Analysis of breast milk to assess exposure to chlorinated contaminants in Kazakhstan: sources of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposures in an agricultural region of southern Kazakhstan

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.

Analysis of breast milk to assess exposure to chlorinated contaminants in Kazakstan: high levels of 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) in agricultural villages of southern Kazakstan

To assess levels of chlorinated contaminants in breast milk, we measured organochlorine pesticides, polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) in breast milk samples collected in 1994 according to the World Health Organization protocol from 92 donors that were representative of regional populations in southern Kazakstan. High levels (10-120 pg/g fat) of 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic of the PCDD/PCDF congeners, were found in breast milk samples from an agricultural region. TCDD was the major contributor (75%) to the international toxicity equivalents of these samples. The same distinctive PCDD/PCDF congener pattern was found in 15 breast milk samples and 4 serum samples collected in 1996 in a follow-up study, and has now been confirmed by three analytical laboratories.

Acquired risk factors and susceptibility to environmental toxicants

Susceptibility to illness after exposure to environmental toxicants is determined by the interaction of numerous factors involving both constitutive and acquired traits. Constitutive susceptibility (risk) factors are the intrinsic traits determined by developmental stage, gender, and genetic makeup. Within a population, changes in constitutive risk factors tend to occur slowly, through aging, alterations in the birth or death rate, or by migration in or out of the population. Often overlooked is the effect of acquired susceptibility factors on susceptibility to environmental toxicants. Acquired susceptibility factors, which are related to the effects of living conditions, psychosocial factors, diet, behavior and access to medical care, may modify the effect of constitutive factors. Three examples demonstrate the interaction of acquired susceptibility factors with exposure and constitutive factors. The increased prevalence of asthma in children is suspected of having a strong environmental component but the underlying acquired susceptibility factors, if any, are difficult to identify because of the multifactorial nature of asthma and the use of surrogate risk factors such as parent's education. β-Carotene is a dietary component which may modify acquired susceptibility. While numerous observational studies find that dietary β-carotene reduces the risk of lung cancer in cigarette smokers, intervention studies do not support this role. Hepatitis B is an example of an infectious agent functioning as an acquired susceptibility factor. Hepatitis B synergistically increases the risk of hepatocellular carcinoma when accompanied by exposure to aflatoxin, a relationship that may be modified by constitutive risk factors, such as epoxide hydrolase capabilities. Acquired risk factors have the potential to greatly influence risk and their impact should be included in future studies of the health effects of environmental toxicants.

Development of an immunoassay to detect hemoglobin adducts formed by benzene exposure

Polyclonal murine antibodies that recognize the adducts formed by benzene metabolites in hemoglobin (Hb) were prepared and used to develop immunoassays. In competitive inhibition assays, the concentration of competitor needed to reduce the signal by 50% (IC50) was less than 10 pmoles for hydroquinone-hemoglobin (HQHb) adducts and less than 1 pmole for 1,2,4 trihydroxybenzene-hemoglobin (TriOH Hb). Hemoglobin (Hb) incubated with either phenol or catechol (CAT) did not elicit antibodies suitable for quantitative immunoassays. The metabolite-directed immunoassays were tested using hemoglobin from mice previously administered [C14] benzene for two to four weeks. The most sensitive assay for hydroquinone measured 0.49 pmoles adduct/40 pmoles Hb (191 pmoles adduct/mg Hb) in mice treated with 200 mg/kg benzene (P < 0.05, Student's t test). TriOH Hb adducts were not detected.