Alteration of physiological responses in aquatic organisms exposed to ecologically relevant insecticides

This research aims to assess the risk of two types of insecticides used in agriculture: thiacloprid, a neonicotinoid, and fenitrothion, an organophosphate, on non-target organisms such as Mytilus galloprovincialis and Danio rerio larvae. Mussels were exposed to both the Bayer produced pesticide Calypso 480 SC (40.4% thiacloprid) and the active molecule thiacloprid (purity 99.9%, Sigma Aldrich) with acute exposure to sublethal concentrations of Calypso(10, 50and 100 mg/L) and thiacloprid (1, 5 and 10 mg/L) at two-time points (3 and 7 days) and sub-chronic exposure to Calypso (7.77 and 77.70 mg/L) and thiacloprid (4.5 and 450 µg/L) at two time points (10 and 20 days). Acute exposure to sublethal concentration showed that in biochemical analysis of haemolymph there were significant changes in electrolytes ions, lactate dehydrogenase enzyme activity and glucose concentration following exposure to both substances. The thiacloprid-exposed mussels showed a significant imbalance in CAT activity in the digestive gland and gills. Calypso caused a significant decrease in SOD activity in gills and CAT activity in both tissues. Sub-chronic exposure to both concentrations of Calypso significantly increased mortality rate in the cells of hemolymph and the digestive gland, while digestive gland cells were no longer able to regulate cell volume. Exposure significantly reduced hemolymph parameters, affected the enzymatic activities of SOD of the digestive gland and CAT of gills. Sub-chronic exposure to thiacloprid affected hemolymph biochemical parameters, cell viability in the digestive gland, antioxidant biomarkers in the digestive gland and gills at thiacloprid environmental relevant concentrations of 4.5 µg/L. Twenty-four-hour exposure to environmental concentrations of fenitrothion, ranging from ng/L to low μg/L, altered the basal locomotor activity, visuomotor response and acoustic/vibrational escape response of zebrafish larvae. The computational analysis identified potential protein targets for this compound. Some of the predictions, including interactions with acetylcholinesterase, monoamine oxidases and the androgen receptor (AR), were experimentally validated. Finally, altered levels of L-DOPA, DOPAC, HVA and 5-HIAA were found, as well as a significant up-regulation of slc18a2 expression at lower fenitrothion concentrations. These data strongly suggest that the concentrations of fenitrothion commonly found in aquatic ecosystems present a significant environmental risk to fish communities. This study attempts to improve the limited information on the effects of these insecticides on aquatic organisms, highlighting how prolonged exposure to low concentrations is harmful to non-target organisms such as mussels.