Behavioural and developmental toxicity of chlorpyrifos and nickel chloride to zebrafish (Danio rerio) embryos and larvae

In order to assess the combined toxicity of environmental chemicals with different modes of action in acute (2 h) and subchronic (11 d) exposures, embryos and larvae of Danio rerio were exposed to a heavy metal salt, nickel chloride (NiCl2), the insecticide chlorpyrifos (CHP) and their binary mixtures. Chlorpyrifos is an acetylcholine esterase inhibitor, which is likely to affect behaviour of the organism. NiCl2 targets the active sites of enzymes and is regarded as an unspecific toxicant for aquatic organisms. Several endpoints, such as locomotor activity, morphological abnormalities, and mortality of D. rerio embryos and larvae were studied. During acute exposures to ⩾0.25 mg/L of chlorpyrifos, locomotor activity tended to increase. However, this activity decreased significantly at ⩾7.5 mg Ni/L. Subchronic exposures to CHP resulted in behavioural changes at much lower concentrations (⩾0.01 mg/L) and considerably earlier than the observed increase in morphological abnormalities and mortality (LC50 (10 d): 0.43 mg/L). Combined CHP and NiCl2 mixtures led to an antagonistic deviation from the concept of independent action, in the case of locomotor activity. Compared to developmental or survival parameters, behaviour was the most sensitive endpoint for CHP exposure in this study; therefore we recommend this parameter to complement already established endpoints.