Developing Population Models for Pesticide Risk Assessment: A Systematic Approach Using the Example of Herbaceous Plants
SETAC Session Title: 21st Century Approaches for Capturing Diversity in Species Sensitivity to Chemicals
Presentation Date: Monday November 13th, 2017
Presentation Time: 10:40 AM
Location: Auditorium 1
The sensitivity of populations to stresses from chemical exposure is not linearly related to sensitivities of individuals, but depend on a species’ life history, population dynamics, and various other factors. Population models provide a means to assess stressors in the context of population-level dynamics, species and habitat characteristics. They are increasingly recognized as important tools in pesticide risk assessment and were recently identified as essential for endangered species assessment in the U.S. However, few population models for this specific purpose have been developed to date. Developing such models in a systematic and transparent way would increase their applicability and credibility and reduce development efforts.
We present a systematic and transparent approach to developing population models. The guidance informs the model developer on necessary steps that consider the specific questions to be addressed by the model through four phases. In the first phase, the model developer systematically reviews details of the model objectives. Data available for the modeled species and stressor(s) are compiled in table format during the second phase. Starting with a conceptual model of the species’ life history in the third phase, seven decision steps guide the model developer through decisions on what and how details should be represented in the model based on the model objectives and data availability. Decision steps may need to be revisited iteratively during the third phase. In the fourth phase, the model developer compiles a summary of the conceptual model including any underlying assumptions. Uncertainties arising from data and model assumptions are also explicitly characterized. We provide an example decision guide for the development of population models of herbaceous plants applied in pesticide risk assessment. We emphasize how different species’ characteristics are represented in population models, and how they can inform species-specific chemical risk assessment. The adaptation of the approach to developing population models for other taxonomic groups and applications will be discussed.
Amelie Schmolke (Waterborne Environmental), Katherine Kapo (Waterborne Environmental), Pamela Rueda-Cediel (University of Minnesota), Pernille Thorbek (Syngenta), Richard Brain (Syngenta), Valery Forbes (University of Minnesota). Developing Population Models for Pesticide Risk Assessment: A Systematic Approach Using the Example of Herbaceous Plants. Platform SETAC 2017. Minneapolis, MN.
Prospective Risk Assessment for Mixtures of Agricultural Chemicals in Surface Water: Results of Two Case Studies
In 2015, a SETAC Pellston workshop was held to help inform decision making around aquatic mixture risk assessments of chemicals using exposure scenarios. The efforts were grouped into three areas of chemical origination: agriculture, domestic, and urban influences. The agricultural land use combined effect measures with exposure scenarios of chemical mixtures for field and catchment-scale using procedures that are recognized and used in regulatory schemes in the U.S., Europe and other parts of the world. Chemicals modeled were those used in crop protection and livestock production, and were considered to occur as mixtures (in time and space). These assessments considered inputs from spray drift, surface runoff and erosion on a daily basis. Case studies included a single unit scenario modeled as a wheat field in the UK, consisting of crop protection applications of 13 substances annually over the course of 20 years. This scenario used standard FOCUS soil, weather and receiving water body information for consistency with regulatory assessments. A second case study of a multi-unit catchment scenario consisted of a combination of corn fields, pasture, and feedlot inputs based in part on the US EPA Iowa corn scenario used in pesticide registration evaluations. Manure from treated cattle containing two pharmaceutical substances was applied to corn fields as fertilizer, and also originated from pastured cattle. Twelve different active substances for crop protection were modeled. A mixture risk assessment looked daily individual substance risk quotients (RQs) and multiple substance ∑RQ, along with implementation of the Maximum Cumulative Ratio (MCR) approach. When assessed on the basis of Tier 1 effects data using the most sensitive of three taxonomic groups and assuming concentration addition, potential risk from individual chemicals and mixtures (even in cases when no single substance triggered risk, i.e., MCR Group III) was quantified in magnitude and duration. Consideration of the sensitivity of individual different taxa in a Tier II assessment reduced the reported risk from chemical mixtures in both case studies. Results demonstrate that a prospective scenario-based approach can be used to determine the potential for mixtures of chemicals to pose risks over and above any identified using existing approaches for single chemicals, how often and to what magnitude, and ultimately which mixtures produced greatest concern.
Christopher Holmes (Waterborne Environmental), Mick Hamer (Syngenta), Colin Brown (University of York), Russell Jones (Bayer CropScience), Lorraine Maltby (The University of Sheffield), Eric Silberhorn (CVM/USDA), Jerold Teeter (Elanco Animal Health), Michael Warne (Queensland Government), Lennart Weltje (BASF). Prospective Risk Assessment for Mixtures of Agricultural Chemicals in Surface Water: Results of Two Case Studies. Platform ACS 2017. Washington DC.
