Learning and Developmental Disabilities
Learning and developmental disabilities (LDDs) are estimated to affect approximately one in six children under age 18 in the U.S. These neurodevelopmental disorders appear to be rising, but more data is needed to confirm that conclusion. Intellectual disability (ID, formerly referred to as mental retardation) impacts 2%, or approximately 1.4 million, children. Attention deficit hyperactivity disorder (ADHD) is conservatively estimated to occur in 3–6%, or approximately 2 million, children. Almost 1% of 8-year-old children are diagnosed with autism spectrum disorder, a 10-fold increase over just a 15-year period. (Steven G. Gilbert, “The Scientific Consensus Statement on Environmental Agents Affiliated with Neurodevelopmental Disorders,” (Bolinas, CA: Collaborative on Health and the Environment, 2008), abstracted in Neurotoxicology and Teratology, 31, no 4, (July–August 2009): 241–2.) (National Institute of Mental Health, “NIMH’s Response to New Autism Prevalence Estimate,” http://www.nimh.nih.gov/about/director/updates/2009/nimhsresponse-to-new-autism-prevalenceestimate.shtml (November 4, 2009).) (Catherine Rice, “Prevalence of autism spectrum disorders — Autism and Developmental Disabilities Monitoring Network, United States, 2006, National Center on Birth Defects and Developmental Disabilities,” MMWR Surveillance Summaries, 58, no. SS10 (December 18, 2009): 1-20. http://www.cdc.gov/mmwr/preview/mmwrhtml/ss5810a1.htm.) About 30% of this dramatic rise in autism cannot be explained by changes in the age of diagnosis and the inclusion of milder cases. (Irva Hertz-Picciotto and Lora Delwiche, “The Rise in Autism and the Role of Age in Diagnosis,” Epidemiology, 20, no. 1 (2009): 84–90.)
These conditions impose tremendous psychological and economic costs on the affected children, their families, and communities. Just the cost of providing special education services to students with disabilities amounted to $77.3 billion in 1999–2000, an average of $12,474 per student. (Steven G. Gilbert, “The Scientific Consensus Statement on Environmental Agents Affiliated with Neurodevelopmental Disorders,” (Bolinas, California: Collaborative on Health and the Environment, 2008), abstracted in Neurotoxicology and Teratology, 31, no 4 (July–August 2009): 241–2.) According to the U.S. Centers for Disease Control and Prevention (CDC) individuals with an autism spectrum disorder have average medical expenditures that exceed those without the disorder by $4,110–$6,200 per year. (Centers for Disease Control and Prevention, “CDC Statement on Autism Data,” http://www.cdc.gov/ncbddd/autism/data.html (accessed October 10, 2009).) (Tom T. Shimabukuro, Scott D. Grosse SD, and Catherine Rice, “Medical Expenditures for Children with an Autism Spectrum Disorder in a Privately Insured Population,” Journal of Autism and Developmental Disorders, 38, no. 3 (March 2008): 546–52.) A 2006 study reported that the economic costs associated with autism in the U.S. are approximately $35 billion dollars per year. (M.L. Ganz, “The Costs of Autism,” Understanding Autism: From Basic Neuroscience to Treatment, Firtst Edition, Steven O. Molden, ed, and John Rubenstein, ed, (Boca Raton, Florida: CRC Press, 2006): 475–502.)
Chemicals, learning and developmental disabilities, and TSCA
Research on occupational exposures and epidemics of industrial chemical poisoning have led to the identification of lead, methyl-mercury, polychlorinated biphenyls (PCBs), arsenic, and toluene as known causes of neurodevelopmental disorders. Industrial chemicals have been identified in the peer reviewed scientific literature as causing neurological effects in humans, mostly through occupational exposures (see Table 2). Many of these chemicals are in common use and are produced in high volumes.
The human brain: more susceptible during development
In the years since TSCA became law, evidence has been accumulating that lead, mercury and other neurotoxic chemicals have a profound effect on the developing brain at levels that were once thought to be safe. Scientists have learned that the developing human brain is much more susceptible to toxic substances than the adult brain. Windows of unique vulnerability occur as the brain begins to develop in utero and continue through adolescence, along a precise and delicate step-bystep sequence involving various neurobiological processes. A chemical exposure at three months gestation may result in a different effect than exposure to the same chemical at six months gestation or at two years of age. If chemicals inhibit, interfere with, or halt a developmental process, the damage may be permanent. This new science suggests that industrial chemicals could be creating a pandemic of subclinical neurotoxicity— harm to the brain and nervous system that is not linked to a specific clinical diagnosis.
This new understanding of subclinical neurotoxicity also suggests that there may be a thousand or more other chemicals that can impact the developing brain, although no authoritative estimate of the true number of neurotoxicants is available. Since TSCA was enacted, very little data has been collected on the effects of chemicals on the developing nervous system. For most of the 3,000 chemicals produced in highest volume (over one million pounds per year), only 12 have been adequately tested for neurotoxicity. To ensure healthy brain development for future generations, TSCA must be updated to require that all existing and new chemicals are tested and shown to be safe for pregnant women, children, workers, and other vulnerable populations. (This entire section is informed by the article “Developmental Neurotoxicity of Industrial Chemicals,” by P. Grandjean and P.J. Landrigan, published in the journal Lancet, 368, no. 9553 (December 16, 2006): 2167–78.)
In the years since TSCA became law, evidence has been accumulating that lead, mercury and other neurotoxic chemicals have a profound effect on the developing brain at levels that were once thought to be safe.
