Toxicity of some aquatic pollutants to fish

Pesticide residues threaten fish that live in rivers. This study investigated the effects of Nemacur, malathion, and diuron on freshwater fish behavior, mortality, acetylcholinesterase (ACHE) activity, liver biomarkers, and residue accumulation. Fish were exposed to individual concentration of Nemacur, malathion, and diuron at 1 mg/L and to binary mixtures in glass aquarium 16 L capacity. Mortality of fish was also investigated at a range of 0.0-1 mg/L of Nemacur and malathion. The biochemical effects of the tested compounds were recorded. The results showed abnormal fish behavior at low concentration (0.1 mg/L) of malathion, high fish mortality at 0.1 mg/L of Nemacur and mixtures with Nemacur, and no mortality with diuron. Mortality increased and became more intense after 48 h rather than after 24 h. Diuron increased the effect of Nemacur and malathion at low concentration. ACHE was inhibited at different percentages in the blood serum and brain homogenate due to exposure to Nemacur, malathion, diuron, and/or a combination of these pesticides. Liver biomarker levels were higher in the blood serum of the treated fish than the control group. The interesting outcome of the study is that Nemacur is several folds more toxic than malathion and diuron. Mixtures showed synergistic effects. The pesticide residues in the fish muscles were less than those in the water. It can be concluded that low concentrations of Nemacur, malathion, and diuron are negatively affecting fish in rivers.