A prospective approach for assessing chemical mixtures in river catchments with diverse land uses
Field-based ecological risk assessments incorporate risks from chemical mixtures and a myriad of stressors because ecosystems are continuously exposed to a wide-array of contaminants and nonchemical stressors. Considering the large numbers potential combinations of mixtures and stressors, this problem could seem insurmountable. We demonstrate that such combinations can be simplified by 3 land-use related chemical emission scenarios: agriculture, domestic, and urban. We applied a tiered methodology to assess the implications of each of the scenarios via a quantitative model. The results showed land use–dependent mixture exposures, clearly discriminating downstream effects of land uses, with unique chemical “signatures” regarding composition, concentration, and temporal patterns. Associated risks were characterized in relation to the land-use scenarios. Comparisons to measured environmental concentrations and predicted impacts showed relatively good similarity. The results suggest that the land uses imply exceedances of regulatory protective environmental quality standards, varying over time in relation to rain events and associated flow and dilution variation. Higher-tier analyses using ecotoxicological effect criteria confirmed that species assemblages may be affected by exposures exceeding no-effect levels and that mixture exposure could be associated with predicted species loss under certain situations. The model outcomes inform various types of prioritization to support risk management, including a ranking across land uses as a whole, a ranking on characteristics of exposure times and frequencies, and various rankings of the relative role of individual chemicals. Though all results are based on in silico assessments, our land use–based approach yields useful insights for simplifying and assessing potential ecological risks of chemical mixtures and can therefore be useful for catchment-management decisions.
Scott Dyer (Waterborne Environmental), Leo Posthuma (RIVM), Colin D. Brown (University of York), Dick de Zwart (RIVM), Jerome Diamond (Tetra Tech), Christopher Holmes (Waterborne Environmental), Stuart Marshall (Bedford, UK), and G. Allen Burton Jr (University of Michigan). A prospective approach for assessing chemical mixtures in river catchments with diverse land uses.
Poster SETAC Europe 2019. Helsinki, Finland.
Papers & ReportsAgriculture and Food, Crop Protection2018
Honey bee colony-level exposure and effects in realistic landscapes: An application of BEEHAVE simulating clothianidin residues in corn pollen
Discerning potential effects of insecticides on honey bee colonies in field studies conducted under realistic conditions can be challenging because of concurrent interactions with other environmental conditions. Honey bee colony models can control exposures and other environmental factors, as well as assess links among pollen and nectar residues in the landscape, their influx into the colony, and the resulting exposures and effects on bees at different developmental stages. We extended the colony model BEEHAVE to represent exposure to the insecticide clothianidin via residues in pollen from treated cornfields set in real agricultural landscapes in the US Midwest. We assessed their potential risks to honey bee colonies over a 1-yr cycle. Clothianidin effects on colony strength were only observed if unrealistically high residue levels in the pollen were simulated. The landscape composition significantly impacted the collection of pollen (residue exposure) from the cornfields, resulting in higher colony-level effects in landscapes with lower proportions of semi-natural land. The application of the extended BEEHAVE model with a pollen exposure-effects module provides a case study for the application of a mechanistic honey bee colony model in pesticide risk assessment integrating the impact of a range of landscape compositions.
Schmolke, A., Abi-Akar, F., Hinarejos, S. (2018), Honey bee colony-level exposure and effects in realistic landscapes: An application of BEEHAVE simulating clothianidin residues in corn pollen. Environ Toxicol Chem. DOI: 10.1002/etc.4314
Papers & ReportsCrop Protection2018
A plea for consistency, transparency, and reproducibility in risk assessment effect models
Ecological risk assessments (ERAs) are moving toward using populations and ecosystem services as explicit protection goals, and impacts on these are difficult, if not impossible, to measure empirically. Mechanistic effect models are recognized as necessary tools for ERA that complement empirical data. But we need a strategy to make them consistent, transparent and reproducible following similar principles as those used to develop standardized experimental designs for empirical tests. Despite some progress, the use of mechanistic effect models in ERA remains rare. Although some general guidance exists, the ERA community lacks a coherent strategy for model design and implementation. The strategy needs to be compatible with different legislative needs, recognize limitations in data and resources, and involve all stakeholder groups to ensure buy-in. Benefits would include increased cost-effectiveness of model development, implementation and interpretation; minimization of effort needed by risk assessors and managers to evaluate models; and more effective communication of model outputs to a broader stakeholder community. More importantly, it would increase mechanistic understanding of the impacts of chemicals and other stressors across levels of biological organization – from the things that we measure to the things that we care about.
