Learning disabilities and related attention deficit disorders affect an estimated 10% to 15% of children. The consequences of these and other neurological, developmental and behavioural disorders are life-long, often serious for both the child and his or her family, and costly for society. The role of toxic chemicals in the etiologies of these disorders has been largely ignored, although the evidence from both experimental animal and clinical research from the few neurotoxic chemicals that have been studied to date is compelling (1), and the possibilities for prevention are enormous. An example of the costs of subtle deficits due to exposure to lead was demonstrated in a groundbreaking economic benefits analysis by Schwartz (1994) (2) based on calculations of the costs of lead-related reductions in intelligence quotient on years of schooling and earnings, and cardiovascular effects. The societal benefits of reducing blood lead concentrations in the population by just 1 μg/dL were estimated at $17.2 billion/year to the American economy. Schwartz (2) noted that these benefit estimates are low, as other known effects of lead – on behaviour, attention, hearing, balance and reduced stature – have not been assigned a monetary value (2). This benefit was revised upward in a subsequent economic analysis (3), based primarily on labour market changes and more recent data on the relationship of intelligence quotient with educational attainment and projected earnings gains. Worldwide, there is growing attention to the differential vulnerability of children to environmental toxicants. Since the mid 1990s, increasing concern, legislation and policy initiatives in the United States, and a joint declaration (4) have brought children’s health and development into the forefront of the environmental agenda. Canada signed the 1997 Declaration of the Environmental Leaders of the Eight on Children’s Environmental Health that pledged action on the following issues: risk assessment and standard-setting that take into account the specific exposure pathways and dose-response characteristics of children; children’s exposures to lead; clean water and water standards; air quality (including environmental tobacco smoke); and emerging threats to children’s health from endocrine-disrupting chemicals (such as polychlorinated biphenyls and dioxins that have been shown to have neurotoxic effects, and to alter thyroid function). Thyroid hormone is critical to most processes involved in brain development – regulating neurite outgrowth, cellular migration, synaptogenesis, myelogenesis and the development of major neurotransmitter systems (5). Despite the above pledges, the effects of toxic exposures on child health and development are receiving little attention in Canada in research or by other federal programs investigating the determinants of health and development. In addition, there are gaps in regulatory programs and policies that need to be revised to protect children. By contrast, a 1997 executive order from the White House (6) acknowledged that children may suffer disproportionately from environmental health risks, and directed all American federal regulatory agencies to ensure that their policies, programs and standards address these risks. The executive order also established a high level interagency task force to recommend federal strategies and research. The above actions have generated a number of new initiatives in the United States: eight centres for children’s environmental health and disease prevention research, and announced this year, an additional four more centres on neurodevelopmental effects; a new Office of Children’s Health Protection at the Environmental Protection Agency (EPA); and a major proposed study, A Prospective Longitudinal Study of Environmental Effects on Children’s Development, that will involve thousands of pregnancies from American intake sites. The need for new approaches to government standard-setting and premarket safety evaluations to protect children was addressed in a five-year United States National Academy of Sciences (NAS) report, Pesticides in the Diets of Infants and Children (1993) (7). Among other findings, the report stated: “The data strongly suggest that exposure to neurotoxic compounds at levels believed to be safe for adults could result in permanent loss of brain function if it occurred during the prenatal and early childhood period of brain development”. Many toxic agents are known to damage the developing, and unprotected, brain by interfering with those processes undergoing development at the time of the exposure (Rodier, 1995) (8). It is clear that even subtle structural or neurochemical defects can nonetheless have devastating functional consequences.
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Aug 1, 2002
George A Warne + 14