Approaches for Defining Spatially Explicit Habitat in the Absence of Federally Declared Critical Habitat
Of the approximately 1,800 listed species in the U.S., nearly 660 terrestrials and 140 aquatics are without federally-declared Critical Habitat (spring 2017) suitable for use in assessing the potential impact that pesticides may have on a species or its habitat. To provide information important in filling this data gap, scientifically-defensible approaches for defining spatially-explicit, sub-county habitat locations were assessed. Thirty aquatic and terrestrial species from within each of the taxonomic groups, some inhabiting wide ranges and others with more specific habitat requirements, were chosen as case studies. The intent was to develop a scalable workflow informed by any number of scenarios that may be faced when mapping the habitats of listed species.
Both deductive and inductive mapping approaches were used to identify locations potentially suitable for a species. Inductive habitat mapping was performed via the Maxent© maximum entropy model which requires a set of input habitat variables determined a priori relevant to the species, in conjunction with species occurrence records, to generate a continuous occurrence prediction map within the defined species range. Deductive mapping, on the other hand, does not require species occurrence data, but rather expert knowledge of a species’ habitat requirements. The modeler must interpret textual habitat descriptors and extract quantitative thresholds specific to the species.
This presentation will discuss the organizational challenges faced when generating spatial habitat data for a large number of species. While the habitat generated in this study does not represent “Critical Habitat”, it is representative of the physical and biological features required by a species and is of appropriate accuracy and resolution for use with the potential pesticide use sites in pesticide risk assessments. Look for a companion poster in this session that elaborates on the technical approaches taken to map the habitats of aquatic species without Critical Habitat.
Joshua Amos, Brian Kearns (Waterborne Environmental), Steve Kay (Pyxis Regulatory Consulting). Approaches for Defining Spatially Explicit Habitat in the Absence of Federally Declared Critical Habitat. Platform ACS 2017. Washington DC.
Inductive Habitat Modeling as a Tool to Predict Listed Aquatic Species’ Occurrence in the Absence of Critical Habitat
Approximately 1,800 species are listed as threatened or endangered within the U.S.; of those, approximately 400 live primarily in aquatic habitats. Although federally declared Critical Habitat has been defined for some species, approximately 450 do not have sub-county habitat other than observations noted in listing documents (spring 2017). While listed terrestrial species face a similar dilemma, an increasingly robust suite of spatial datasets has enabled the estimation of spatially explicit habitat using deductive mapping (e.g. USGS GAP). Defining the habitat of aquatic species is particularly challenging given the complex relationship between aquatic ecosystems and the terrestrial landscape (i.e., watershed) contributing to the habitat. For this study, over a dozen listed aquatic species were assessed for the purposes of developing a methodology for defining sub-county, spatially-explicit habitat in the absence of federally declared Critical Habitat.
The Maxent© species distribution model (SDM) was used to inductively determine species occurrence likelihood for aquatic species within the counties and HUC-08 watersheds of known occurrence. Species observation records from USFWS documents were used in conjunction with textual habitat descriptions to train the model to predict occurrence likelihood. The NHDPlus was used as the modelling framework, which captures hydrologic variation at the catchment basin scale and describes physical variables including velocity, flow, and stream order. Other habitat variables like runoff potential and dam density from the StreamCAT database, also built around NHDPlus, were also used in the model. Ultimately, a habitat suitability map was generated and while it is not officially “Critical Habitat”, setting prediction thresholds to show where species are likely to occur may allow conservation managers and pesticide risk assessors to make informed decisions based on a higher resolution species habitat than currently available. This presentation pairs with another in the same session discussing the larger mapping effort of thirty aquatic and terrestrial species without Critical Habitat.
Brian Kearns, Joshua Amos (Waterborne Environmental), Steve Kay (Pyxis Regulatory Consulting). Inductive Habitat Modeling as a Tool to Predict Listed Aquatic Species’ Occurrence in the Absence of Critical Habitat. Poster ACS 2017. Washington DC.
Comparison of Surface Water Pesticide Environmental Risk Assessment Tools in U.S. and China
Given the emerging regulatory development in pesticide environmental exposure risk assessments, China has established a set of ecological risk assessment guidelines for its pesticide registration regulation. There are established tools for rice paddy and groundwater exposure risk assessment, but a higher tier risk assessment tool for pesticide exposure in surface water from dryland crops has not been finalized yet. The Pesticide Risk Assessment Exposure Simulation Shell (PRAESS) model is a platform designed to evaluate the potential for pesticide exposure to occur in surface water resources in China. The Pesticide Root Zone Model (PRZM) component in the PRAESS model has been accepted as the tool to evaluate potential pesticide exposure to soil organisms. The PRAESS model was evaluated systematically with comparisons to the existing U.S. and E.U. regulatory surface water models (i.e. Pesticide Water Calculator (PWC) from the U.S. and FOCUS SWASH model from the E.U.). Respective standard crop scenarios were modeled to understand the PRAESS results in relative comparison to the distribution of those from U.S. and E.U. modeling results. Surface water runoff and pesticide concentrations from the PRAESS and PWC models are also compared to each other under the same weather, crop and soil settings. In addition, the PWC and PRAESS models are evaluated against past small plot field runoff study data. The evaluation is expected to provide scientific and technical support for the tested models to be used as surface water exposure assessment tools with understood predictability for regulatory decision-making.
