Submitted to: Organohalogen Compounds
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 1, 2003
Publication Date: January 1, 2003
Citation: Huwe, J.K., Smith, D.J. 2003. Uptake and excretion of pcdd/fs from a magnesium mineral supplement fed to dairy cows. Organohalogen Compounds. 64:419-422. 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. Thirty 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. This study shows that dioxins present in mineral supplements are readily absorbed by dairy cows and transferred into the milk. Once the source of dioxins has been removed, milk levels may take several months to return to background.
Technical Abstract: Two dairy cows were fed a dioxin-contaminated feed supplement to study the uptake and excretion of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F). The contaminated supplement was substituted for the regular magnesium oxide in the animals' feed to give a dioxin toxic equivalency (TEQ) of 2.3 ppt in the wet feed. The cows were fed the contaminated feed for 40 days and then fed uncontaminated feed for an additional 40 days. Milk samples were collected twice a week and analyzed for PCDD/Fs and co-planar polychlorinated biphenyls (PCBs). PCDD/F and PCB levels reached a steady state in the milk by 21 days. At steady state, 30% of the daily ingested TEQ was excreted into the milk. The TEQ of the milk fat increased from 1 ppt to 35 ppt during the dosing phase and bioconcentrated by a factor of 16 from the wet feed. After removal of the contaminated feed, PCDD/F and PCB levels rapidly declined in the milk for the first week and then began a more gradual decline. Using a biphasic curve to describe excretion, half-lives of 5.5 days and 146 days were calculated for PCDD/Fs during the first and second excretion phases, respectively. The PCBs had somewhat longer half-lives.