Effect Measure

Brains at risk

The Lancet has just published (NOvember 8, 2006, online publication) a major review of the scientific evidence suggesting developmental disorders in children traceable to chemicals in the environment is significant and largely overlooked. Authored by two internationally recognized scientists, Philippe Grandjean (Harvard School of Public Health and University of Southern Denmark) and Philip Landrigan (Mt. Sinai School of Medicine), the paper identifies 201 industrial chemicals with the capacity to cause a neurodevelopmental defect (NDD) such as autism, attention deficit disorder and mental retardation:

A developing brain is much more susceptible to the toxic effects of chemicals than an adult brain. During development, the brain undergoes a highly complex series of processes at different stages. An interference–for example, from toxic substances–that disrupts those processes, can have permanent consequences. That vulnerability lasts from fetal development through infancy and childhood to adolescence. Research has shown that environmental toxicants, such as lead or mercury, at low levels of exposure can have subclinical effects – not clinically visible, but still important adverse effects, such as decreases in intelligence or changes in behavior. (HealthOrbit)

“The human brain is a precious and vulnerable organ. And because optimal brain function depends on the integrity of the organ, even limited damage may have serious consequences,” Grandjean pointed out. Developmental defects, usually involving the nervous system, are extremely common, estimated to afflict one in six children. But relating NDDs to environmental chemicals is technically difficult. When Grandjean and Landrigan examined the published literature on just five of the chemical — the well-known neurotoxins lead, methylmercury, arsenic PCBs and toluene — they found a characteristic pattern. Adult toxicity was recognized first, usually in an occupational setting. Then childhood poisonings were reported. Finally, there is a steadily growing body of epidemiological evidence showing neurobehaviioral effects in children at lower and lower levels. Grandjean and Landrigan are among the world’s authorities on the effects of these compounds.

These well-documented chemicals are only five on the list of 202 chemicals that also have neurodevelopmental effects:

“Even if substantial documentation on their toxicity is available, most chemicals are not regulated to protect the developing brain,” says Grandjean. “Only a few substances, such as lead and mercury, are controlled with the purpose of protecting children. The 200 other chemicals that are known to be toxic to the human brain are not regulated to prevent adverse effects on the fetus or a small child.”

Grandjean and Landrigan conclude that industrial chemicals are responsible for what they call a silent pandemic that has caused impaired brain development in millions of children worldwide. It is silent because the subclinical effects of individual toxic chemicals are not apparent in available health statistics. To point out the subclinical risk to large populations, the authors note that virtually all children born in industrialized countries between 1960 and 1980 were exposed to lead from petrol, which may have reduced IQ scores above 130 (considered superior intelligence) by more than half and increased the number of scores less than 70.


“Other harmful consequences from lead exposure include shortened attention spans, slowed motor coordination and heightened aggressiveness, which can lead to problems in school and diminished economic productivity as an adult. And the consequences of childhood neurotoxicant exposure later in life may include increased risk of Parkinson”s disease and other neurogenerative diseases,” says Landrigan.

A word of explanation of the IQ score statements. If you think of IQ scores as dstiributed in a bell shaped curve, the two “tails,” the upper (above 130) and lower (below 70) parts of the curve are small. If you take the whole curve and shift it slightly to the left, even a few IQ points, you can substantially reduce the area below the curve above 130 relative to its previous amount and increase the area of the curve below 70, relative to its previous amount. Thus even a rather small effect on IQ, say a point or two, not easily noticeable in any particular individual, can have fairly large effects on a population basis in terms of and increase in the proportion of the population considered mentally retarded (IQ below 70) or a decrease in those considered of high IQ (above 130).

Grandjean and Perez, in a supplement, note that 21 of the chemicals are among the top fifty in a list commonly found in hazardous waste sites in the US.

The majority of the 201 compounds are therefore undoubtedly present in the environment, in food, or in consumer goods.


The number of neurotoxic chemicals is likely to be much larger, as indicated by toxicology tests. Twenty years ago, about 750 chemicals had shown neurotoxic effects in laboratory animals9. The number is thought to exceed 1,000 today, although no authoritative estimate of the true number of neurotoxicants is available.


The incomplete information and the associated uncertainties can easily lead to underestimation of the pandemic of developmental neurotoxicity. Because of the vast societal importance of optimizing human brain development, we propose immediate action to protect the brains of future generations:

1. Documentation of chemicals that have caused toxic effects on the nervous system in humans to facilitate targeted preventive action against releases of these chemicals;

2. Documentation of human exposures to neurotoxic chemicals and identification of subgroups at risk due to residence, occupation, diet, and other factors;

3. Research on the consequences of developmental exposures to neurotoxic chemicals to expand our understanding of the long-term consequences of such exposures; and

4. Screening for neurotoxicity of commonly used chemicals to identify those that may present a hazard to brain development. (Supplement ot Lancet paper)

This is a sobering account by two highly respected scientists (full disclosure: the Reveres know both of them well). It is not a cause for panic about the health of our children. It is a cogent argument for investing in prudent measures to identify and limit developmental neurotoxicants in our environment for the sake of coming generations.


  1. #1 crfullmoon
    November 9, 2006

    Been pretty obvious all along that each chemical that business claims to be ok at time and quantity at point of use, was joining a whole envirnment of pollution we’re all exposed to our whole lives, in combinations that the impacts of are not being studied.

    Young people are going to have to be taught to guard their health better, and avoid what can be avoided, and how their present choices may negatively impact their future reproduction, and their child’s brain health in ways that can’t be completely remedied by schools.

