A silent pandemic

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A silent pandemic: Industrial chemicals are impairing the brain ...

A silent pandemic: Industrial chemicals are impairing the brain

development of children worldwide 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. "

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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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