Since then, modern manufacturing from the United States to China has continued to innovate in the field of plastics, and the material is in nearly every consumer product we buy and use. However, researchers also continue to study the effect such products wreak on human health, as many plastics are composed of polymers that may decompose into toxic substances when heated. A couple of years ago, researchers reported that nearly all plastic products sampled released chemicals with estrogenic activity, disrupting the normal fetal development process in pregnant women.
Bisphenol A (BPA), particularly, came under scrutiny. BPA is an estrogenic endocrine disrupter widely used in the manufacture of plastics and found in many consumer products. In a recent study, investigators found that more than 90 percent of Americans have detectable levels of BPA in urine, with exposure coming from diet, absorption through the skin, and through breathing. Although potentially toxic to adults, researchers say the biggest concern is with early exposure to BPA, particularly in the womb.
"Animal studies have shown that in utero exposure to BPA produces prenatal and postnatal adverse effects on multiple tissues, including the brain," researchers from Columbia University reported Tuesday in PNAS, the Proceedings of the National Academy of American Sciences of the United States of America. "Prenatal BPA exposure affects brain development, sexual differentiation, social and anxiety-like behavior, and learning [and] memory."
In people, new evidence shows similar consistency with associations between BPA exposure and disruption to brain development, and has also shown sex-specific effects of gestational BPA levels on emotional regulation and aggression in children.
"Importantly, childhood BPA levels did not predict these measures, emphasizing the importance of gestational BPA exposure for neurobehavioral outcomes," the researchers wrote.
The Columbia University study, led by Marija Kundakovic, provides evidence that low exposures to BPA is enough to cause enduring disruption to epigenetic pathways in the developing brain — changes that are linked to gene expressions correlating with anxious behavior in children, along with social problems. In the animal study, investigators exposed pregnant mice to multiple doses of BPA, including doses below the level considered "safe" for people.
"Low doses of BPA reversed sex differences in the expression patterns of estrogen receptor genes in the brains of juvenile male and female offspring," the researchers wrote. These changes were accompanied by sex-specific alterations in the expression of enzymes that catalyze the addition of methyl groups to DNA, and by the differential methylation of an estrogen receptor gene. "In mice, these hazardous exposures played out among offspring in increased frequency of sniffing and chasing," behaviors that might mirror forms of aggression in children, the study says.
Although the researchers say the ubiquitous material is nearly impossible to avoid, experts offer recommendations to pregnant women for limiting exposure to BPA, including consuming fewer canned foods in favor of more fresh fruits and vegetables, and avoiding contact with canned food items in general. Experts also advise pregnant women to avoid heating plastic containers, a staple of most refrigerators, in the microwave. Finally, experts also recommend checking to ensure baby bottles are BPA-free.
The study is available online at PNAS.
Source: Kundakovica, M., Gudsnuka, K., Franksa, B., et al. "Sex-speciﬁc epigenetic disruption and behavioralchanges following low-dose in utero bisphenolA exposure." PNAS, Proceedings of the National Academy of Sciences of the United States of America. 2013.