Mar. 25, 1999 ANAHEIM, Calif., March 24 -- Kentucky researchers have demonstrated, for the first time, that a class of common chemical contaminants known as butyltins disrupt the function of critical human immune cells. The scientists also say biologically significant concentrations of butyltins were found in random human blood samples. The findings are being presented at a national meeting of the American Chemical Society, the world's largest scientific society.
Butyltin compounds come in either single, double, or triple forms. They are used to inhibit the growth of unwanted organisms such as bacteria, algae, and barnacles. Tributyltin (TBT) is used as a wood preservative as well as on fish culture nets, docks, and boat hull paints. Though TBTs have been banned on small boats for about a decade, they are still commonly used on large ships. TBTs have been detected in seafood, such as fish and oysters, collected from coastal areas.
Various groups have done studies suggesting that tributyltin levels have decreased in U.S. waters in recent years, and some studies suggest that seafood does not contain enough tributyltins to cause human health problems. However, Murray State University chemist Bommanna G. Loganathan, Ph.D., who performed the study with another Murray State chemist, Margaret M. Whalen, Ph.D., says statistics for production of butyltins used in many everyday applications are not available.
The scientists found that butyltins disrupt the function of human natural killer cells, or NK cells, in the laboratory. The job of these blood cells is to destroy tumor cells and cells infected with viruses. When exposed to "environmentally relevant" concentrations of tributyltin in the lab for as little as an hour, Loganathan says the tumor-killing ability of NK cells was inhibited. Mono- and di- butyltins were found to be only slightly less harmful to the NK cells.
Mono- and dibutyltins are found in a variety of household products including some types of diaper covers, sanitary napkins, shower curtains, gloves, cellophane wraps, dish sponges, wines, fruit juices, and poultry.
Loganathan notes that the human body can degrade butyltins fairly efficiently and eliminates them in 24 - 48 hours. However, previous studies in rats have shown butyltins to have various toxic effects, including disruption of the immune system. Loganathan says his current study, using blood cells from adult male and female volunteers, was the first to demonstrate the effect of butyltin compounds on human immune cell function.
Loganathan and Whalen also measured butyltin levels in the blood of eight people who he says should have had no extraordinary exposure to butyltins. He says he found "concentrations, in some cases, approaching levels where we saw inhibitory effects on NK cell cytotoxic function in the lab."
Loganathan feels that while human exposure is highly likely, researchers do not yet know for sure how the compounds will affect human health. His study strongly emphasizes the need for further blood monitoring studies and risk assessment.
A nonprofit organization with a membership of nearly 159,000 chemists and chemical engineers, the American Chemical Society publishes scientific journals and databases, convenes major research conferences, and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.
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