Extrapolating Metal (Cu, Ni, Zn) Toxicity from Individuals to Populations Across Daphnia Species Using Mechanistic Models: The Roles of Uncertainty Propagation and Combined Physiological Modes of Action

Mechanistic effect modeling is a promising tool to improve the ecological realism of environmental risk assessment. An open question for the mechanistic modeling of metal toxicity is whether the same physiological mode of action (PMoA) could be assumed for closely related species. The implications of various modeling choices, such as the use of parameter point estimates and assumption of simplistic toxicodynamic models, are largely unexplored. We conducted life-table experiments with Daphnia longispina, Daphnia magna, and Daphnia pulex exposed to the single metals Cu, Ni, and Zn, and calibrated toxicokinetic-toxicodynamic (TKTD) models based on dynamic energy budget theory. We developed TKTD models with single and combined PMoAs to compare their goodness-of-fit and predicted population-level sensitivity. We identified the PMoA reproduction efficiency as most probable in all species for Ni and Zn, but not for Cu, and found that combined-PMoA models predicted higher population-level sensitivity than single-PMoA models, which was related to the predicted individual-level sensitivity, rather than to mechanistic differences between models. Using point estimates of parameters, instead of sampling from the probability distributions of parameters, could also lead to differences in the predicted population-level sensitivity. According to model predictions, apical chronic endpoints (cumulative reproduction, survival) are conservative for single-metal population effects across metals and species. We conclude that the assumption of an identical PMoA for different species of Daphnia could be justified for Ni and Zn, but not for Cu. Single-PMoA models are more appropriate than combined-PMoA models from a model selection perspective, but propagation of the associated uncertainty should be considered. More accurate predictions of effects at low concentrations may nevertheless motivate the use of combined-PMoA models. Environ Toxicol Chem 2024;43:338-358. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Metal Mixture Toxicity of Ni, Cu, and Zn in Freshwater Algal Communities and the Correlation of Single-Species Sensitivities Among Single Metals: A Comparative Analysis

The effects assessment of metals is mainly based on data of single metals on single species, thereby not accounting for effects of metal mixtures or effects of species interactions. Both of these effects were tested in combination, thereby hypothesizing that the sensitivity of a community to synergistic mixture toxicity depends on the correlation of single-species sensitivities among the single metals. Single-metal and metal-mixture effects were tested in full concentration-response experiments (fixed ray of 1:1:3 and 5:1:13 mass ratio Ni:Cu:Zn) on eight single freshwater algal species and 14 algal communities of four species each. The mean correlation of single-species median effect concentrations among the single metals (Ni-Cu, Cu-Zn, and Zn-Ni) for all species in a community (r ̅ ) ranged from -0.4 to 0.9 among the communities; most of these (12/14) were positive. Functional endpoints (total biomass) were overall less sensitive than structural endpoints (Bray-Curtis similarity index) for communities with positively correlated single-species sensitivities among the single metals (r ̅ > 0.33 ), suggesting that such correlations indicate functional redundancy under metal-mixture stress. Antagonistic metal-mixture interactions were predominantly found in single species, whereas metal-mixture interactions were antagonistic and surprisingly synergistic for the communities, irrespective of the reference mixture model used (concentration addition or independent action). The mixture interactions close to the carrying capacity (day 7) of communities gradually shifted from antagonism to more noninteractions with increasing correlation of single-species sensitivities among the single metals. Overall, this suggests that functional redundancy under mixed-metal stress comes at the cost of reduced biodiversity and that synergisms can emerge at the community level without any synergisms on the single-species level. Environ Toxicol Chem 2023;42:2666-2683. © 2023 SETAC.

