Temperature induced changes in species distribution increases sensitivity of aquatic invertebrate communities to chemicals.

In this commentary, I will discuss how climate warming might influence the impacts of chemicals on (aquatic) ecosystems. It provides a commentary on Sinclair et al. (2024).

Toxicokinetic-Toxicodynamic Model to Assess Thermal Stress.

Temperature is a crucial environmental factor affecting the distribution and performance of ectothermic organisms. This study introduces a new temperature damage model to interpret their thermal stress. Inspired by the ecotoxicological damage model in the General Unified Threshold model for Survival (GUTS) framework, the temperature damage model assumes that damage depends on the balance between temperature-dependent accumulation and constant repair. Mortality due to temperature stress is driven by the damage level exceeding a threshold. Model calibration showed a good agreement with the measured survival of Gammarus pulex exposed to different constant temperatures. Further, model simulations, including constant temperatures, daily temperature fluctuations, and heatwaves, demonstrated the model's ability to predict temperature effects for various environmental scenarios. With this, the present study contributes to the mechanistic understanding of temperature as a single stressor while facilitating the incorporation of temperature as an additional stressor alongside chemicals in mechanistic multistressor effect models.

Interactive effects of multiple stressors vary with consumer interactions, stressor dynamics and magnitude.

Predicting the impacts of multiple stressors is important for informing ecosystem management but is impeded by a lack of a general framework for predicting whether stressors interact synergistically, additively or antagonistically. Here, we use process-based models to study how interactions generalise across three levels of biological organisation (physiological, population and consumer-resource) for a two-stressor experiment on a seagrass model system. We found that the same underlying processes could result in synergistic, additive or antagonistic interactions, with interaction type depending on initial conditions, experiment duration, stressor dynamics and consumer presence. Our results help explain why meta-analyses of multiple stressor experimental results have struggled to identify predictors of consistently non-additive interactions in the natural environment. Experiments run over extended temporal scales, with treatments across gradients of stressor magnitude, are needed to identify the processes that underpin how stressors interact and provide useful predictions to management.

Combined effects of heatwaves and micropollutants on freshwater ecosystems: Towards an integrated assessment of extreme events in multiple stressors research.

Freshwater ecosystems are strongly influenced by weather extremes such as heatwaves (HWs), which are predicted to increase in frequency and magnitude in the future. In addition to these climate extremes, the freshwater realm is impacted by the exposure to various classes of chemicals emitted by anthropogenic activities. Currently, there is limited knowledge on how the combined exposure to HWs and chemicals affects the structure and functioning of freshwater ecosystems. Here, we review the available literature describing the single and combined effects of HWs and chemicals on different levels of biological organization, to obtain a holistic view of their potential interactive effects. We only found a few studies (13 out of the 61 studies included in this review) that investigated the biological effects of HWs in combination with chemical pollution. The reported interactive effects of HWs and chemicals varied largely not only within the different trophic levels but also depending on the studied endpoints for populations or individuals. Hence, owing also to the little number of studies available, no consistent interactive effects could be highlighted at any level of biological organization. Moreover, we found an imbalance towards single species and population experiments, with only five studies using a multitrophic approach. This results in a knowledge gap for relevant community and ecosystem level endpoints, which prevents the exploration of important indirect effects that can compromise food web stability. Moreover, this knowledge gap impairs the validity of chemical risk assessments and our ability to protect ecosystems. Finally, we highlight the urgency of integrating extreme events into multiple stressors studies and provide specific recommendations to guide further experimental research in this regard.

Explicit Consideration of Temperature Improves Predictions of Toxicokinetic-Toxicodynamic Models for Flupyradifurone and Imidacloprid in Gammarus pulex.

In the face of global climate change, where temperature fluctuations and the frequency of extreme weather events are increasing, it is needed to evaluate the impact of temperature on the ecological risk assessment of chemicals. Current state-of-the-art mechanistic effect models, such as toxicokinetic-toxicodynamic (TK-TD) models, often do not explicitly consider temperature as a modulating factor. This study implemented the effect of temperature in a widely used modeling framework, the General Unified Threshold model for Survival (GUTS). We tested the model using data from toxicokinetic and toxicity experiments with Gammarus pulex exposed to the insecticides imidacloprid and flupyradifurone. The experiments revealed increased TK rates with increasing temperature and increased toxicity under chronic exposures. Using the widely used Arrhenius equation, we could include the temperature influence into the modeling. By further testing of different model approaches, differences in the temperature scaling of TK and TD model parameters could be identified, urging further investigations of the underlying mechanisms. Finally, our results show that predictions of TK-TD models improve if we include the toxicity modulating effect of temperature explicitly.

