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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations 3 Lead Exposure of Sensitive Populations A complete assessment of exposure in sensitive populations requires knowledge of the sources of exposure. That is especially important for lead: it has multiple sources, and knowledge of them helps to define exposure to lead and to identify sensitive populations. The conventional approach to identifying lead exposure in a population has been to attribute lead intoxication to single sources of lead at high concentrations, such as leaded paint. However, current understanding calls for a more comprehensive view. First, there is a growing consensus that lead induces a continuum of toxic effects in humans, starting with small exposures that cause subtle, but important, early effects. Our understanding of what constitutes a safe exposure has increased; as a result, the upper limit of a safe lead content in blood has declined to one-sixth to one-fourth of what it was in a matter of a few decades. Second, once lead is absorbed from a specific source, it is added to a body burden that contributes to various health effects. Therefore, exposures small enough to have viewed as of little importance now are taken more seriously. In other words, we must consider the aggregate impact of multiple small lead sources in assessing health risk. This chapter is divided into three sections. The first provides a historical perspective on lead contamination, addressing such topics as natural concentrations of environmental lead and the chronologic record of anthropogenic contamination with lead. The second section discusses the major current sources and pathways of lead exposure in sensitive populations, including paint, air, dust and soil, drinking water and
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations food. The section includes a brief discussion of occupational lead exposure and ends with sources that can produce large, but not necessarily pervasive, exposure, such as improperly lead-glazed food and beverage containers and lead-based ethnic medicinal preparations. The chapter concludes with a detailed summary. HISTORICAL OVERVIEW OF ANTHROPOGENIC LEAD CONTAMINATION Lead production dates to the discovery of cupellation—a metallurgic process for separating silver from lead ores—some 5,000 years ago (Nriagu, 1985a). However, such anthropologic artifacts as the lead beads in the Hittite ruins of Catal Hüyück from 6500 BC and the lead statuette from the temple of Osiris in Abydos from 3000 BC reveal earlier uses of lead. The historical record of industrial lead production over the last 5,000 years is illustrated in Figure 3-1. The current production rate is approximately 3.4 million metric tons per year (U.S. Bureau of Mines, 1989). The total amount of lead over the last 5,000 years is estimated to be 300 million metric tons (Flegal and Smith, 1992). Lead has a long history of wide use. A lead glaze in a Babylonian tablet from 1700 BC has been described; these glazes had become common in China during the Chou Dynasty of 1122–256 BC. In the Roman Empire, lead was used in cooking pots and other utensils, in syrups, in beverage adulterants (e.g., sapa), in medicines, and in the construction of pipes and cisterns to transport water (Nriagu, 1983b). The wide use of lead for the latter explains the word plumbing (from the Latin plumbum, lead). Lead was so pervasive during that period that there is little doubt that lead poisoning was endemic in the Roman population. In fact, it has been speculated (Gilfillan, 1965; Nriagu, 1983b) that chronic lead poisoning contributed substantially to the decline of the Roman Empire. One of the environmental tragedies of that period is that, despite some Romans' recognition of the problems associated with lead toxicity, awareness did not restrict its use. For example, Vitruvius (Nriagu, 1985b) observed:
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations FIGURE 3-1 Historical record of industrial lead production in last 5,000 years. Source: Adapted from Settle and Patterson, 1980.
