Childhood Lead Poisoning and Its Prevention
Idamarie Laquatra, PhD, RD In November 1997, the Centers for Disease Control (CDC) released Screening Young Children for Lead Poisoning: Guidance for State and Local Public Health Officials 1. The new guidance reflects the latest knowledge on lead exposure patterns and was designed to assist state and local health departments determine which children in their jurisdictions are most likely to benefit from screening. The document focuses on decision- making processes, screening and follow-up for children with lead exposure. Steps are outlined for examining local conditions that can contribute to lead hazards and for developing data-driven screening recommendations based on findings. Through procedures outlined in the documents, the CDC expects that more children who are actually exposed to lead will be screened, while children with low risk for lead exposure will not receive unnecessary screening, increasing the efficiency and benefits of screening efforts. CDC's guidance reflects the U.S. Public Health Service's continued commitment to eliminate childhood lead poisoning. The understanding of lead's health effects, the blood levels at which these effects occur, and the approach for dealing with lead exposure have undergone considerable change over the years. A ubiquitous environmental toxicant, absorbed by ingestion or inhalation, lead exhibits its adverse effects on the nervous, blood, renal, and reproductive systems. The major sources of childhood lead poisoning include lead-based paint, lead-contaminated household dust, soil, water, household renovations, infant formula reconstituted with lead contaminated water, occupational/ avocational exposures with subsequent poisoning of children, and lead-containing folk medicines and cosmetics 2. Porcelain bathtubs containing leachable lead on their surfaces was one of America's most unexpected sources of lead exposure for children 3. Worldwide, airborne lead is the largest contributor to background lead levels. The two major sources of ambient lead contamination are auto exhausts and industrial emissions 4. In the United States and Canada, the almost complete elimination of lead from gasoline and containers used for canned foods, plus its reduction in paints have reduced the incidence of elevated lead levels during childhood. In fact, the removal of lead from gasoline, which began in the US in 1972 and was completed in 1995, is responsible for an almost fourfold reduction in median blood lead levels in US children from 1976 to 19915. Phase 2 of NHANES III, conducted during 1991 to 1994, documented a continued decline of mean blood lead levels of the US population aged one year and older to 2.3 micrograms/dL. Despite the recent and large declines, the data indicated that close to one million U.S. children aged one to five years continue to have blood lead levels that are considered to be elevated; that is 10 micrograms/dL or higher 6. Risk for lead exposure continues to be disproportionately high for children who are poor, non-Hispanic black, Mexican-American, living in large metropolitan areas, or living in older housing. Currently, in the United States, the most common source of lead exposure for children is lead-based paint that has deteriorated into paint chips and lead dust. Approximately 83% of privately owned housing units and 86% of public housing units built before 1980 contain some lead-based paint 6. Outside of North America, lead in gasoline remains a major problem in Latin American and Caribbean countries 7, as well as in China 8, Africa 9, and the Czech Republic 10. Infants and children are at special risk for lead poisoning due to their developing nervous systems, small body size, and high absorption rate 11. Gastrointestinal absorption of lead is inversely related to age: adults absorb 10-20% of lead, young children absorb 30-50%. Infants are particularly vulnerable to lead intoxication from water. The use of infant formulas which require reconstitution may present inadvertent lead hazards to young infants if reconstituted with lead contaminated water. A recent pilot study of a convenience sample of metropolitan Boston infants less than nine months of age showed that lead contamination exceeded the Environmental Protection Agency action level of 15 micrograms/Liter in 5% of formula samples tested 12. Parents need education about safe infant formula preparation practices such as reconstituting formula with cold tap water which has run for 1-2 minutes and warming in a clean, lead-free vessel, avoiding old kettles which may contain lead solder. The toddler years present special hazards. In fact, the highest blood lead levels are observed between 13 and 36 months of age 4. The high rate of hand-to-mouth activity and increased mobility increase a toddler's susceptibility to lead poisoning. Exacerbating the problem is the high prevalence of iron deficiency in this age group, which increases gastrointestinal absorption of ingested lead. The neurotoxic properties of lead at high doses have been recognized for years. Very high blood lead levels cause devastating health consequences, including seizures, coma and death. Until the mid to late 1960s, lead poisoning was viewed as an acute disease, and diagnosed children generally had blood levels exceeding 80 micrograms/dL13. Continued careful study of the health effects of lead have demonstrated neurobehavioral effects at increasingly lower blood levels. Blood lead levels as low as 10 micrograms/dL can adversely affect children's learning and behavior 6. A meta-analysis of 12 controlled studies clearly established a strong link between low dose lead exposure reflected in blood levels of 13 to 30 micrograms/ dL and intellectual deficits in children 14. As the understanding of the impact of lower blood levels of lead became apparent, the focus in the medical community shifted from detection and treatment of lead poisoning to prevention. The CDC first published guidance on lead poisoning prevention in 1975, listing intervention blood lead levels as 30 micrograms/dL. These guidelines have been updated regularly as new information becomes available. In response to studies which demonstrated neurobehavioral effects at increasingly lower levels, the CDC has reduced the intervention levels over the years. Their 1991 update of prevention guidelines established 10 micrograms/dL as the blood lead levels that are considered to be elevated. The 1991 guidelines also recommended virtually universal blood lead screening for lead poisoning in children aged 12 to 72 months of age, except for children who live in a community that has demonstrated that it does not have a childhood lead poisoning problem 2. In 1993, the American Academy of Pediatrics (AAP) adopted similar guidelines 15. The universal screening recommendation proved to be controversial and not as effective as hoped. Results of an AAP survey of a nationally representative sample of its members indicated that 53% of respondents reported screening of their patients. The findings suggested that many pediatricians were not convinced that universal screening was needed16. In 1994, a national survey showed that only about 24 percent of young children had been screened and fewer than one-third of those at increased risk for lead exposure because of poverty or residence in older housing had been screened 17. Concerns about cost/benefit issues and barriers to universal screening prompted the CDC to release Screening Young Children for Lead Poisoning: Guidance for State and Local Public Health Officials in November, 1997. The CDC recommended that state health officials develop a plan for childhood lead screening. To help states implement such a plan, the CDC details specific steps. The first step is to form an advisory committee of all parties with an interest in child health. Step two involves assessment of lead exposure and screening capacity. Lead exposure information can be derived from blood lead level data, housing data (since homes built before 1950 pose the greatest risk for lead exposure), demographic characteristics of children and the presence of other sources of lead. In step three, boundaries are determined which define areas for which a screening recommendation can be made. As shown in Table 1, information on the percentage of one to three-year old children with blood levels 10 micrograms/dL or higher and the percentage of housing built before 1950 is used to determine if universal or targeted screening should be used. The final step is the implementation of the statewide plan including monitoring, evaluating and revising the plan as needed. Because no lower threshold for some of the adverse effects of lead in children has been identified, and the effects of early lead exposure can persist 15, health care providers need to provide education to parents to prevent exposure of their children to lead. Although identification and treatment of the child poisoned with lead is essential, identifying the source and preventing subsequent exposures for that child and other children in the future is crucial to prevent serious disease and disability in the population 15. The guidance document, Screening Young Children for Lead Poisoning: Guidance for State and Local Public Health Officials can be obtained by calling the toll free number: 888-232-6789 or can be accessed through the Internet at: http://www.cdc.gov/nceh/programs/lead/lead.htm Interested individuals can obtain more information by writing to: Lead Poisoning Prevention Branch Division of Environmental Hazards and Health Effects National Center for Environmental Health Mailstop F42, 4770 Buford Highway, Atlanta, GA 30341 References
|
