The University of Massachusetts Amherst

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Brain, Disrupted

The environmental effects of toxins on brain development
  • Brain scans and magnified brain cell

One of the most telling effects, says Zoeller, is the lowering of IQ in affected children. Studies show that prenatal exposure in development has caused decreases in IQs related to the PCB body burden of the mother.

Long suspected to be protected by the mother, UMass biologist Tom Zoeller’s work shows how susceptible unborn children can be to environmental chemicals. The ubiquity of PCBs, long banished but still existent in daily life, along with outdated legislation and health risk evaluations, ensure our endocrine system is at risk from long before birth.

The endocrine system, specifically the thyroid gland, governs healthy brain development. In gestation, growing babies are dependent on the mother for thyroid hormone production. For this reason, anything that may impair the mother’s thyroid activity can have life-long consequences on the developing fetus.

“Low thyroid hormone in the mom during pregnancy results in a variety of cognitive deficits in kids,” Zoeller says.  “As more research emerges, you realize that even small, modest changes in thyroid hormone levels produce modest deficits in cognitive functions.”

Unfortunately, defects of this nature are usually only noticed in extreme cases, where the symptoms are overt. In reality, the range of effects on children is directly proportionate to the mother’s thyroid insufficiency.

“There are a number of examples outside the area of thyroid hormones where the same thinking occurs: if you don’t see these extreme deficits, then there must not be a problem. The intensity of the deficit of thyroid hormone is correlated to the intensity of the defect in the offspring.”

So how are endocrine systems getting disrupted?

“That part gets a lot more attention,” Zoeller says, referring to his research into the effects of chemicals on thyroid hormone action and the role that plays in public health. “Seventy-three billion pounds of chemicals are produced or imported in the U.S. everyday. I’m convinced, based on what we’re finding, that the way in which public health groups like the EPA, FDA, Food Safety, and also European organizations, evaluate chemicals for their ability to interfere with thyroid hormone action isn’t working.”

The Endocrine Disrupter Screening Program’s evaluation method, Zoeller says, is to weigh organs and infer toxicity based upon change in mass. Zoeller maintains that this approach is outdated and leads to toxic changes going unnoticed. He compares this blanket strategy to a mechanic weighing your car’s engine to see if the brakes are shot.

Among the most harmful chemicals taken for granted in our environment are PCBs: Polychlorinated Biphenyls. Banned by law, not industry regulation, in 1979, their nearly indestructible, non-biodegradable nature makes them a permanent fixture in backyards to this day.

“The October 2011 snowstorm we had here in New England; you could look across building tops and see transformers on all the electrical poles exploding. Those blue sparks are PCBs,” says Zoeller.

Despite “production” being banned over thirty years ago, PCBs remain in place today. Improvement is needed, Zoeller says, in how we screen our chemicals in this country.

“Europe is farther ahead than we are by quite a bit.  They’ve put a lot more effort into improving their means of testing and evaluating their chemicals. They also have a very different ethic in that they require companies who produce these chemicals to show that they’re safe,” says Zoeller.

So while some chemicals, like PCBs and DDT, are deemed unsafe and taken off the market, most of the 80,000 patented chemicals are let loose in our environment until proven harmful to human life. According to Zoeller, it’s up to the government, meaning taxpayers, to pay to determine whether something is safe after it gets out into the human population. “It’s a system that does not protect public health,” Says Zoeller.

Since thyroid hormones regulate normal brain development, the effect of PCBs on the mother’s capacity to produce these hormones can result in a wide range of defects: impulsivity, attention deficit, and in extreme cases, cretinism. This means the complete lack of thyroid action and a failure for genes to differentiate themselves, resulting in severe physical abnormalities.

One of the most telling effects is the lowering of IQ in affected children. Studies show that prenatal exposure in development has caused decreases in IQs related to the PCB body burden of the mother. “The same kind of problems you see with sub-clinical hypothyroidism in mothers,” Zoeller adds.

These deficits are often not noticed outside of the most severe cases, wherein there is an obvious behavioral or cognitive defect. Looking at only the extreme instances, Zoeller warns, is ignoring the more insidious, dangerous issue.

“You may think a 5-10 IQ deficit isn't’t a clinical problem, but on a population level, it’s a massive problem, and the economic impact of IQ deficits on the population is staggering.”

Isolating which chemicals have these effects, making sure people understand the harm, and developing new alternatives would then have a substantial effect on the mental and financial well-being of the community. A reduction in environmental contaminants, Zoeller notes, would directly lead to a reduction in the number of kids that require institutional support, education, etc.

Showing these connections, that PCBs affect thyroid production, that impaired thyroid action results in cognitive defects, and extending that to directly linking PCBs to these clinical changes, has been a difficult thing to prove. It has been proven to occur in rats, but the cognitive differences between rodents and humans are vast. Zoeller’s work is helping to change the way we think about, treat, and legislate chemicals in a time when the protection agencies’ methods are antiquated and the chemical companies can out lobby public health.

“When you really think about it, what we’re talking about is, ‘does an industry have the right to rob human potential from people?’ And I don’t know any other way to put it. As a parent, you think about these things.”

Ryan Morin