Laboratory and on-farm studies on the bioaccumulation and elimination of dioxins from a contaminated mineral supplement fed to dairy cows.

A dioxin-contaminated mineral supplement was used to study the bioaccumulation and elimination of dioxins in two dairy cows. The supplement was mixed into the total maintenance ration and fed to the cows for 40 days after which unfortified diets were fed for 40 additional days. Dioxins and coplanar polychlorinated biphenyls (PCBs) were measured twice a week in the milk and in selected tissues of the cows, one at death (day 10 of withdrawal) and one at slaughter (day 40 of withdrawal). The dioxins and PCBs were readily transferred into the milk, and at steady state, total toxic equivalents were concentrated 6-fold into the milk fat from the diet. Bioaccumulation was inversely related to chlorination number. The elimination of dioxins and PCBs in milk was biphasic. With the exception of 1,2,3,4,6,7,8-heptachlorodioxin and both octachlorinated congeners, dioxin and furan half-lives in milk were approximately 3-5 days for the alpha-phase and 35-50 days for the beta-phase. PCB-169 had a longer half-life: 11 (alpha) and 200 days (beta). When milk and feed samples from Minnesota farms that had used similar contaminated mineral supplements were analyzed, no elevated dioxin levels were found in milk. It appeared that although the dioxins from the mineral supplements have the potential to bioaccumulate, dilution into the total diet was sufficient to prevent a significant rise in the dioxin concentrations in the milk at these farms.