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What We Don’t Know Can Hurt Us: Toxic Chemicals, Science, and Policy

June 21st, 2017

Environmental protection is the subject of heated debate these days. In February of this year, President Trump signed an executive order to roll back the clean water rule, which limits corporations’ ability to pollute about 60% of U.S. waterways. The irony is that we know more than ever before about how toxic chemicals adversely affect people, and we can be certain that what we don’t yet know can hurt us. Scientific research on potential chemical contaminants is both more advanced and more needed than ever before, according to an article by Christopher Newland and Jordan Bailey in the recent issue of Policy Insights from the Behavioral and Brain Sciences.

“Approximately 80,000 chemicals have been registered for commercial use, and of these, more than 3,000 have been identified as high priority” because industries produce more than a million pounds per year, according to the authors’ review of research. Exposure to many of these chemicals, like pesticides and solvents, causes damage to the human nervous system, especially if developing fetuses are exposed before birth. But for the vast majority of industrial chemicals, we simply don’t know the specific effects. Could that be justification for the reduction in environmental regulations and standards? Scientists say no; what we know about chemical contaminants so far isn’t good news, and it should make us very concerned about the chemicals we have yet to study and regulate.

As a cautionary tale, Newland and Bailey describe the scientific methods, findings, and policy impacts of the well-studied chemical methylmercury (MeHg). It is formed when mercury, released from activities like burning fossil fuels and mining gold, combines with sediments in rivers and other waterways. According to scientists, “MeHg currently poses the largest health threat,” because it concentrates in certain fish like tuna and swordfish that are popular among consumers.

The initial discovery of its harmful effects resulted from a tragic epidemic in 1956 in Minimata City, Japan. After two sisters began having trouble walking and talking, thousands of other town residents came forward with what turned out to be MeHg poisoning. A local factory had been dumping MeHg-contaminated wastewater into the local water supply, where the fish consumed it and passed it on to people. Those exposed had a wide range of impairments, from difficulty with motor skills and speech to deformed limbs to cerebral palsy, and the consequences were lifelong, with functioning declines as victims aged. Future epidemics in other locations gave researchers a grim view into the effects of MeHg on children who had been exposed to high doses of the chemical in utero, including impairments in learning, attention, and memory.

Fortunately, these studies raised awareness of the danger and reduced the chances of future epidemics. But a key question remained: does chronic exposure to low-levels of MeHg cause impairment as well? Lab studies with animals addressed that question in relation to an array of sensory, behavioral, and cognitive functions, and the results are not reassuring. For example, rodents and primates with chronic exposure struggled to learn new information and develop strategies to get simple rewards. As a result, pregnant women are now advised to strictly limit the amount of fish they eat.

But what about the contaminants scientists haven’t studied, or the effects they haven’t been able to isolate because the chemicals are often combined with other compounds? That’s why we need support for more science on environmental exposure to chemicals, Newland and Bailey argue. They are sensitive to the fact that regulations and other public policies have to balance “considerations for protecting public health and setting realistic goals.” Arguments against environmental regulations are often framed in terms of boosting economic growth, but there are significant monetary costs to toxic exposure.

Newland and Bailey acknowledge that it can be difficult to estimate the cumulative costs, but they point to some illuminating approaches. “One approach has been to estimate the number of additional individuals diagnosed with a specific disorder, such as autism or intellectual disabilities, due to the presence of a neurotoxicant substance,” they write. Another is looking at the impact of the chemical on IQ, then factoring in the correlation between IQ and income. One such study found that “MeHg-induced loss of IQ” resulted in more than eight billion dollars of lost income in one year. An increased rate of mental retardation meant a loss of two billion dollars alone. And, of course, that’s to say nothing of the physical and emotional pain of the disabilities.

As the authors point out, none of our current knowledge about protecting ourselves and our children from mercury exposure would have been possible without lab research and field studies. In the face of untold chemical-exposure risk, they urge readers to consider how carefully-designed studies can guide reasonable policies and help us to take reasonable precautions.


Drawn from “Behavior Science and Environmental Health Policy: Methylmercury as an Exemplar” by M. Christopher Newland and Jordan M. Bailey in Policy Insights from the Behavioral and Brain Sciences.

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