The Flint Lead Crisis
The multiple tragedies that have attended the knowledge that large amounts of lead contaminates the water supply for Flint, Michigan, have refocused national attention on the toxin that was forgotten, but not gone. The modern focus on lead gained momentum in the 1970s with the establishment of the EPA and passage of amendments to the Clean Air Act.
As a result, lead was identified as one of six criteria pollutants and ambient air quality standards were established. This lead to a ban on the use of lead in paint designed for use in housing in 1978 and a phase out of leaded gasoline. Paint dust and paint chips remain an important source for exposure to this toxic metal. Lead pipes also pose a threat, as exemplified by the Flint problem. These pipes may be in the municipal water system, in the supply lines that bring water from water mains to homes, or in homes themselves. States, with the exception of Wyoming and the District of Columbia, have the primary responsibility for assuring safe municipal water supplies. The Navajo Nation is the only tribe to have sought this primacy. Periodic reports are typically published by various water systems. Since the safety of municipal water systems can’t be assured once water leaves the water mains, individual consumers may wish to seek the aid of Health Departments for guidance.
Evidence for lead poisoning dates back to early Romans. Lead is not required for any biochemical or physiological process in humans. There is no known level of lead in the body that is demonstrably safe. This metal has adverse effects on virtually every organ system, including the heart, kidneys, the reproductive organs, and others. However, its effects on the nervous system are typically the most worrisome. Detailed information about the effects of low blood lead concentrations on cognition began to emerge after a landmark study of lead levels in 3,221 dentine samples from the teeth of children. After controlling for 39 other variables, high lead levels were associated with intellectual deficits measured by the Wechsler Intelligence Scale for Children (Revised), on the verbal subtest and other measures of speech and auditory function along with reports by teachers of increasingly maladaptive behavior among the high lead children.(1) Subsequent studies have paradoxically shown that the impact of lead was higher among the 101 children whose lifetime average blood lead level was below 10 μg/dL than it was in the entire sample of 172 children.(2) As a result of these and other studies, the CDC set the reference value for lead at 5 μg/dL (based on the 97.5th percentile based on all children aged 1 - 5 - not on safety concerns). Stupor, coma, and death are complications of very high lead levels.
Herbert Needleman, MD on porch shedding lead paint chips
The effects of lead on brain function persist into adulthood. Workers with occupational exposure to lead who had elevated bone lead levels have a significantly poorer performance neuropsychological tests than controls.(3) Similar effects on cognition were found in another community-based study of almost 1000 adults age 50 - 70.(4) Brain MRI scans in these subjects revealed significant reductions in several measures of brain volume, including the frontal lobe a region of the brain responsible in part for impulse control.(5) Subsequent studies have linked lead exposure to criminal behavior in adolescents and young adults - thought to be closely related to educational underachievement.(6) Thus the legacy of early-life lead exposure appears to persist for life and has an adverse impact on society as a whole as well as the exposed individual.
Flint is but the tip of the iceberg. According to data from the Michigan Department of Health 5,702 children less than 6 years of age had blood lead levels above 5 μg/dL in 2013.(7) Since only around 20% of the children were tested statewide, the actual number of children with high levels is much higher. Nationwide, according to the CDC, just under 2.4 million children less than 6 years of age, about 10% of the total population, were tested in 2014. Of that number 105,966 had confirmed lead levels of 5 μg/dL or more.(8) Thus nationwide the total number exceeding the reference value is likely to be close to one million. The lead burden is unevenly divided. A second CDC report covering the years 2007 - 2010 shows that children 1 - 2 are more likely to have elevated blood levels (3.1% and 2.3%, respectively) and that 1.9% of Mexican Americans, 2.4% of non-Hispanic Whites, and 5.6% of non-Hispanic Blacks have elevated blood lead levels.(9) In addition, the poorer one is, the more likely one is to have elevated blood lead levels. Housing built prior to 1950 is more likely to be home to individuals with elevated lead levels than newer homes (0.4% verus 5.3%).
Although lead can be removed from affected individuals using chelation therapy, this treatment is complicated to administer and is of limited effectiveness because of the large amounts of lead that are typically present in bone that act as a reservoir. Chelation is usually reserved for patients with the most severe manifestations of lead poisoning. As with most public health problems, prevention is essential. Keeping children from ingesting lead paint dust and paint chips is the most important of various preventive measures.
The Flint lead crisis, caused by re-routing the city’s water supply to a source that leached lead from pipes, is but one example of a continuing epidemic of lead poisoning in America. In spite of the removal of lead from gasoline and household paint, the epidemic persists. It is an important public health and environmental justice issue.
1. Needleman HL, Gunnoe C, Leviton A et al. Deficits in psychologic and classroom performance of children with elevated dentine lead levels.[erratum appears in N Engl J Med. 1994 Sep 1;331(9):616-7; PMID: 8047098]. New Engl J Med 1979;300(13):689-695.
2. Canfield RL, Henderson CR, Jr., Cory-Slechta DA, Cox C, Jusko TA, Lanphear BP. Intellectual impairment in children with blood lead concentrations below 10 microg per deciliter. N Engl J Med 2003;348(16):1517-1526.
3. Schwartz BS, Stewart WF, Bolla KI et al. Past adult lead exposure is associated with longitudinal decline in cognitive function. Neurology 2000;55(8):1144-1150.
4. Shih RA, Glass TA, Bandeen-Roche K et al. Environmental lead exposure and cognitive function in community-dwelling older adults. Neurology 2006;67(9):1556-1562.
5. Stewart WF, Schwartz BS, Davatzikos C et al. Past adult lead exposure is linked to neurodegeneration measured by brain MRI. Neurology 2006;66(10):1476-1484.
6. Fergusson DM, Boden JM, Horwood LJ. Dentine lead levels in childhood and criminal behaviour in late adolescence and early adulthood. Journal of epidemiology and community health 2008;62(12):1045-1050.
7. Michigan Department of Health and Human Services. 2013 Data Report on Childhood Lead Testing and Elevated Levels. 2014
8. Centers for Disease Control and Prevention. CDC's National Surveillance Data (1997 - 2014). 2014
9. Centers for Disease Control and Prevention. Blood Lead Levels in Children Aged 1–5 Years — United States, 1999–2010. 2013