Effects of a Technical PCB Preparation and Fractions Thereof on Ethoxyresorufin O-Deethylase Activity, Vitamin A Levels and Thymic Development in the Mink (<i>Mustela vison</i>)*

Clophen A50, a technical preparation of polychlorinated biphenyls (PCBs), was separated into four fractions; three containing chlorobiphenyls with 0, 1, or 2 to 4 ortho chlorines and one containing di‐ and tricyclic impurities such as naphthalenes and dibenzofurans. Clophen A50, the four fractions, and a synthetic mixture of the biologically most active non‐ortho‐chlorinated congeners (3,3′,4,4′‐tetra‐, 3,3′,4,4′,5‐penta‐, and 3,3′,4,4′,5,5′,‐hexachlorobiphenyl), were separately mixed in the feed and given to female mink during the reproductive season. The concentration of a given compound in the feed mixture was equivalent to its concentration in the feed mixed with Clophen A50. Hepatic 7‐ethoxyresorufin O‐deethylase (EROD) activity in adults was enhanced 2‐3 times by Clophen A50, the fractions containing non‐ or mono‐ortho‐chlorinated congeners, and the synthetic mixture. In neonatal kits delivered by females treated with non‐ or mono‐ortho‐chlorinated congeners, EROD was enhanced to about 30 times the control value. No live kits were delivered by the females treated with unfractionated Clophen A50. The fractions containing congeners with two to four ortho chlorines or di‐ and tricyclic compounds did not significantly induce EROD in either adults or kits. Clophen A50 reduced hepatic and pulmonary vitamin A contents in adult mink, while renal vitamin A was unaffected. Responses to the fractions containing the non‐ and mono‐ortho‐chlorinated congeners were similar to those obtained with Clophen A50. Their effects were, however, less pronounced, particularly with respect to the hepatic vitamin A reduction. The fractions containing congeners with two to four ortho chlorines and the di‐ and tricyclic compounds had no significant effects on tissue vitamin A contents. Thymocyte number was significantly reduced in kits exposed to the fractions containing non‐ or mono‐ortho‐chlorinated congeners. Thymocyte number was also lower in kits exposed to the synthetic mixture of non‐ortho‐chlorinated congeners than in control kits, but the difference was not statistically significant. To sum up, the non‐ and mono‐ortho‐chlorinated congeners in Clophen A50 enhanced EROD activities in adults and kits, reduced vitamin A concentrations in adults, and reduced thymocyte numbers in kits. Effects of the synthetic mixture of 3,3′,4,4′‐tetra‐, 3,3′,4,4′,5‐penta‐and 3,3′,4,4′,5,5′‐hexachlorobiphenyl were similar to those of the fraction from Clophen A50 containing non‐ortho‐chlorinated congeners, and it is probable that the three coplanar congeners in the synthetic mixture, together with certain mono‐ortho‐chlorinated congeners, were largely responsible for the effects of Clophen A50 observed in this study.