Effect of chlorination on the distribution and excretion of polychlorinated biphenyls

The distribution and excretion of four 14C-labeled polychlorinated biphenyls (PCB), 4-chloro-, 4,4'-dichloro-, 2,4,5,2',5'-pentachloro-, and 2,4,5,2',4',5'-hexachlorobiphenyl, were studied in the rat. Total radioactivity was determined in the major organs and tissues at times varying from 15 min up to 42 days after an intravenous injection of a single 0.6-mg dose of each of the PCB's per kg. Each of the PCB's was removed rapidly from the blood and initially stored largely in the liver and muscle. The rates of the subsequent redistribution of the PCB's and their metabolites to the adipose tissue and skin and/or excretion could be related to the degree of chlorination. The relative amounts of each PCB and its metabolites in each major tissue were determined at selected time points. The percentage of the total radioactivity accounted for by metabolites of the PCB's decreased as the chlorination of the PCB's increased, but storage of metabolites did not account for a significant portion of any of the PCB doses. Excretion accounted for more than 90% of the dose of the mono-, di-, and pentachlorobiphenyls during the time period studies, whereas extrapolation of the hexachlorobiphenyl data indicated that less than 20% of the dose would ever be excreted. The rates of elimination of the PCB's were apparently determined primarily by their rates of metabolism. The effect of degree and position of chlorination on the rate of metabolism of the biphenyl molecule is discussed.