The present study was performed to investigate the bioconcentration of BPMC, chlorothalonil, dichlorvos and methidathion. The BCFs(bioconcentration factors) and depuration rate constants for four pesticides in zebrafish(bracJxydanio rerio) were measured under semi-static conditions(OECD guideline 305-B) in a concentration of one-hundredth of the 96 hours LC_(50) of each pesticide at the equilibrium condition. The results obtained are summarized as follows : The BCFs of BPMC, chlorothalonil, dichlorvos and methidathion were 1.44±0.09, 2.223±0.063, 0.81±0.08 and 5.53±0.13, respectively. Depuration rate constants of BPMC, chlorothalonil, dichlorvos and methidathion were 0.028, 0.015, 0.220 and 0.152, respectively. The concentrations of BPMC, dichlorvos and methidathion in zebrafish reached an equilibrium in 3 days, and the equilibrium of chlorothalonil was reached after 14 days. Depuration rate of dichlorvos was the fastest followed by methidathion, BPMC and chlorothalonil. The lower BCF of BPMC was due to its relatively high K_(OW), slow K_(DEP), and low S_W and V_P, compared to chlorothalonil and methidathion. The BCF of chlorothalonil was much lower than that expected on the basis of high K_(OW) slow K_(DEP), low S_W and V_P. The reason is that the experimental concentration for chlorothalonil is 1/100 - 1/1000 lower than that of BPMC, dichlorvos and methidathion. The BCF of dichlorvos was lower than that of other pesticides due to its very rapid K_(DEP), very high V_P and S_W, and very low K_(OW). The BCF of methidathion was higher than that of other pesticides due to its very low V_P and S_W. Therefore, these data suggest that physicochemical properties of pesticides may be important in the bioconcentration.

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