Genotoxicity in fishes environmentally exposed to As, Se, Hg, Pb, Cr and toxaphene in the lower Colorado River basin, at Mexicali valley, Baja California, Mexico.

The environmental exposure to As, Se, Hg, Pb, Cr and toxaphene was assessed for 11 freshwater fish species in irrigation channels, agricultural return flow drains, a drain collecting lagoon and sections of the Colorado River at the Mexicali valley in Baja California, Mexico, during August 2015-April 2016. Arsenic (2.90 ng ml(-1)) and Se (1.41 ng ml(-1)) in water had the highest concentrations in the return flow drains (Hardy River and Xochimilco Lagoon, respectively). However, fish axial muscle tissue had the highest concentration of Se (8.3 microg g(-1)) and Hg (0.36 microg g(-1)) in Colorado River fresh water, while As (1.7 microg g(-1)) in Hardy River fish was highest. Selenium concentrations in all fishes and toxaphene in Cyprinus carpio and Ameiurus natalis are above the safe levels for human consumption (0.3 microg g(-1) and 180 ng g(-1) respectively). Toxaphene was detected in the fish axial tissue, having the highest concentrations in Poecilia latipinna (690 ng g(-1)) in the Colorado River. The low proportion of the 8-Cl toxaphene congeners in fish suggests degradation of this pollutant. Tilapia. sp. cf. zillii had the most genotoxic damage with 7.4 micronucleated erythrocytes per 10,000 erythrocytes in Xochimilco Lagoon and 2 in Hardy River. The genotoxicity in all the fish species studied was significantly correlated to the concentrations of As and Se in water.