The crisis in Flint, Michigan over sustained exposure to lead and other toxins from the city’s water supply has many people concerned about lead poisoning and its long-term health effects. According to the World Health Organization, lead exposure accounts for an estimated 143,000 deaths a year, with developing countries facing the greatest burden. In the United States, the percentage of children experiencing high levels of lead exposure has declined substantially since 1997, with the number of confirmed cases falling from approximately 125,000 to nearly 13,000 in 2014. Despite these reductions, lead exposure remains a critical public health issue given its widespread damaging effects.
Lead exposure harms every organ system in the body, but the most serious damage occurs in the central nervous system. According to the U.S. Centers for Disease Control and Prevention (CDC), high blood lead levels in adults (40 µg/dL to 120 µg/dL) are associated with a wide array of acute neurological and behavioral consequences, including fatigue, dizziness, depression, paralysis, impotence and slowed nerve conduction. The neurological effects of lead exposure are irreversible and, in the long term, lead also has been implicated in the development of renal diseases, anemia, depleted Vitamin D levels and persistent gastrointestinal pain as well as hypertension. Additionally, since lead becomes stored in the body through teeth and bones, lead poisoning among pregnant women may expose growing fetuses to lead as it remobilizes into the blood and crosses the placenta.
Children are a particularly vulnerable population with respect to lead exposure because the developing brain is more susceptible to its effects than the adult brain. Also, children may come into more frequent contact with lead via hand-to-mouth exposure with lead-contaminated soil, house dust or toys. At high blood lead levels (70 µg/dL to 80 µg/dL), children may show signs of encephalopathy, a disease that can alter the function and structure of the brain. In extreme cases, it can result in convulsions, coma or even death. In its early stages, high levels of lead exposure in children can cause lethargy, stomach cramps and irritability but can progress rapidly into more severe symptoms, including vomiting, clumsiness and seizures. Perhaps more concerning than extreme cases of lead poisoning are lower blood lead levels in children, which cause little to no outward physical ailments but are associated with enduring neurological and behavioral effects. Even in cases of very low lead exposures, neurodevelopmental deficits have been observed, leading scientists to conclude that no level of lead exposure is safe for children. For example, a 2000 report from researchers at Children’s Hospital Medical Center in Cincinnati estimates that as the blood lead level increases from 1 µg/dL to 10 μg/dL, children’s IQ may drop anywhere from 3.9 to 7.4 points.
A substantial body of research has explored the damaging effects of lead exposure in childhood. Deficits in intellectual functioning, academic performance, problem solving skills, motor skills, memory and executive functioning are consistently observed in lead-exposed children, in addition to an increased likelihood of experiencing ADHD and having conduct problems in childhood, and decreased brain volume in adulthood. Because lead exposure has been linked with altered executive functioning and impulse control, researchers have also begun to explore links between childhood lead exposure and different risky behaviors in adulthood, including criminal activity, substance use and sexually transmitted infections.
In light of the damaging effects of lead, in 2012 the CDC lowered the threshold of concern from blood lead levels of 10 µg/dL to 5 µg/dL for both children and adults. Based on the new threshold, an estimated 535,000 U.S. children between the ages of 1 and 5 experienced elevated blood lead levels in 2010. Although these numbers represent a substantial decline compared to population rates in the 1970s, racial and socioeconomic disparities still persist, with minority children and children in low-income families experiencing higher average blood lead levels, likely due to differences in living conditions, housing and nutrition. Because calcium decreases lead absorption in the body, malnourished children face a greater burden of disease. Eliminating racial and class disparities in lead exposure is a CDC priority.
Because there is no way to reverse the harmful effects of lead, pediatricians emphasize prevention strategies and minimizing or eliminating environmental exposure. Historically, lead exposure has come from multiple sources, including manufacturing, lead paint, leaded gasoline and lead pipes used for drinking water. Cities with industrial histories — Baltimore, Cincinnati, and Chicago, for example — have long histories of exposure to lead in the air, soil and water. Although the emergency in Flint has brought national attention to lead in drinking water, lead-based paint and lead-contaminated dust are the most hazardous sources of lead in the U.S. In 1978, lead was banned in paint and other consumer goods made and sold in this country. Despite significant reductions in levels of lead in the environment, approximately 24 million housing units in the U.S. have deteriorated leaded paint and elevated levels of lead-contaminated house dust. According to the CDC, “at least 4 million households have children living in them that are being exposed to high levels of lead.”
