Lead Management
Lead management
Lead , a naturally occurring bluish gray metal, is extensively used throughout the world in the manufacture of storage batteries, chemicals including paint and gasoline , and various metal products including sheet lead, solder, pipes, and ammunition. Due to its widespread use, large amounts of lead exist in the environment , and substantial quantities of lead continue to be deposited into air, land, and water. Lead is a poison that has many adverse effects, and children are especially susceptible. At present, the production, use, and disposal of lead are regulated with demonstrably effective results. However, because of its previous widespread use and persistence in the environment, lead exposure is a pervasive problem that affects many populations. Effective management of lead requires an understanding of its effects, blood action levels, sources of exposure, and policy responses, topics reviewed in that order.
Effects of Lead
Lead is a strong toxicant that adversely affects many systems in the body. Severe lead exposures can cause brain and kidney damage to adults and children, coma, convulsions, and death. Lower levels, e.g., lead concentrations in blood (PbB) below 50 μg/dL, may impair hemoglobin synthesis, alter the central and peripheral nervous systems, cause hypertension, affect male and female reproductive systems, and damage the developing fetus. These effects depend on the level and duration of exposure and on the distribution and kinetics of lead in the body. Most lead is deposited in bone, and some of this stored lead may be released long after exposure due to a serious illness, pregnancy, or other physiological event. Lead has not been shown to cause cancer in humans, however, tumors have developed in rats and mice given large doses of lead and thus several United States agencies consider lead acetate and lead phosphate as human carcinogens.
Children are particularly susceptible to lead poisoning . PbB levels as low as 10 μg/dL are associated with decreased intelligence and slowed neurological development. Low PbB levels also have been associated with deficits in growth, vitamin metabolism , and effects on hearing. The neurological effects of lead on children are profound and are likely persistent. Unfortunately, childhood exposures to chronic but low lead levels may not produce clinical symptoms, and many cases go undiagnosed and untreated. In recent years, the number of children with elevated blood lead levels has declined substantially. For example, the average PbB level has decreased from over 15 μg/dL in the 1970s to about 5 μg/dL in the 1990s. As described later, these decreases can be attributed to the reduction or elimination of lead in gasoline, food can and plumbing solder, and residential paint. Still, childhood lead poisoning remains the most widespread and preventable childhood health problem associated with environmental exposures, and childhood lead exposure remains a public health concern since blood levels approach or exceed levels believed to cause effects. Though widely perceived as a problem of inner city minority children, lead poisoning affects children from all areas and from all socioeconomic groups.
The definition of a PbB level that defines a level of concern for lead in children continues to be an important issue in the United States. The childhood PbB concentration of concern has been steadily lowered by the Centers for Disease Control (CDC) from 40 μg/dL in 1970 to 10 μg/dL in 1991. The Environmental Protection Agency lowered the level of concern to 10 μg/dL ("10-15 and possibly lower") in 1986, and the Agency for Toxic Substances and Disease Registry (ATSDR) also identified 10 μg/dL in its 1988 Report to Congress on childhood lead poisoning.
In the workplace, the medical removal PbB concentration is 50 μg/dL for three consecutive checks and 60 μg/dL for any single check. Blood level monitoring is triggered by an air lead concentration above 30 μg/m3. A worker is permitted to return to work when his blood lead level falls below 40 μg/dL. In 1991, the National Institute for Occupational Safety and Health (NIOSH) set a goal of eliminating occupational exposures that result in workers having PbB levels greater than 25 μg/dL.
Exposure and Sources
Lead is a persistent and ubiquitous pollutant. Since it is an elemental pollutant, it does not dissipate, biodegrade, or decay. Thus, the total amount of lead pollutants resulting from human activity increases over time, no matter how little additional lead is added to the environment. Lead is a multi-media pollutant, i.e., many sources contribute to the overall problem, and exposures from air, water, soil , dust, and food pathways may be important.
