 high levels of 2,3,7,8-tetrachlorodibenzo - p - dioxin ( tcdd ; up to 208 pg / g fat ) were measured in samples of breast milk collected in 1997 from 64 donors [ 41 first - time mothers ( primiparae ) ] living on state farms in southern kazakhstan . 
 tcdd was the major contributor ( 70% ) to the toxic equivalents , matching the congener patterns found in breast milk and serum samples collected in 1994 and 1996 from donors in nearby villages . 
 the highest tcdd levels were found in state farms adjacent to a reservoir ( zone a ) , which receives agricultural runoff from cotton fields . 
 tcdd levels in zone a were significantly higher than levels in a region more distant ( zone b ; > 10 miles ) from the reservoir ( zone a : mean 53 pg / g , n = 17 ; zone b : mean 21 pg / g , n = 24 ; p = 0.0017 ) . levels of tcdd in breast milk and animal - derived foodstuffs were 10 times u.s . 
 levels . body burden and dietary data suggest that exposures to tcdd are chronic , environmental , and long term and may be related to the use of chemicals in cotton agriculture . 
 the data suggest that the most likely source is the use of cotton defoliants contaminated with tcdd , and the most likely pathway for human exposure is via the consumption of contaminated foodstuffs.imagesfigure 1figure 2figure 3 
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