Pregnant women's exposure to phthalates has adverse effects on genital development in their male children

For the first time, researchers have identified an association between pregnant women’s exposure to a nearly ubiquitous class of chemicals known as phthalates and adverse effects on genital development in their male children.

The findings, reported in a study published today in the online edition of the peer-reviewed journal Environmental Health Perspectives, are the first to “support the hypothesis that prenatal phthalate exposure at environmental levels can adversely affect male reproductive development in humans,” the authors write.

Most previous studies focusing on phthalate prenatal exposure were in rodents. The current study analyzed human exposure to phthalates, which are commonly used in consumer products as solvents and to soften plastics. Phthalates are also found in soft vinyl plastic toys, medical tubing and fluid bags, and a variety of cosmetics such as perfume, lotion, shampoo, make-up, nail polish, and hairspray. Often, the presence of these chemicals is not noted on labels. A 1999–2000 national study found that the majority of the general population of the United States had measurable exposure to multiple phthalates.

Researchers collected data from 85 eligible mother–son pairs. All mothers had previously participated in a multicenter pregnancy cohort study. Prenatal urine samples were analyzed for the presence and quantity of nine phthalate metabolites at the Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention. The 85 male children were examined for genital characteristics that serve as markers of normal sexual development. These measurements were then correlated with the mothers’ prenatal urinary phthalate levels. The findings suggest that some phthalates have antiandrogenic effects, meaning they may suppress the hormones involved in male sexual development.

Higher levels of four phthalate metabolites (mono-ethyl phthalate [MEP], mono-n-butyl phthalate [MBP], mono-benzyl phthalate [MBzP], and mono-isobutyl phthalate [MiBP]) were found to correlate with a higher-than-expected number of abnormalities in genital development including smaller anogenital distance, scrotum, and penis, and an increased likelihood of undescended testicles.

These findings were consistent with those from previous rodent studies on phthalate exposure. “These changes in humans associated with prenatal exposure to some of the same phthalate metabolites that cause such alterations in male rodents suggest that these widely used phthalates may undervirilize humans as well as rodents,” the authors write.

The study also noted that the median concentration of phthalate metabolites associated with adverse male genital development was below the levels found in one in four women in the United States, based on a nationwide sample.

The lead author of the study was Shanna H. Swan of the University of Rochester, Department of Obstetrics and Gynecology. Other authors included Katharina M. Main, Fan Liu, Sara L. Stewart, Robin L. Kruse, Antonia M. Calafat, Catherine S. Mao, J. Bruce Redmon, Christine L. Ternand, Shannon Sullivan, and J. Lynn Teague. Funding sources for the research as reported by the authors included the Environmental Protection Agency, the National Institute of Environmental Health Sciences, and the State of Iowa. The article is available free of charge at http://ehp.niehs.nih.gov/docs/2005/8100/abstract.html, and will be published in an upcoming print edition of the journal.