Metabolism 2,4 ,5-trichlorobiphenyl

Along with degree of chlorination another determinant of PCB metabolism in fish is species. Green sunfish and goldfish rapidly metabolize 2,2, 5-trichlorobiphenyl whereas bullheads and rainbow trout metabolize it slowly (26,29). There is little evidence for PCB metabolism in brook trout fed 4-chloro-, 4,4 -dichloro-, 2,2, 5,5 -tetrachloro- or 2,2, 4,4, 5,5 -hexachloro-biphenyl (31) and this was confirmed in rainbow trout by less than 1% of 2,2, 5,5 -tetrachlorobiphenyl accumulated being recovered as polar metabolites (25). 

Elimination. Rate that PCBs are eliminated by fish is strongly influenced by their rate of metabolism. Figure 7 shows concentration of PCB in green sunfish after being exposed to a high or low dose of 2,2, 5-trichlorobiphenyl or 2,2, 4,5,5r-pentachlorobiphenyl on day 0 and again on day 9 (26). Of these... 

A comprehensive review of the metabolism of PCBs was published in 1976 by Sundstrom et al. (ref. 139a) confirming the importance of degree of substitution and location of halogens on toxicity. The lesser chlorinated biphenyls are more readily metabolized. The presence of at least two adjacent hydrogens—preferably in positions 3. 4, 5 or 3, 4, 5 —is required for the rapid metabolism of PCBs. This requirement is satisfied by all mono-, di- and trichlorobiphenyls, and by the tetrachlorobiphenyls with the exception of the 3. 3. 5. 5 -chlorinated PCB. This compound was reported particularly toxic to monkeys, and the intermediate formation of chlorinated dibenzofuran was postulated to account for this toxicity (ref. 139c). 

Table V. Rat Lung Residues of 4-Methylsulfonyl-2,4, 5-trichloro-biphenol Resulting from Metabolism of 2,4, 5-Trichlorobiphenyl...

Figure 5. Metabolism and possible routes of interorgan translocation of 2,41,5-trichlorobiphenyl.

Experimental evidence using P -postlabeling supports the hypothesis that lower chlorinated biphenyls are metabolically activated to electrophilic species which bind to DNA (McLean et al. 1996 Oakley et al. 1996). The incubation of 2-chloro-, 4-chloro-, 3-chloro-, 3,4-dichloro-, and 3,4,5-trichlorobiphenyl with calf thymus DNA and rat liver microsomes followed by oxidation with a peroxidase, produced... 

Felt GR, Mueller WF, latropoulos MJ, et al. 1977. Chronic toxicity of 2,4,5 -trichlorobiphenyl in young Rhesus monkeys I. Body distribution, elimination, and metabolism. Toxicol Appl Pharmacol 41 619-627. 

Metabolism of 2,2 -dichlorobiphenyl (DCBP), 2,5,4 -trichlorobiphenyl (TriCBP) and 2,4,6,2 4 -pentachlorobiphenyl (PCBP) by Nereis virens (from Goerke and Ernst 1977 and Ernst et al. 1977). 

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