A Silent Pandemic: Industrial Chemicals Are Impairing The Brain Development Of C

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A Silent Pandemic: Industrial Chemicals Are Impairing The Brain

Development Of Children Worldwide

http://www.eurekalert.org/pub_releases/2006-11/hsop-asp110306.php

Boston, MA -- Fetal and early childhood exposures to industrial

chemicals in the environment can damage the developing brain and can

lead to neurodevelopmental disorders (NDDs)--autism, attention deficit

disorder (ADHD), and mental retardation. Still, there has been

insufficient research done to identify the individual chemicals that

can cause injury to the developing brains of children.

In a new review study, published online in The Lancet on

November 8, 2006, and in an upcoming print issue of The Lancet,

researchers from the Harvard School of Public Health and the Mount

Sinai School of Medicine systematically examined publicly available

data on chemical toxicity in order to identify the industrial

chemicals that are the most likely to damage the developing brain.

The researchers found that 202 industrial chemicals have the

capacity to damage the human brain, and they conclude that chemical

pollution may have harmed the brains of millions of children

worldwide. The authors conclude further that the toxic effects of

industrial chemicals on children have generally been overlooked.

To protect children against industrial chemicals that can injure

the developing brain, the researchers urge a precautionary approach

for chemical testing and control. Such an approach is beginning to be

applied in the European Union. It puts in place strong regulations,

which could later be relaxed, if the hazard were less than

anticipated, instead of current regulations that require a high level

of proof. At present in the U.S., requirements for toxicity testing of

chemicals are minimal.

" 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, " says Philippe

Grandjean, adjunct professor at Harvard School of Public Health and

the study's lead author.

One out of every six children has a developmental disability,

usually involving the nervous system. Treating NDDs is difficult and

costly to both families and society. In recent decades, a gathering

amount of evidence has linked industrial chemicals to NDDs. Lead, for

example, was the first chemical identified as having toxic effects to

early brain development, though its neurotoxicity to adults had been

known for centuries.

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.

Grandjean and co-author Philip J. Landrigan, Professor at Mount

Sinai School of Medicine, compiled a list of 202 environmental

chemicals known to be toxic to the human brain using the Hazardous

Substances Data Bank of the National Library of Medicine and other

data sources. (The authors note that the list should not be regarded

as comprehensive; for example, the number of chemicals that can cause

neurotoxicity in laboratory animal tests exceeds 1,000.) The authors

then examined the published literature on the only five substances on

the list--lead, methylmercury, arsenic, PCBs and toluene--that had

sufficient documentation of toxicity to the developing human brain in

order to analyze how that toxicity had been first recognized and how

it led to control of exposure. They found a similar pattern in how the

risks of each substance were documented: first, a recognition of adult

toxicity and episodes of poisoning among children, followed by a

growing body of epidemiological evidence that exposure to lower levels

of the substances caused neurobehavioral deficits in children.

" 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. Today, it's estimated

that the economic costs of lead poisoning in U.S. children are $43

billion annually; for methylmercury toxicity, $8.7 billion each year.

" 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.

The researchers believe that the total impact of the pandemic is

much greater than currently recognized. In supplementary documentation

(see below for a link), about half of the 202 chemicals known to be

toxic to the brain are among the chemicals most commonly used.

Testing chemicals for toxicity is a highly efficient public

health measure. However, less than half of the thousands of chemicals

currently used in commerce have been tested to assess acute toxicity

and, although new chemicals undergo more thorough testing, access to

the data may be restricted because companies fear exposing proprietary

information. Also, current toxicity testing rarely includes

neurobehavioral functions.

" The brains of our children are our most precious economic

resource, and we haven't recognized how vulnerable they are, " says

Grandjean. " We must make protection of the young brain a paramount

goal of public health protection. You have only one chance to develop

a brain. "

To view supplementary documentation on industrial chemicals and

risks of toxic effects on brain development, click here:

http://www.hsph.harvard.edu/neurotoxicant/appendix.doc Support for

this research was provided by the Danish Medical Research Council, the

(U.S.) National Institute of Environmental Health Sciences and the

U.S. Environmental Protection Agency.

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