Tissue-specific accumulation, transformation, and depuration of fipronil in adult crucian carp (Carassius auratus)

Accumulation and biotransformation of pesticides in fish tissues are essential to assess their toxicity and asso-ciated human exposure risk. The mechanisms on time-dependent and tissue-specific accumulation and trans-formation of fipronil in adult fish are limited. An experiment consisting of 25-d uptake of fipronil at two levels (10 and 50 mu g/L) and 25-d depuration in adult crucian carp (Carassius auratus) was conducted. Fipronil con-centration at 25-d exposure was tissue-specific with the order of liver > kidney > blood > muscle. The uptake rate constant of fipronil in the liver (low exposure group: 2.38 +/- 0.27 L/kg/d; high exposure group: 1.10 +/- 0.11 L/kg/d) was significantly higher than that in other tissues (p < 0.05), and the lowest in muscle (low exposure group: 0.10 +/- 0.01 L/kg/d; high exposure group: 0.16 +/- 0.11 L/kg/d). The bioconcentration factors of fipronil in different tissues were 1.04-12.7 L/kg wet weight and 177-4268 L/kg lipid. The tissue-blood distribution co-efficients of the liver and kidney were lower than 1 based on lipid normalized concentration but higher than 1 based on wet weight concentration, suggesting fipronil was dispersed into other tissues mainly via blood in the lipid-combination pattern. Fipronil sulfone had 1.2-32 times higher concentration and longer depuration time than fipronil, implying fipronil sulfone was more retender in fish bodies. The estimated daily intake of fipronil via fish muscle consumption at 25-d exposure was 8.5-101 and 27-320 ng/kg bw/d for adults and children, respectively. Overall, the human health risk of fipronil and its metabolites with consumption of the polluted fish cannot be negligible.