Individual and joint toxicity of Zn2+ and Cd2+ during the early em-bryonic development of zebrafish (Danio rerio)

Abstract

We evaluated the individual and joint toxicity of zinc and cadmium during the early embryonic devel-opment of the zebrafish(Danio rerio).Embryos were exposed to various concentrations of Zn2+ and Cd2+ 24 h post-fertilization(24 hpf).We monitored the number of embryonic coagulated eggs and the rhythm of the heart at 48 hpf and the number of embryonic coagulated eggs,hatching rate,and malfomation rate at 72 hpf.The effects of Zn2+ and Cd2+ differed among the stages of development.In general,Zn2+ was more toxic than Cd2+.The embryos were most sensitive to Zn2+ and Cd2+ toxicity at 72 hpf.Regardless of the ratio of Zn2+ and Cd2+ during joint ex-posure(1﹕1,1﹕2 or 2﹕1),the two chemicals tended to act synergistically.However,the joint toxicity was de-fendant on the endpoints and the ratio of each metal.For example,at equal concentrations of Zn2+ and Cd2+(1﹕1),the effect tended to be synergistic.However,at a ratio of 1﹕2(Zn2+:Cd2+) the effect was synergistic at 48 hpf but antagonistic at 72 hpf.Furthermore,at a ratio of 2﹕1(Zn2+:Cd2+) the effect on egg coagulation was synergistic whereas the effect on the rate of hatching was antagonistic.Thus,our results suggest that joint toxicity is affected by both the concentration of each chemical and the exposure time.