Investigating Population-Level Toxicity of the Antidepressant Citalopram in Harpacticoid Copepods Using In Vivo Methods and Bioenergetics-Based Population Modeling

Recent research has revealed various lethal and sublethal effects of the selective serotonin reuptake inhibitor citalopram hydrobromide on the harpacticoid copepod Nitocra spinipes. In the present study, an individual-based model (IBM) grounded in the dynamic energy budget (DEB) theory was developed to extrapolate said effects to the population level. Using a generic DEB-IBM as a template, the model was designed to be as simple as possible, keeping model components that are outside the scope of the core DEB theory to a minimum. To test the model, a 56-day population experiment was performed at 0, 100, and 1000 μg citalopram hydrobromide L^-1 . In the experiment, the populations quickly reached a plateau in the control and at 100 μg L^-1 , which was correctly reproduced by the model and could be explained by food limitations hindering further population growth. At 1000 μg L^-1 , a clear mismatch occurred: Whereas in the experiment the population size increased beyond the supposed (food competition-induced) capacity, the model predicted a suppression of the population size. It is assumed that the IBM still misses important components addressing population density-regulating processes. Particularly crowding effects may have played an important role in the population experiment and should be further investigated to improve the model. Overall, the current DEB IBM for N. spinipes should be seen as a promising starting point for bioenergetics-based copepod population modeling, which-with further improvements-may become a valuable individual-to-population extrapolation tool in the future. Environ Toxicol Chem 2023;42:1094-1108. © 2023 SETAC.

Side Effects of Insecticides on Leaf-Miners and Gall-Inducers Depend on Species Ecological Traits and Competition with Leaf-Chewers

Internal feeding is considered to shield sessile herbivorous insects from exposure to nonsystemic insecticides aerially sprayed against forest defoliators, although this has not been tested. It is, however, established that leaf damage caused by defoliators affects the survivorship and oviposition behavior of sessile herbivores. Thus feeding ecology and competition may mediate nontarget effects of insecticides on these insects. We tested the ecological sensitivity of 3 guilds of sessile herbivores (upper-surface leaf-miners, lower-surface leaf-miners, and gall-inducers) to the lipophilic larvicides diflubenzuron and tebufenozide aerially applied either at operational rates (12 g active ingredient [a.i.]/ha and 69.6 g [a.i.]/ha, respectively) or at maximum legal rates (60 g [a.i.]/ha and 180 g [a.i.]/ha, respectively), in German oak forests. Diflubenzuron affected leaf-miners at different life stages depending on their position on the leaf but had no effect on gall-inducers. Tebufenozide showed a similar, but not significant, pattern in leaf-miners and did not affect gall-inducers. By reducing the incidence of chewing damage on leaves, both insecticides offset the negative effect of competition on leaf-miner and gall-inducers. The net outcome of insecticide treatment was positive for guilds avoiding exposure, but negative for upper-surface leaf-miners. Exposure to insecticides in situ can be mediated by subtle differences in species biology and species interactions, with potential implications for organisms usually considered safe in risk assessment studies. Environ Toxicol Chem 2021;00:1-17. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

A Multiple Life-History Trait-Based and Time-Resolved Assessment of Imidacloprid Effects and Recovery in the Widely Distributed Collembolan Folsomia quadrioculata

Life-history traits determine individual fitness and the fate of populations. Imidacloprid, a widely used neonicotinoid insecticide, which persists in soil for more than 100 d at biologically relevant levels, may affect nontarget and ecologically important species, such as collembolans. In the present study, we determined the sublethal effects of short-term imidacloprid exposure and postexposure recovery in the collembolan Folsomia quadrioculata, which occurs abundantly across the northern hemisphere. We assessed survival, egg production, and hatching success in adult springtails exposed for 14 d through the diet to imidacloprid, followed by a 28-d postexposure phase. Survival and hatching success were high throughout the experiment in all the treatments, with no clear concentration dependence. However, egg production declined during the exposure phase and nearly stopped between 8 and 14 d in all the treatments (except the control) but resumed during the postexposure phase. Moreover, the resumption of egg production showed a concentration-dependent delay. Our findings suggest that low imidacloprid exposures can restrict reproduction, with potentially severe consequences for the population, notwithstanding the partial recovery in egg production. Environ Toxicol Chem 2021;40:139-147. © 2020 SETAC.

