Why is learning about lead exposure in children important?
Lead is a poisonous metal found in small amounts in the earth's crust. It is ever-present in the human environment today because of industrialization.1 Lead provides no known physical benefit for human beings, and its toxic effects, which are extensive, are especially dangerous for children. Children are more vulnerable than adults are to these toxic effects because:
- a greater proportion of ingested lead is absorbed from the gastrointestinal tract of children than of adults;
- a greater proportion of lead circulating in the body gains access to the brains of children, especially those 5 years of age or younger, than of adults; and
- the developing nervous system is far more vulnerable to lead's toxic effects than the mature brain.2
Lead poisoning, for the most part, is silent: most poisoned children have no symptoms and the vast majority of cases go undiagnosed and untreated. Although lead poisoning is disproportionately a problem of inner city and minority children, no socioeconomic group, geographic area, or racial or ethnic population is spared.3 While lead poisoning can affect every system in the body, it is especially dangerous to the developing brains and nervous systems of unborn children and children under 6 years old.
Lead poisoning in children presents a critical challenge for educators because even at very low levels of exposure evidence shows that:
- it can cause serious, permanent damage to a child's developing brain;
- its neurotoxic effects can interfere with a child's ability to think, learn, pay attention, and behave appropriately;
- it is directly associated with lower IQ scores and lower scores on standardized performance tests; and
- research shows that it is a contributing factor to the achievement gap among Connecticut children.
It is also important for educators to address because:
- lead poisoning is entirely preventable;
- its neurotoxic and behavioral effects may be ameliorated by early enrichment; and
- educators have abundant opportunity, in collaboration with others, to contribute to the prevention and effective management of lead poisoning in children.
History of lead poisoning — an overview
The toxic effects of lead exposure in children were observed and reported in the medical literature as early as the late 1800s. Initially, the most severe cases were recognized by major symptoms such as seizures and other neurological abnormalities, mental retardation, coma, and death. As physicians in the 1920s and 1930s were better prepared to recognize the symptoms of lead poisoning, including milder symptoms such as vomiting, colic, abdominal pain and irritability, the majority of cases still went undiagnosed because symptoms were easily confused with those related to other conditions, such as meningitis, brain tumors, and gastrointestinal conditions. Nevertheless, before 1940, both the medical community and the lead industry recognized that lead posed a major public health problem, especially for children.
It takes very little exposure to cause high blood lead levels.
Early in the 1900s, paint containing lead was recognized internationally as a major source of lead poisoning in young children, and by the end of the 1920s, several countries had banned the use of lead paint indoors and on certain products such as cribs and toys. By the 1940s, the lead industry in the United States had begun to decrease the amount of lead used in interior paints, but it was not until 1978 that lead-based paint was actually banned from use and subsequently phased out. Most homes built before 1978, like so many in Connecticut, were painted both inside and out with lead paint. In 1998, of the 16.4 million US homes with one or more children younger than 6 years, percent still had significant amounts of lead-contaminated deteriorated paint, dust, or adjacent bare soil.4
Dust and soil become a final resting place for airborne lead from gasoline and dust from old paint and industrial sites. Lead in dust and soil can re-contaminate cleaned houses and contribute to elevating blood lead concentrations in children who play on bare, contaminated soil.5 When old paint deteriorates, or during remodeling, paint dust becomes prevalent in the environment. Exposed pregnant women can inhale the dust, increasing lead in their blood and in the blood of the fetus. Exposed young children can breathe in paint dust and ingest it by putting their dust-covered hands and toys to their mouths. They may also be exposed to lead by playing with paint chips or contaminated soil, or chewing on painted toys, cribs, or windowsills. It takes very little exposure to cause high blood lead levels.