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations Water supply by earthen pipes has advantages. First, if any fault occurs in the work, anybody can repair it. Again, water is much more wholesome from earthenware pipes than from lead pipes, for it seems to be made injurious by lead because some white lead is produced from it; and this is said to be harmful to the human body. Thus if what is produced by anything is injurious, it is not doubtful but that the thing is not wholesome in itself. We can take example by workers in lead who have complexions affected by pallor. For when, in casting, the lead receives the current of air, the fumes from it occupy the members of the body, and burning then thereupon, robs the limbs of the virtues of the blood. Therefore, it seems that water should not be brought in lead pipes if we desire to have it wholesome. Current uses of lead are much more extensive. It is still used in some glazes, eating utensils, folk medicines, and plumbing. It is also used in paint pigments, solders, wall and window construction, cosmetics, sheeting of ships, roofs, guttering, containers, sealants, protective coatings, printing type, insecticides, batteries, plastics, lubricants, ceramics, machine alloys, and gasoline additives (NRC, 1980; EPA, 1986a). The amount of contaminating lead released into the environment closely parallels the record of lead production over the last 5,000 years. Approximately half the lead produced is released into the environment as contamination (NRC, 1980). Current production is about 3.4 million metric tons per year, and current lead release is about 1.6 million metric tons per year. About 150 million metric tons of lead has been released into the environment in the last 5,000 years. The latter value, total release, is probably closer to the total amount of lead put to use, approximately 300 million metric tons, inasmuch as the element is indestructible and cannot be transformed into an innocuous form. Much of the lead released into the environment is emitted into the atmosphere (about 330,000 metric tons/year) (Nriagu and Pacyna, 1988). Those releases are currently dominated by emissions from leaded gasoline (over 248,000 metric tons/year), but emissions from other sources—including coal and oil combustion, mining, manufacturing, incineration, fertilizers, cement production, and wood combustion—are substantial (Table 3-1). In fact, the latter exceed emissions of the most other contaminants by orders of magnitude. The magnitude of industrial emissions of lead is illustrated by comparisons with natural emissions of lead and other contaminants. The
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations TABLE 3-1 Worldwide Emissions of Lead to the Environment, 1983a Source Amount, 103 kg/yr Coal combustion 1,765–14,550 Oil combustion 948–3,890 Mining 30,060–69,640 Manufacturing 1,065–14,200 Incineration 1,640–3,100 Fertilizers 55–274 Cement production 18–14,240 Wood combustion 1,200–3,000 Leaded gasoline 248,030 Miscellaneous 3,900–5,100 Total 288,700–376,000 a Data from Nriagu and Pacyna, 1988. sum of industrial lead emissions is approximately 700 times the sum of natural emissions of lead into the atmosphere (Patterson and Settle, 1987; Nriagu, 1989). Emission of industrial lead aerosols to land and aquatic ecosystems is now predominant. It accounts for approximately 15–20% (202,000–263,000 metric tons/year) of the total anthropogenic emission of lead to land (approximately 1,350,000 metric tons/year) and approximately 63–82% (87,000–113,000 metric tons/year) of the total lead that enters aquatic ecosystems (approximately 138,000 metric tons/year) (Nriagu and Pacyna, 1988). The historical record of atmospheric emissions of industrial lead aerosols has been measured in the environment by various investigators (Figure 3-2). It was initially documented by the 230-fold increase in lead deposition rates in Greenland ice cores over the last 3,000 years, from 0.03 ng/cm2 per year in prehistoric ice cores (800 BC) to about 7 ng/cm2 per year in contemporary ice cores (Murozumi et al., 1969; Ng and Patterson, 1981; Wolff and Peel, 1985). Comparable increases in the Northern Hemisphere have since been documented in pond and lake
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations FIGURE 3-2 Lead contamination from industrial aerosols as recorded in chronologic strata. Circles, Greenland snow (Murozumi et al., 1969); squares, dated pond sediment from remote Sierras (Shirahata et al., 1980); open triangles, lake sediments (Edgington and Robbins, 1976); closed triangles, marine sediments (Ng and Patterson, 1982). Source: Adapted from EPA, 1986a, Vol. II.