The Impact of Metal-Rich Sediments Derived from Mining on Freshwater Stream Life

Metal-rich sediments have the potential to impair life in freshwater streams and rivers and, thereby, to inhibit recovery of ecological conditions after any remediation of mine water discharges. Sediments remain metal-rich over long time periods and have long-term potential ecotoxicological interactions with local biota, unless the sediments themselves are physically removed or replaced by less metal-rich sediment. Laboratory-derived environmental quality standards are difficult to apply to the field situation, as many complicating factors exist in the real world. Therefore, there is a strong case to consider other, field-relevant, measures of toxic effects as alternatives to laboratory-derived standards and to seek better biological tools to detect, diagnose and ideally predict community-level ecotoxicological impairment. Hence, this review concentrated on field measures of toxic effects of metal-rich sediment in freshwater streams, with less emphasis on laboratory-based toxicity testing approaches. To this end, this review provides an overview of the impact of metal-rich sediments on freshwater stream life, focusing on biological impacts linked to metal contamination.

Time-Variable Exposure Experiments in Conjunction with Higher Tier Population and Effect Modeling to Assess the Risk of Chlorotoluron to Green Algae

An algae population model was applied to describe measured effects of pulsed exposure to chlorotoluron on populations of Pseudokirchneriella subcapitata in 2 laboratory flow-through chemostat tests with different exposure regimes. Both tests enabled evaluation of adverse effects on algae during the exposure and population recovery afterward. Impacts on population densities after chlorotoluron exposure were directly visible as biomass loss in the chemostats. Recovery was observed after each exposure peak. The test results indicate that P. subcapitata is unlikely to show an increased sensitivity to chlorotoluron after pulsed exposure. No altered response or adaptation of the algae to chlorotoluron was observed, with the exception of the last high peak in flow-through test 2. Therefore, an adaptation to the test substance cannot be excluded after long-term exposure. However, recovery to the steady-state level after this peak indicates that the growth rate (fitness) was not significantly reduced in the population with higher tolerance. No differences in chlorotoluron impact on the populations over time in terms of growth were detected. Model predictions agreed well with the measured data. The tests and modeling results validate the model to simulate population dynamics of P. subcapitata after pulsed exposure to chlorotoluron. Model predictions and extrapolations with different exposure patterns are considered reliable for chlorotoluron. The good reproducibility of the population behavior in the test systems supports this conclusion. An example modeled extrapolation of the experimental results to other (untested) exposure scenarios shows a potential approach to using the validated model as a supportive tool in risk assessment. Environ Toxicol Chem 2019;38:2520-2534. © 2019 SETAC.

Joint Toxicity of Acetamiprid and Co-Applied Pesticide Adjuvants on Honeybees under Semifield and Laboratory Conditions

The evaluation of adverse effects of pesticides, pesticide adjuvants, and their combination on honeybees is hampered by a lack of colony-level bioassays reflecting productivity and survival over longer term exposure. In the present study, the joint toxicity of acetamiprid and co-applied pesticide adjuvants (N-methyl pyrrolidone [NMP], Silwet L-77, and Triton X-100) to honeybees was determined both in the laboratory and under semifield conditions. The 3 pesticide adjuvants caused no significant acute toxicity to honeybees by themselves; however, in the laboratory tests, they significantly increased the acute contact toxicity of acetamiprid to honeybees. For the semifield tests, in the T2 group (treatment with 5% acetamiprid soluble concentrate [SL] containing 10% Silwet L-77), the mortality of honeybees was significantly higher (p < 0.05) than that of the blank control on the fourth day after application (DAA + 4), that of the T1 group (5% acetamiprid SL containing 10% NMP) on DAA + 4 and DAA + 7 (seventh day after application), and that of the T3 group (5% acetamiprid SL containing 10% Triton X-100) on DAA + 4. Furthermore, the flight intensity in the T2 group on DAA + 7, the colony intensity on DAA + 28 (28th day after application), and the mean areas covered by pupae on DAA + 15 (15th day after application) were significantly lower (p < 0.05) than those of the blank control. Therefore, pesticide adjuvants may be important factors in increasing the toxicity of neonicotinoids to honeybees. Measures should be taken to manage the environmental risk of pesticide adjuvants during the process of formulation development and registration. Environ Toxicol Chem 2019;38:1940-1946. © 2019 SETAC.

