Assimilation and metabolism of polybrominated diphenyl ethers by the common carp

Polybrominated diphenyl ethers (BDEs) are anthropogenic compounds applied to numerous types of plastics, textiles, and electronic equipment to retard the outbreak of fire. BDEs are similar in structure and in their physicochemical properties to the renowned contaminants polychlorinated biphenyls (PCBs). While there is much information available on the accumulation and metabolism of PCBs by aquatic organisms, little information is available for BDEs.; Several field investigations have observed a very low accumulation of 2,2′,4,4′,5-pentabromodiphenyl ether (BDE 99) in tissues of the common carp (Cyprinus carpio) (Dodder et al., 2002; Hale et al., 2001; Rice et al., 2002). To investigate this unusual observation, juvenile common carp were exposed daily in the laboratory to a mixture of BDE congeners in their food to assess the bioaccumulation potential of BDEs based upon measurements of uptake rates, assimilation efficiencies and depuration rates. As a positive control, three PCB congeners of similar log K_ow values were included in the mixture. Of all the BIDE and PCB congeners in the mixture, the most rapid uptake and assimilation was observed for BIDE 47, which displayed an apparent assimilation efficiency of 93 ± 10%. All three PCB congeners averaged 40% assimilation while 2,4,4 ′-tribromodiphenyl ether (BDE 28) and 2,2′,4,4 ′,5,5′-hexabromodiphenyl ether (BDE 153) displayed assimilation efficiencies of 20 and 4% respectively. BIDE 99 was not assimilated at all throughout the exposure. The lack of BDE 99 accumulation and the high assimilation of BDE 47 within carp tissues implicated debromination of BIDE 99 to BDE 47 within carp tissues.; To investigate the possibility of debromination, several additional studies were conducted in which juvenile carp were exposed to food spiked solely with either BDE 99, BIDE 183 or BIDE 209 at rates ranging from 100 to 940 ng/day. Results indicated that there was significant and rapid debromination of all three of these congeners within the intestinal tract of common carp and implicated either intestinal microflora or endogenous enzyme systems in this metabolism. Meta-substituted bromine atoms are preferentially cleaved from the BDE congeners, which implicates deiodinase enzymes in the debromination process.