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

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A Silent Pandemic: Industrial Chemicals Are Impairing The Brain

Development Of Children Worldwide

Main Category: Pediatrics

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Article Date: 13 Nov 2006 - 0:00am (PST)

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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.

See the latest news from the Harvard School of Public Health.

Harvard School of Public Health is dedicated to advancing the public's health

through learning, discovery, and communication. More than 300 faculty members

are engaged in teaching and training the 900-plus student body in a broad

spectrum of disciplines crucial to the health and well being of individuals and

populations around the world. Programs and projects range from the molecular

biology of AIDS vaccines to the epidemiology of cancer; from risk analysis to

violence prevention; from maternal and children's health to quality of care

measurement; from health care management to international health and human

rights. For more information on the school visit: http://www.hsph.harvard.edu/

Contact: Todd Datz

Harvard

School of Public Health