The Unexpected Absence of Nickel Effects on a Daphnia Population at 3 Temperatures is Correctly Predicted by a Dynamic Energy Budget Individual-Based Model

Recent studies have shown that temperature affects chronic nickel (Ni) toxicity to Daphnia magna at the individual (apical) level. However, the effect of temperature on Ni toxicity to D. magna at the population level is unknown. The present study investigated whether the effect of temperature on chronic Ni toxicity to D. magna assessed on apical endpoints can be extrapolated to the population level. The results of the population experiment showed no consistent Ni effects on total D. magna population abundance at 15, 20, and 25 °C, although the Ni concentrations tested were previously reported to significantly reduce reproduction in D. magna individuals. This result supports the idea that ecological risk assessment should not extrapolate as such from apical endpoints to the population level. A dynamic energy budget individual-based model (DEB-IBM) was calibrated using apical Ni toxicity data at 15, 20, and 25 °C. The goal was to investigate whether the calibrated DEB-IBM would be able to predict the unexpected absence of effects at the population level and to further investigate the effect of temperature on Ni toxicity to a D. magna population. At the population level, the calibrated DEB-IBM correctly predicted the unexpected absence of an effect of Ni on a D. magna population. Detailed analysis of simulation output suggests that the predicted lower Ni sensitivity at the population level occurs because Ni-induced mortality is compensated by reduced starvation (less intraspecific competition). Extrapolated median effective concentration (EC50) values for population density predicted that the effect of temperature on Ni toxicity to D. magna populations was smaller (1.9-fold higher at 25 °C than at 15 °C) than on Ni toxicity to D. magna apical reproduction (the EC50 is 6.5-fold higher at 25 °C than at 15 °C). These results show that the DEB-IBM can help to replace population experiments by in silico simulations and to optimize the experimental design of population studies. Environ Toxicol Chem 2019;38:1423-1433. © 2019 SETAC.

Effects of increased temperature, drought, and an insecticide on freshwater zooplankton communities

In the present study we performed a microcosm experiment to assess the effects of the insecticide lufenuron on zooplankton communities exposed to increased temperature and drought in (semi-)arid regions. The experiment consisted of 3 environmental scenarios, assessed in 2 parts. Firstly, we assessed how water temperature (20 and 28 °C) affects the sensitivity and resilience of the zooplankton community to lufenuron. Secondly, we investigated the influence of drought on the structure of the zooplankton community at a high water temperature (28 °C) and evaluated its possible interaction with lufenuron. The results show that the community exposed to lufenuron at 28 °C had a faster lufenuron-related response and recovery than the community at 20 °C. The combined effects of lufenuron and temperature resulted in a synergistic effect on some taxa (Daphnia sp., Cyclopoida, and Copepoda nauplii). The tested zooplankton community had a high resilience to drought, although some particular taxa were severely affected after desiccation (Calanoida). Interactions between drought and lufenuron were not statistically significant. However, rewetting after desiccation contributed to lufenuron remobilization from sediments and resulted in a slight Cyclopoida population decline at high exposure concentrations. The study shows how environmental conditions related to global change in (semi-)arid regions may influence chemical fate and the vulnerability of zooplankton communities to chemical stress. Environ Toxicol Chem 2019;38:396-411. © 2018 SETAC.

Coupling toxicokinetic-toxicodynamic and population models for assessing aquatic ecological risks to time-varying pesticide exposures

Population modeling evaluations of pesticide exposure time series were compared with aspects of a currently used risk assessment process. The US Environmental Protection Agency's Office of Pesticide Programs models daily aquatic 30-yr pesticide exposure distributions in its risk assessments, but does not routinely make full use of the information in such time series. We used mysid shrimp Americamysis bahia toxicity and demographic data to demonstrate the value of a toxicokinetic-toxicodynamic model coupled with a series of matrix population models in risk assessment refinements. This species is a small epibenthic marine crustacean routinely used in regulatory toxicity tests. We demonstrate how the model coupling can refine current risk assessments using only existing standard regulatory toxicity test results. Several exposure scenarios (each with the same initial risk characterization as determined by a more traditional organism-based approach) were created within which population modeling documented risks different from those of assessments based on the traditional approach. We also present different acute and chronic toxicity data scenarios by which toxicokinetic-toxicodynamic coupled with population modeling can distinguish responses that traditional risk evaluations are not designed to detect. Our results reinforce the benefits of this type of modeling in risk evaluations, especially related to time-varying exposure concentrations. Environ Toxicol Chem 2018;37:2633-2644. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

A cross-national study of the population-level association between alcohol consumption and suicide rates

INTRODUCTION

The objective of this study was to explore the association between population-level alcohol consumption and cross-national suicide rates. Suicide mortality rates vary substantially by nation, as do the level and character of alcohol consumption. Only a few prior studies examined this association, however, and they used a small number of nations and failed to test for the multiple hypothesized pathways through which any association may operate.