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations sediments (Lee and Tallis, 1973; Edgington and Robbins, 1976; Robbins, 1978; Livett et al., 1979; Shirahata et al., 1980; Davis et al., 1982) the oceans (Schaule and Patterson, 1981, 1983; Flegal and Patterson, 1983; Boyle et al., 1986), pelagic sediments (Veron et al., 1987; Hamelin et al., 1988), and marine corals (Shen and Boyle, 1988). Smaller increases by a factor of 2–5 have been detected in Antarctic ice cores (Boutron and Patterson, 1983, 1986; Patterson et al., 1987) and in the South Pacific (Flegal and Patterson, 1983; Flegal, 1986). The contrast reflects the localization of 90% of lead emissions in the northern hemisphere and the short residence time (10 days) of lead aerosols relative to the interhemispheric mixing rate of 1–2 years (Turekian, 1977; Flegal and Patterson, 1983). Other releases of lead to the land range from 540,000 to 1,700,000 metric tons/year (Nriagu and Pacyna, 1988). These include industrial lead from commercial wastes, smelter, wastes, and mine tailings (each approximately 300,000 metric tons/year); fly ash (approximately 140,000 metric tons/year); urban refuse (approximately 40,000 metric tons/year); agricultural wastes (approximately 14,000 metric tons/year); animal wastes (approximately 12,000 metric tons/year); solid wastes (approximately 8,000 metric tons/year); wood wastes (approximately 7,000 metric tons/year); municipal sewage sludge (approximately 6,000 metric tons/year); peat (approximately 2,000 metric tons/year); and fertilizers approximately 1,000 metric tons/year). Many of those are projected to increase and become, at least relatively, more important with the reduction in atmospheric emission of gasoline lead. Nonatmospheric input of industrial lead into aquatic ecosystems is smaller, but still substantial (Nriagu and Pacyna, 1988). It ranges from 25,000 to 50,000 metric tons/year and includes lead from manufacturing (approximately 14,000 metric tons/year), sewage sludge (approximately 9,000 metric tons/year), domestic wastewater (approximately 7,000 metric tons/year), smelting and refining (approximately 6,000 metric tons/year), and mining (1,000 metric tons/year). Lead contamination in urban areas is often much greater than in remote areas (Table 3-2). That is due to the extensive use of lead in industrial processes and the relatively limited mobility of a sizable fraction of this lead. Long-distance transport of a fraction of the lead to the atmosphere also occurs. Terrestrial, aeolian, and fluvial gradients show that most of the lead emitted in urban areas has remained as a
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations TABLE 3-2 Environmental Lead Concentrations in Remote and Rural Areas and Urban Areasa Remote and Rural Lead Concentration, µg/gb Reference Urban Lead Concentration, µg/gb References Air 0.05 Lindberg and Harriss, 1981 0.3 Facchetti and Geiss, 1982; Galloway et al., 1982 Fresh water 1.7 x 10-5 Elias et al., 1982 0.005–0.030 EPA, 1986a, Vol. II Soil 10–30 EPA, 1986a, Vol. II 150–300 EPA, 1986a, Vol. II Plants 0.18c Elias et al., 1982 950d Graham and Kalman, 1974 Herbivores (bone) 2.0d Elias et al., 1982 38d Chmiel and Harrison 1981 Omnivores (bone) 1.3d Elias et al., 1982 67d Chmiel and Harrison 1981 Carnivores (bone) 1.4d Elias et al., 1982 193d Chmiel and Harrison, 1981 a Values can be highly variable, depending on organism and habitat location. b Except µg/m3 in air. c Fresh weight. d Dry weight.
