ACCUMULATION AND PERSISTENCE OF INDIVIDUAL POLYCHLORINATED BIPHENYL CONGENERS IN LIVER, BLOOD, AND ADIPOSE-TISSUE OF RATS FOLLOWING DIETARYEXPOSURE TO AROCLOR(R)-1254

Female F344/NCr rats were exposed continuously to Aroclor (R) 1254 (1, 3.3, 10, 33, or 100 ppm in the diet) for 7, 28, or 84 days in order t o assess the accumulation of polychlorinated biphenyls (PCBs) in liver , blood, and adipose tissue. The persistence of the individual PCB con geners which are detected in liver was examined in the three tissues o f additional groups of rats exposed for 7 days followed by 21 days on control diet, or for 28 days followed by 56 days on control diet. Limi ted accumulation of PCB congeners with low chlorine substitution (tri- and tetrachlorobiphenyls) in the liver and blood, and preferential re tention of highly substituted PCB congeners (penta- and hexachlorobiph enyls) were observed in rats continuously exposed to Aroclor. In these rats, time- and dose-dependent increases in the relative levels of tw o congeners which cause profound phenobarbital-type induction [2,2',3, 4,4',5'-hexachlorobiphenyl (BZ# 138) and 2,2',4,4',5,5'-hexachlorobiph enyl (BZ# 153)] were detected in the liver and adipose tissue. Rats re ceiving control diet following Aroclor treatment displayed a time- and dose-dependent decrease in the relative levels in blood, adipose and hepatic tissue of 2,3,3',4,4'-pentachlorobiphenyl (BZ# 105) and 2,3',4 ,4',5-pentachlorobiphenyl (BZ# 118), two of the major congeners showin g both TCDD- and phenobarbital-type induction. These rats also display ed increases in the relative adipose levels of another relatively pote nt mixed-type inducer, 2,3,3',4,4',5-hexachlorobiphenyl (BZ# 156), and increases in adipose and hepatic levels of the pure phenobarbital-typ e inducer, 2,2',4,4',5-pentachlorobiphenyl (BZ# 99).