MATERIAL AND METHODS

We obtained data from the World Health Organization for a sample of 83 nations. Controlling for potential structural covariates, we tested four theoretical mechanisms through which population-level alcohol consumption may influence national suicide rates.

RESULTS

Results showed no evidence of threshold effects, nor were risky national drinking patterns associated with higher suicide rates. We found evidence for the most common explanation that total per capita consumption is linearly associated with suicide rates. Our other findings, however, suggested this linear association masks more complex beverage-specific effects. Per capita wine consumption was not associated with male or female suicide rates, per capita spirits consumption was associated with both male and female suicide rates, per capita beer consumption was associated with male suicide rates, and per capita consumption of "other" alcohol types was associated with female suicide rates.

DISCUSSION AND CONCLUSIONS

Testing for only a linear association between total alcohol consumption and suicide rates fails to tell the whole story. Further research requires exploration of beverage-specific effects and other potential mechanisms, and consideration of national alcohol policies to reduce suicide rates.

Colony impact of pesticide-induced sublethal effects on honeybee workers: A simulation study using BEEHAVE

Research on neonicotinoids and honeybees have changed focus from direct mortality to sublethal effects. In the present study, a published honeybee model, BEEHAVE, is used to compare induced colony level impact of pesticides including direct mortality, poor brood care, disorientation, and increased handling time in oilseed rape and sunflower crops. Actual effects on individual bees will depend on exposure concentrations, but in the present study large effects were enforced. In oilseed rape, poor brood care had the largest colony impact, because it created a bottleneck for spring build-up of the workforce, and colony impact for all effect types peaked 1 mo after exposure ceased. In sunflower, the later exposure changed the response so colony impact peaked during exposure, and the bottleneck was honey store build-up. In all scenarios, good forage mitigated effects substantially. It is concluded that field studies should continue at least 1 mo after exposure to ensure detection of ecologically relevant sublethal effects. The results indicated that even if a sublethal effect is difficult to detect in the field, subsequent ecologically relevant colony level impacts would be clear if studies are continued for 1 mo after exposure. Guidance for regulatory studies recommends extended observation periods, and published field studies already use extended observation periods, so it is concluded that current methods are adequate for detecting ecologically relevant sublethal effects. Although published laboratory and semifield studies conducted under controlled exposure conditions suggest that sublethal effects may occur, published field studies with neonicotinoid seed treatments, naturally foraging bees, and extended observation periods do not report colony-level effects, suggesting that in these studies no ecologically relevant sublethal effects occurred. Environ Toxicol Chem 2017;36:831-840. © 2016 SETAC.

Using BEEHAVE to explore pesticide protection goals for European honeybee (Apis melifera L.) worker losses at different forage qualities

Losses of honeybee colonies are intensely debated and although honeybees suffer multiple stressors, the main focus has been on pesticides. As a result, the European Food Safety Authority (EFSA) revised the guidance for pesticide risk assessment for honeybees. The European Food Safety Authority reported a protection goal of negligible effect at 7% of colony size and then used the Khoury honeybee colony model to set trigger values for forager losses. However, the Khoury model is very simplistic and simulates colonies in an idealized state. In the present study, the authors demonstrate how a more realistic published honeybee model, BEEHAVE, with a few simple changes, can be used to explore pesticide risks. The results show that forage availability interacts with pesticide-induced worker losses, and colony resilience increases with forage quality. Adding alternative unexposed forage to the landscape also substantially mitigates the effects of pesticide exposure. The results indicate that EFSA's reported protection goal of 7% of colony size and triggers for daily worker losses are overly conservative. The authors conclude that forage availability is critical for colony resilience and that with adequate forage the colonies are resilient to even high levels of worker losses. However, the authors recommend setting protection goals using suboptimal forage conditions to ensure conservatism and for such suboptimal forage, a total of 20% reduction in colony size was safe. Environ Toxicol Chem 2017;36:254-264. © 2016 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Critical perspectives on mercury toxicity reference values for protection of fish

