ACCUMULATION AND ELIMINATION KINETICS OF HERBICIDES BUTACHLOR, THIOBENCARB AND CHLOMETHOXYFEN BY ARISTICHTHYS-NOBILIS

Bioconcentration kinetics of three major paddy-field herbicides, butac hlor, thiobencarb and chlomethoxyfen were investigated by accumulation and elimination measurements in laboratory experiments with black sil ver carp (Aristichthys nobilis). The biological half-lives of the thre e herbicides on exposure at high and low concentrations were 11.6 and 23.1 days for butachlor, 13.9 and 17.3 days for thiobencarb and 5.6 an d 4.5 h for chlomethoxyfen, respectively. One- and two-compartment mod els were used to elucidate the bioconcentration kinetics. Data from a short-term, 14-day expiry experiment were used to estimate the paramet ers in the models by non-linear regression analysis, and the bioconcen tration factors (BCF) in the steady state were calculated from those p arameters. The BCF in the steady state have the descending order thiob encarb > chlomethoxyfen > butachlor at high concentration, and butachl or > thiobencarb > chlomethoxyfen at low concentration. One-compartmen t model for butachlor and thiobencarb and a two-compartment model for chlomethoxyfen are useful to predict the BCF on prolonged exposure and , further, to assess the influence of these pollutants.