Brain development: chemical overreaction
5. May 2014
Behavioural and developmental disorders in children are increasing dramatically in
number. Neuroscientists make an insidious chemical poisoning accountable for
this, and urge a radical rethinking: rightly so?
"10 to 15% of all children enter the world these days with a neurological developmental
disorder", write Philippe Grandjean from the University of Southern Denmark in Odense and
Philip Landrigan from Harvard University in their current publication in the journal Lancet
Neurology. The consequences of these developmental disorders they say are dramatic:
"They reduce the quality of life, make employment and workplace training difficult, leave
behavioural disorders in their wake and thus affect the welfare and productivity of an entire
society". Neuroscientists hold among other things an insidious poisoning by chemicals in the
environment to be accountable for this. "Genetic factors indeed also play a role in these
diseases, but cannot explain the rapid increase in neurological behavioural and
developmental disorders", say the scientists. Only 30 to 40% of all neurodegenerative
disorders are attributable to genetic factors, state the researchers in explaining why they see
environmental chemicals to be highly significant in the emergence of these diseases. But is
this argument conclusive? In their meta-analysis, the researchers collected data
demonstrating a brain-damaging effect for eleven common chemicals. However they make
assumptions on there being many other unrecognised toxins.
Brain, right hemisphere, medially
Georg Graf von Westphalen
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Brain particularly sensitive during development
As early as 2006, scientists were able to show in a meta-analysis that the five chemicals
lead, methyl mercury, arsenic and arsenic compounds, polychloridated biphenyls and the
solvent toluene interfere with the brain development of children to a detectable extent.
Reduced brain volume, decreased mental performance, motor disturbances, and a loss in
social behaviour were recorded here among these.
In particular it's the brain of a foetus in the womb that is sensitive to toxic substances that
may be completely harmless to an adult organism. The brains of babies and young children
as well can be much more greatly harmed by chemicals than is a mature brain. Unborn
children come into contact with environmental chemicals through the bloodstream of the
mother, and later through breast milk or through their own independent contact.
New insights into old acquaintances
About seven years later, the researchers have again addressed the issue and included
current studies on the neurological effects of chemicals in their meta-analysis. In this period
there emerged both evidence on already known neurodegenerative chemicals as well as on
new chemicals that have been added to this group. Thus, for example, seven international
studies came to the conclusion that there appears to be no safe level of contact with lead
and that this substance, even in small doses, can be toxic. The evidence is mounting that
contact with lead inflicts irreparable damage to the human brain. Brain images of young
adults who as children showed increased blood lead concentrations pointed to a decreased
brain volume. This was accompanied by poor school performance and behavioural problems.
New neurotoxins
Following on from the five already known environmental chemicals, the researchers in their
current meta-analysis encountered six more which seem to negatively impact on the brain
development of children. These include manganese, fluoride, the solvent tetrachlorethylene,
the pesticides chlorpyrifos and DDT / DDE, and polybrominated diphenylether, which are
classified as organic compounds.
Manganese
As an example, studies in Canada and Bangladesh suggest that manganese in drinking water
could be the cause of dyscalculia and hyperactivity in children. 840 pupils aged between
eight and eleven years of age from Bangladesh who were regularly exposed to elevated
manganese concentrations in drinking water (> 400 μg/L) were less able to calculate than
children who consumed uncontaminated drinking water. Canadian school children who lived
near a manganese mine showed significantly inferior performance to their peers from
uncontaminated areas in their intellectual, motor and olfactory abilities. In
addition, experiments on mice confirmed these results. Whether there indeed is a causal
relationship between the observations is not answered by the studies.
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Fluoride
Elevated fluoride concentrations in drinking water apparently reduced the intellectual abilities
of Chinese children by an average of 7 IQ points, as a meta-study from 27 individual studies
showed. "The fact that other substances might be responsible for the neurodegenerative
effects was able to be excluded in most of the studies", the researchers say. Yet even here
the evidence of causality has not yet been provided, because fluoride in drinking water can
also bring positive effects with it: ameta-study in 2008 came to the conclusion that the
enrichment of drinking water with fluoride is an effective and safe measure for caries
prevention. Whether drinking water should be enriched in certain regions with fluoride is a
matter always subject to scientific discussions.
Solvent
Solvents are also suspected to harm the child's brain development. A French cohort study of
3,000 children showed that children of mothers who were exposed to solvents such as
tetrachlorethylene had tendencies toward aggressive behaviour, hyperactivity and mental
illness. Every fifth mother in these cohort study stated that in their work environment they
regularly came into contact with solvents. The women worked as nurses or as other staff
members in hospitals, as cleaners, pharmacists, hairdressers or beauticians. Whether the
mental illness and behavioural problems could however be attributed to other causes using
the data of the cohort study was something not able to be fully defined.
Pesticides
Pesticides such as DDT also appear to affect the brain development of children. Studies
indicate thatcontact occurring with organophosphate pesticides in the womb can lead to a
reduced head circumference among school aged children and to deficits in mental and social
development of children. Indeed, the insecticide because of its known side effects on
humans and animals since the coming into force of the Stockholm Convention in 2004 may
only be used to combat disease-carrying insects, especially the carriers of malaria, but this
rule is not adhered to in all states.
Large-scale production of over 100 neurodegenerative substances
Children who suffer from attention disorders, delayed development and poor school grades
for no apparent reason provide the researchers with the most concerns, because their
number is increasing steadily. For the researchers the reasons are obvious: "The brains of
these children have been harmed by neurotoxic chemicals. The consequences are obvious,
but these children have never received a formal diagnosis", they write. Yet are these really
the sole reasons for the school problems of these children? What kind of influence the
pressure to perform in an increasingly faster-running society could potentially have on the
abilities of children was not dealt with as part of the meta-analysis.
So far there are 214 substances with known neurotoxic effect - this long list is expanded by
adding about two new substances each year. At least half of them are produced industrially
on a large scale and sooner or later manage to find their way into the environment.
Instances of brain damage occurring in the womb or during early childhood are not yet
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treatable and lead to lifelong limitations for those affected, their families and society.
"Around the world, children come into contact with toxins that though unnoticed reduce their
intellectual abilities, change their behaviour and thus destroy their future. This leaves us
greatly concerned", write Grandjean and Landrigan.
Calls for stricter approval criteria
Redress could only be achieved by stricter approval requirements and environmental
guidelines, according to the study authors. The scientists call for more extensive testing
criteria, which also capture the insidious and prenatal effects in addition to the acute
neurotoxic effects of a substance. This they say has previously not been the case and should
also be applied to already approved chemicals. To classify chemicals as non-hazardous until
the contrary is proved would be a fatal fallacy, the researchers warn. In order to protect
children and society, they add that a shift in paradigm has to take place, which then unfolds
into decisive action. However until causal connections between neurogenerative disorders
and environmental chemicals are made clear, this process of reconsideration will only be able
to be set in motion with great difficulty.
Article bySonja Schmitzer