Silver nanoparticles inhibit the gill Na⁺/K⁺-ATPase and erythrocyte AChE activities and induce the stress response in adult zebrafish (Danio rerio).

Silver nanoparticles (AgNPs) are the most commonly used metallic nanoparticles in industrial applications, including medical and consumer products. In the recent years, however, concerns regarding their environmental and health impacts have emerged. Aquatic organisms are of special concern since water bodies often serve as sinks for anthropogenic activities. This study assessed the effects of AgNPs on the activities of the gill Na(+)/K(+)-ATPase and erythrocyte acetylcholinestrase (AChE), as well as the plasma biochemistry in adult zebrafish (Danio rerio). In an acute exposure scenario the fish were exposed for 4d to 16.76 mg/L AgNPs, which was the 96 h LC50 value determined in preliminary experiments. In a prolonged exposure scenario the fish were exposed for 1, 2, or 3 weeks to AgNPs at concentrations of 2 and 4 mg/L, corresponding to the 1/10th and 2/10th of the 96 h LC50 value. Generally the activity of the gill Na(+)/K(+)-ATPase decreased, but this was only significant starting at 14 d of the prolonged exposure scenario, whereas the activity of the erythrocyte AChE was significantly decreased in both exposure scenarios. Finally, the plasma electrolytes levels were reduced and the plasma glucose and cortisol levels were increased in exposed fish. This study demonstrates that AgNPs could inhibit the activities of Na(+)/K(+)-ATPase and AChE, thus interfering with the proper ionoregulation and neuroregulation, respectively, and act as stressors.

Impact of a short-term diazinon exposure on the osmoregulation potentiality of Caspian roach (Rutilus rutilus) fingerlings.

The stocks of Caspian roach (Rutilus rutilus), an economically important species in the Caspian Sea, are depleting. Each year millions of artificially produced fingerlings of this species are restocked in the mouth of rivers of the Southern Caspian Sea (e.g. Qare Soo River), where they are exposed to pesticides originating from regional rice and orchard fields. This early exposure to pesticides could affect the hypo-osmoregulatory ability of juvenile fish. Thus, in this study, Caspian roach fingerlings were exposed to environmentally-relevant concentrations of the organophosphate insecticide diazinon for 96 h in fresh water and then transferred to diazinon-free brackish water (BW) for another 96 h. We report that cortisol and glucose levels were significantly increased in all diazinon treatments at all sampling time points in comparison to the control group. Moreover, the thyroid hormone levels of TSH, T4, and T3 significantly decreased in diazinon-exposed fish even after the transfer to BW. The electrolytes were differentially affected during the exposure to diazinon and after the transfer to BW. The number of chloride cells in the gill tissue was significantly increased during diazinon exposure at the higher concentrations and decreased to control levels after transfer to BW. Finally, gill and kidney tissues showed many histopathological changes in diazinon-exposed fish even after 240 h in BW. These results suggest that the release of Caspian roach fingerlings into the diazinon-contaminated Caspian Sea regions may alter their physiology and jeopardize their survival, which could lead to a failure in rebuilding the Caspian roach stocks in the Caspian Sea.