The effects of ortho chloro substituents on the retention of PCB isomers in rat, rabbit, japanese quail, guinea pig and trout

A mixture of 2,2',4,4',6,6'-, 2,2',4,4',5',6-, 2,2',4,4',5,5'-, 2',3,4,4',5,5'- and 3,3',4,4',5,5'-hexachlorobiphenyls (HCBP) was administered by gastric lavage to rats, guinea pigs, rabbits, Japanese quail and trout, and the concentrations in the fat or whole carcass were determined after 29 days. The total HCBP levels in rat, rabbit and guinea pig fatty tissue were 8.27, 6.84 and 4.74 ppm, respectively: whereas 3.02 and 2.15 ppm of the HCBPs were detected in the trout and Japanese quail carcasses. The extent of ortho chloro substitution markedly affected the levels of the individual HCBP isomers retained in the test animals; the rabbit and guinea pig preferentially retained the HCBPs with 0,1 and 2 ortho chloro substituents, the Japanese quail retained only the 3,3',4,4',5,5'-HCBP isomer, whereas no striking preferences in HCBP isomer retention in the rat and trout were observed. The marked differences in the retention of HCBP isomers with 0, 1, 2, 3 and 4 ortho chloro substitution by different animal species should be considered in chronic toxicity studies since the most toxic polychlorinated biphenyls have minimal (1 or 0) ortho chloro substituents.