Dazhi Mao, Mark Cheplick (Waterborne Environmental), Wenlin Chen (Syngenta). Comparison of Surface Water Pesticide Environmental Risk Assessment Tools in U.S. and China. Platform ACS 2017. Washington DC.
Using Population Models to Gain Insights into Direct and Indirect Effects of Pesticides on Listed Fish Populations
The current approach of assessing risks to fish from exposure to pesticides relies on effects data on individuals. However, the effect of a single stressor on populations may depend on multiple factors including a species’ life history, which life-history traits are impacted by the stressor and to what degree, the duration and frequency of stress occurrence, and variability in population dynamics. Population models can combine effects of stressors observed on organisms with species-specific life histories and variability in population dynamics, and project population-level outcomes over extended time periods. In this study, we used an existing matrix population model of the Slackwater darter (Etheostoma boschungi), a species listed as threatened under the U.S. Endangered Species Act, to assess stress levels that may cause population decline. We represented direct effects as changes in survival and fecundity, and indirect effects as decreased food availability. From the scientific literature, we used information on the relationships between reduced food availability, body size and survival and fecundity in fish, and incorporated these relationships in the Slackwater darter model. We analyzed exposure-effects relationships of a pesticide with the model to estimate exposure levels that could cause long-term impacts on population abundance and persistence. Further, we assessed the applicability of the modeling approach to a range of species by analyzing model predictions for potential pesticide impacts on survival and reproductive rates for related fish species with similar life histories. By combining information on life history and direct and indirect effects, population models can provide a valuable tool to assess potential risks of pesticides to populations of listed and other non-target species over ecologically relevant time periods.
Amelie Schmolke, Brian Kearns, Matthew Kern, Katherine Kapo, Colleen Moloney (Waterborne Environmental), Valery Forbes ( University of Minnesota), Aldos Barefoot (DuPont Crop Protection), Hugo Ochoa-Acuna. Using Population Models to Gain Insights into Direct and Indirect Effects of Pesticides on Listed Fish Populations. Poster ACS 2017. Washington DC.
Vegetative Filter Strip (VFS) Modeling in Risk Assessment
Growers have been mandated to use 10-ft maintained vegetative filter strips (VFS) on all PWG pyrethroid agricultural labels for several decades. Since the ability of VFS to trap sediment is known with greater certainty than any other performance aspect and was used for calibrating the VFSMOD model, uncertainty in predicted pyrethroid removal by VFS will be less than for other compounds due to the pyrethroid’s extreme hydrophobicity. Essentially 100% of pyrethroid being transported by runoff/erosion will be adsorbed to sediment as it leaves the treated field; consequently, the trapping efficiency of pyrethroids should be very similar to the trapping efficiency of sediment. The impact of the mandatory VFS on total loads of eroded sediment and pyrethroid entering receiving waters was modeled using VFSMOD with a 10-ft VFS linked with EFED’s PWC model across a range of 10 crop scenarios and 8 pyrethroids. The fractions of the pyrethroid mass loading entering receiving waters after the VFS in the dissolved or absorbed states were examined. The impact of running VFSMOD with and without assuming carryover of residues in the VFS from one event to the next was also explored. The magnitude of VFSMOD’s effect on EECs is highly scenario dependent due to weather and soil properties, resulting in a wide range of EEC and sediment load reductions. Importantly, since some scenarios are dominated by aerial drift entry, the impact of VFS on water column EECs can be lower than expected; however, their impact on reducing sediment loading to receiving waters is vital. Moreover, VFS responses are often non-linear since they can be less effective during extreme rainfall events and therefore, their effect needs to be examined across the entire period as well as for the year corresponding to the 1-in-10 EECs since this mitigation is so important for reducing pyrethroid mass loading in all years.
Amy Ritter, Mark Cheplick, Dean Desmarteau (Waterborne Environmental), Paul Hendley (Phasera Ltd). Using Models to Evaluate Exposure to Non-target Plants Through Runoff and Drift From Agricultural Fields. Poster ACS 2017. Washington DC.