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations contaminant in those areas (Huntzicker et al., 1975; Roberts, 1975; Ragaini et al., 1977; Biggins and Harrison, 1979; Palmer and Kucera, 1980; Harrison and Williams, 1982; Ng and Patterson, 1982; Elbaz-Poulichet et al., 1984; Flegal et al., 1989). For example, in the Great Lakes (Flegal et al., 1989), surface-water lead concentrations in the highly industrialized Hamilton harbor (290 pmol/kg) are nearly 50 times higher than those of some offshore waters in Lake Ontario (6.5 pmol/kg). Complementary stable lead-isotope composition measurements show that essentially all (over 99%) of that lead, in even the most remote regions of Lake Ontario and Lake Erie, is derived from releases of industrial lead from Canada and the United States. Those measurements are consistent with those in numerous other studies that have shown the pandemic scale of lead contamination, which has increased lead concentrations throughout the Northern Hemisphere by a factor of at least 10. Lead concentrations in the atmosphere are now 100 times natural concentrations (Patterson and Settle, 1987). Lead concentrations in remote surface waters of the North Pacific and the North Atlantic are at least 10 times natural concentrations (Flegal and Patterson, 1983; Boyle et al., 1986). Lead concentrations in terrestrial organisms are 100 times natural concentrations (Elias et al., 1982). Studies incorporating rigorous trace-metal analysis have shown that the natural background lead concentration of North American Indians in pre-Columbian times was 0.3 mg per 70-kg adult (Patterson et al., 1987; Ericson et al., 1991). The body of an average North American urban adult contains 100–1,000 times as much lead. Some uses of lead are being reduced in the United States and other countries in response to growing concern over pervasive lead toxicity even at low exposures. For example, lead in gasoline has been decreased in recent decades (Figure 3-3), as noted widely (EPA, 1986a; Nriagu, 1990). The United States has also seen a major reduction in the use of lead-soldered cans for foods and beverages (EPA, 1986a; ATSDR, 1988); lead in such containers can increase food lead content by a factor of up to 4,000 over the lead content of fresh food (Settle and Patterson, 1980). The dispersion of industrial lead is not constrained by national boundaries. For example, stable-isotope composition measurements, which can identify specific sources of industrial lead, have shown that industrial lead from Canada and the United States is transported across the
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations FIGURE 3-3 Lead in gasoline in United States. Source: Adapted from Nriagu, 1990.
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations Great Lakes (Flegal et al., 1989). Similar analyses have documented that over 95% of the lead in the North Pacific represents deposition of Asian and North American industrial lead aerosols (Figure 3-4). SOURCE-SPECIFIC LEAD EXPOSURE OF SENSITIVE POPULATIONS This chapter presents a general picture of the common modes of human exposure to lead—through leaded paint, air (which it enters from leaded gasoline and stationary emission), dust and soil, tap water, the workplace, and miscellaneous sources. Many of the sources and pathways of lead exposure are connected in ways that complicate exposure analysis and frustrate reduction and removal strategies (Figure 3-5); in this regard, lead in the air, lead in paint, and lead in drinking water are of particular concern. Lead in Paint Lead-based paint in and around U.S. urban housing has long been recognized as a serious and pervasive source of lead poisoning of young children. It also accounts for exposure to lead through its appearance in dust and soils. This source of lead poisoning has expanded to include workers in housing-lead abatement and homeowners who attempt rehabilitation of old housing. It also affects such workers as salvagers, construction crews, and marine maintenance staff who encounter mobilized lead in burning, cutting, chipping, and grinding. Physicochemical and Environmental Considerations Lead compounds have served as pigments for painting media for millennia; for example, the use of white lead pigment—basic lead carbonate—dates to prehistoric times (Friedstein, 1981). Older leaded paints included a linseed-oil vehicle plus a lead-based pigment and in some cases a long-chain fatty acid and a lead-based drying catalyst, or
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations FIGURE 3-9 Blood lead in Ayr Scotland, mothers before water treatment (1980, pH 5.0) and after water treatment (1982, pH 8.5). Source: Adapted from Richards and Moore, 1984.
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations TABLE 3-8 Selected Studies of Relation of Blood Lead to Tap-Water Lead Study Details Form of Model Reference 524 Boston residents; water lead up to 1,108 µg/L; blood lead up to 71 µg/dL ln(blood lead) = ln[0.041 (water lead) 0.000219 (water lead)2] EPA (1986a) analysis of Worth et al., 1981 128 Glasgow mothers; water lead up to 1,060 µg/L; blood lead up to 39 µg/dL Blood lead = 13.2 + 1.18 (water lead)1/3 U.K. Central Direct., 1982 126 Glasgow infants of above mothers Blood lead = 9.4 + 2.4 (water lead)1/3 U.K. Central Direct., 1982 114 Ayr, Scotland, mothers before and after water treatment Blood lead = 5.6 + 2.62 (water lead)1/3 Sherlock et al., 1984 7,735 middle-aged British men; water lead less than 100 µg/L Blood lead = 14.48 + 0.062 (water lead) Pocock et al., 1983 Source: Adapted from EPA, 1986a, Vol. III.
