A study published Friday featuring UC Berkeley researchers found that a variety of environmental chemicals were more concentrated in fetuses than in the pregnant mothers who were exposed to them — a discovery that complicates previous research.

The study examined levels of mercury, organochlorine pesticides and other potentially harmful chemicals in a group of 77 pregnant mothers. These chemicals may be associated with the later development of conditions such as ADHD, obesity, cancer and autism, according to Tracey Woodruff, senior author of the study and UC San Francisco professor.

“The assumption that the placenta can protect the fetus from exposure to environmental chemicals is not true,” said Rachel Morello-Frosch, the study’s lead author and a UC Berkeley professor.  “In certain cases it appears that some chemicals can bioaccumulate in higher levels in the fetus than in the mother.”

Fetuses are particularly vulnerable to chemical exposure, Woodruff said.

“If we are just assuming the risks are based on what the pregnant women are exposed to, we could be underestimating the impact of the chemicals on the fetus,” Woodruff said.

Researchers found that concentrations of lead, which has been banned from paint and gasoline products, where it was formerly common, have declined. However, Woodruff said the use of other chemicals — and rates of childhood ADHD and autism — are on the rise.

“(Chemical exposure) is actually much more common than people are aware of,” said John Balmes, a UC Berkeley environmental health sciences professor unaffiliated with the study. “That’s why (this) work is important, to hopefully get the word out.”

Exposure to potentially harmful chemicals can be found in a variety of sources, including fish, pesticides used on crops and flame retardants, Woodruff said. People can also be exposed through pesticides used for home pests, food packaging, and plastic utensils, according to Balmes.

Some toxic environmental chemicals continue to resurface in studies of fetuses despite being banned for years, Woodruff said.

“We’re making fewer (toxic) chemicals now, thank goodness, but we went through an era when we didn’t pay attention to how toxic chemicals were,” said Ken Cook, president of the Environmental Working Group, an environmental health research and advocacy group. “Those were some of the chemicals Tracey found in those babies.”

Researchers also hoped the study, which examined low-income Latina women, could shed new light on how toxins affect socioeconomic groups traditionally underrepresented in scientific research. Woodruff cited the case of one woman in the study whose unusually high levels of mercury could be explained by the makeup she used — a gift from relatives in Mexico.

“Some of these exposures are uniquely visited upon communities of color,” Cook said. “They might live in places that are near pollution sites, they might have occupations that bring them into contact with these substances.”