Forbes, V.E., Schmolke, A., Accolla, C., Grimm, V. (2018), A plea for consistency, transparency, and reproducibility in risk assessment effect models. Environ Toxicol Chem. 38: 9-11. doi.org/10.1002/etc.4291
Papers & ReportsCrop Protection2018
Plant guttation water as a potential route for pesticide exposure in honey bees: a review of recent literature
Because honey bees periodically collect water, guttation water from treated crops has been suggested as a potential exposure route to systemic pesticides. We reviewed studies that were published in the scientific literature since a previous review of the topic. We identified several studies that reported residue levels of pesticides in guttation water. However, few studies addressed guttation water as a potential exposure route to honey bees. In these studies, no significant effects on honey bee colony health or overwintering survival were observed when colonies were located within fields of treated crops during guttation periods. The previous and current review suggests that exposure to pesticides via guttation water alone is unlikely to negatively affect honey bee colonies. A better understanding of water foraging by honey bees would be needed to address whether guttation water could represent a relevant exposure route of honey bees to systemic pesticides.
Schmolke, A., Kearns, B., O’Neil, B. (2018), Plant guttation water as a potential route for pesticide exposure in honey bees: a review of recent literature. Apidologie. Volume 49, 637-646. doi.org/10.1007/s13592-018-0591-1
Papers & ReportsWater/Wastewater Assessments2018
Simplifying environmental mixtures-An aquatic exposure-based approach via land use scenarios
Posthuma, L., Brown, C., de Zwart, D., Diamond, J., Dyer, S.D., Hamer, M., Holmes, C.M., Marshal, S., Burton Jr., G.A. (2018), Simplifying environmental mixtures-an aquatic exposure-based approach via land use scenarios. Environ Toxicol Chem. 37: 671-673. doi.org/10.1002/etc.4063
Papers & ReportsCrop Protection2018
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.
Schmolke, A., Roy, C., Brain, R., Forbes, V. (2018), Adapting population models for application in pesticide risk assessment: A case study with Mead’s milkweed. Environ Toxicol Chem. 37: 2235-2245. doi.org/10.1002/etc.4172
Papers & ReportsWater/Wastewater Assessments2017
Prospective aquatic risk assessment for chemical mixtures in agricultural landscapes
Environmental risk assessment of chemical mixtures is challenging because of the multitude of possible combinations that may occur. Aquatic risk from chemical mixtures in an agricultural landscape was evaluated prospectively in 2 exposure scenario case studies: at field scale for a program of 13 plant‐protection products applied annually for 20 yr and at a watershed scale for a mixed land‐use scenario over 30 yr with 12 plant‐protection products and 2 veterinary pharmaceuticals used for beef cattle. Risk quotients were calculated from regulatory exposure models with typical real‐world use patterns and regulatory acceptable concentrations for individual chemicals. The results could differentiate situations when there was concern associated with single chemicals from those when concern was associated with a mixture (based on concentration addition) with no single chemical triggering concern. Potential mixture risk was identified on 0.02 to 7.07% of the total days modeled, depending on the scenario, the taxa, and whether considering acute or chronic risk. Taxa at risk were influenced by receiving water body characteristics along with chemical use profiles and associated properties. The present study demonstrates that a scenario‐based approach can be used to determine whether mixtures of chemicals pose risks over and above any identified using existing approaches for single chemicals, how often and to what magnitude, and ultimately which mixtures (and dominant chemicals) cause greatest concern.
Holmes, C.M., Brown, C.D., Hamer, M., Jones, R., Maltby, L., Posthuma, L., Silberhorn, E., Teeter, J.S., St J Warne, M., Weltje, L. (2017), Prospective aquatic risk assessment for chemical mixtures in agricultural landscapes. Environ Toxicol Chem. 37: 674-689. doi.org/10.1002/etc.4049
Papers & ReportsHome and Personal Care Products, Water/Wastewater Assessments2017
Use of Prospective and retrospective risk assessment methods that simplify chemical mixtures associated with treated domestic wastewater discharges
A framework is presented that is intended to facilitate the evaluation of potential aquatic ecological risks resulting from discharges of down‐the‐drain chemicals. A scenario is presented using representatives of many of the types of chemicals that are treated domestically. Predicted environmental chemical concentrations are based on reported loading rates and routine removal rates for 3 types of treatment: trickling filter, activated sludge secondary treatment, and activated sludge plus advanced oxidation process as well as instream effluent dilution. In tier I, predicted effluent concentrations were compared with the lowest predicted‐no‐effect concentration (PNEC) obtained from the literature using safety factors as needed. A cumulative risk characterization ratio (cumRCR) < 1.0 indicates that risk is unlikely and no further action is needed. Otherwise, a tier 2 assessment is used, in which PNECs are based on trophic level. If tier 2 indicates a possible risk, then a retrospective assessment is recommended. In tier 1, the cumRCR was > 1.0 for all 3 treatment types in our scenario, even though no chemical exceeded a hazard quotient of 1.0 in activated sludge or advanced oxidation process. In tier 2, activated sludge yielded a lower cumRCR than trickling filter because of higher removal rates, and the cumRCR in the advanced oxidation process was << 1.0. Based on the maximum cumulative risk ratio (MCR), more than one‐third of the predicted risk was accounted for by one chemical, and at least 90% was accounted for by 3 chemicals, indicating that few chemicals influenced the mixture risk in our scenario. We show how a retrospective assessment can test whether certain chemicals hypothesized as potential drivers in the prospective assessment could have, or are having, deleterious effects on aquatic life.
