowth of colonies. Human and yeast cdc2 acted as functionally equivalent extragenic suppressors of the mutant-induced growth arrest allowing the establishment of viable p53 expressor strains. In cotransformation assays the mutant allele was found to be dominant over wt p53. Our results provide the first evidence of a functional relationship between p53 and p34cdc2 in an in-vivo system and suggest that the wide variety of mutant proteins present in human tumours may fall into functionally distinct subclasses.

p53 interacts with p34cdc2 in mammalian cells: implications for cell cycle control and oncogenesis

The p53 gene product has been implicated in both human and animal tumorigenesis. p53 complexes with the transforming proteins encoded by several different DNA tumour viruses. We demonstrate that human p53 is phosphorylated by the mammalian p34cdc2 kinase in vitro and coprecipitates with p34cdc2 in vivo. Our observations suggest that phosphorylation of p53 by p34cdc2 kinase may regulate the known activities of p53 in the initiation steps of DNA replication in mammalian cells.

Mouse p53 blocks SV40 DNA replication in vitro and downregulates T antigen DNA helicase activity

Immunopurified mouse p53 proteins were used to gain experimental access to the mechanisms underlying nonprimate p53 directed suppression of SV40 origin directed DNA replication in vivo. In replication competent HeLa cell extracts containing exogenous T antigen, mouse p53 blocks T antigen dependent DNA synthesis as in vivo. However, in transcription competent HeLa extracts, mouse p53 has no effect either on overall transcription or on the ability of immunopurified T antigen to downregulate SV40 early transcription. We show that although mouse p53 has no significant effect on T antigen encoded activities such as ATPase and DNA binding, helicase activity is somewhat reduced suggesting that the in vivo suppression by mouse p53 of SV40 replication may be due, at least in part, to direct modulation of T antigen function.