Environmental toxins can damage neurons, especially in children.
It is a sobering thought: Each of us, even the newly born, carries multiple toxins within as the ongoing legacy of living in an industrialized world. And it’s even more unsettling when we realize that many of these chemicals affect the brain—especially a young, vulnerable one—in ways that we do not yet fully understand.
What we do know is worrisome enough. “Brain development is such a complicated process,” says David Bellinger, PhD, professor of neurology at Harvard Medical School and Children’s Hospital Boston. “It’s a choreography; things have to happen in the right order at the right time. A toxin that interferes with any of these processes could create problems that are difficult to reverse.” Such problems can include reduced intellectual capacity, diminished attention and increased impulsivity—the inability to control one’s emotions.
Nervous system toxins, known as neurotoxins, abound among the chemicals that contaminate our environment. The oldest, and best-known, is lead; historians believe that this metal’s mentally incapacitating effects help account in part for the Roman Empire’s decline, at a time when wine was often sweetened with lead and water pipes fashioned from it. Lead’s deadly sweetness also helps explain its danger to modern-age children. Lead used to be a paint additive and while that usage has been banned for many years, toddlers living in older homes may chew paint chips or be exposed to the dust that forms as lead paint degrades.
Today lead has plenty of neurotoxic buddies. Among those included on the website of the Environmental Working Group (www.ewg.org) are organophosphate pesticides, which can leave a residue on foods; volatile organic compounds (VOCs), a huge family of chemicals found in everything from adhesives to solvents; polybrominated diphenyl ethers (PBDEs), flame retardants used in fabrics and electronics; and polychlorinated biphenyls (PCBs), which were used in electrical insulators and transformers.
“New chemicals are put into the environment by the hundreds every year with no testing,” says Deborah Rice, PhD, toxicologist with the Maine Center for Disease Control and Prevention. “We all have at least dozens of chemicals on board, and we know virtually nothing about their interactions.” In 2005, a study backed by the EWG tested the umbilical-cord blood of 10 newborns from across the country and found 217 neurotoxins. Such studies in adults have shown similar results.
Minds at Risk
Scientists are still struggling to understand exactly how these chemicals affect the brain; one problem is that neurotoxins can be subtle in their effects. “Exposure to trace levels in foods causes no specific symptoms,” says Donald Wigle, MD, PhD, MPH, at the Institute for Population Health, University of Ottawa. Another problem is that the damage toxins do cause differs from substance to substance. “Lead, for instance, increases the unstimulated release of neurotransmitters [chemical messengers within the brain] and decreases the stimulated release—you end up with a lot of static in the system,” explains Bellinger. “Certain areas of the brain generate new cells that then migrate to where they belong, and that’s where methylmercury hits.”
Researchers are also trying to discover what makes some people’s brains especially sensitive to toxins. What they do know is that genetic vulnerability is only one factor in toxin response. “Poorer children may be more vulnerable to lead,” says Bellinger. “And there’s some evidence that children with micronutrient deficiencies are more susceptible.”
Scientists are starting to learn how neurotoxins disrupt functioning on the cellular level. In tiny worm-like creatures known as nematodes, the pesticide lindane led neurons to misfire, which in turn caused proteins to become misshapen and nonfunctional (Genes & Development 11/15/07). What’s more, damage may occur at exposure levels a lot lower than anyone previously thought possible. In a journal article, Wigle and Bruce Lanphear of the Cincinnati Children’s Hospital Medical Center state, “Findings from some of the most thoroughly studied and widely dispersed environmental contaminants indicate that there is no apparent safe exposure level” (PLoS Medicine 12/05). Some scientists think that toxic exposure may help explain the increasing occurrence of such developmental disorders as autism (The Lancet 12/10/06); others see links between pesticides and Parkinson’s disease (Annals of Neurology 8/06). This explains why neurotoxicity is one of the issues that will be examined as part of the National Children’s Study, a large research effort to learn how various environmental factors affect children’s health and development over time (www.nationalchildrensstudy.gov).
Simply scrubbing neurotoxins away is unrealistic at this point. “PCBs are still with us, and they were banned in the 1970s. They’re still affecting the brains of our children,” says Rice. “Dioxins, flame retardants, PCBs—we’re talking decades to get rid of these things.” There is the 1976 Toxic Substances Control Act, but it has “barriers that make it difficult to keep chemicals out of the environment before they’re released,” she says. “It really needs to be rewritten.” Bellinger would like to see controls similar to the European Union’s REACH regulations, under which chemicals need to pass safety tests before going to the marketplace.
There are ways you can reduce your family’s exposure to these powerful chemicals. Rice says that eating organically helps, as does consuming grass-fed meat. “Don’t use chemical sprays in your home and yard,” she says. “Go back to old-fashioned products.”
A neurotoxic world? The thought is scary. That’s why Rice urges awareness “of what you expose yourself to in your environment. It’s a matter of living very consciously.”