Combined effect of nickel and chlorpyrifos on the ground beetle Pterostichus oblongopunctatus

The pace-of life explains whether gills improve or exacerbate pesticide sensitivity in a damselfly larva

Trait-based approaches are promising to make generalizations about the sensitivity of species and populations to pesticides. Two traits that may shape the sensitivity to pesticides are the surface area (related to pesticide uptake) and the metabolic rate (related to pesticide elimination). We compared the sensitivity of damselfly larvae to the pesticide chlorpyrifos and how this was modified by loss of external gills (autotomy, reducing the surface area) in both fast pace-of-life (high metabolic rate) and slow pace-of-life (low metabolic rate) populations of Ischnura elegans. The slow-paced populations were more sensitive to the pesticide than the fast-paced populations in terms of survival, growth and energy metabolism. This suggests the higher metabolic rate of fast-paced populations enabled a faster pesticide elimination. Pesticide exposure also reduced heat tolerance, especially in slow-paced larvae under hypoxia. Gill loss had opposite effects on pesticide sensitivity in slow- and fast-paced populations. In slow-paced larvae, gill loss lowered the sensitivity to the pesticide, while in fast-paced larvae, gill loss increased the sensitivity. This difference likely reflects the balance between the roles of the gills in pesticide uptake (more detrimental in slow-paced populations) and oxygen uptake (more important in fast-paced populations). Our results highlight the need to consider trait interactions when applying trait-based approaches to predict the sensitivity to pesticides.

A widespread morphological antipredator mechanism reduces the sensitivity to pesticides and increases the susceptibility to warming

Pollution and predation are two omnipresent stressors in aquatic systems that can interact in multiple ways, thereby challenging accurate assessment of the effects of pollutants in natural systems. Despite the widespread occurrence of morphological antipredator mechanisms, no studies have tested how these can affect the sensitivity of prey to pesticides. Sensitivity to pesticides is typically measured via reductions in growth rates and survival, but also reductions in heat tolerance are to be expected and are becoming increasingly important in a warming world. We investigated how autotomy, a widespread morphological antipredator mechanism where animals sacrifice a body part (here the caudal lamellae) to escape when attacked by a predator, modified the sensitivity to the insecticide chlorpyrifos in larvae of the damselfly Coenagrion puella. Exposure to chlorpyrifos reduced the growth rate and heat tolerance (measured as CTmax). A key finding was that the pesticide had a greater impact on growth rates of intact animals, i.e. those that retained their lamellae. This reduced sensitivity to chlorpyrifos in animals without lamellae can be explained by the reduced outer surface area which is expected to result in a lower uptake of the pesticide. Larvae that underwent autotomy exhibited a lower heat tolerance, which may also be explained by the reduced surface area and the associated reduction in oxygen uptake. There is a wide diversity of morphological antipredator mechanisms, suggesting that there will be more examples where these mechanisms affect the vulnerability to pollutants. Given the importance of pollution and predation as structuring forces in aquatic food webs, exploring the potential interactions between morphological antipredator mechanisms and sensitivity to pollutants will be crucial for risk assessment of pollutants in aquatic systems.

Comparing bee species responses to chemical mixtures: Common response patterns?

Pollinators in agricultural landscapes can be exposed to mixtures of pesticides and environmental pollutants. Existing mixture toxicity modelling approaches, such as the models of concentration addition and independent action and the mechanistic DEBtox framework have been previously shown as valuable tools for understanding and ultimately predicting joint toxicity. Here we apply these mixture models to investigate the potential to interpret the effects of semi-chronic binary mixture exposure for three bee species: Apis mellifera, Bombus terrestris and Osmia bicornis within potentiation and mixture toxicity experiments. In the potentiation studies, the effect of the insecticide dimethoate with added propiconazole fungicide and neonicotinoid insecticide clothianidin with added tau-fluvalinate pyrethroid acaricide showed no difference in toxicity compared to the single chemical alone. Clothianidin toxicity showed a small scale, but temporally conserved increase in exposure conducted in the presence of propiconazole, particularly for B. terrestris and O. bicornis, the latter showing a near three-fold increase in clothianidin toxicity in the presence of propiconazole. In the mixture toxicity studies, the dominant response patterns were of additivity, however, binary mixtures of clothianidin and dimethoate in A. mellifera, B. terrestris and male O. bicornis there was evidence of a predominant antagonistic interaction. Given the ubiquitous nature of exposures to multiple chemicals, there is an urgent need to consider mixture effects in pollinator risk assessments. Our analyses suggest that current models, particularly those that utilise time-series data, such as DEBtox, can be used to identify additivity as the dominant response pattern and also those examples of interactions, even when small-scale, that may need to be taken into account during risk assessment.

Combined effects of chlorpyriphos, copper and temperature on acetylcholinesterase activity and toxicokinetics of the chemicals in the earthworm Eisenia fetida

In polluted environments organisms are commonly exposed to a combination of chemicals with different modes of action, and their effects can be additionally modified by natural abiotic conditions. One possible mechanism for interactions in mixtures is via toxicokinetics, as chemicals may alter the uptake, distribution, biotransformation and/or elimination of each other, and all these processes can be affected by temperature. In this study, the effect of temperature (T) on the toxicokinetics of copper (Cu) and chlorpyriphos (CHP), applied either singly or in binary mixtures, was studied in the earthworm Eisenia fetida. The experiments were conducted at 10 or 20 °C and the earthworms were exposed to environmentally realistic concentrations of Cu and/or CHP for 16 d, followed by a depuration period of 4 d in uncontaminated soil. The earthworms were sampled for body Cu and/or CHP concentrations and acetylcholinesterase (AChE) activity measurements. The CHP degradation rate in the soil was substantially higher at 20 °C and in soil treated with Cu. The significant (p < 0.05) inhibition of AChE activity in the earthworms exposed to CHP was found. The effect of Cu was significant only at p < 0.1. No synergistic effect of the parallel CHP and Cu exposure was found. Four days after transferring the earthworms to uncontaminated soil, the AChE activity recovered to the level observed in control animals. The temperature effect on the toxicokinetic parameters was more pronounced for CHP than for Cu. In the case of CHP, the assimilation rate constant (k_A) was significantly higher at 20 °C than at 10 °C, both in CHP-only and CHP + Cu treatments. A similar trend was found for the elimination rate constant (k_E), but the difference was statistically significant only for non-Cu treatments. In the case of Cu, the general trend of higher k_A and k_E at 20 °C and in the absence of CHP was observed.