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The population level is often the biological endpoint addressed in ecological risk assessments (ERAs). However, ERAs tend to ignore the metapopulation structure, which precludes an understanding of how population viability is affected by multiple stressors (e.g., toxicants and environmental conditions) at large spatial scales. Here we integrate metapopulation model simulations into a regional‐scale, multiple stressors risk assessment (Bayesian network relative risk model [BN‐RRM]) of organophosphate (OP) exposure, water temperature, and DO impacts on Chinook salmon (Oncorhynchus tshawytscha). A matrix metapopulation model was developed for spring Chinook salmon in the Yakima River Basin (YRB), Washington, USA, including 3 locally adapted subpopulations and hatchery fish that interact with those subpopulations. Three metapopulation models (an exponential model, a ceiling density‐dependent model, and an exponential model without dispersal) were integrated into the BN‐RRM to evaluate the effects of population model assumptions on risk calculations. Risk was defined as the percent probability that the abundance of a subpopulation would decline from their initial abundance (500 000). This definition of risk reflects the Puget Sound Partnership's management goal of achieving "no net loss" of Chinook abundance. The BN‐RRM model results for projection year 20 showed that risk (in % probability) from OPs and environmental stressors was higher for the wild subpopulations—the American River (50.9%–97.7%) and Naches (39.8%–84.4%) spring Chinook—than for the hatchery population (CESRF 18.5%–46.5%) and the Upper Yakima subpopulation (21.5%–68.7%). Metapopulation risk was higher in summer (58.1%–68.7%) than in winter (33.6%–53.2%), and this seasonal risk pattern was conserved at the subpopulation level. To reach the management goal in the American River spring Chinook subpopulation, the water temperature conditions in the Lower Yakima River would need to decrease. We demonstrate that 1) relative risk can vary across a metapopulation's spatial range, 2) dispersal among patches impacts subpopulation abundance and risk, and 3) local adaptation within a salmon metapopulation can profoundly impact subpopulation responses to equivalent stressors. Integr Environ Assess Manag 2021;17:95–109. © 2020 SETAC KEY POINTS: Fine‐scale risk estimates can be produced by integrating metapopulation model simulations into a Bayesian network relative risk model (BN‐RMM).Risk differed across spring Chinook salmon subpopulations in the Yakima River Basin, Washington, USA, highlighting the importance of considering life history differences when making risk predictions for environmental stressors.Water temperature is the risk factor that requires management to prevent loss of Chinook population abundance, given our modeling efforts.Small sample sizes for organophosphate in winter introduced sufficient uncertainty to increase the influence of toxicological effects in winter. [ABSTRACT FROM AUTHOR]

We estimated the risk to populations of Chinook salmon (Oncorhynchus tshawytscha) due to chlorpyrifos (CH), water temperature (WT), and dissolved oxygen concentration (DO) in 4 watersheds in Washington State, USA. The watersheds included the Nooksack and Skagit Rivers in the Northern Puget Sound, the Cedar River in the Seattle–Tacoma corridor, and the Yakima River, a tributary of the Columbia River. The Bayesian network relative risk model (BN‐RRM) was used to conduct this ecological risk assessment and was modified to contain an acetylcholinesterase (AChE) inhibition pathway parameterized using data from CH toxicity data sets. The completed BN‐RRM estimated risk at a population scale to Chinook salmon employing classical matrix modeling runs up to 50‐y timeframes. There were 3 primary conclusions drawn from the model‐building process and the risk calculations. First, the incorporation of an AChE inhibition pathway and the output from a population model can be combined with environmental factors in a quantitative fashion. Second, the probability of not meeting the management goal of no loss to the population ranges from 65% to 85%. Environmental conditions contributed to a larger proportion of the risk compared to CH. Third, the sensitivity analysis describing the influence of the variables on the predicted risk varied depending on seasonal conditions. In the summer, WT and DO were more influential than CH. In the winter, when the seasonal conditions are more benign, CH was the driver. Fourth, in order to reach the management goal, we calculated the conditions that would increase juvenile survival, adult survival, and a reduction in toxicological effects. The same process in this example should be applicable to the inclusion of multiple pesticides and to more descriptive population models such as those describing metapopulations. Integr Environ Assess Manag 2019;00:1–15. © 2019 SETAC KEY POINTS: The incorporation of acetylcholinesterase (AChE) inhibition (biomarker) and the output from a population model can be combined with environmental factors in a quantitative fashion.Environmental conditions contributed to a larger proportion of the risk compared to the toxicological pathways, but toxicology contributed up to 20% of the risk.The sensitivity analysis describing the influence of the variables on the predicted risk varied, depending on seasonal conditions.In order to reach the management goal, we calculated that an increase in juvenile and adult survival and a reduction in toxicological effects are required. [ABSTRACT FROM AUTHOR]

