Embryo development, stress protein (Hsp70) responses, and histopathology in zebrafish (Danio rerio) following exposure to nickel chloride, chlorpyrifos, and binary mixtures of them.

Two different classes of chemicals were tested in a multilevel approach in this study: NiCl(2) as a representative for heavy metals and chlorpyrifos, a pesticide. Both, the single substances and mixtures of them were investigated for their effects on embryonic development, histological alterations, and the stress protein (Hsp70) response in the zebrafish Danio rerio. Fishes were exposed from fertilization of eggs up to a maximum of 168 h post fertilization, depending on the investigated endpoint. NiCl(2) led to effects in all tests which, however, were less severe at the histopathological level than in developmental (hatching success) and stress protein studies. Chlorpyrifos did not lead to developmental alterations but it was found to induce the Hsp70 response as well as histopathological damages. Mixtures of both substances resulted in similar results as the single substances; the results suggest an independent mode of action of these two substances and additivity of their effects.