Below are a series of studies to help journalists understand how lead impacts adults and children in an array of areas and the implications for policymakers:
Neurocognitive and behavioral effects on children
“Pb Neurotoxicity: Neuropsychological Effects of Lead Toxicity”
Mason, L.H.; Harp, J.P.; Han, D.Y. BioMed Research International, 2014. doi: dx.doi.org/10.1155/2014/840547.
Summary: “Lead exposure is one of the most common exposures that can lead to significant neuropsychological and functional decline in humans. In this review, neurotoxic lead exposure’s pathophysiology, etiology, and epidemiology are explored. In addition, commonly associated neuropsychological difficulties in intelligence, memory, executive functioning, attention, processing speed, language, visuospatial skills, motor skills, and affect/mood are explored.”
“Blood Lead Exposure and Academic Achievement: Evidence from Detroit Public Schools, 2008-2010”
Zhang, N.; et al. American Journal of Public Health, March 2013, Vol. 103(3). doi: 10.2105/AJPH.2012.301164.
Summary: Researchers assessed the long-term impact of early childhood exposure to lead on performance in math, science and reading among elementary and junior high school students using surveillance data from the Detroit Department of Health and Wellness Performance, as well as testing data from Detroit Public Schools. Analyses found that high blood level in early childhood was strongly associated with poorer academic outcomes for children in grades 3, 5 and 8. The authors conclude that, “the control of lead poisoning should focus on primary prevention of lead exposure in children and development of special education programs for students with lead poisoning.”
“Childhood Lead Exposure and Educational Outcomes”
National Center for Healthy Housing, 2008.
Summary: This issue brief from the National Center for Healthy Housing provides recent research on the dangers posed by low-level lead exposure and the resulting financial and social costs. The report shows that lead exposure occurs more frequently in low-income children and children of color and is an important factor in the educational achievement gap between children of different racial and income groups.
“Low-Level Environmental Lead Exposure and Children’s Intellectual Function: An International Pooled Analysis”
Lanphear, B.P.; et al. Environmental Health Perspectives, July 2005, Vol. 113(7). doi: 10.1289/ehp.7688.
Abstract: “The objective of this study was to examine the association of intelligence test scores and blood lead concentration, especially for children who had maximal measured blood lead levels < 10 μg/dL. We examined data collected from 1,333 children who participated in seven international population-based longitudinal cohort studies, followed from birth or infancy until 5–10 years of age. The full-scale IQ score was the primary outcome measure. The geometric mean blood lead concentration of the children peaked at 17.8 μg/dL and declined to 9.4 μg/dL by 5–7 years of age; 244 (18%) children had a maximal blood lead concentration < 10 μg/dL, and 103 (8%) had a maximal blood lead concentration < 7.5 μg/dL. After adjustment for covariates, we found an inverse relationship between blood lead concentration and IQ score. Using a log-linear model, we found a 6.9 IQ point decrement [95% confidence interval (CI), 4.2–9.4] associated with an increase in concurrent blood lead levels from 2.4 to 30 μg/dL. The estimated IQ point decrements associated with an increase in blood lead from 2.4 to 10 μg/dL, 10 to 20 μg/dL, and 20 to 30 μg/dL were 3.9 (95% CI, 2.4–5.3), 1.9 (95% CI, 1.2–2.6), and 1.1 (95% CI, 0.7–1.5), respectively. For a given increase in blood lead, the lead-associated intellectual decrement for children with a maximal blood lead level < 7.5 μg/dL was significantly greater than that observed for those with a maximal blood lead level ≥7.5 μg/dL (p = 0.015). We conclude that environmental lead exposure in children who have maximal blood lead levels < 7.5 μg/dL is associated with intellectual deficits.”
“Lead and Attention-Deficit/Hyperactivity Disorder (ADHD) Symptoms: A Meta-Analysis”
Goodlad, J.K.; Marcus, D.K.; Fulton, J.J. Clinical Psychology Review, April 2013, Vol. 33(3). doi: 10.1016/j.cpr.2013.01.009.
