Blood Lead Levels and Children's Disabilities
Sam Goldstein, Ph.D.
Copyright © 2007
Joel Nigg, author of the comprehensive volume, What Causes ADHD? (Guilford, 2007), will soon publish research suggesting that very low levels of lead in the blood, levels previously believed to be safe, could be contributing to the incidence of ADHD. Nigg, a professor at Michigan State University, studied 150 children in the Lansing, Michigan community finding that all of them had at least some lead in their blood but none had levels higher than 10 micrograms per deciliter, the level currently considered unsafe by the Centers for Disease Control and Prevention. The safe level for lead in the blood was lowered from 25 micrograms per deciliter to 10 in 1991. Children with ADHD had higher levels of lead in the blood than those without the disorder according to Nigg's study conducted with the cooperation of the Michigan Department of Community Health. This research supports a growing body of evidence indicating that there is no safe level of lead in the blood. Nigg's study will continue for a number of years. His findings will appear in print in mid-February in the Journal of Biological Psychiatry.
In this month's issue of the Journal of Attention Disorders, of which I serve as Editor-in-Chief, Dr. Rudolf Bustos of Webster University and myself, author an Editorial advocating for the inclusion of the assessment of blood lead levels of all immigrant children when evaluating for ADHD. Dr. Nigg's research, if replicated and substantiated over time, provides a strong foundation for screening blood lead levels (BLL) in all at risk children evaluated for ADHD. In this article I will briefly review the literature on lead exposure in particular for immigrant children and advocate for lead screening, for this population.
As a trace element, lead has no known use in the human body. Ingested flakes of lead paint can poison the energy production within brain cells. As the brain becomes more and more swollen, general brain function decreases and thinking becomes confused. Convulsions can occur and swelling can progress to brain injury and ultimate death. Nigg's studies and others demonstrate a correlational relationship between lead and development. But is there a cause and effect relationship? Can lead intoxication too mild to produce brain swelling and convulsions cause ADHD or other developmental conditions? In the last forty years, researchers have in fact demonstrated that the very low blood lead levels, those that may have no initial clinical symptoms, do in fact adversely impact intelligence, motor coordination and behavior in children. The findings of these studies suggest there may be a group of children with ADHD or other developmental conditions that at least in part are the result of lead exposure. How much of the behavior, developmental problems and symptoms of conditions like ADHD is caused by other differences (e.g., genetic influences, environment, etc.) is still yet to be completely determined. The significant correlation between blood and dentine lead levels on the one hand and full scale I.Q., verbal and auditory processing reaction time and behavioral ratings on the other suggest that lead, as Nigg's study again points out, may be a contributor to ADHD symptoms. However, there is a large body of research demonstrating that ADHD is a strongly inherited condition with genetics contributing to the majority of risk that a child will receive a diagnosis of ADHD.
The dangers of lead to the human brain have been well recognized for nearly half a century. The reported incidence of severe lead poisoning in children appears to be decreasing. The generally low incidence of elevated blood lead levels in most children referred for developmental problems including ADHD over the past twenty years has eliminated the routine use of blood or dentine lead screening as part of developmental assessments. However, in certain subgroups of our childhood population, particularly children of immigrants, the incidence of elevated blood lead levels continues to appear at an alarming level. Current Federal Guidelines appear inadequate in addressing this problem.
A large and growing body of evidence indicates that children are more sensitive to the neurotoxic effects of lead than are adults. As evidenced by levels of retained lead in mineralized tissue, children retain more lead in soft tissue than do adults—about 5 to 10 times greater and no BLL should be recognized as safe. Children between two and four years old are most likely to suffer from elevated BLL. Despite these scientific advances, a number of current studies demonstrate that we have failed to consider the risks of lead poisoning in refugees and other immigrant children coming from third world and underdeveloped countries. For example, "State and local surveillance data and previous …analyses indicate children who are … Hispanic are more likely to have elevated BLL than those who are non-Hispanic whites" (Meyer et al., 2003, p. 20). "From 1999 through September 30, 2004, 81% of the [Sonoma County, CA] county's children (age 0-20) with reported high blood lead levels (>20 :g/dL) were Hispanic" (Sonoma County Health Profile, p. 35).
In 2004, the New York City Lead Poisoning Prevention Program reported 33% of children with BLL (>20 :g/dL) were Hispanic. In Miami Beach, Florida, 55% of Hispanic homes exceeded EPA's lead standards. In San Bernardino County, California, 65% of lead poisoned children are Hispanic. Finally, in 2002, 77% of children diagnosed with lead poisoning in Arizona were Hispanic (Quintero-Somaini & Quirindongo, 2004).