For children, an important source of lead exposure is from swallowing nonfood items, an activity known as pica (an abnormal eating habit e.g., chips of lead-containing paint), most prevalent in 2 and 3 year-olds. Children who put toys or other items in their mouths may also swallow lead if lead-containing dust and dirt are on these items. Touching dust and dirt containing lead is commonplace, but relatively little lead passes through the skin. The most important source of high-level lead exposure in the United States is household dust derived from deteriorated lead-based paint. Numerous homes contain lead-based paint and continue to be occupied by families with small children, including 21 million pre-1940 homes and rental units which, over time, are rented to different families. Thus, a single house with deteriorated lead-based paint can be the source of exposure for many children.
In addition to lead-based paint in houses, other important sources of lead exposure include (1) contaminated soil and dust from deteriorated paints originally applied to buildings, bridges, and water tanks; (2) drinking water into which lead has leached from lead, bronze, or brass pipes and fixtures (including lead-soldered pipe joints) in houses, schools, and public buildings; (3) occupational exposures in smelting and refining industries, steel welding and cutting operations, battery manufacturing plants, gasoline stations, and radiator repair shops; (4) airborne lead from smelters and other point sources of air pollution , including vehicles burning leaded fuels; (5) hazardous waste sites which contaminate soil and water; (6) food cans made with lead-containing solder and pottery made with lead-containing glaze; and (7) food consumption if crops are grown using fertilizers that contain sewage sludge or if much lead-containing dust is deposited onto crops. In the atmosphere , the use of leaded gasoline has been the single largest source of lead (90%) since the 1920s, although the use of leaded fuel has been greatly curtailed and gasoline contributions are now greatly reduced (35%). As discussed below, leaded fuel and many other sources have been greatly reduced in the United States, although drinking water and other sources remain important in some areas. A number of other countries, however, continue to use leaded fuel and other lead-containing products.
Government Responses
Many agencies are concerned with lead management. Lead agencies in the United States include the Environmental Protection Agency, the Centers for Disease Control, the U.S. Department of Health and Human Services , the Department of Housing and Urban Development, the Food and Drug Administration , the Consumer Product Safety Commission, the National Institute for Occupational Safety and Health, and the Occupational Safety and Health Administration . These agencies have taken many actions to reduce lead exposures, several of which have been very successful. General types of actions include: (1) restrictions or bans on the use of many products containing lead where risks from these products are high and where substitute products are available, e.g., interior paints, gasoline fuels, and solder; (2) recycling and safer ultimate disposal strategies for products where risks are lower, or for which technically and economically feasible substitutes are not available, e.g., lead-acid automotive batteries, lead-containing wastes, pigments and used oil; (3) emission controls for lead smelters, primary metal industries, and other industrial point sources, including the use of the best practicable control technology (BPCT) for new lead smelting and processing facilities and reasonable available control technologies (RACT) for existing facilities, and; (4) education and abatement programs where exposure is based on past uses of lead.
The current goals of the Environmental Protection Agency (EPA) strategy are to reduce lead exposures to the fullest extent practicable, to significantly reduce the incidence of PbB levels above 10 μg/dL in children, and to reduce lead exposures that are anticipated to pose risks to children, the general public, or the environment. Several specific actions of this and other agencies are discussed below.
The Residential Lead-based Paint Hazard Reduction Act of 1992 (Title X) provides the framework to reduce hazards from lead-based paint exposure, primarily in housing. It establishes a national infrastructure of trained workers, training programs and proficient laboratories, and a public education program to reduce hazards from lead exposure in paint in the nation's housing stock. Earlier, to help protect small children who might swallow chips of paint, the Consumer Product Safety Commission (CPSC) restricted the amount of lead in most paints to 0.06 percent by weight. CDC further suggests that inside and outside paint used in buildings where people live be tested for lead. If the level of lead is high, the paint should be removed and replaced with a paint that contains an allowable level of lead. CPSC published a consumer safety alert/brochure on lead paint in the home in 1990, and has evaluated lead test kits for safety, efficacy, and consumer-friendliness. These kits are potential screening devices that may be used by the consumer to detect lead in paint and other materials. Title X also requires EPA to promulgate regulations that ensure personnel engaged in abatement activities are trained, to certify training programs, to establish standards for abatement activities, to promulgate model state programs, to establish a laboratory accreditation program, to establish a information clearinghouse, and to disclose lead hazards at property transfer.
