Acute co-exposure to anticholinesterase insecticides and arsenic: biochemical effects in two different Hyalella curvispina populations

Abstract

In agricultural areas, aquatic invertebrates can be exposed to mixtures of pesticides and metal(loid)s. In the fruit-production region of north Argentine Patagonia, the insecticides azinphos-methyl (AM) and carbaryl (Cb) have been widely applied. Besides, in this region, arsenic (As) occurs naturally in streams near volcanic areas. This study aimed to evaluate survival and biochemical markers in Hyalella curvispina amphipods acutely co-exposed to As and insecticides, comparing populations from a reference and an agricultural site. Co-exposure to As and AM increased mortality in both populations, indicating potentiation of acute toxicity, while co-exposure to As and Cb also increased mortality in the more susceptible population. Joint exposure inhibited acetylcholinesterase (AChE) activity, confirming it as a reliable biomarker of acute exposure and co-exposure. Population-specific differences in glutathione S-transferase (GST) and reduced glutathione (GSH) responses to the toxicants were observed, likely linked to different tolerance to anticholinesterase insecticides. According to the Relative Interaction Index, the combined effects of As and insecticides were mainly antagonistic (15 cases), followed by synergistic (5) and additive (4). The results obtained demonstrate that co-exposure can alter responses to single toxicants and enhance acute toxicity, emphasising the need to assess joint exposures to better reflect realistic environmental scenarios.