Physiological and histopathological response of non-target organisms to emamectin benzoate: an effective innovative insecticide or a new ecosystem health hazard?

Emamectin benzoate (EB) is a macrocyclic lactone insecticide, belonging to the avermectins class and ivermectin family and is produced by Streptomyces avermitilis. EB is widely used in agriculture and aquaculture to reduce the damaging effects of pests. This study aimed to investigate the 1) acute toxicity (median lethal concentration values, LC₅₀) and 2) sublethal toxicity (immunological, biochemical and histopathological effects of sublethal concentrations) of EB on non-target freshwater mussels (Unio delicatus). The 96-h LC₅₀ value of EB for U. delicatus was determined as 0.21 mg/L. U. delicatus individuals were exposed to sublethal concentrations at ¹/₁₀ and ¹/₁₀₀ of the LC₅₀ value for 48 h, 7d and 21d. Acute exposure to sub-lethal concentrations resulted in a significant decrease in the total haemocyte count compared to the control groups (p < 0.05). Changes in total antioxidant status and total oxidant levels occurred in the haemolymph. While changes in gill and digestive gland glutathione and advanced oxidation protein products were not significant during acute (48 h and 7d) and chronic (21d) exposure to sub-lethal concentrations of EB, significant increases or decreases were observed in malondialdehyde, compared to control groups (p < 0.05). In addition to immunological and biochemical changes, histopathological changes were observed in gill and digestive gland tissues. The results of this study showed that exposure to EB at two sublethal concentrations in U. delicatus caused biochemical and histopathological changes in the tissues of the haemolymph, gills and digestive glands. The overall results of this study showed that EB is toxic to mussels even at sub-lethal concentrations in acute and chronic exposure.