While dust from old paint is not the only source of potential lead exposure for children, today it is the main source of high-dose exposure.6 Contaminated soil and water from lead pipes also continue to be sources of lead exposure. Leaded gasoline was considered the greatest source of environmental lead contamination in the United States from the 1950s through the 1980s; it was phased out for use in cars starting in 1973 and completely banned for use in on-road vehicles in 1996. This phase-out resulted in an estimated 78 percent drop in average blood lead levels in this country between 1976 and 1991. Leaded gas can still be sold for off-road uses, such as farm equipment, racing cars, and aircraft. Furthermore, individual children may still be exposed to airborne lead in fumes or breathable dust resulting from sanding or heating old paint, burning or melting automobile batteries, or melting lead for use in a hobby or craft. 7
The Centers for Disease Control and Prevention (CDC) defines lead poisoning according to the amount of lead found in a person's blood; it is measured in micrograms (mcg) per deciliter (dL). Over time, the CDC has identified a "blood lead level of concern" based on available scientific evidence. This level of concern, which designates the standard for diagnosis and intervention by public health officials and physicians, has significantly changed over time. In 1960, the CDC minimum level of concern was 60 mcg/dL; in 1985, it was 25 mcg/dL, and in 1991, it was decreased to 10 mcg/dL. In June 2012, the CDC eliminated the term “blood lead level of concern” and adopted the term “reference value.” The “reference value” is based on the population of children ages 1-5 years in the United States whose blood lead levels are in the highest 2.5 percent of children tested. Today, that level is 5 mcg/dL. However, current scientific evidence has established that there is no safe level of lead in a child's body.8
Any lead is too much lead!9
Scientific research findings provide evidence that blood lead levels (BLLs) in children between 1 mcg/dL and 5 mcg/dL and 5 mcg/dL and 9 mcg/dL cause a more precipitous drop in IQ than BLLs in ranges above 10 mcg/dL.10, 11 Of greater concern, research demonstrates that even when the drop in IQ is small (two to three points), there can be significant neuropsychological deficits in one or more domains of brain function.12, 13, 14 Research in children further suggests that the adverse health effects of BLLs less than 10 mcg/dL extend beyond cognitive function to include cardiovascular, immunological, and endocrine effects. The evidence is based on studies with large numbers and diverse groups of children with low BLLs and associated IQ and neuropsychological deficits. Effects at BLLs under 10 mcg/dL are also reported for behavioral domains, particularly attention-related behaviors and academic achievement, and do not appear to be confined to lower socioeconomic status populations.15, 16, 17
Effective interventions to improve cognitive functioning in children with lead poisoning must be multifaceted.
Research confirms that elevated lead concentrations in the blood are more common among children living in poverty and provides some evidence that socioeconomic status and parenting influence associations between lead and child outcomes.18, 19 Micronutrients that have been shown to influence the effects of lead include iron and zinc, indicating a relationship between lead poisoning and nutritional status. Also of importance, research findings indicate that effective interventions to improve child cognitive functioning must be multifaceted, including identification and reductions of toxins in the environment; monitoring and addition of appropriate nutrients in children's diets; parental education to increase involvement and other parenting skills such as limit setting and effective requests for child compliance,20 and early enrichment.
Despite strong evidence of the harmful effects of lead poisoning in children demonstrated through population-based research, individual case studies also confirm that there can be considerable variability in functional outcomes among children with lead poisoning. One child with exposure to lead resulting in BLLs between 5 mcg/dL and 9.9 mcg/dL may sustain brain damage resulting in significant neurocognitive and behavioral deficits, while another child with an exposure level resulting in BLLs far exceeding 10 mcg/dL may not show any functional deficits in cognition or behavior.21, 22 The reasons for this variability in functional outcomes are not fully understood, and are likely to be multifactorial. Furthermore, study outcomes vary on the relative importance of duration of exposure, peak BLL, and age of exposure.
One child with exposure to lead resulting in BLLs between 5 mcg/dL and 9.9 mcg/dL may sustain brain damage resulting in significant neurocognitive and behavioral deficits, while another child with an exposure level resulting in BLLs far exceeding 10 mcg/dL may not show any functional deficits in cognition or behavior.
