Neurological impairment in Children
In Europe, widespread damage to children’s brain function has resulted from exposure to neurotoxic chemicals, including lead, mercury, and PCBs. 1 in 6 children in the USA now has a developmental disability, which include learning disabilities, attention deficit disorders, and behavioural problems. The statistics for Europe are likely to be comparable. Interacting genetic, environmental, and social factors are important determinants of childhood brain development and function. However, chemicals in the environment are a preventable cause of deficits in brain function in many children.
Failure to control chemicals has resulted in measurable deficits in IQ and attention disorders in children. Data suggest that in Europe the brain development of thousands of children has been affected by exposure to levels of man-made pollutants called PCBs. Lead and mercury have also affected the brain function of a great many children throughout Europe. For mercury and PCBs, exposure mainly arises from contamination of the food chain, particularly fish. Lead exposure arises from old paints, water supplies, including lead piping and solder, and historically from leaded petrol.
The developmental neurotoxic properties of lead, mercury and PCBs were picked up by epidemiology, after the damage to children had been done. Prior testing of these chemicals was inadequate, and therefore widespread exposure and harm to the population at large occurred and was not prevented.
Just recently, some 200 eminent scientists from five continents declared that exposure to common chemicals makes babies more likely to develop an array of health problems later in life, including diabetes, attention deficit disorders, prostate cancer, fertility problems, thyroid disorders and even obesity. When foetuses and newborns are exposed to various toxic substances, growth of critical organs and functions can be skewed. In a process called "fetal programming," the children have become susceptible to diseases later in life, and possibly pass on the susceptibility to their offspring.
The possibility that chemicals might also interfere with the normal ageing process and contribute to memory deficits in old age should also be a concern. With an increasingly aged population this could also have gross financial and societal repercussions.
Unfortunately, only a very few chemicals have ever been tested for their ability to de-rail brain development. Current test methods are costly and time consuming, and there is a need to develop better methods to identify chemicals with developmental neurotoxic properties.
Much of the testing may not be adequate to predict the human consequences of long-term, low-level exposures. For example, the neurotoxic effects of prenatal or early-life exposure to lead, polychlorinated biphenyls, and methylmercury in humans occur at intake levels about three orders of magnitude lower than those predicted from tests on rats. Indeed, there may be no safe levels. Current methods of risk assessment, which extrapolate safe levels for humans from tests on rats and mice, may over-estimate safe levels for humans, and therefore leave people unprotected.
Worryingly some chemicals have been shown to have developmental neurotoxic properties in animal experiments but regulatory action is not quickly forthcoming. For example deca-BDE (deca brominated diphenyl ether), is a flame retardant retardant used in many consumer products. A Swedish study on mice, reported in 2003, that deca-BDE caused effects on brain development. Then in 2006, another study from the USA also showed that deca-BDE may cause effects on brain function in rodents. But four years since concern about developmental neurotoxicity was first raised, the use of this substance in consumer products is still widespread.
Humans may be particularly sensitive because of the complexity of the human brain and because brain development in humans occurs over a long period. There may be no safe levels.