For over a decade, Assistant Professor of Epidemiology Joseph Braun has followed hundreds of pregnant women and their growing children in an attempt to determine what, if any, developmental consequences follow from exposure to chemicals in the environment. His results suggest that many of these chemicals do indeed impact children's health; but what happens when they combine, and what preventive actions parents can take, are still open questions.

Pervasive compounds

Chemical additives are ubiquitous in today's industrialized world. Some, like flame retardants in carpeting, may be required by law. Others, such as scent-stabilizing phthalates in perfumes, are deemed necessary to a product's usefulness. Still others, like pesticides, are vital to maintaining an abundant food supply. But their presence is often less than obvious.

"They're everywhere," says Braun. "That's the thing that makes them most unsettling to a lot of people, particularly the lay public, because we often don't know where they are."

Infants and young children are especially vulnerable to the effects of these chemicals for a variety of reasons. Some are behavioral: babies spend much of their time on the floor, and infants and toddlers explore the world by way of their mouths. Others are biological, owing to fetuses' and children's underdeveloped capacities to detoxify harmful substances.

Indeed, there is mounting evidence that some gestational experiences can and do cause health effects years or even decades after birth.

"There are classic studies from World War II, when women were on starvation rations during the Nazi occupation of the Netherlands," Braun explains. "The children who were in utero during this period of starvation were at increased risk for many chronic diseases later in life."

Braun and his colleagues wondered whether similar associations arose from prenatal exposure to environmental chemicals; but they were also interested in examining effects from exposures that might occur later on, in early childhood and beyond. After all, he explains, an infant's body systems will continue to grow rapidly for the next two decades or more.

And nowhere is this process more vital than in the child's center for executive control: the brain.

"The brain doesn't stop developing the moment the baby pops out of the womb," he says. "It keeps going. There are a lot of events that continue to go on in the brain, well into adolescence and even early adulthood."

Developmental consequences

In 2003, Braun's colleagues launched the Health Outcomes and Measures of the Environment (HOME) Study. They began by measuring the presence of five neurotoxicants in pregnant women and their children, from birth to 5 years: mercury, lead, tobacco smoke, pesticides, and a class of industrial chemicals called polychlorinated biphenols (PCBs) that were banned in the 1970s but still remain in the environment due to their persistence.

Later, the team added tests for bisphenol-A (BPA), phthalates, flame retardants, and perfluroroalkyl substances such as PFOA, a chemical used to manufacture stain- and water-repellant coatings.

Their findings suggest that some of these chemicals do lead to adverse neurological outcomes in children. For instance, prenatal exposure to tobacco smoke was associated with later alterations in infants' brain activity. The team also observed an increase in behavioral problems in girls aged 2-3 whose mothers had been exposed to BPA, and an increase in autistic behaviors in toddler and young children whose mothers had been exposed to flame retardants and a specific pesticide.

When the team began examining the effect of certain exposures on obesity and cardiometabolic outcomes, more connections began to arise. Mothers with high levels of PFOA tended to give birth to children who gained fat tissue more quickly as toddlers and retained a higher than normal level of this tissue at age 8.

Braun and his colleagues are currently reassessing the children, who are now adolescents, for additional cardiometabolic outcomes including blood pressure and fasting glucose, insulin, and lipid levels.

Fixing the problem

So what are concerned parents to do? The good news is that some exposures can be reduced by simple lifestyle changes. For example, consumers can limit exposure to chemicals like phthalates by avoiding the practice of microwaving food in plastic containers, or by replacing plastic stretch film with wax paper. Families can also reduce their exposure to certain pesticides by eating organic fruits and vegetables. Similarly, parents can use water filtration systems as a potential defense against water-borne neurotoxicants like lead that can be found in the water pipes of older homes.

But sometimes, these recommendations come at the expense of larger public health concerns.

"We found that some behaviors like consuming beverages and food out of cans was predictive of BPA levels in the kids," says Braun. "But you don't want people to be replacing the healthy stuff that's in canned foods with junk food."

"Don't replace your kidney beans with cheeseburgers or milkshakes," he laughs. "That's an extreme example, but there's lots of healthy stuff in canned foods."

Moreover, Braun explains, exposure to environmental chemicals is really quite difficult to eradicate completely.

"If you want to avoid all of it, you almost have to disconnect from the modern world," he says. "And I think what that speaks to is that we can't rely on individuals to simply change their behavior to reduce their exposures. We need to rely on policies and interventions from governments and regulators to do something to keep exposures below a level of concern."

Progress on that front is slowly evolving. Under the new Frank R. Lautenberg Chemical Safety Act, signed in June 2016, the chemical industry will be required to conduct pre-market toxicity testing of all new chemicals and to make this information publicly available; however, regulations surrounding the testing itself have not yet been specified, so it is unclear how much of a difference in transparency this new law will make.

"The devil is in the details," says Braun.

Expanding in understanding

Even accounting for additional regulatory oversight, scientists still struggle to understand how all of these different chemicals interact once they combine in children's body systems.

"There's this very large chemical soup that we're exposed to," says Braun. "What's either the joint or cumulative effect of these exposures on children's health? We don't have a good handle on that."

Public health scientists are currently working to develop new statistical methods that will be powerful enough to examine the effects of combined exposures. Until that happens, Braun and his colleagues plan to continue following their cohort of children as they grow. They hope that their results will begin to inform the decisions that both parents and regulators choose to make with regard to environmental chemicals.

"I think what's important about these studies, where we have long-term follow-up, is we really get the chance to see children's trajectory of development, and not only to investigate children's health at one time in life." says Braun. "We can be thinking about children as a dynamic entity that's changing over time, not as this static individual at any one age."

"They're growing in physical size, they're maturing, their brain is growing and doing different things, they're developing new skills as they get older," he continues, "And a lot of it is happening in a very short period of time, so we get to observe it."

Indeed, the same factors that make children most vulnerable to chemical exposures are also those that make this kind of research the most impactful.

"It's quite profound [in children]," he says, "how rapidly things change."