Combined effects of λ-cyhalothrin and imidacloprid formulated insecticides on the embryo-larval development of Danio rerio.

Brazil is the world's largest consumer of pesticides, with intensive agricultural practices contributing to the widespread contamination of aquatic ecosystems. Insecticides are of particular concern due to their toxicity and persistence, entering water bodies through runoff, leaching, and atmospheric deposition, and posing risks to aquatic organisms, especially fish. Since these compounds often occur in mixtures, studying their combined effects is essential for understanding their ecological impact. The insecticides λ-cyhalothrin (LC) and imidacloprid (IMI) are widely used in agriculture alone and in mixtures. They have been detected in surface waters and sediments near agricultural areas, raising concerns about their effects on aquatic organisms. The objective of this study was to evaluate the effects of sublethal concentrations (0.08% of LC_50-96h) of LC (0.15 μg L^-1) and IMI (100 μg L^-1), alone and in a binary mixture (LC+IMI), on the embryo-larval stage of Danio rerio, over 96 h of post-fertilization exposure (hpf). The results demonstrated that LC, IMI, and MIX caused an increase in embryonic mortality at 24 hpf. In addition, IMI increased DNA damage and decreased the larval hatching rate after 72 hpf. Furthermore, the mixture, in addition to causing a decrease in the larval hatching rate, increased lipid peroxidation and glutathione concentrations after 96 hpf. Thus, we conclude that these insecticides harm the early stages of D. rerio. Their toxicity is increased when they are mixed, since exposure to MIX was the one that most affected the embryonic phase. These effects, observed in a model species, indicate a relevant ecological risk, as they may compromise the survival of fish populations and, consequently, affect the structure and balance of aquatic ecosystems where these compounds are present.