A review of climatic zone-related variations in toxicity of imidacloprid towards aquatic species and ecosystems

The widely used insecticide imidacloprid (IMI) is a major concern of water pollution worldwide. In this review study, monitoring values of IMI in water bodies, toxicity results, and possible geographical-related toxicity modifiers are summarized to highlight research gaps that hamper a mechanistic understanding of the variation in IMI toxicity observed between (sub)-tropical and temperate aquatic organisms. The average monitoring values of IMI ranged from 0.00019 to 59 μg/L. 27 % and 75 % of these average IMI values exceeded the freshwater invertebrates-based acute and chronic benchmarks, respectively. The median acute LC50 values of 109 μg/L and 68 μg/L are reported for temperate and (sub)-tropical arthropods, respectively. The reported ranges in nominal NOEC values for mesocosm studies are 0.5-7.5 μg/L, <0.1-1 μg/L, 0.03-0.3 μg/L and <0.01-0.1 μg/L for temperate, Mediterranean, sub-tropical and tropical regions, respectively. These toxicity threshold values of IMI to aquatic arthropods were significantly different between the regions, where (sub)-tropical organisms are more sensitive to IMI as compared to their Mediterranean-temperate counterparts. These differences in sensitivity can result from geographically related factors such as differences in temperature, food availability, and altitude, leading to changes in the toxicokinetics and toxicodynamics of the chemical in the organisms, but also to changes in life-history parameters of the test organisms. Our review shows an increase in IMI toxicity to aquatic arthropods with rising temperatures, which partly explains the observed differences in toxicity.