Several studies indicate that concurrent (current BLL of school age child) or lifetime average blood lead concentrations are better predictors of children's IQ scores than measures taken in early childhood.23 In any event, a blood lead level alone is not a reliable biomarker of total lead exposure, except for short-term exposure, since the half-life of lead in the blood is 36 days. From the blood stream, lead is deposited in the brain, other soft tissues of the body, bones, and teeth, where it may remain for years; some of it is eliminated through the kidneys and gastrointestinal tract. Blood lead levels do not measure lead deposits in the brain or other tissues of the body. Additionally, lead stored in the bones and other tissues can leach back into the blood stream and recirculate through the body under certain circumstances, for example, during pregnancy.
The next section discusses research specific to the effects of lead exposure on Connecticut children.
Lead Exposure: A Contributor to the Achievement Gap in Connecticut
In response to the health concerns cited by experts in Connecticut and nationally, the Connecticut State Department of Education (CSDE) in collaboration with the State Departments of Public Health (DPH) and Social Services engaged researchers at Duke University's Children's Environmental Health Initiative (CHEI) to conduct an analysis of the effects of early childhood lead exposure on test performance among Connecticut school children. Early in 2011, the first phase of the study results were released in a report titled, The Impact of Early Childhood Lead Exposure on Educational Test Performance among Connecticut Schoolchildren, Phase I Report (also referred to as "The Miranda Study"). Phase II of the Miranda Study was released in 2013. Based on scientific analysis of the Connecticut data, Dr. Marie Lynn Miranda and other researchers at CHEI found the following:
- early childhood lead exposure negatively affected Connecticut Mastery Test scores in reading and mathematics;
- disparate exposures by race suggest that exposure to lead may account for part of the achievement gap among Connecticut schoolchildren;24 and
- negative associations were statistically significant at blood lead levels below the current Centers for Disease Control and Prevention's blood lead action level of 5 mcg/dL.25
These results emphasize the ongoing, critical necessity of protecting children from lead exposure, and underscore important implications for Connecticut's students and educators. Indeed, the study's outcomes provided the motivating force for the development of these guidelines and collaborative statewide efforts to inform practice within school districts regarding:
- lead poisoning prevention;
- effects of lead exposure on early childhood development;
- early identification of students with a history of exposure to lead;
- educational programming in response to lead exposure in order to mitigate existing and potential deficits; and
- educational resources available for educators.
Prevalence of Childhood Lead Poisoning in the U.S. and Connecticut
Approximately 250,000 children in the United States today are identified with blood levels equal to or greater than 10 mcg/dL.26 Approximately 450,000 U.S. children have BLLs at or above 5 mcg/dL, almost double the total number with BBLs at or above 10 mcg/dL.
In Connecticut, public health officials follow the current CDC standard of BLL equal to or greater than 10 mcg/dL to activate public health and medical interventions for children with lead poisoning.
In Connecticut, state and local officials follow the current CDC standard for public health and medical interventions (see Appendixes E and Appendixes F). Based on the 2011 Connecticut screening data, 84,008 children, age birth to 6 years, were screened in 2011.27 Of the 84,008 children tested, 4,365 (6.5%) had blood lead levels (BLLs) between 5 mcg/dL and 9.9 mcg/dL, 355 (0.8%) had BLLs between 10 mcg/dL and 14.9 mcg/dL, 153 (0.3%) had BLLs between 15 mcg/dL and 19.9 mcg/dL, and 111 (0.1%) had BLLs greater than or equal to 20 mcg/dL.
Primary Prevention Goals and Persistence of Lead Poisoning
In 1991, the U.S. Department of Health and Human Services made eradication of lead poisoning in children a public health goal for the nation.28, 29 Also in 1990-91, the U.S. Department of Housing and Urban Development and the Environmental Protection Agency released plans dealing with the elimination of lead hazards. Eradication of lead poisoning in children was also included in Healthy People 2010: Objectives for Improving Health, as a priority health goal for the nation to achieve within the 2000-2010 decade.30Eradication of lead paint and dust in housing and soil was deemed the best method of primary prevention because it eliminates the source of the problem before exposure occurs. Early screening of young children and rapid intervention to prevent lead poisoning as defined by the CDC was recognized as the next best step in prevention efforts.
