Correlations between the molecular structures of polyhalogenated biphenyls and their metabolism by hepatic microsomal monooxygenases.

1. Collation of the data presented in the preceding papers (references 4,5) showed a significant correlation (r = 0.83; P < 0.001) between the molecular mass (and hence the extent of halosubstitution) of halogenated biphenyls and their rate of hydroxylation by hepatic microsomal monooxygenases. 2. There was no relationship between the extent of polyortho halosubstitution of biphenyl and the rate of metabolism. 3. A marginal correlation (r = 0.33; P < 0.001) was found when the number of adjacent unsubstituted meta-para positions were linked to the rate of metabolism of PCBs. This structural feature facilitates microsomal oxidation. 4. The results support the proposal that PCBs with meta-para hydrogen atoms are less enriched in tissues of animals and humans as this structural feature favours their metabolism by P450 isoenzymes.