Abstract: “This meta-analysis examined the association between Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms and lead exposure in children and adolescents. Thirty-three studies published between 1972 and 2010 involving 10,232 children and adolescents were included. There was a small to medium association between inattention symptoms and lead exposure (r=.16, k=27, p<.001) and a similar association between hyperactivity/impulsivity symptoms and lead exposure (r=.13, k=23, p<.001). There was significant heterogeneity among the effect sizes for both inattention symptoms and for hyperactivity/impulsivity symptoms, with studies using hair analysis to assess lead burden yielding substantially larger effect sizes than those using other methods. Excluding the hair analysis studies, the average rs were 0.14 for inattention (k=23, p<.001) and 0.12 for hyperactivity/impulsivity (k=21, p<.001). Overall, the relation between lead exposure and ADHD symptoms was similar in magnitude to the relation between lead exposure and decreased IQ and between lead exposure and conduct problems.”
“Lead and Conduct Problems: A Meta-Analysis”
Marcus, D.K.; Fulton, J.J.; Clarke, E.J. Journal of Clinical Child and Adolescent Psychology, 2010, Vol. 39(2). doi: 10.1080/15374411003591455.
Abstract: “This meta-analysis examined the association between conduct problems and lead exposure. Nineteen studies on 8,561 children and adolescents were included. The average r across all 19 studies was 0.19 (p < .001), which is considered a medium effect size. Studies that assessed lead exposure using hair element analysis yielded considerably larger effect sizes than those that assessed lead exposure using blood, tooth, or bone lead levels. Excluding the 3 hair analysis studies, the average r was 0.15 (p < .001). The age of the participants did not significantly moderate the relation between lead exposure and conduct problems. Overall, the relation between lead exposure and conduct problems was strikingly similar in magnitude to the relation between lead exposure and decreased IQ.”
Long-term health effects from childhood exposure
“Decreased Brain Volume in Adults with Childhood Lead Exposure”
Cecil, K.M.; et al. PLoS Medicine, May 2008, Vol. 5(5). doi: 10.1371/journal.pmed.0050112.
Summary: Researchers conducted whole brain MRI scans on 157 young adults (average age 20) who grew up in neighborhoods in Cincinnati with historically high rates of child lead poisoning to study the relationship between childhood blood lead concentration and brain volume approximately 20 years later. Findings showed that “childhood lead exposure is associated with region-specific reductions in adult gray matter volume, [affecting the] prefrontal cortex and regions of the brain responsible for executive functions, mood regulation, and decision-making.”
“Associations Between Blood Lead Level and Substance Use and Sexually Transmitted Infection Risk Among Adults in the United States”
Hu, H.; Scheidell, J.; Xu, X.; Coatsworth, A.M.; Khan, M.R. Environmental Research, November 2014, Vol. 135. doi: 10.1016/j.envres.2014.05.037.
Abstract: “Using the National Health and Nutrition Examination Survey (NHANES) 2005–2010, we estimated multivariable logistic regression models to measure odds ratios (ORs) and 95 percent confidence intervals (CIs) for the cross-sectional associations between blood lead level and risk behaviors including binge drinking, drug use, and indicator of sexually transmitted infection (STI) risk. STI indicators included past 12 month sexual risk behaviors (age mixing with partners who were at least five years younger or older and multiple partnerships), self-reported STI, and biologically-confirmed herpes simplex virus type 2 (HSV-2) infection. Dose–response like relationships were observed between blood lead and substance use, age mixing with younger and older partners, self-reported STI, and HSV-2. In addition, participants with lead levels in highest quartile versus those with levels in the lowest quartile had over three times the odds of binge drinking and over twice the odds of injection drug or cocaine use in the past 12 months, while being in one of the top two quartiles was significantly associated with 30–70 percent increased odds of multiple partnerships, sex with older partners, and self-reported and biologically confirmed STI.”
“Association of Prenatal and Childhood Blood Lead Concentrations with Criminal Arrests in Early Adulthood”
Wright, J.P.; et al. PLoS Medicine, May 2008. doi:10.1371/journal.pmed.0050101.