    Can we ever get laws and enforcement strengthened, and, lose certain chemicals? Maybe more public knowledge of pollution finally showing up as impacting humans and not just all sorts of other animals reproduction and health will help, too. Our “lifestyle” needs to be “negotiable”, for ecology’s sake, including our own species.

  2. #2 Rich
    November 9, 2006

    It’s a ssame you don’t link directly to the Lancet article (which doe not yet appear to be online). Your discussion of IQ is misleading. Not all IQ measures are created equal and group IQ tests (commonly used in clinical studies have more error than those administered individually). A point or two difference on a population or individual basis is meaningless. Diffreences in scores at extreme ends of the spectrum also become limited in meaning. The difference between an IQ of 120 and 130, in terms of predicting achievement (the principle function of IQ tests) is less meaningful than a 10 point different near the mean (of 100). A lot of horrible things have been done & said based on misinterpretation of what an IQ is and we’d all be better off if you didn’t show off your (and probably the author’s obvious ignorance).

    Although I have no trouble believing that environmental toxins may effect barin development, the diagnosis of neurological disorder in children has gotten better but remains crude. The epidemiological evidence often lacks exploration of explanatory pathways. If the full article were available, it would be easier to evaluate what this paper adds to the literature by waiting until you can also share the data with readers.

  3. #3 revere
    November 9, 2006

    Rich: Your points about IQ are good, although they miss my point, which I grant could have been said better. The point I was trying to make could as easily have been made (and has been) for any continuous measure, such as blood pressure. Dietary sodium can shift diastolic blood pressure a couple of points, which for most people is not of clinical significance but on a population basis, with diagnostic cutoffs for hypertension, can greately increase the number of people classified as having high blood pressure.

    In other words, my point was not IQ (in fact the wording of the pullquote I thought was misleading and alarming about the IQ effect and I was trying to clarify it)k, but effects on the tails of a distribution.

  4. #4 name
    November 9, 2006

    As the parent of such a child, the thought of what I might have inadvertently exposed my unborn child to during pregnancy has haunted me since the dreaded autism diagnosis. Leaded gasoline? Bug sprays? Contact with pesticides and medications while trying to rescue a sick stray? Mercury in the tuna I ate thinking it was great nutrition? Flame retardants etc in the adorable new baby clothes? Stain repellents in the car seat I diligently installed? Something in the pile of vaccinations and anitbiotics that a substitute doctor administered all together at 24 months while he was obviously very ill?

    This generation of damaged children is paying far too high a price for our privileged Western standard of living. Sadly, I suspect we’ll conclude that much of the damage was done with the best of intentions. Nothing is worth this. We have been far too cavalier about playing with the fruits of progress and it seems we will have a lot to answer for.

    Hopefully, though, such studies will help overcome society’s great reluctance to adapt our world to accommodate the challenges we have imposed on our own children, and teach us to be more careful in the future!

  5. #5 anon_22
    November 9, 2006

    revere, thank you for raising this IMHO is one of the central issues of environmental toxicity today. Part of the problem is in establishing sufficient ‘proof’ of causation, to make the case for banning certain substances.

    The other one is that the ‘maximum permissible dose’ concept has to be thrown out. A developing brain responds to subtle molecular signals in ways that can be completely disproportionate to the dose.

    Hence the immense difficulties in regulation.

    In addition, in response to ‘name’, there is the issue of bioaccumulation, where toxins are not excreted but accumulate in the mother’s body throughout her life, until they are ‘excreted’ via the placenta to the fetus. Thus the fetus receives a huge dose in relation to its size.

    So, if anyone is worried about what they might have been exposed to during pregnancy (not that you shouldn’t), they need to know that the total exposure pre-preganancy may be even more important.

    To protect our future generations, we need to protect girls and young women, long before the thought of motherhood has entered their minds.

  6. #6 M. Randolph Kruger
    November 10, 2006

    Revere. They did a study in my 60,000 person town (DEA) and found that there were 15 pediatric facilities including the near free one at the hospital. They also determined that if they went to the three middle schools that have a student population in the thousands, that nearly 1/3rd of the students were on ADHD or ADD medicines. They also were using psycho-altering drugs on 10% of those kids. They cant indict anyone because the protocol for use (issued of course by big pharma) is met and therefore when Little Jane or Little Johnny cant perform they pump them up on the old Ritalin or something else. Coupled up with neurotoxic crap in the environment, its a wonder they can read and write any longer.

    There have been 11 suicides in the last three years. One last week in fact. A 7th grader just up and off’ed himself by hanging. My daughters friend in the 11th capped himself a month ago with a large bore weapon. On one hand its no child left behind, on the other its no child left unmedicated too.

  7. #7 revere
    November 10, 2006

    Randy: I have no doubt there is too much medication used. However I know the two scientists who did this study very well. They are not light weights. So these are two separate issues.

  8. #8 anon
    November 10, 2006

    So in your opinion, which is a greater risk…complications caused by normal influenza, or the small amount of mercury in each children’s flu shot?


  9. #9 revere
    November 10, 2006

    anon: Influenza.

  10. #10 BA in MI
    November 10, 2006

    A number of years ago, I worked in a small school of about 200 kids. There were 4 of us in the office, 3 of us have kids who were diagnosed with Hodgkins lymphoma. Environmental factors? It’s the only thing I can come up with.

  11. #11 revere
    November 10, 2006

    BA: Infectious factors (including Epstein-Barr virus) and organic solvents have been discussed with HD. HD now has a reasonable prognosis. Hope yours is in that category.