Single and combined effects of pesticides and cadmium on endocrine and antitoxic systems of the amphipod Gammarus pulex.

Abstract

As climate change expands the distribution of disease-carrying mosquitoes, more and more larvicides (known as insect growth regulators or IGRs) will be used to control their populations, with the risk of spreading to the environment. Two largely used IGRs, methoprene and pyriproxyfen, have been shown to affect non-target aquatic organisms such as crustaceans, due to the similarity of their endocrine system with that of insects. Consequently, this study aimed at (i) investigating potential endocrine disruption (ED) effects by IGRs on the amphipod Gammarus pulex, and (ii) identifying potential biomarkers useful for the detection of ED in crustaceans. Using the RT-qPCR method, variations of expression of genes related to moult and growth processes, as well as antioxidant and antitoxic stress response systems, were determined after exposure to environmentally relevant concentrations of methoprene (5 and 50 μg/L) and pyriproxyfen (0.1 and 1 μg/L). Furthermore, effects of binary mixtures were investigated by adding cadmium, an inorganic toxicant, to pesticide exposures (methoprene/cadmium and pyriproxyfen/cadmium). Results revealed contrasting effects between pesticides, with methoprene mainly affecting genes associated with 20-hydroxyecdysone (20HE) signalling and pyriproxyfen mainly affecting genes associated with the methylfarnesoate (MF) pathway. Addition of cadmium resulted in unpredictable effects that did not conform to a set pattern of known cocktail effects (e.g. synergy, antagonism), highlighting the need to go further in the study of their separate mechanisms of action to elucidate their cumulative effects. Finally, although the present work did not allow the identification of specific biomarkers of ED in crustaceans, suggesting more research is needed, it highlighted that it is not possible to generalize the effects of IGRs in non-target species, as methoprene and pyriproxyfen seemed to affect two different biological pathways of G. pulex.