P Grandjean and PJ Landrigan, Lancet, 2006

“The two main impediments to prevention of neurodevelopmental deficits of chemical origin are the great gaps in testing chemicals for developmental neurotoxicity and the high level of proof required for regulation. New, precautionary approaches that recognise the unique vulnerability of the developing brain are needed for testing and control of chemicals.”

“One in every six children has a developmental disability and in most cases these disabilities affect the nervous system. … Treatment of these disorders is difficult, and the disabilities they cause can be permanent; they are therefore very costly to families and to society.”

“The developing human brain is inherently much more susceptible to injury caused by toxic agents than is the brain of an adult. … Because of the extraordinary complexity of human brain development, windows of unique susceptibility to toxic interference arise that have no counterpart in the mature brain, or in any other organ.”

“The human brain continues to develop postnatally, and the period of heightened vulnerability therefore extends over many months, through infancy and into early childhood.”

“The susceptibility of infants and children to industrial chemicals is further enhanced by their increased exposures, augmented absorption rates, and diminished ability to detoxify many exogenous compounds, relative to that of adults.”

“The underlying idea is that there is a dose-dependent continuum of toxic effects, in which clinically obvious effects have subclinical counterparts. A pandemic of subclinical neurotoxicity is therefore likely to be silent — ie, not apparent from standard health statistics.”

“Studies in animals support the notion that a wide range of industrial chemicals can cause developmental neurotoxicity at low doses that are not harmful to mature organisms. Such injury seems to result in permanent changes in brain function that might become detectable only when the animal reaches maturity.”

“We identified industrial chemicals that have caused neurotoxic effects in man from the hazardous substances data bank of the US National Library of Medicine, supplemented by fact sheets by the US Agency for Toxic Substances and Disease Registry, and the integrated risk information system of the US Environmental Protection Agency.”

“Documentation of developmental effects in human beings for the other compounds [besides lead, methylmercury, arsenic, polychlorinated biphenyls and solvents] listed in the panel is poor. However, three obvious candidate substances deserve particular attention…”

“Fluoride can cause neurotoxicity in laboratory animals, but is not shown in the panel as a substance proven to be neurotoxic in man. … In rural communities in China, high fluoride concentrations in well water might cause skeletal abnormalities. In one such community, 222 children aged 8–13 years showed significantly worse IQs than 290 unexposed controls. Parallel results were obtained in a smaller study of 118 children of similar age. Another study of 477 schoolchildren from 22 villages suggested that both increased water fluoride concentrations and very low concentrations were associated with IQ deficits, compared with children exposed to normal concentrations (below 1 mg/L).”

“The combined evidence suggests that neurodevelopmental disorders caused by industrial chemicals has created a silent pandemic in modern society. Although these chemicals might have caused impaired brain development in millions of children worldwide, the profound effects of such a pandemic are not apparent from available health statistics.”

“The consequences of a pandemic of developmental neurotoxicity extend beyond descriptive data for incidence and prevalence of clinically diagnosed disorders. Increased risk of Parkinson’s disease or other neurodegenerative diseases is a further potential consequence of the pandemic.”

“The population at risk of subclinical neurotoxicity from industrial chemicals is very large. … Because of the absence of dose-response associations for other neurotoxic compounds, the total costs are unknown.”

“Absence of information about the neurotoxic potential of most industrial chemicals is therefore the main impediment to prevention of developmental disorders induced by neurotoxic pollutants.”

“The few substances proven to be toxic to human neurodevelopment should therefore be viewed as the tip of a very large iceberg.”

“… research should move beyond repeated assessments of known neurotoxins to examine chemicals, whose toxicity is just beginning to be recognised. The substances listed in the panel, especially those most prevalent in food, drinking water, and the environment, should provide a useful starting point.”

“The vulnerability of the human nervous system and its special susceptibility during early development suggest that protection of the developing brain should be a paramount goal of public health protection. The high level of proof needed for chemical control legislation has resulted in a slow pace of interventions to prevent exposures to lead and other recognised hazards. Instead, exposure limits for chemicals should be set at values that recognise the unique sensitivity of pregnant women and young children, and they should aim at protecting brain development. This precautionary approach, which is now beginning to be used in the EU, would mean that early indications of a potential for a serious toxic effect, such as developmental neurotoxicity, should lead to strict regulation, which could later be relaxed, should subsequent documentation show less harm than anticipated. As physicians, we should use prudence when counselling our patients, especially pregnant mothers, about avoidance of exposures to chemicals of unknown and untested neurotoxic potential.”