Because a child's chronic exposure to low lead levels can cause developmental and neurological anomalies that may be problematic to detect through routine physical examination, blood lead screenings become essential. All children are considered at risk and must be screened for lead poisoning as part of required prevention services offered through the Early and Periodic Screening, Diagnosis and Treatment Program (EPSDT). "Children between the ages of 36 months and 72 months of age must receive a screening blood lead test if they have not been previously screened for lead poisoning. A blood lead test must be used when screening Medicaid-eligible children" (Medicaid and EPSDT, 2005, p. 2).
Although initial BLL tests are performed for Medicaid-eligible children, about half the children with elevated BLL do not receive any follow-up. Kemper et al. (2005) performed a retrospective, observational cohort study of 3,682 Michigan Medicaid-enrolled children six years or younger who had a screening blood lead level of at least 10 :g/dL (0.48 :mol/L) between January 1, 2002 and June 30, 2003. The findings indicate that follow-up testing was "received by 53.9% of the children. Among children who did not have follow-up testing, 58.6% had one medical encounter in the six-month period after the elevated screening blood lead level, including encounters for evaluation and management or preventive care" (p. 2237).
The prevalence of elevated BLL among newly arrived refugee children is significantly higher than the 2.2% prevalence of U.S. children (CDC recommendations, refugee children, 2005). Therefore, Federal guidelines include a medical screening within 90 days after a refugee's arrival in the United States. However, "most states do not have a BLL screening protocol for refugee children and that lead program surveillance data cannot identify which children are refugees" (p.2). However, it is difficult if not impossible to assess the children of illegal aliens entering the United States.
Evaluators must not only cautiously interpret the results of intellectual, academic and developmental testing due to English as a second language in immigrant children but also consider the possibility that the contributing etiology for many developmental problems, including those symptomatically related to ADHD may be lead or other forms of toxic poisoning. The deleterious effects of even modest BLL to learning, behavior, intellectual development, memory, attention and motor coordination is undeniable. Hispanic and other immigrant children coming to America legally or illegally, often leave environments poisoned by lead. Though Federal Guidelines exist mandating assessment, many states appear to be inconsistent in screening children for lead. As researchers and professionals we must recognize that elevated BLL is not a thing of the past and advocate for broader community awareness and screening. Immigrant children should be carefully evaluated to ensure they receive appropriate diagnosis and care for this almost common condition. It is critical that schools in partnership with community agencies initiate preventive, diagnostic and management measures in accordance with the Center for Disease Control guidelines. Educators, medical and mental health professionals, should become knowledgeable about the behavioral and developmental impacts of lead exposure. Finally, upon entering school, all children with histories of possible lead exposure, in particular immigrants should be screened for BLL.
It is still difficult to know what should be done as the result of these studies. It would appear that no level of lead in the blood should be considered safe relative to the potential for even mild impairments in development and behavior. This will require a continued and aggressive policy to find and eradicate sources of lead in the environment, including paint and water pipes. Unfortunately at this time, however, there is no evidence that treatment for lead poisoning will improve the performance of affected children. In addition, the data from these group studies is simply not sufficiently powerful to argue that blood or dentine lead levels can be used to help diagnose ADHD.
References
Byers, R. K. (1959). Lead poisoning: Review and report of 45 cases. Pediatrics, 23, 585.
CDC recommendations for lead poisoning prevention in newly arrived refugee children. (2005). Atlanta, GA: Centers for Disease Control and Prevention.
Kemper, Alex R., Cohn, Lisa M., Fant, Kathryn E., Dombkowski, Kevin J., Hudson, Sharon R. (2005). Follow-up testing among children with elevated screen blood lead levels. Journal of the American Medical Association, 293(18), 2232-2237.
Medicaid and EPSDT. (2005). Baltimore, MD: Centers for Medicare & Medicaid Services: US Department of Health and Human Services.
Meyer, P. A., Pivetz, T., Dignam, T. A., Homa, D. M., Schoonover, J., & Brody, D. (2003). Surveillance for elevated blood lead levels among children: United States, 1997--2001. Atlanta, GA: Centers for Disease Control and Prevention.
Needleman, H. L., Gunnoe, C., Leviton, A., Reed, R., Peresie, H., Maher, C., & Barrett, P. (1979). Deficits in psychologic and classroom performance of children with elevated dentine lead levels. New England Journal of Medicine, 300, 689-695.
Quintero-Somaini, A., & Quirindongo, M. (2004). Hidden dangers: Environmental health threats in the Latino community. New York, NY: Natural Resources Defense Council.
Sonoma County Health Profile (2005). Santa Rosa, CA: Sonoma County Department of Health Services.
