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The global biodiversity crisis emphasizes our need to understand how different stressors (climatic, chemical, parasitic, etc.) interact and affect biological communities. We provide a comprehensive meta‑analysis investigating joint effects of chemical and parasitic stressors for 1064 chemical‑parasitic combinations using the Multiplicative model on mortality of arthropods. We tested both features of the experimental setup (control mortality, stressor effect level) and the chemical mode of action, host and parasite phylogeny, and parasite‑host interaction traits as explanatory factors for deviations from the reference model. Synergistic interactions, defined as higher mortality than predicted, were significantly more frequent than no interactions or antagony. Experimental setup significantly affected the results, with studies reporting high (> 10%) control mortality or using low stressor effects (< 20%) being more synergistic. Chemical mode of action played a significant role for synergy, but there was no effects of host and parasite phylogeny, or parasite‑host interaction traits. The finding that experimental design played a greater role in finding synergy than biological factors, emphasize the need to standardize the design of mixed stressor studies across scientific disciplines. In addition, combinations testing more biological traits e.g. avoidance, coping, and repair processes are needed to test biology‑based hypotheses for synergistic interactions., The global biodiversity crisis emphasizes our need to understand how different stressors (climatic, chemical, parasitic, etc.) interact and affect biological communities. We provide a comprehensive meta-analysis investigating joint effects of chemical and parasitic stressors for 1064 chemical-parasitic combinations using the Multiplicative model on mortality of arthropods. We tested both features of the experimental setup (control mortality, stressor effect level) and the chemical mode of action, host and parasite phylogeny, and parasite-host interaction traits as explanatory factors for deviations from the reference model. Synergistic interactions, defined as higher mortality than predicted, were significantly more frequent than no interactions or antagony. Experimental setup significantly affected the results, with studies reporting high (> 10%) control mortality or using low stressor effects (< 20%) being more synergistic. Chemical mode of action played a significant role for synergy, but there was no effects of host and parasite phylogeny, or parasite-host interaction traits. The finding that experimental design played a greater role in finding synergy than biological factors, emphasize the need to standardize the design of mixed stressor studies across scientific disciplines. In addition, combinations testing more biological traits e.g. avoidance, coping, and repair processes are needed to test biology-based hypotheses for synergistic interactions.

Background: Triterpenoid saponins are bioactive compounds synthesised by plants in defence against insects or fungi. With a demand for new, sustainable, plant protection products saponins are under consideration as green insecticides. This study tries to identify the acute toxic effects of 10 saponin structures towards different non-target organisms and relate the effects to their chemical structure. Results: a-Hederin showed effects towards all test organisms, such as the aquatic crustacean Daphnia magna, the annelid worm Enchytraeus crypticus, the green algae Raphidocelis subcapitata and the yeast Saccaromyces cerevisiae. Highest toxicity was observed for a-Hederin (EC50 8.6 mg L-1) and Hederacolchisid-A1 (EC50 2.03 mg L-1) towards the annelid worm E. crypticus. The aquatic crustacean Daphnia magna was sensitive to Hederacolchisid- A1, a-Hederin, Arjunetin and Quillaja-mix with EC50 values from 12.52 mg L-1 - 16.90 mg L-1. S. cerevisiae was tested against a-Hederin and Quillaja-extract only and was more susceptible to a-Hederin (EC50 6.77 mg L-1 and 243.20 mg L-1). R. subcapitata showed minor effects when exposed to a-Hederin (EC50 42.99 mg L-1) and Madecassosid (267.65 mg L-1). This indicates that the algae, are the least sensitive species when exposed to saponins. Conclusion: Saponin toxicity depends on the interactions with sterols embedded in cell membranes. Our results indicate that a glycosylation at their C3 position together with a free carboxylic acid group at the C28 position allow triterpenoid saponins to interact with cholesterol and ergosterol and to a weaker extent with the plant sterol stigmasterol. Arjunetin and Quillaja-extract might be capable of interfering with chitin.