Despite the significant reduction in average BLLs in recent decades, exposure in unborn and young children persists, as do racial and income disparities.
Although progress has been made with state and federal funding targeted both to educational programs about lead poisoning, housing improvement and abatement projects, and early childhood screening and intervention programs, many children in Connecticut and across the country continue to live and play in homes where they are exposed to lead. In the objectives for environmental health in Healthy People 2020, the U.S. Department of Health and Human Services states:
The number of children with elevated blood lead levels in the U.S. is steadily decreasing. As a result, determining stable national prevalence estimates and changes in estimated prevalence over time is increasingly difficult. Eliminating elevated blood lead levels in children remains a goal of utmost importance to public health. The sample sizes available preclude the ability to have a viable target for HP2020 Efforts must and will continue to reduce blood lead levels and to monitor the prevalence of children with elevated blood lead levels.31
Thus, reducing lead poisoning remains a high public health priority at the federal, state, and local levels for the 2011-2020 decade. While a priority objective, it is unclear what level of funding will be available to support ongoing primary prevention programs over this decade.
Despite the significant reduction in average BLLs in recent decades, exposure in unborn and young children persists, as do racial and income disparities.32, 33 According to the Advisory Committee on Childhood Lead Poisoning Prevention report, racial and income differences can be traced to differences in housing quality, environmental conditions, nutrition, and other factors.34 Others point out that those who are poor and disadvantaged are more likely to:
- live in lead-contaminated environments, especially in dilapidated housing with flagrant lead paint hazards;
- live in urban neighborhoods where years of traffic have left tons of lead deposits from leaded gasoline; and
- live near point sources of lead, such as smelters, or hazardous waste sites.35
Given the most current evidence that "there is no known BLL without harmful effects" and that "these effects, in the absence of other interventions, appear to be irreversible," the ACCLPP 2012 report calls for renewed efforts in primary prevention. It states:
The goal of primary prevention is to ensure that all homes become lead-safe and do not contribute to childhood lead exposure. Prevention requires that we reduce environmental exposures from soil, dust, paint and water, before children are exposed to these hazards. Efforts to increase awareness of lead hazards and ameliorative nutritional interventions are also key components of a successful prevention policy.
The CDC is in the process of reviewing these recommendations. If supported, they could lead to CDC guidance recommending interventions starting at BLL of 5 mcg/dL or even lower.
Public Health Standard for Intervention
"In January 2012, the Advisory Committee on Childhood Lead Poisoning Prevention (ACCLPP) recommended that the CDC change its ‘blood lead level of concern,’ which has been 10 micrograms of lead per deciliter. Over the last several years, a growing body of scientific evidence has suggested adverse effects in children with BLLs below 10 micrograms of lead per deciliter of blood. On May 16, 2012, the ACCLPP officially announced their agreement with that recommendation and the change in the CDC policy.
The ACCLLP recommends that CDC eliminate the term 'level of concern.' Instead, the committee recommends linking elevated blood lead levels to data from the National Center for Environmental Health (NCEH) National Exposure Report to identify children living or staying for long periods in environmentsthat expose them to lead hazards. This new level, called a ‘reference value,’ is based on the population of children aged 1-5 years in the United States whose blood lead levels are in the highest 2.5 percent of children tested. Today, that level is 5 micrograms of lead per deciliter of blood.
For more than 20 years, NCEH’s work to eliminate lead poisoning in children has been one of CDC’s most visibly successful initiatives. It has contributed significantly to lowering blood lead levels, increasing the number of children tested for elevated blood lead levels, and promoting state and local lead screening plans and abatement laws."36