The Department of Housing and Urban Development (HUD) has begun activities that include updating regulations dealing with lead-based paint in HUD programs and federal property; providing support for local screening programs; increasing public education; supporting research to reduce the cost and improve the reliability of testing and abatement; increasing state and local support; and providing more money to support abatement in low and moderate income households. HUD estimated that the total cost of testing and abatement in high-priority hazard homes will be $8 to 10 billion annually over 10 years, although costs could be substantially lowered by integrating abatement with other renovation activities.
CPSC, EPA, and states are required by the Lead Contamination Control Act of 1988 to test drinking water in schools for lead and to remove lead if levels are too high. Drinking water coolers must also be lead-free and any that contain lead must be removed. EPA regulations limit lead in drinking water to 0.015 mg/L.
To manage environmental exposures resulting from inhalation, EPA regulations limit lead to 0.1 and 0.05 g/gal (0.38 and 0.19 g/L) in leaded and unleaded gasoline, respectively. Also, the National Ambient Air Quality Standards set a maximum lead concentrations of 1.5 μg/m3 using a three month average, although typical levels are far lower, 0.1 or 0.2 μg/m3.
To identify and mitigate sources of lead in the diet, the Food and Drug Administration (FDA) has undertaken efforts that include voluntary discontinuation of lead solder in food cans by the domestic food industry, and elimination of lead in glazing on ceramic ware. Regulatory measures are being introduced for wine, dietary supplements, crystal ware, food additives , and bottled water.
For workers in lead-using industries, the Occupational Safety and Health Administration (OSHA) has established environmental and biological standards that include maximum air and blood levels. This monitoring must be conducted by the employer, and elevated PbB levels may require the removal of an individual from the work place (levels discussed previously). The Permissible Exposure Level (PEL) limits air concentrations of lead to 50 μg/m3, and, if 30 μg/m3 is exceeded, employers must implement a program that includes medical surveillance, exposure monitoring, training, regulated areas, respiratory protection, protective work clothing and equipment, housekeeping, hygiene facilities and practices, signs and labels, and record keeping. In the construction industry, the PEL is 200 μg/m3. The National Institute for Occupational Safety and Health (NIOSH) recommends that workers not be exposed to levels of more than 100 μg/m3 for up to 10 hours, and NIOSH has issued a health alert to construction workers regarding possible adverse health effects from long-term and low-level exposure. NIOSH has also published alerts and recommendations for preventing lead poisoning during blasting, sanding, cutting, burning, or welding of bridges and other steel structures coated with lead paint.
Finally, lead screening for children has recently increased. The CDC recommends that screening (testing) for lead poisoning be included in health care programs for children under 72 months of age, especially those under 36 months of age. For a community with a significant number of children having PbB levels between 10-14 μg/dL, community-wide lead poisoning prevention activities should be initiated. For individual children with PbB levels between 15-19 μg/dL, nutritional and educational interventions are recommended. PbB levels exceeding 20 μg/dL should trigger investigations of the affected individual's environment and medical evaluations. The highest levels, above 45 μg/dL, require both medical and environmental interventions, including chelation therapy. CDC also conducts studies to determine the impact of interventions on children's blood lead levels.
These regulatory activities have resulted in significant reductions in average levels of lead exposure. Nevertheless, lead management remains an important public health problem.
[Stuart Batterman ]
RESOURCES
BOOKS
Breen, J. J., and C. R. Stroup, eds. Lead Poisoning: Exposure, Abatement, Regulation. Lewis Publishers, 1995.
Kessel, I., J. T. O'Connor, and J. W. Graef. Getting the Lead Out: The Complete Resource for Preventing and Coping with Lead Poisoning. Rev. ed. Cambridge, MA: Fisher Books, 2001.
Pueschel, S. M., J. G. Linakis, and A. C. Anderson. Lead Poisoning in Childhood. Baltimore: Paul H. Brookes Publishing Co., 1996.
OTHER
Farley, Dixie. "Dangers of Lead Still Linger." FDA Consumer January-February 1998 [cited July 2002]. <http://www.cfsan.fda.gov/~dms/fdalead.html>.