Diamond, J., Altenburger, R., Coors, A., Dyer, S.D., Focazio, M., Kidd, K., Koelmans, A.A., Leung, K.M.Y., Servos, M.R., Snape, J., Tolls, J., Zhang, X. (2017), Use of prospective and retrospective risk assessment methods that simplify chemical mixtures associated with treated domestic wastewater discharges. Environ Toxicol Chem. 37: 690-702. doi.org/10.1002/etc.4013
Papers & ReportsWater/Wastewater Assessments2017
Aquatic exposures of chemical mixtures in urban environments: approaches to impact assessment
Urban regions of the world are expanding rapidly, placing additional stress on water resources. Urban water bodies serve many purposes, from washing and sources of drinking water to transport and conduits for storm drainage and effluent discharge. These water bodies receive chemical emissions arising from either single or multiple point sources, diffuse sources which can be continuous, intermittent, or seasonal. Thus, aquatic organisms in these water bodies are exposed to temporally and compositionally variable mixtures. We have delineated source‐specific signatures of these mixtures for diffuse urban runoff and urban point source exposure scenarios to support risk assessment and management of these mixtures. The first step in a tiered approach to assessing chemical exposure has been developed based on the event mean concentration concept, with chemical concentrations in runoff defined by volumes of water leaving each surface and the chemical exposure mixture profiles for different urban scenarios. Although generalizations can be made about the chemical composition of urban sources and event mean exposure predictions for initial prioritization, such modeling needs to be complemented with biological monitoring data. It is highly unlikely that the current paradigm of routine regulatory chemical monitoring alone will provide a realistic appraisal of urban aquatic chemical mixture exposures. Future consideration is also needed of the role of nonchemical stressors in such highly modified urban water bodies.
de Zwart, D., Adams, W., Burgos, M.G., Hollender, J., Junghans, M., Merrington, G., Muir, D., Parkerton, T., De Schamphelaere, K.A.C., Whale, G., Williams, R. (2017), Aquatic exposures of chemical mixtures in urban environments: Approaches to impact assessment. Environ Toxicol Chem. 37: 703-714. doi.org/10.1002/etc.3975
Papers & ReportsWater/Wastewater Assessments2017
Prospective mixture risk assessment and management prioritizations for river catchments with diverse land uses
Ecological risk assessment increasingly focuses on risks from chemical mixtures and multiple stressors because ecosystems are commonly exposed to a plethora of contaminants and nonchemical stressors. To simplify the task of assessing potential mixture effects, we explored 3 land use-related chemical emission scenarios. We applied a tiered methodology to judge the implications of the emissions of chemicals from agricultural practices, domestic discharges, and urban runoff in a quantitative model. The results showed land use-dependent mixture exposures, clearly discriminating downstream effects of land uses, with unique chemical “signatures” regarding composition, concentration, and temporal patterns. Associated risks were characterized in relation to the land‐use scenarios. Comparisons to measured environmental concentrations and predicted impacts showed relatively good similarity. The results suggest that the land uses imply exceedances of regulatory protective environmental quality standards, varying over time in relation to rain events and associated flow and dilution variation. Higher‐tier analyses using ecotoxicological effect criteria confirmed that species assemblages may be affected by exposures exceeding no‐effect levels and that mixture exposure could be associated with predicted species loss under certain situations. The model outcomes can inform various types of prioritization to support risk management, including a ranking across land uses as a whole, a ranking on characteristics of exposure times and frequencies, and various rankings of the relative role of individual chemicals. Though all results are based on in silico assessments, the prospective land use–based approach applied in the present study yields useful insights for simplifying and assessing potential ecological risks of chemical mixtures and can therefore be useful for catchment‐management decisions.
Posthuma, L., Brown, C.D., de Zwart, D., Diamond, J., Dyer, S.D., Holmes, C.M., Marshall, S., Burton Jr., G.A. (2017), Prospective mixture risk assessment and management prioritizations for river catchments with diverse land uses. Environ Toxicol Chem. 37: 715-728. doi.org/10.1002/etc.3960