Unnerving developments in the state of the evidence on developmental neurotoxicity

Rachel Shaffer is a research assistant.

Seven years ago, leading children’s environmental health experts Philippe Grandjean and Philip Landrigan published a groundbreaking review that identified five chemicals prevalent in the environment—lead, methylmercury, polychlorinated biphenyls (PCBs), arsenic, and toluene—as developmental neurotoxicants. In their follow-up review released last week, they have added six more chemicals—manganese, fluoride, polybrominated diphenyl ethers (PBDEs), chlorpyrifos, DDT, and tetrachloroethylene (PERC)—to this list. The implications of early-life exposures to these common compounds, say the authors?  A “global silent pandemic of neurodevelopmental toxicity.” 

The developing fetus and newborn are uniquely susceptible to chemical exposures, and disruptions to critical developmental “programming” during this sensitive period can have life-long consequences.  In the environmental health field, this concept is known as the “Developmental Origins of Health and Disease” and suggests that even low-level exposures that would have little or no effect on adults could forever alter the development and life-course of a newborn or young child.

The individual and societal consequences of early-life exposures to developmental neurotoxicants can be devastating.  Damage to the brain can lead to permanent decreases in IQ or developmental disabilities, which in turn have implications for academic potential, earning capacity, and, at a population level, effects on national gross domestic product (GDP).  Research also suggests that these developmental neurotoxicants can lead to antisocial or criminal behavior; evidence is particularly strong for the case of lead.  Yet, in contrast to high-dose poisoning events, effects of these exposures can be subtle and often do not manifest until years later, making it difficult to identify and characterize the linkages to chemical exposures.

Based on mounting data from recent epidemiological studies, Grandjean and Landrigan have now classified the following compounds as known human developmental neurotoxicants:

  • Metals and inorganic compounds: arsenic/arsenic compounds, lead, methylmercury, fluoride, manganese
  • Organic solvents: toluene, tetrachloroethylene
  • Pesticides: chlorpyrifos, DDT/DDE
  • Other halogenated organic compounds: polychlorinated biphenyls, polybrominated diphenyl ethers

Their updated report should serve as yet another wake-up call that we are jeopardizing the health and full potential of future generations because of early-life exposures to these common toxic chemicals.

To tackle this growing problem, we need further research and improved chemical testing techniques to identify additional developmental neurotoxicants, and stronger regulatory policies to reduce exposures to them.  Fortunately, progress is being made in all three of these areas.

Because of the growing recognition of the severe consequences of exposure to developmental neurotoxicants, researchers across the country are working to identify these compounds and better understand how they act in the body.  In fact, earlier this week, the EPA awarded over $3 million in grants to several research institutions to support these investigations. Sustained funding for such critical public health research is essential.  

In conjunction with an improved understanding of these toxicants, we need to advance our capacity to screen and test chemicals for their neurodevelopmental effects.  New toxicity testing techniques may hold promise towards this end, and engagement with the scientific community studying such chemicals and adverse effects is necessary to ensure that challenges and limitations associated with applying these new tools can be resolved.

And finally, we need a new framework for our national chemicals policy– one that will give the EPA the authority to get and use this information to effectively protect public health.  A bipartisan proposal in the Senate opens a path to securing the necessary improvements, and many stakeholders and members of both houses of Congress are working hard on the measure to ensure it delivers the needed reforms.

While challenging, progress in all of these areas is essential to the well-being of our society.  As study co-author Grandjean has said, “the brains of our children are our most precious economic resource… You only have one chance to develop a brain.”

 

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2 Comments

  1. Bill Maas
    Posted February 25, 2014 at 7:04 pm | Permalink

    I was going to make a contribution because of the important work the EDF does, but then I saw this blog noting the Lancet paper in which Professor Grandjean mischaracterizes the conclusions reached about fluoride in a paper that he co-authored in a peer-reviewed journal less than two years ago. The studies he reviewed earlier had so many deficiencies, as noted in the paper's discussion section, that conclusions about the association of fluoride and neurological development could not be reached. More and better research may be justified, but not conclusions about whether fluoride at the levels found in U.S. drinking water has any neurologic effects. While we do need to protect children from environmental hazards, we also need to be honest about the evidence, especially when mischaracterizing the evidence threatens to undermine the use of public health measures, such as community water fluoridation, that protect children from real health problems. I have lost confidence that EDF can make a distinction between real and imagined health threats.

  2. Rachel Shaffer
    Posted March 10, 2014 at 11:59 am | Permalink

    Bill,

    Thank you for your comments. We have not analyzed the studies on specific chemicals cited by the authors in this review, and we understand that there may be disagreements about the conclusions they reached. But we do not believe that this should detract from the overall concerns they express about the widespread presence of developmental neurotoxicants in our environment. Additional research is needed to better understand the effects of these common exposures and characterize the levels at which they occur, so that we can better protect public health.

    Best,
    Rachel

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