Man-made chemicals are a significant contributor to the ongoing deterioration of numerous ecosystems. Currently, risk assessment of these chemicals is based on observations in a single generation of animals, despite potential adverse intergenerational effects. Here, we investigate the effect of the fungicide prochloraz across three generations of Daphnia magna. We studied both the effects of continuous exposure over all generations and the effects of first-generation (F0) exposure on two subsequent generations. Effects at different levels of biological organization from genome-wide gene expression, whole organism metabolite levels, CYP enzyme activity and key phenotypic effects, such as reproduction, were monitored. Acclimation to prochloraz was found after continuous exposure. Following F0-exposure, embryonically exposed F1-offspring showed no significant effects. However, in the potentially germline exposed F2 animals, several parameters differed significantly from controls. A direct association between these F2 effects and the toxic mode of action of prochloraz was found, showing that chemicals can be harmful not only to the directly exposed generation, but also to prenatally exposed generations and in that way effects may even appear to skip a generation. This implies that current risk assessment practices are neglecting an important aspect of toxicity, such as delayed effects across generations due to a time gap between chemical exposure and emergence of effects.

Hydrolysis catalyzed by general esterases (GEs) is the most efficient route for hydrolyzation of pyrethroid insecticides. Organophosphate (OP) and carbamate (CB) insecticides are known to inhibit GEs in addition to acetylcholinesterase (AChE), which is their main target. We hypothesize that synergies can be induced by OPs and CBs when mixed with pyrethroids, due to their inhibition of GE-dependent detoxification of pyrethroids. To test this hypothesis, we conducted mixture toxicity experiments with Daphnia magna using alpha-cypermethrin (alpha-cyp) in combination with the noninsecticidal OP tetraisopropyl pyrophosphoramide (iso-OMPA) and five AChE inhibitors diazinon, chlorpyrifos, chlorfenviphos, parathion, and aldicarb. In addition, the in vivo GE activity inhibition was measured for all compounds. Up to 10-fold synergy was found between alpha-cyp and iso-OMPA, and the degree of synergy correlated linearly with the inhibition of the GE activity. No synergy, however, was found in any of the insecticide mixtures nor was the GE activity inhibited within the nonlethal concentration range tested. It was concluded that the effect of the insecticides on AChE occurred at lower concentrations than their effect on GEs, making the daphnids become immobilized before any synergistic effects on mortality could be observed. The implications of the findings are discussed from a risk assessment perspective.

Acetylcholinesterase (AChE) and general-esterase (GE) activities are important to understand detoxification processes of xenobiotics. The assays to quantify them have employed different substrates, inhibitors, types of experiments (in vitro and in vivo) and model organisms. The aim of this work was to give a systematic overview of the effect of the above factors on the outcome of AChE and GE activity measurements. We showed that AChE activity could be measured with the substrate acetylthiocholine iodide (AChI) but not with acetylcholine bromide (AChB) and only in in vitro assays. For GE activity, Michaelis-Menten kinetics differed between the substrates 4-methylumbellifery butyrate (4-MUB) and 1-naphtyl acetate (1-NA) in the measurements of in vitro activity, but their inhibition curves and IC50 values for the general inhibitor tetraisopropyl pyrophosphoramide (iso-OMPA) were similar, confirming that both substrates targeted the same group of enzymes. The GE substrate 4-MUB was applicable both in vitro and in vivo, while 1-NA was only applicable in vitro due to its high acute toxicity. When comparing the zooplankton crustacean Daphnia magna and the sediment dwelling Chironomus riparius, the latter had a four-fold higher maximal AChE activity (Vmax) and a higher susceptibility to the AChE inhibitor BW284c51 (four-fold lower 50% inhibitory concentration, IC50), but a lower maximal GE activity and lower susceptibility to iso-OMPA (higher IC50), indicating significant species differences between in C. riparius and D. magna. We conclude that both choice of substrate and exposure method matters for the outcome of esterase assays and that esterase compositions between species may vary significantly.