A cohort study of in utero polychlorinated biphenyl (PCB) exposures in relation to secondary sex ratio
1 Department of Public Health Sciences, School of Medicine, TB #168, University of California-Davis, Davis, CA, 95616, USA
2 Department of Epidemiology, School of Public Health and Community Medicine, University of Washington, Box 357236, Seattle, WA, 98195, USA
3 Department of Environmental Toxicology, University of California-Davis, Davis, CA, 95616, USA
4 Ecolab, Eagen, MN, 55121, USA
5 Department of Epidemiology, School of Public Health, University of North Carolina-Chapel Hill, Chapel Hill, NC, 27599, USA
6 Quintiles, Inc, 5927 South Miami Blvd, Morrisville, NC, 27560, USA
7 Center for the Study of Development and Learning, Department of Pediatrics, University of North Carolina-Chapel Hill School of Medicine, Chapel Hill, NC, 27599, USA
Environmental Health 2008, 7:37 doi:10.1186/1476-069X-7-37Published: 15 July 2008
Polychlorinated biphenyls (PCBs) are ubiquitous industrial chemicals that persist in the environment and in human fatty tissue. PCBs are related to a class of compounds known as dioxins, specifically 2,3,7,8-TCDD (tetrachloro-dibenzodioxin), which has been implicated as a cause of altered sex ratio, especially in relation to paternal exposures.
In the 1960's, serum specimens were collected from pregnant women participating in the Child Health and Development Study in the San Francisco Bay Area. The women were interviewed and their serum samples stored at -20°C. For this study, samples were thawed and a total of eleven PCBs were determined in 399 specimens. Secondary sex ratio, or sex ratio at birth, was evaluated as a function of maternal serum concentrations using log-binomial and logistic regression, controlling for hormonally active medications taken during pregnancy.
The relative risk of a male birth decreased by 33% comparing women at the 90th percentile of total PCBs with women at the 10th percentile (RR = 0.67; 95% CI, 0.48–0.94; p = 0.02), or by approximately 7% for each 1 μg/L increase in total PCB concentration. Although some congener-specific associations with sex ratio were only marginally statistically significant, all nine PCB congeners with < 30% of samples below the LOQ showed the same direction of association, an improbable finding under the null hypothesis.
Maternal exposure to PCBs may be detrimental to the success of male sperm or to the survival of male embryos. Findings could be due to contaminants, metabolites or PCBs themselves.