| Abstract
| - A dioxin-contaminated mineral supplement was used to study the bioaccumulation and eliminationof dioxins in two dairy cows. The supplement was mixed into the total maintenance ration and fed tothe cows for 40 days after which unfortified diets were fed for 40 additional days. Dioxins and coplanarpolychlorinated biphenyls (PCBs) were measured twice a week in the milk and in selected tissues ofthe cows, one at death (day 10 of withdrawal) and one at slaughter (day 40 of withdrawal). Thedioxins and PCBs were readily transferred into the milk, and at steady state, total toxic equivalentswere concentrated 6-fold into the milk fat from the diet. Bioaccumulation was inversely related tochlorination number. The elimination of dioxins and PCBs in milk was biphasic. With the exceptionof 1,2,3,4,6,7,8-heptachlorodioxin and both octachlorinated congeners, dioxin and furan half-lives inmilk were approximately 3−5 days for the α-phase and 35−50 days for the β-phase. PCB-169 hada longer half-life: 11 (α) and 200 days (β). When milk and feed samples from Minnesota farms thathad used similar contaminated mineral supplements were analyzed, no elevated dioxin levels werefound in milk. It appeared that although the dioxins from the mineral supplements have the potentialto bioaccumulate, dilution into the total diet was sufficient to prevent a significant rise in the dioxinconcentrations in the milk at these farms. Keywords: Dioxins; polychlorinated biphenyls; cows; milk; bioaccumulation; half-life; mineral supplement
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