Size- and sex-related sensitivity differences of aquatic crustaceans to imidacloprid.

Field collected aquatic invertebrates are often used as test organisms in the refinement of the standard Tier 1 risk assessment of various pollutants. This approach can provide insights into the effects of pollutants on the natural environment. However, researchers often pragmatically select test organisms of a specific sex and/or size, which may not represent the sensitivity of the whole population. To investigate such intraspecies sensitivity differences, we performed standard acute toxicity and toxicokinetic tests with different size classes and sex of Gammarus pulex and Asellus aquaticus. Furthermore, toxicokinetics and toxicodynamics models were used to understand the mechanism of the intraspecies sensitivity differences. We used neonates, juveniles and male and female adults in separate dedicated experiments, in which we exposed the animals to imidacloprid and its bioactive metabolite, imidacloprid-olefin. For both species, we found that neonates were the most sensitive group. For G. pulex, the sensitivity decreased linearly with size, which can be explained by the size-related uptake rate constant in the toxicokinetic process and size-related threshold value in the toxicodynamic process. For A. aquaticus, female adults were least sensitive to imidacloprid, which could be explained by a low internal biotransformation of imidacloprid to imidacloprid-olefin. Besides, imidacloprid-olefin was more toxic than imidacloprid to A. aquaticus, with differences being 8.4 times for females and 2.7 times for males. In conclusion, we established size-related sensitivity differences for G. pulex and sex-related sensitivity for A. aquaticus, and intraspecies differences can be explained by both toxicokinetic and toxicodynamic processes. Our findings suggest that to protect populations in the field, we should consider the size and sex of focal organisms and that a pragmatic selection of test organisms of equal size and/or sex can underestimate the sensitivities of populations in the field.

Comparing the acute and chronic toxicity of flupyradifurone and imidacloprid to non-target aquatic arthropod species.

Flupyradifurone (FPF) is a new type of butenolide insecticide. It was launched on the market in 2015 and is considered an alternative to the widely used neonicotinoids, like imidacloprid (IMI), some of which are banned from outdoor use in the European Union. FPF is claimed to be safe for bees, but its safety for aquatic organisms is unknown. Its high water solubility, persistence in the environment, and potential large-scale use make it urgent to evaluate possible impacts on aquatic systems. The current study assessed the acute and chronic toxicity of FPF for aquatic arthropod species and compared these results with those of imidacloprid. Besides, toxicokinetics and toxicokinetic-toxicodynamic models were used to understand the mechanisms of the toxicity of FPF. The present study results showed that organisms take up FPF slower than IMI and eliminate it faster. In addition, the hazardous concentration 5th percentiles (HC05) value of FPF derived from a species sensitivity distribution (SSD) based on acute toxicity was found to be 0.052 µmol/L (corresponding to 15 µg/L), which was 37 times higher than IMI (0.0014 µmol/L, corresponding to 0.36 µg/L). The chronic 28 days EC10 of FPF for Cloeon dipterum and Gammarus pulex were 7.5 µg/L and 2.9 µg/L, respectively. For G. pulex, after 28 days of exposure, the no observed effect concentration (NOEC) of FPF for food consumption was 0.3 µg/L. A toxicokinetic-toxicodynamic (TKTD) model parameterised on the acute toxicity data well predicted the observed chronic effects of FPF on G. pulex, indicating that toxicity mechanisms of FPF did not change with prolonged exposure time, which is not the case for IMI.

Linking Macroinvertebrates and Physicochemical Parameters for Water Quality Assessment in the Lower Basin of the Volta River in Ghana.

