Neurodevelopmental Disorders

Genetic, environmental, and social factors all play a critical role in normal neurological development. These factors can interact in complex ways. Brain development begins in utero and continues into adolescence through a complex array of biological processes (Rice, Barone 2000). During this development, there are critical windows of vulnerability in which exposure to environmental toxicants can be particularly debilitating. Timing, pattern, and level of exposure are all key factors in determining potential neurological effects (GBPSR 2000). Given the right combination of events, exposures during childhood to even small amounts of toxicants can cause lasting effects on brain development.

Twenty five million pounds of neurotoxic chemicals were released to Michigan’s air in 2002 alone (Scorecard, 2011). Eighteen million pounds of developmental toxicants were also released to the air in Michigan that year (Scorecard, 2011). Both human and animal studies show that exposure to certain chemicals can contribute to neurological disorders, including developmental, learning, and behavioral disabilities. Many of the chemicals with demonstrated links to neurodevelopmental disorders are commonly encountered in homes and schools. Recent research makes it clear that, at least in some cases, there may be no “safe” levels of exposure to neurotoxicants.

The U.S. Environmental Protection Agency (EPA) estimates that up to 28% of the 80,000 registered chemicals in the United States, including more than 2,800 high production volume chemicals, have the potential to be neurotoxic (GBPSR, 2000). Despite this, the EPA has completed a full battery of neurotoxicity tests for only 12 chemicals (see Figure 1). Many common environmental pollutants such as lead, mercury, pesticides, PCBs, dioxins, and PBDEs, have been linked to neurodevelopmental harm (GBPSR 2000).

Figure 1. Status of Developmental Toxicity Testing for the 2,863 Chemicals Produced Above One Million Pounds per Year in the U.S. (GBPSR, 2000).

Approximately 12 million children in the U.S. suffer from some type of developmental, behavioral, or learning disability (GBPSR 2000). It has been estimated that the lifetime prevalence of learning disabilities in U.S. children is 9.7%, and that learning disabilities affect nearly 3 million U.S. children. Learning disabilities include varying difficulties (or combinations of difficulties) with skills related to listening, speaking, reading, writing, reasoning, mathematics, foreign languages, spatial adaptation, and/or memorization. Such disabilities have been associated with a complex array of factors that include education, gender, income level, age, family structure, family social environment, and other environmental influences such as household smoking nutrition status, exposure to toxicants, air quality, and exercise (Altarac, Saroha 2007; Mayron 1978).

Of the 1.7 million children in Michigan school system (based on 2006 data), 249,000 (14.4%) were in special education. It is estimated that the cost of providing special education services is approximately 12,000/child/year. This amounts to 2.7 billion/year in Michigan (Weil 2007).

The Michigan Network for Children’s Environmental Health, in a report released in 2010, estimated that the environmentally attributable cost of lead poisoning, asthma, cancer, and select neurobehavioral disorders in Michigan’s children is roughly $5.8 billion annually. Lead poisoning contributes the majority of this cost at $4.85 billion, followed by neurobehavioral disorders at $845 million (range $423 million-1.69 billion) (Glaser et al. 2010). The national estimate for these disorders based on a recently published review is $76.6 billion per year (Trasande, 2011). This data comes from an updated and expanded analysis of the national costs of lead poisoning, prenatal methylmercury exposure, childhood cancer, asthma, intellectual disability, autism, and attention deficit hyperactivity disorder. The authors of that update note: “ to prevent further increases in these costs, efforts are needed to institute premarket testing of new chemicals; conduct toxicity testing on chemicals already in use; reduce lead-based paint hazards; and curb mercury emissions from coal-fired power plants.”

Although scientific evidence demonstrates clear associations between many neurotoxic chemicals and health impacts in children, much remains to be learned. One project that will augment the scientific knowledge is the National Children’s Study (NCS) – a prospective cohort study that will follow 100,000 children from birth to age 21 in part to examine the effects of environmental influences on health and development. Michigan will host five NCS sites: Genesee County, Grand Traverse County, Lenawee County, Macomb County, and Wayne County. A major focus of the study will be neurodevelopment and behavior. The NCS will provide a reservoir of information about children’s health and development and will inform child health guidance, interventions, and public policy for generations to come (NCS 2007).

While there is clearly a need for additional research, there is also an immediate need to take steps now to prevent childhood exposure to neurotoxicants based on available evidence. The weight of scientific evidence supports the need for immediate action to prevent children’s exposure to environmental neurotoxicants wherever possible. Protecting children from potentially harmful exposures requires effective, comprehensive policies (GBPSR 2000). This chapter will examine potential exposures, health effects, and related state policies associated with seven categories of environmental chemicals that have been linked to neurodevelopmental effects: pesticides, mercury, PBDEs, PCBs, dioxins, lead, and environmental tobacco smoke (ETS).

Each section of this chapter will introduce the sources of exposure and evidence of neurotoxicity associated with the chemical group of interest. Data will be presented on potential childhood exposures to the chemical, both nationwide and in Michigan. State policies related to the toxicants will then be analyzed and compared to best practices in other states for effectiveness in protecting children’s health. Lastly, recommendations will be made to further protect Michigan’s children from exposure to these neurotoxicants.

Neurotoxicants

• Pesticides
• Mercury
• PBDEs
• PCBs
• Dioxins
• Lead
• Second Hand Smoke
• Arsenic

References

Altarac M, Saroha E. 2007. Lifetime prevalence of learning disability among US children. Pediatrics 119:S77-S83. Glaser, A, et al. The Price of Pollution: Cost estimates of environmentally-related childhood disease in Michigan. Michigan Network for Children’s Environmental Health (MNCEH). 2010

Greater Boston Physicians for Social Responsibility (GBPSR). Schettler T, Stein J, Reich F, Valenti M, Wallinga D. In Harm’s Way: Toxic Threats to Child Development. May 2000.

Landrigan P, Schechter C, Lipton J, Fahs M, Schwartz J. 2002. Environmental Pollutants and Disease in American Children: Estimates of Morbidity, Mortality, and Costs for Lead Poisoning, Asthma, Cancer, and Developmental Disabilities. Environmental Health Perspectives 110:721–728.

Mackinac Center for Public Policy. 2007. Michigan Education Report. http://www.educationreport.org/images.aspx?ID=3218.

Mayron LW. 1978. Ecological factors in learning disabilities. Journal of Learning Disabilities. 11(8):495-505.

National Children’s Study (NCS). National Children’s Study Research Plan. 2007. http://www.nationalchildrensstudy.gov/research/research_plan/Appendices.cfm.

Rice D, Barone S. 2000. Critical periods of vulnerability for the developing nervous system: evidence from humans and animal models. Environmental Health Perspectives 108(3):511-533.

Scorecard: The pollution information site. 2011. Environmental Release Report: Michgan. http://scorecard.goodguide.com/env-releases/state.tcl?fips_state_code=26#pollution_rank_health_impact

Trasande, Leo, Liu Y. 2011. Reducing the staggering costs of environmental disease in children, estimated at $76.6 billion in 2008. Health Aff (Millwood). 2011 May;30(5):863-70. Epub 2011 May 4.

Weil, William. Email to Genevieve Howe. April 24, 2007