New study suggests "universal fetal exposure" to BPA
Gerona, RR, TJ Woodruff, CA Dickenson, J Pan, JM Schwartz, S Sen, M Friesen, VY Fujimoto and PA Hunt. 2013. BPA, BPA glucuronide, and BPA sulfate in mid-gestation umbilical cord serum in a northern California cohort. Environmental Science and Technology http://dx.doi.org/10.1021/es402764d
All samples of umbilical cord blood obtained from pregnant women in California had detectable levels of bisphenol A, suggesting "universal fetal exposure," according to newly published research.
The study is the first to show that second-trimester fetuses are widely exposed to relatively high levels of BPA, an estrogen-like substance found in polycarbonate plastic, food can liners and other commonplace consumer products.
The scientists sampled cord blood from the fetuses of 85 women who had undergone elective abortions at a San Francisco clinic that serves Northern and Central California.
Three of the samples had BPA levels higher than ever reported in other umbilical cord blood, which had been collected from full-term fetuses. Thirty-six percent had levels comparable to or higher than those associated with developmental effects in animal tests.
"Our findings suggest universal fetal exposure to BPA in our study population, with some at relatively high levels, and we provide the first evidence of detectable BPA sulfate in mid-gestation fetuses," the scientists from University of California, San Francisco and Washington State University wrote in the study, which was published in the journal Environmental Science & Technology last week.
BPA at low doses has been linked to an array of developmental effects in animals, particularly neurological and behavioral changes, according to published studies. Whether there are effects on the human fetus is unknown, however. The National Toxicology Program, based on the animal experiments, concluded that there is "some concern" for brain, behavior and prostate effects in infants and children.
Some scientists have said that there should be no detectable levels of the active form of BPA in human blood. They say that the BPA found in people must be caused by laboratory error because nearly all active BPA should be metabolized when it passes through the liver. But in this study, the scientists reported that they tested all the materials used in sample collection and storage to make sure they were BPA-free.
Laura Vandenberg, a scientist at the University of Massachusetts, Amherst, who studies BPA but was not part of this study, said "these results should go a long way toward dispelling the myth that all BPA in human blood is the result of accidental contamination during sampling."
For this study, the scientists developed a new technology for testing BPA in cord blood, allowing them to measure three types of BPA, including the first discovery of BPA sulfate in cord blood. BPA sulfate is a form that is created when BPA passes through the liver.
Previous studies have tested pregnant women's blood, amniotic fluid, placenta and cord blood, but none had examined mid-gestation samples.
"Our median BPA levels are similar to those measured in term umbilical cord serum from larger studies, [however] the concentrations of BPA in our study include the highest levels reported to date," the researchers wrote.
The data suggest that the immaturity of the fetus's metabolic system and its "saturation" with BPA "may both act to increase fetal exposure to BPA during early to mid-gestation," the authors wrote. Animal studies previously have shown that fetal levels of BPA in certain tissues can exceed the mother's levels.
One possible explanation for the higher levels is that the women were primarily low-income and more ethnically diverse than the general U.S. population. Previous research suggests ethnicity and socio-economic factors may contribute to exposure differences. Also, the new analytic technique could be more accurate than the techniques used to test other cord blood.
In this population, there was large variability in the amount of active BPA compared to the converted forms. Active BPA ranged from less than one one-hundredth to over 400 times the other two forms. If the liver's metabolism were as effective as assumed by the Food and Drug Administration, active BPA would be virtually undetectable in blood and less than a tiny fraction of metabolized BPA.
These findings challenge the regulatory assumptions about BPA safety. It has been assumed that all consumed BPA passes into the liver. But a study published earlier this year suggested why this assumption may be false. It showed that significant amounts of active BPA can be absorbed in the mouth and then passed directly into the bloodstream. These new data are consistent with that finding.
"Overall our findings point to the importance of fetal exposure to BPA during development and the need to accurately assess the full range of human exposure during pregnancy," the authors wrote.