Using Models to Evaluate Exposure to Non-target Plants Through Runoff and Drift From Agricultural Fields
The U.S. EPA uses the screening model, TerrPlant, to estimate exposure to non-target terrestrial plants from a single application of pesticide. Audrey III is a higher tier exposure model that has been developed by U.S. EPA to estimate exposure to plants in a Plant Exposure Zone (PEZ). The objective of this study was to investigate the magnitude and likelihood of exposure of non-target plants to pesticide residues through runoff from agricultural field to an adjacent PEZ. TerrPlant and AUDREYIII will be compared to two vegetative filter models: VFSMOD and PRZM-Buffer. VFSMOD is a vegetative filter strip (VFS) model designed to simulate VFS processes to remove sediment and pesticides from field runoff/erosion. PRZM-Buffer is a modified version of the Pesticide Root Zone Model (PRZM), a rainfall-runoff simulation model, to simulate pesticide fate and transport in a PEZ. Current EPA Tier II scenarios for PRZM were used to represent main field simulations. Movement of pesticide through the PEZ and the concentrations for the segments were modeled with the PRZM-Buffer model and VFSMOD. Results from these two models will be compared to each other and to U.S. EPA models TerrPlant and AUDREYIII. PRZM-Buffer can model metabolites formation and degradation in the VFS. The total residues from the PRZM-Buffer model will be compared to total residues calculated with AUDREYIII. Multiple widths of buffers were assessed to determine distance required for soil concentrations to drop below level of concern for non-target crop.
Amy Ritter, Mark Cheplick, Dean Desmarteau, Megan Guevara. Using Models to Evaluate Exposure to Non-target Plants Through Runoff and Drift From Agricultural Fields. Poster ACS 2017. Washington DC.
Using Web-Based Technologies to Inform Stakeholders – CoPST
Increasingly the Internet is a means to relay complex information to stakeholders. Underlying GIS-based technologies now allow organizations to serve up complex information is meaningful manners and provide additional information in an interactive environment. CoPST is an integrated GIS-modeling framework that incorporates 40 high-risk pesticides and 12 aquatic endangered species presence to identify areas and timing of greatest risk in the Sacramento and San Joaquin river watersheds of California.. The framework uses data from the California Pesticide Use and Reporting database in combination with PRZM, RICEWQ models to estimate pesticide loadings to surface water at the public land survey system section level. Results are combined with species distribution maps to determine co-occurrence. Results are depicted as a series of maps was generated for the study area. These maps include several pesticide heat maps that depict pesticide use intensity. Included are a Total heat map, an Agricultural heat map and pesticide specific heat maps. Tied in with this these maps are the option to retrieve relevant monitoring information for each pesticides of interest. Heat map series include temporal information that allows the users to stepwise walk through each month of the year to see which areas are potentially of concern.
Cornelis Hoogeweg (Waterborne Environmental), Rich Breuer (California Water Control Board), Debra Denton (USEPA), W Williams (Waterborne Environmental). Using Web-Based Technologies to Inform Stakeholders – CoPST. Presentation ACS 2017. Washington DC.
Soil Sustainability: The Reality of Erosion Reduction Practices by Farmers and the Impact to Estimated Environmental Concentrations in a Risk Assessment
Since 1985, USDA National Resources Conservation Service (NRCS) has had joint responsibility to carry out the Highly Erodible Land (HEL) and Wetland conservation provisions of the Food Security Act that helps farmers by delivering technical and financial assistance for conservation. HEL is identified as a field that contains soils which have an erodibility index of ≥8. If a farmer has a field that is identified as HEL, they are required to maintain a system of conservation practices to substantially reduce erosion rates to long-term sustainable levels. If the conservation practices are not adequate to reduce erosion, the farmer may be ineligible for certain USDA payments. Conservation practices that are recommended include grassed waterways, grade stabilization structures, terraces, and tillage management. A field is considered to be sustainable if the soil erosion loss is less than 5 tons/acre per year (on average). However, some US EPA Tier II modeling scenarios used in regulatory screening assessments are parameterized for the PRZM model to have a 30-year average of greater than 30 tons/acre per year; a level which would not be sustainable for continued agricultural production. These Tier II PRZM scenarios do not reflect that growing crops as parameterized is not an option open to the grower expecting program payments. For pyrethroids, which are exceptionally hydrophobic; and therefore, almost exclusively bound to soil, modeling such unsustainable soil erosion leads to predictions of very high pyrethroid loads entering receiving water bodies. This presentation will explore the impact on the estimated water and sediment environmental concentrations for pyrethroids by adjusting input parameters in standard EPA model crop-specific scenarios to match USDA recommended practices for cultivating the crops concerned on HEL land.
Amy Ritter, Dean Desmarteau (Waterborne Environmental), Paul Hendley (Phasera Ltd). Soil Sustainability: The Reality of Erosion Reduction Practices by Farmers and the Impact to Estimated Environmental Concentrations in a Risk Assessment. Presentation ACS 2017. Washington DC.