The health of the lower basin of the Volta River in Ghana was evaluated in January-February and May-June 2016 using physicochemical parameters and benthic macroinvertebrates sampled at 10 locations. Selected environmental variables were compared to accepted environmental water quality standard values where applicable. Principal component analysis (PCA) and redundancy analysis (RDA) were used to analyse the association between the benthic macroinvertebrates distribution and physicochemical variables. Pesticide concentrations were generally below the limit of detection 0.01 and 0.005 µg/L for organophosphate/synthetic pyrethroid and organochlorines respectively. Nutrient levels were also generally low; however, significant differences existed between the values of physicochemical parameters at the different sampling sites and seasons (Monte Carlo permutation test; p = 0.002), as well as between the abundance of macroinvertebrates at the different sites and seasons (p = 0.002). The environmental variables dissolved oxygen (DO), phosphate, pH, substratum (p < 0.05), turbidity, conductivity, total dissolved solids, total solids and nitrate (0.05 < p < 0.10) significantly explained the variation in macroinvertebrate composition between sampling stations in the Volta River. Polypedilum fuscipenne, was positively correlated with turbidity and DO concentrations; Physa sp., Centroptilum sp., Centroptiloides sp., Phaon iridipennis and juvenile fish were positively correlated with nitrate concentration and pH and negatively correlated with turbidity and DO. Polluted sites were dominated by the snail Lymnaea glabra. This demonstrates that physicochemical parameters and macroinvertebrates could be applied to describe the water quality and improve the biomonitoring for water resources management and the environmental protection in the Lower Volta River.

Towards a unified study of multiple stressors: divisions and common goals across research disciplines.

Anthropogenic environmental changes, or 'stressors', increasingly threaten biodiversity and ecosystem functioning worldwide. Multiple-stressor research is a rapidly expanding field of science that seeks to understand and ultimately predict the interactions between stressors. Reviews and meta-analyses of the primary scientific literature have largely been specific to either freshwater, marine or terrestrial ecology, or ecotoxicology. In this cross-disciplinary study, we review the state of knowledge within and among these disciplines to highlight commonality and division in multiple-stressor research. Our review goes beyond a description of previous research by using quantitative bibliometric analysis to identify the division between disciplines and link previously disconnected research communities. Towards a unified research framework, we discuss the shared goal of increased realism through both ecological and temporal complexity, with the overarching aim of improving predictive power. In a rapidly changing world, advancing our understanding of the cumulative ecological impacts of multiple stressors is critical for biodiversity conservation and ecosystem management. Identifying and overcoming the barriers to interdisciplinary knowledge exchange is necessary in rising to this challenge. Division between ecosystem types and disciplines is largely a human creation. Species and stressors cross these borders and so should the scientists who study them.

Influence of pH on the toxicity of ionisable pharmaceuticals and personal care products to freshwater invertebrates.

The majority of pharmaceuticals and personal health-care products are ionisable molecules at environmentally relevant pHs. The ionization state of these molecules in freshwater ecosystems may influence their toxicity potential to aquatic organisms. In this study we evaluated to what extent varying pH conditions may influence the toxicity of the antibiotic enrofloxacin (ENR) and the personal care product ingredient triclosan (TCS) to three freshwater invertebrates: the ephemeropteran Cloeon dipterum, the amphipod Gammarus pulex and the snail Physella acuta. Acute toxicity tests were performed by adjusting the water pH to four nominal levels: 6.5, 7.0, 7.5 and 8.0. Furthermore, we tested the efficiency of three toxicity models with different assumptions regarding the uptake and toxicity potential of ionisable chemicals with the experimental data produced in this study. The results of the toxicity tests indicate that pH fluctuations of only 1.5 units can influence EC50-48 h and EC50-96 h values by a factor of 1.4-2.7. Overall, the model that only focuses on the fraction of neutral chemical and the model that takes into account ion-trapping of the test molecules showed the best performance, although present limitations to perform risk assessments across a wide pH range (i.e., well above or below the substance pKa). Under such conditions, the model that takes into account the toxicity of the neutral and the ionized chemical form is preferred. The results of this study show that pH fluctuations can have a considerable influence on toxicity thresholds, and should therefore be taken into account for the risk assessment of ionisable pharmaceuticals and personal health-care products. Based on our results, an assessment factor of at least three should be used to account for toxicity differences between standard laboratory and field pH conditions. The models evaluated here can be used to perform refined risk assessments by taking into account the influence of temporal and spatial pH fluctuations on aquatic toxicity.