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations TABLE 3-9 Estimated Numbers of Children at Risk of Exposure to Lead in Household Plumbing Housing Type Population at Risk New Housinga 8.8 million people in new housing with lead soldered piping: (8.8 million) (7.6% of population less than 5 years old) 0.7 million (8.8 million) (12.8% of population 5–13 years old) 1.1 million Total number of children at risk in new housing 1.8 million Old Housingb If one-third of units built before 1939 contain lead pipes,c then (0.33) (0.29) = 10% of housing has lead pipes: (0.10) (17.8 million children less than 5 years old) 1.8 million (0.10) (30.1 million children 5–13 years old) 3.0 million Total number of children at risk in old housing 4.8 million a Data from Levin, 1986; based on 9.6 million in new homes, of which 92% have metal plumbing. b Data from U.S. Bureau of the Census, 1985. c Data from David Moore, Office of Policy Development and Research, HUD, Submissions to ATSDR, January 1987, and EPA Source: ATSDR, 1988. were less than 5 years old. The corresponding tally for old leaded plumbing is 4.8 million, of whom 1.8 million were under 5 years old. The two groups yield a total of 6.6 million children. According to Levin's (1986) analyses, 42 million U.S. residents receive water from public supplies having lead concentrations above 20 µg/L. ATSDR (1988) estimates that 3.8 million of those are chil-
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations 20 µg/L. ATSDR (1988) estimates that 3.8 million of those are children less than 6 years old. Levin (1987) has used regression-analysis methods described by Schwartz et al. (1985) to estimate that 240,000 children less than 6 years old will have blood lead concentrations over 15 µg/dL, in part because of exposure to lead in tap water. Lead in the Diet Physicochemical and Environmental Considerations Lead contaminates food through various pathways: deposition of airborne lead, binding of soil lead to root crops, use of lead-contaminated water and equipment in processing, use of lead-soldered cans for canned foods, and lead leaching from poorly made lead-glazed food and beverage containers. Lead is readily deposited on leaf surfaces of edible plants (e.g., Schuck and Locke, 1970) and accumulates over the life of the crop. The deposition rate in areas with high air lead content can measurably increase the lead content of leafy crops, and such surface contamination is difficult to remove by either harvest washing or rainfall (Page et al., 1971; Arvik and Zimdahl, 1974). Transfer of lead from soil to edible roots is a complex function of physicochemical factors that govern the plant uptake of lead, including those mentioned earlier in this chapter. Camerlynck and Kiekens (1982) reported that normal soils contain exchangeable lead at approximately 1 µg/g or less, and presumably some portion of the mobile lead will bind to plant roots. Lead in processing water can sometimes be the major contributor to dietary lead (Moore et al., 1979; Smart et al., 1981). However, the more common source of food contamination in processing is the use of lead-soldered cans. When lead is used as seam solder, the material can spatter on the interior of the can or the toxicant can migrate to the canned-food matrix itself. Acidic foods induce more lead release from the soldering material, although the leaching phenomenon also occurs
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations with relatively low-acidity foods, such as corn and beans, and in all cases the total amounts liberated are a function of the shelf-life of the canned goods. Lead release is accelerated by contact with oxygen once a can is opened. Lead in wine has been shown to be a potentially important source of dietary lead exposure (e.g., Elinder et al., 1988). Pottery, dinnerware, and other ceramic items are used to store foods. If containers so used have been made with poorly fired leaded glazes, lead can migrate from them into the food (extensively discussed in Lead in Housewares, U.S. House, 1988; see also Wallace et al., 1985). Key factors affecting lead release include characteristics of the glaze, the temperature and duration of food storage, and the acidity of the food. Lead can also be released on extended scrubbing and cleaning of even well-prepared