Fipronil is widely used against insects in agriculture and ectoparasites in domestic areas and veterinary medicine. However, fipronil may influence non-target species as a result of the contamination of aquatic ecosystems. The present study aimed to investigate the acute and sublethal effects of fipronil in freshwater mussels (Unio delicatus), a non-target species, with physiological, antioxidant action mechanisms and histopathological observations. The 96-h LC₅₀ value of fipronil was found to be 2.64 (1.45–4.56) mg/L. Sublethal concentrations were applied at ¹/₁₀ and ¹/₅ of 96-h LC₅₀ as 0.264 mg/L and 0.528 mg/L for 48-h and 7-d. Haemolymph samples, digestive gland and gill tissues of mussels were taken after exposure times. While the Total Haemocyte Counts decreased in 48-h of exposure, it was only high at 0.264 mg/L fipronil-exposed for 7-d (p < 0.05). While glutathione values in digestive glands and gills were higher in the fipronil applied groups (p < 0.05), the AOPP values were only higher in the digestive glands at 7-d of exposure (p < 0.05). Moreover, fipronil caused histopathological alterations on gills and digestive glands. These things considered, the principal component analysis revealed that the most pronounced changes in the antioxidant action mechanisms were caused by the fipronil exposure. These results show that sublethal concentrations of fipronil are toxic to freshwater mussels.

The overuse of pesticides has been increasing since the 20th century. Depending on this use, non-target organisms are also affected apart from target organisms. Cyfluthrin is a synthetic pyrethroid pesticide used in agriculture, domestic and veterinary medicine against insects. It may also affect nontarget aquatic organisms as a result of mixing with aquatic ecosystems. This study was aimed to investigate the effect of cyfluthrin on freshwater mussels, one of the aquatic invertebrate species, with hemocyte parameters. Total hemolymph counts, hemolymph cell morphology, and differential hemocyte counts were performed from hemolymph taken from mussels exposed to different cyfluthrin doses exposures for 24 and 48 hours. Compared to the control group, the total hemocyte counts of the experimental groups were found to increase in 24h and decrease in 48h significantly (p<0.05). In the examination of hemocyte morphologies, granular, semi granular, and hyalinocyte cells were observed. Similar values of differential hemocyte counts were found both 24 and 48h exposure times. As a result, in aquatic toxicology studies, besides total hemocyte count, analysis of hemocyte morphologies and differential hemocyte counts are found to be good biomarkers.

Nowadays, there are a lot of researches about the effects of endocrine disruptors on human and wildlife organisms. Endocrine disruptors are exogenous substances or substance mixtures that cause undesired effects in the organism or in future generations by altering the endocrine system of the exposed organism. Fish are exposed to endocrine disruptors in several ways including water, sediment, and diet. The toxic effects of endocrine disruptors on fish vary according to the exposure period, duration of exposure, chemical properties of the substances, and whether the exposed substance is single or mixed with other substances. Within the scope of this review, the classification of endocrine disruptors, their usage areas, their way of mixing into the aquatic ecosystem, and their toxic effects on fish will be explained.