Chemicaliën verstoren wereldwijd de
ontwikkeling van hersenen.*
In een studie gepubliceerd in the Lancet vinden wetenschappers meer dan 200 chemische stoffen die de ontwikkeling van de hersenen flink kunnen verstoren. Zij concluderen dat wereldwijd de hersenen van honderden miljoenen kinderen door deze chemische milieuvervuiling beschadigd zijn en dat doorgaans overheden deze vorm van milieuvervuiling totaal onderschat hebben. Liefst 1 op de 6 kinderen lijkt door chemische milieuvervuiling een hersenafwijking te hebben. Pas nu begint in Europa schoorvoetend actie ondernomen te worden door onderzoek vooraf te gaan eisen bij de introductie van chemicaliën. Doch nu al is de vraag of een dergelijk onderzoek ook de neurologische gevolgen wel zal omvatten. Volgens de wetenschappers zijn hersenen een heel delicaat orgaan dat zeker bij de ontwikkeling geen schade mag oplopen, want kleine foutjes kunnen grote gevolgen hebben in de verdere ontwikkeling en tot allerlei ziektes leiden. In het verleden stonden lood-, kwik-, arsenicumverbindingen, PCB’s en tolueen al bekend als gevaarlijk voor de ontwikkeling van hersenen. Lood bijvoorbeeld zorgt o.a. voor een duidelijk lager IQ, minder aandacht en veel meer agressie. Alleen al in Amerika kosten de gevolgen van loodvergiftiging 35 miljard dollar per jaar.
A
Silent Pandemic: Industrial Chemicals Are Impairing Brain Development Of
Children Worldwide
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 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. (Nov. 2006)