Environmental management decisions at mercury-contaminated sediment sites are predicated on the understanding of risks to various receptors, including fish. Toxicity reference values (TRVs) for interpreting risks to fish have been developed to assess mercury concentrations in fish or fish prey. These TRVs were systematically evaluated based on several lines of evidence. First, their conceptual basis and specific derivation were evaluated, including a close review of underlying toxicity studies. Second, case studies were reviewed to investigate whether TRVs are predictive of effects on fish populations in the field. Third, TRVs were compared with available information regarding preindustrial and present-day background concentrations of mercury in fish. The findings show that existing TRVs are highly uncertain, because they were developed using limited data from studies not designed for TRV derivation. Although field studies also entail uncertainty, several case studies indicate no evidence of adverse effects despite mercury exposures that exceed the available TRVs. Some TRVs also fall within the range of background mercury concentrations in predatory or prey fish. Lack of information on the selenium status of mercury-exposed fish is a critical confounding factor, and the form of methylmercury used in toxicity testing may also contribute to differences between TRV-based predictions and field observations of mercury effects on fish. On balance, the available information indicates that several of the TRVs reviewed are lower than necessary to protect fish populations. The 20% effect concentration from a previously published dose-response analysis appears closer to an effect threshold, based on available laboratory data. Additional research is needed to provide a stronger basis to establish dose-response relationships for mercury effects on fish.

Linking feeding inhibition with reproductive impairment in Gammarus confirms the ecological relevance of feeding assays in environmental monitoring

The in situ feeding bioassay in Gammarus fossarum is recognized as a reliable tool for monitoring the toxicity of freshwater contamination. However, whether recorded feeding inhibitions can potentially provoke population-level adverse outcomes remains an open question. In the present study, the authors present an experimental study in G. fossarum, which contributes to the quantitative description of the links between feeding inhibitions and impacts on female reproductive performance. The authors studied the impacts of food deprivation on reproductive endpoints (i.e., fecundity, fertility, molt cycle) during 2 successive molting cycles. Among the main results, the authors found that food deprivation triggered a slowdown of the molting process and a reduction in fertility but no alteration to embryonic development. These reproductive impairments appeared for feeding inhibition values usually recorded in monitoring programs of environmental pollution. Using a population model translating Gammarus life-history, the authors predicted that the observed reproductive alterations predict a strong degradation of population dynamics. The present study underlines the importance of feeding inhibition in population-level risk assessment and discusses how establishing upscaling schemes based on quantitative mechanistic links between impacts at different levels of biological organization can be applied in environmental monitoring to propose an ecotoxicological assessment of water quality, which would be sensitive, specific, and ecologically relevant.

Implications of interacting microscale habitat heterogeneity and disturbance events on Folsomia candida (Collembola) population dynamics: a modeling approach

The authors implemented a fractal algorithm in a spatially explicit individual-based model to generate landscapes with different microscale patterns of habitat fragmentation and disturbance events and studied their effects on population dynamics of the collembolan Folsomia candida. Among human activities that may cause habitat destruction, the present study focused on agricultural practices. Soil organisms living in a cultivated field are subjected to habitat loss and fragmentation as well as disturbance events generated by the application of agrochemicals and related activities. In addition, they are exposed to natural stressors, which might influence the effects of chemicals on populations. The authors designed simulation experiments that incorporate these 3 factors and investigated their effects on populations of F. candida in the presence or absence of behavioral avoidance of contaminated habitat. Simulation results show that spatial autocorrelation of contamination has different effects on population growth and equilibrium size according to the percentage of clean habitat. This pattern changes when avoidance behavior is excluded from the model, as does population recovery after a series of disturbance events. The model suggests that a combination of heterogeneous contamination and multiple stressors can lead to unexpected effects of toxicants at the population level. Individual-based models can help to understand these effects and therefore add ecological realism to environmental risk assessment of chemicals and can help to explore the effects of different risk management options.