glazes. Commercial American products have led to fewer problems in this regard than commercial products from other countries—such as countries in southern Europe and Latin America and mainland China—or items made by artisans and hobbyists. Most cases of lead toxicity have been associated with repeated use of vessels with problematic glazes or with prolonged food storage. Glassware is often decorated with decals or decorative surfaces that contain lead. Those surfaces have a potential for exposure through contact with young children's lips and mouths. Characteristics of General Exposure The contribution of foods and beverages to body lead burden, as reflected in blood lead, has been measured in epidemiologic surveys of infants, toddlers, and older people (EPA, 1986a). Various studies have shown that dietary lead can contribute substantially to blood lead in complex ways that reflect the influence of the tap-water lead component, dietary habits, and individual differences in lead toxicokinetics (see, e.g., EPA, 1986a). Ryu et al. (1983, 1985) found that dietary lead affects blood lead in infants in a simple linear fashion, at least in moderate exposures. Sherlock et al. (1982) and the U.K. Central Directorate on Environmental Pollution (1982) examined the relation in infants and mothers via a duplicate-diet survey. Blood lead in the infants in the U.K. study was
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations related to dietary lead by both linear and cube-root functions, whereas Sherlock and co-workers found a cube-root relation for mothers and infants. The relation becomes curvilinear when intake exceeds 100 µg/day. The slopes of the curves (µg/dL of blood vs. µg/day), which can be estimated from the above studies for an intake of 100–200 µg/day, are 0.034 for adults (Sherlock et al., 1982), 0.06 for infants (Sherlock et al., 1982), 0.053–0.056 for infants (U.K. Central Directorate, 1982), and 0.16 for infants (Ryu et al., 1985). The relation of Ryu and co-workers has the steepest slope and is based on the lowest average lead intake; the slope might level at much higher lead intakes. Dietary intakes of lead are being reduced in the United States (EPA, 1986a; ATSDR, 1988). For 2-year-olds, for example, there was a decline of approximately 75%, from 52.9 to 13.1 µg/day, from 1978 to 1985. It should be remembered that there is a distribution of lead content about the average and that the diet-survey numbers are based on relatively small samples, compared with the volume and diversity of the U.S. food supply. Several important factors in the decline include the domestic phaseout of lead-seamed beverage and food cans and the reduction in movement of lead to agronomic crops, as a result of a lowering exposure of growing crops to air lead. The latter is associated with the phaseout of leaded gasoline and tighter stationary-source regulations. Table 3-10 shows U.S. production of lead-seamed cans in 1980 and 1988; these are production figures supplied by a trade group and do not reflect independent surveys of lead-seamed cans on grocery-store shelves. The latter would include some carryover from past years' production, depending on canned-food shelf life. Scope of the Problem As noted by Mushak and Crocetti (1989), virtually all sensitive populations are exposed to some lead in food, owing to the relatively centralized food production and distribution system in the United States and other developed nations. They also estimated on the basis of food-lead concentration distribution profiles, adjustments for lead reduction in foods, intakes from other lead sources—that approximately 5% of the 21 million U.S. children less than 6 years old, or 1 million children,
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations TABLE 3-10 Changes in Percentage of Lead-Soldered Food and Soft-Drink Cans (millions of cans)a 3-Piece Cans Year Category Total No. Cans (2-piece + 3-piece) No. % of Total No. Lead-Soldered, millions % of Total 1980 Food and soft-drink cans 54,173 30,568 56.4 25,433 46.9 Food cans 28,432 26,697 93.9 24,405 85.8 Soft-drink cans 25,741 3,871 15.0 1,028 4.0 1988 Food and soft-drink cans 73,001 19,062 26.1 1,626 2.2 Food cans 28,071 19,062 67.9 1,626 5.8 Soft-drink cans 44,930 0 0 0 0 a Data from Can Manufacturers Institute, unpublished material.