The effects of a mixture of two biopesticides, Success (spinosad) and the neem-based product, Azatin, were evaluated against the water flea, Daphnia magna Straus using a toxic unit approach. These two products are being used in organic agriculture and as such may end up in surface water systems together through drift and/or runoff. Results of an acute study indicated that Success was approximately 93 times more toxic than Azatin at LC50. Results of a chronic study (12 d) showed that exposure of population founders to the mixture of these two insecticides resulted in lower mortality than exposure to either product alone. Exposure to Azatin and Success separately and as a mixture resulted in concentration-dependent decline in the number of offspring/female, final population size, and population growth rate. It took higher toxic units of the mixture than either pesticide alone to cause population growth rates of zero (stable growth), indicating that the mixture was less toxic than predicted by the toxicity of each pesticide separately. The results of this study indicate that exposure of D. magna to a mixture of these insecticides would be less detrimental to D. magna than exposure to either product alone. [ABSTRACT FROM AUTHOR]

In this study, lethal concentration (LC) estimates for the semi-natural pesticide, spinetoram (Delegate?), were developed for three Cladoceran species: Ceriodaphnia dubia, Daphnia pulex, and Daphnia magna and compared to a previously published data set for these same species exposed to the related natural insecticide, spinosad. LC50's and 95% confidence limits (CL) were 12.47 (3.97-25.21), 3.44 (1.00-9.48), and 10.52 (2.52- 36.83) µg/L for C. dubia, D. pulex, and D. magna, respectively. Because the 95% CL for all the three species overlapped, spinetoram is equally susceptible to these species. However, spinetoram was found to be significantly less toxic than spinosad to C. dubia, significantly more toxic than spinosad to D. pulex, and equally toxic to D. magna. Therefore, even though spinetoram is derived from the same bacterial species as spinosad, there was no clear pattern of toxicity between these two related insecticides to the three species evaluated in this study. The results demonstrate the perils of inferring that the effects of one pesticide on indicator species will be similar to those of other chemicals despite similar modes of action and highlight the need to develop more nuanced risk assessment protocols. [ABSTRACT FROM AUTHOR]

A genetic variant of the entomopathogenic fungus Metarhizium anisopliae var anisopliae S54 (S54) was discovered and isolated from soil in Alberta, Canada and has been tested as a potential control agent for use against crop pest insects, principally grasshoppers (Orthoptera:Acrididae). The present study was conducted to evaluate the toxicity of this entomopathogenic fungus to a non-target cladoceran, Ceriodaphnia dubia Richard, a species commonly used in aquatic ecotoxicology tests. Acute mortality and population-level responses after chronic exposure were determined. Acute mortality of S54 (144 h exposure time) ranged from 5% in treatments of 1.33 x 104 spores/ml to 10% after exposure to 5.32 x 105 spores/ml. For the chronic population study, C. dubia populations were exposed to the expected environmental concentration (EEC) of the agricultural adjuvant R-11, the commonly used insecticide imidacloprid, the biopesticide, Azatin®, and S54. Imidacloprid had the greatest negative impact on C. dubia, reducing the number of founding individuals, offspring/female, final population size, and population growth rate compared to the control. Exposure to imidacloprid caused significantly greater reductions in the production of population parameters than the other compounds. R-11, Azatin®, and S54 were much less toxic to C. dubia than imidacloprid and these products are not expected to pose a significant risk to C. dubia after acute exposure to the EEC. Results of this study indicate that M. anisopliae var anisopliae S54 may be valuable as a natural insecticide applied in the context of integrated pest management of grasshoppers and other pest species with minimal impact on non-target aquatic organisms. [ABSTRACT FROM AUTHOR]