“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 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.
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.
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.
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: a meta-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.
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 such as DDT also appear to affect the brain development of children. Studies indicate that contact 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 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.