Summary: Using data from county criminal justice records, researchers assessed associations between both prenatal maternal and childhood lead concentrations and arrests among 376 children living in neighborhoods with historically high rates of childhood lead exposure in Cincinnati. Findings showed that “arrest rates were greater for each 5 μg/dl (0.24 μmol/l) increase in blood lead concentration: RR = 1.40 (95% confidence interval [CI] 1.07–1.85) for prenatal blood lead, 1.07 (95% CI 0.88–1.29) for average childhood blood lead, and 1.27 (95% CI 1.03–1.57) for 6-year blood lead.” Additionally, lead exposure was also associated with higher rates of violent crimes.
Health impact on adult populations
“Altered Executive Function in the Lead-Exposed Brain: A Functional Magnetic Resonance Imaging Study”
Seo, J.; et al. Neurotoxicology, September 2015, Vol. 50. doi: 10.1016/j.neuro.2015.07.002.
Summary: Researchers conducted functional MRI scans on 43 lead-exposed and 41 healthy adults and compared brain activity during executive functioning tasks. Results showed that healthy participants showed elevated brain activity in the left dorsolateral prefrontal cortex (a region of the brain associated with executive functioning), and that activity was inversely related to blood lead concentrations. Ultimately, the authors conclude that “lead exposure can induce functional abnormalities in distributed cortical networks related to executive function, and that lead-induced neurotoxicity may be persistent rather than transient.”
“Environmental Lead Exposure is Associated with Visit-to-Visit Systolic Blood Pressure Variability in U.S. Adults”
Faramawi, M.F.; et al. International Archives of Occupational and Environmental Health, April 2015, Vol. 88(3). doi: 10.1007/s00420-014-0970-5.
Summary: Associations between lead exposure in adulthood and blood pressure variability was assessed using data from 13,757 participants aged 17 years or older from the cross-sectional National Health and Nutrition Examination Survey III. Using multivariable regression analyses adjusted for age, gender, race, smoking and socioeconomic status, researchers found that environmental lead exposure was significantly associated with systolic blood pressure variability (adjusted β = 0.07, P < 0.01).
“Economic Impacts of Lead Exposure and Remediation in Michigan”
Swinburn, T. Report from the University of Michigan Risk Science Center and the Michigan Network for Children’s Environmental Health, June 2014.
“Understanding the Cumulative Impacts of Inequalities in Environmental Health: Implications for Policy”
Morello-Frosch, R.; Zuk, M.; Jerrett, M.; Shamasunder, B.; Kyle, A.D. Health Affairs, May 2011, Vol. 30(5). doi: 10.1377/hlthaff.2011.0153.
Abstract: “Racial or ethnic minority groups and low-income communities have poorer health outcomes than others. They are more frequently exposed to multiple environmental hazards and social stressors, including poverty, poor housing quality, and social inequality. Researchers are grappling with how best to characterize the cumulative effects of these hazards and stressors in order to help regulators and decision makers craft more-effective policies to address health and environmental disparities. In this article we synthesize the existing scientific evidence regarding the cumulative health implications of higher rates of exposure to environmental hazards, along with individual biological susceptibility and social vulnerability. We conclude that current environmental policy, which is focused narrowly on pollutants and their sources, should be broadened to take into account the cumulative impact of exposures and vulnerabilities encountered by people who live in neighborhoods consisting largely of racial or ethnic minorities or people of low socioeconomic status.”
“Childhood Lead Poisoning: Conservative Estimates of the Social and Economic Benefits of Lead Hazard Control”
Gould, E. Environmental Health Perspectives, July 2009, Vol. 117(7). doi: 10.1289/ehp.0800408.
Abstract: “This research updates estimates of elevated blood lead levels among a cohort of children ≤ 6 years of age and compiles recent research to determine a range of the costs of lead paint hazard control ($1–$11 billion) and the benefits of reduction attributed to each cohort for health care ($11–$53 billion), lifetime earnings ($165–$233 billion), tax revenue ($25–$35 billion), special education ($30–$146 million), attention deficit–hyperactivity disorder ($267 million), and the direct costs of crime ($1.7 billion). Each dollar invested in lead paint hazard control results in a return of $17–$221 or a net savings of $181–269 billion. In conclusion, there are substantial returns to investing in lead hazard control, particularly targeted at early intervention in communities most likely at risk. Given the high societal costs of inaction, lead hazard control appears to be well worth the price.”
Keywords: Flint, Michigan, children, IQ, intelligence, health, lead poisoning, lead exposure, drinking water