(NaturalNews) Prenatal exposure to the endocrine-disrupting chemical bisphenol A (BPA) may increase aggressive behavior in toddler girls, according to a study conducted by researchers from the University of North Carolina-Chapel Hill and published in the journalResearchers measured bodily levels of BPA in 249 pregnant women, then followed their daughters for two years. Children who had been exposed to the highest levels of the chemical before the 16th week of gestation had significantly higher scores on tests for aggression than girls of the same age with less exposure.The study is the first to examine the effect of BPA on behavior in human children. It is consistent with the results of prior animal studies, which have also found that BPA can affect the brain and reproductive system. The National Toxicology Program concluded in 2008 that there was evidence to support the chemical's effects on human children.Because BPA mimics the effect of estrogen, which plays a critical role in the male brain during the 11th and 12th weeks of pregnancy, researchers believe that the chemical might be "masculinizing" the female brain."In the developing brain, timing is everything," said neuropsychiatrist Louann Brizendine, author of"I'm worried that tiny amounts of this stuff, given at just the wrong time, could partly masculinize the female brain."Although the study found no change in male behavior and no increase in behavioral disorders among girls, scientists noted that the population effects may be much greater than those seen in the study. Michelle Macias, spokesperson for the American Academy of Pediatrics, noted that children in the study came from predominantly well-educated families, which tend to have lower aggression and hyperactivity rates than the average. In addition, neurologist David Bellinger noted that a population can become more aggressive as a whole without there being strong observable effects in individual children.The researchers intend to continue studying the children until the age of five.Sources for this story include: www.usatoday.com