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations will have increases in blood lead concentrations because of intake of lead in food. Although the main theme of this report is ordinary environmental exposure to lead, occupational settings present the highest, continuous lead exposures of all. Furthermore, workers transport lead from work to their homes, where their families, including children, are exposed to it (e.g., Baker et al., 1977; Milar and Mushak, 1982). Various traditional customs and medications can result in high lead exposures. Reports of such exposures are numerous in the clinical literature from various regions—Arab countries (Aslam et al., 1979), the Indian-Pakistani subcontinent (Pontifex and Garg, 1985), China (CDC, 1983a), and Latin America (Bose et al., 1983; CDC, 1983b; Trotter, 1985; Baer et al., 1987). The preparations often include lead compounds as major or principal ingredients, so the poisoning potential is high. In the United States, the most familiar type of lead-containing preparation is a Mexican-American folk preparation that contains lead oxides (Bose et al., 1983; Trotter, 1985; Baer et al., 1987). Greta (lead (II) oxide) and azarcon (mixed-valence lead tetroxide, PbO2.2PbO) are used to treat digestive disorders; their use produces diarrhea or vomiting. Use of these medicines is widespread and can result in serious lead poisoning in children. SUMMARY It is difficult to rank sources of lead exposure by their importance for health by such simple criteria as numbers of affected persons. Simultaneous exposure to multiple lead sources is inevitable; different sources of lead are often associated with different degrees of lead poisoning, which would make it necessary to rank by effect severity, as well as frequency; and sources differ in distribution among sensitive populations. An alternative is to provide a ranking by relative overall impact, which includes the potential of a source for the most severe poisoning, its relative pervasiveness, estimates of numbers of persons exposed to it, and the relative difficulty of abating it. The sensitive populations within the general, nonoccupational sector are preschool children, fetuses (via maternal exposure), and pregnant
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations women (as surrogates for fetuses). On the basis of overall public-health impact on those populations, sources can be combined into two groups. Lead in paint, lead in dusts and soils, and lead in drinking water constitute the more important group today. In that group, leaded paint ranks first in importance for young children, followed closely by lead in dusts and soils, and then by tap-water lead. For adults, tap-water lead is probably the exogenous source of most concern. (Endogenous exposure to lead can occur when subjects mobilize lead and calcium from bone; this typically occurs in adults or in children who break bones.) In the United States, leaded gasoline at present concentrations and dietary lead make up the second group, of somewhat less concern. These statements of importance are relative; they do not imply that any specific source is unimportant as a contributor to lead body burdens or to earlier effects in populations as a whole. The body combines lead absorbed from all sources into one dose. The phasedown of leaded gasoline is greatly reducing the input of lead to environmental compartments. However, the inventory of 4–5 million metric tons of lead still in the environment because of past leaded-gasoline use will continue to contribute to the risk of exposure of sensitive populations. Outside the United States, various approaches to leaded-gasoline control are being taken, from modest control actions to phaseout and phasedown regulations. Leaded paint (and its transport to dusts and soils) is a major national source of exposure of children. Dust and soil lead comes from leaded-paint transfer and atmospheric fallout, and many studies have documented its contribution to lead body burdens of young children. Quantitative assessments of the relative contributions of dust and soil lead to total body lead, such as blood lead concentration, have been the subject of diverse studies. In addition, particle size, chemical species of lead, and soil and dust matrices are important modifiers of the soil and dust lead hazard eventually reflected in lead intake and absorption. Pathways of exposure to tap-water lead are multiple: direct drinking, beverages prepared with contaminated water, and foods cooked in lead-contaminated water. Patterns of leaded-water use can amplify toxicity risk. Ingestion on an empty stomach, a common occurrence, greatly increases the rate of lead absorption. The use of water in elementary schools and other child facilities is intermittent, with extended standing time over weekends and in vacation periods. That allows buildup of lead in fountains and water lines.
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Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations Most developed countries, including the United States, have complex food production and food distribution systems that permit lead contamination. Virtually everyone has some exposure to dietary lead, and lead concentrations in food can be quite high. But lead in foods of older children and infants has been reduced through phasing out of lead-soldered cans for milk and fruit juices and reduced input into food crops. There does appear to be a persisting problem with lead leaching mainly from poorly made and lead-glazed food and beverage pottery. It could also be that even well-made vessels with lead glazes will lose lead through extended surface abrasion, as in scrubbing, washing, and rinsing.
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