Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2005
Publication Date: 2/25/2005
Citation: Huwe, J.K., Smith, D.J. 2005. Laboratory and on-farm studies on the bioavailability of dioxins from a contaminated mineral supplement fed to dairy cows. Journal of Agriculture and Food Chemistry 53:2362-2370.
Interpretive Summary: In March of 2002, dioxin-contaminated mineral supplements used in animal feeds were discovered during routine screening and subsequently removed from the market. In order to characterize the dioxin exposure that may have been associated with the contaminated minerals, we obtained a portion of the contaminated supplement and conducted controlled feeding studies with dairy cattle. Two dairy cows were fed the dioxin-contaminated supplement at typical usage levels in their feed for 40 days. Twenty percent of the daily ingested dioxins were excreted into the cows= milk. The level of dioxins in the milk rose by a factor of almost 30 during the dosing period. After removal of the contaminated feed, dioxin levels rapidly declined in the milk for the first week and then began a more gradual decrease. When milk from ten Minnesota dairy farms that had used the contaminated supplements was tested, no elevated levels of dioxins were found. Comparison of the laboratory and on-farm results shows that the dioxins in the mineral supplements are readily absorbed by dairy cows and transferred into the milk; however, in practice, the mineral supplements are diluted in the commercial products and feeds to a degree that does not elevate dioxins in the milk to any noticeable level. Once the source of dioxins was removed from the dosed cows, milk levels dropped by half within one week but took several months to return to background.
Technical Abstract: A dioxin-contaminated mineral supplement was used to study the bioavailability and elimination of dioxins in two dairy cows. The supplement was mixed into the total diet and fed to the cows for forty days after which unfortified diets were fed for forty additional days. Dioxins and co-planar 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 six-fold into the milk fat from the diet. Bioavailability 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 days (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. 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.