PCB body burdens in US women of childbearing age 2001–2002: An evaluation of alternate summary metrics of NHANES data☆
Introduction
Polychlorinated biphenyls (PCBs) are persistent and bioaccumulative environmental contaminants have been associated with a wide range of health effects. There are 209 different PCBs congeners that are defined by the number of chlorine atoms (1–10) and their positioning on the biphenyl rings. Manufacture of PCBs in the US was banned in 1977. Although levels of PCBs in environmental samples have declined from their peak, the rate of decline has slowed in recent years (Hickey et al., 2006; Sun et al., 2007), and the persistent nature of PCBs and their distribution through the food chain has resulted in continuing human exposure. An important recent development for assessing human exposure levels in the US has been the publication of nationally representative body burden data for a number of PCB congeners, gathered through the National Health and Nutrition Examination Survey (NHANES) (Centers for Disease Control and Prevention, 2005).
Much of the concern for health effects from PCB exposure is focused on the effects of in utero exposure. Children born to mothers with high exposures to a mixture of PCBs and polychlorinated dibenzofurans, in poisoning incidents in Taiwan and Japan, exhibited a number of adverse health effects, including neurodevelopmental effects such as cognitive deficits and developmental delays (Chen et al., 1992; Chen and Hsu, 1994; Lai et al., 2002; Rogan et al., 1988).
Following the poisoning incidents, a number of epidemiologic studies have been conducted to examine the neurodevelopmental effects of PCBs at more typical exposure levels, including longitudinal cohort studies with assessments at several different ages conducted in Michigan, North Carolina, New York, the Netherlands, Germany and the Faroe Islands (Table 1). Other studies with neurodevelopmental evaluations only at a single age, or with neurodevelopmental results still forthcoming, include studies in Northern Quebec (Saint-Amour et al., 2006) and Massachusetts (Sagiv et al., 2008), and analyses of archived data from California (Hertz-Picciotto et al., 2005) and the Collaborative Perinatal Project (Gray et al., 2005).
Overall, the epidemiologic studies indicate that prenatal PCB exposures are likely to be associated with deficits in cognition, attention, and behavior (Ribas-Fito et al., 2001; Schantz et al., 2003, Schantz et al., 2004). In general, the studies do not provide any basis for distinguishing among the effects of different congeners, with the possible exception of the Oswego (New York) study, which conducted separate analyses for the sum of all PCBs measured in the study and for the sum of the more highly chlorinated congeners (Darvill et al., 2000; Schantz et al., 2003; Stewart et al., 2005). Most findings of associations between PCB exposure and neurodevelopment have been related to prenatal exposure, although some relationships with postnatal exposure have been detected (Jacobson et al., 1990a; Schantz et al., 2003; Vreugdenhil et al., 2004; Walkowiak et al., 2001); there is likely a bias to the null for assessments of postnatal exposure, due to exposure misclassification (Rice, 2004). Prenatal PCB exposures have also been associated with immunological endpoints (Dallaire et al., 2004, Dallaire et al., 2006; Heilmann et al., 2006; Park et al., 2008; Weisglas-Kuperus et al., 2000, Weisglas-Kuperus et al., 2004) and with altered sex ratios (Karmaus et al., 2002; Taylor et al., 2007; Weisskopf et al., 2003).
Because PCBs are widely distributed in the environment, are commonly found in many foods, and because they can adversely affect human health, it is important to monitor body burdens in the general population on a continuing basis. Beginning in 1999, NHANES has provided nationally representative PCB body burden data for the US population aged 12 years and older. Interpretation of these data is challenging due to the large number of congeners tested, the high frequency of non-detects for many congeners, and differences between the 1999–2000 and 2001–2002 data sets. Our goal is to develop summary quantitative measures of PCB body burdens in the US general population, relevant for characterizing changes over time in potential risks to children's health. We conducted an analysis to identify preferred metrics for summarizing the NHANES PCB data. We focused on women of childbearing age (16–39 years) because of the scientific findings emphasizing the role of in utero exposures for neurodevelopmental effects, the lower frequency of non-detect values in this population compared with children aged 12 years and older, and the absence of data for younger children.
Section snippets
Data collection
NHANES is a nationally representative survey of the health and nutritional status of the civilian non-institutionalized US population, conducted by the Centers for Disease Control and Prevention (CDC). Interviews and physical examinations are conducted for approximately 5000 people each year. Non-Hispanic Blacks and Mexican Americans were oversampled in 1999–2002 to increase the reliability of estimates for these populations. Exposure to environmental chemicals is assessed through analysis of
Results
PCB body burden data were available for 496 women. All 9 congeners were detected in 45 women (9%); 166 women (32%) had detectable values of 5–8 congeners and 206 women (41%) had detectable values of 1–4 congeners. There were 79 women (17%) for whom all values were either non-detect or missing. PCBs 126 and 169 were each missing for 74 of these 79 women and for 238 of the total 496 women. There were 178 participants aged 16–19 years; measurements of these two congeners were not attempted in
Discussion
Regular and consistent measurements of the body burdens of environmental chemicals in the US population have become an important means for tracking changes in exposure. Body burdens of lead in children aged 1–5 years have been measured by CDC in NHANES since the 1970s; the decline over three decades has been used to illustrate the public health accomplishment (Meyer et al., 2003; US Environmental Protection Agency, 2003) and have become the basis for an important public health goal (US
Acknowledgments
We appreciate the many helpful suggestions from Linda Birnbaum, Danelle Lobdell, Marian Olsen, Margaret McDonough, Pauline Mendola, and Deborah Rice, as well as the statistical advice from Jonathan Cohen.
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Disclaimer: The views expressed in this article are those of the authors and do not necessarily represent the views of the US Environmental Protection Agency.