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193 <br /> 5. POTENTIAL FOR HUMAN EXPOSURE <br /> ed on a survey of 900 public water supply systems, EPA (1988b) estimated that 99% of the 219 million <br /> pie in the United States using public water supplies are exposed to drinking water with levels of lead <br /> S µg/L and approximately 2 million people are served by drinking water with levels of lead greater than <br /> µg/L. A survey of 580 cities in 47 states indicated that the national mean concentration of lead in <br /> as nking water was 29 µg/L after a 30-second flushing period (EPA 1988f, 1989h); however, it was estimated <br /> )ut at in 1988 the average lead content of drinking water was 17 µ91L (Cohen 1988b). In 1986, the Safe <br /> 3.g rinking Water Act Amendments banned the use of lead solder or flux containing more than 0.2% lead <br /> )m d the use of lead pipes or fittings that contained more than 8% lead (EPA 1988f, 1989h). <br /> ary <br /> ing between 10 and 30 µg/L can be found in drinking water from households, schools, and <br /> ing d levels rang <br /> result of plumbing corrosion and subsequent leaching of lead. The combination of <br /> as (fice buildings as a <br /> of rrosive water and lead pipes or lead-soldered joints in either the distribution system or individual houses <br /> vel n create localized zones of high lead concentrations that exceed 500 µg/L (EPA 19890. <br /> 979 <br /> at survey of 1,484 drinking water samples taken from various districts of the American Water Works <br /> of rvice Company showed that average lead levels in a 1-liter first-draw sample for copper, galvanized, and <br /> %) lastic pipes were 9, 4.2, and 4.5 µg/L, respectively. These data show that even plumbing that did not use <br /> d solder for copper pipes (e.g., plastic pipes) contained significant levels of lead, primarily from the brass <br /> ucet fixtures which are used in almost all plumbing. The brass fixtures may account for approximately <br /> air ae-third of the lead in the first-draw water (Lee et al. 1989). <br /> lies. <br /> ring .4.3 Soll <br /> the <br /> il derived from <br /> ). a natural lead content of so crustal rock, mostly as galena (PbS), typically ranges from <br /> a0c <br /> 97). e a 30 µ91g soil. However, the concentration of leafrom anthropogenic sources. The concentration <br /> in the top layers of soil varies widely due to <br /> )Oc). tposition and accumulation of atmospheric particulates ion <br /> f soil lead generally decreases as distance from contaminating sources increases. Next to roadways, it is <br /> tim µated that the levels of lead in the upper layer of soil are typically 30-2,000 higher than natural <br /> �vels, although these levels drop exponentially up to 25 m from the roadway (EPA 1986a). Soil adjacent <br /> o a smelter in Missouri had lead levels in excess of 60,000 µg/g (Palmer and Kucera 1980). Soils adjacent <br /> hout <br /> houses with exterior lead-based paints may have lead levels of >10,000 µg/g (EPA 1986a). Extractable <br /> fable din surface soil samples (0-5 cm depth) from an agricultural area near Within car battery <br /> mer the plan <br /> (pH, lant (taken at 0.3 km from the source) decreased from 117 µ919 to 1 µg/9 Y <br /> tions opped operating as a result of lead reactions with the soil (Schalscha et al. 1987). Soil collected by <br /> ough aping the top 2.5 cm of soil surface near homes and streetside in Louisiana and Minnesota contained <br /> nater Mian lead concentrations of greater than 840 µg/g in New Orleans and 265 µg/g in Minneapolis,whereas <br /> areas k small towns of Natchitoches, Louisiana and Rochester, Minnesota, had soil lead concentrations of less <br /> khan 50 µg/g and 58 µg/g, respectively, suggesting that lead contaminated soil is a major source of lead <br /> 0sure in urban areas (Mielke 1992). <br /> lead <br /> and and Min <br /> �astal ladies carried out in Marylnesota indicate that within large light-industrial urban settings such <br /> Is generally occur in inner-city areas, especially where high traffic <br /> ound Baltimore, the highest soil lead leve <br /> 1983, 1985, 1989) and that the amount of lead in the soil is <br /> lakes bws have long prevailed (Mielke et al. <br /> a the %trelated with the size of the city (Mielke 1991). In 1981, soil lead levels in the Minneapolis/St. Paul <br /> ;ition �t►er-city area were 60 times higher (423 µg/g) than levels found in rural Minnesota (6.7 µg/g),with almost <br /> into the increase (95%n) resulting from the combustion of leaded gasoline. A study conducted in <br /> Minneapolis, Minnesota after the lead content of gasoline has been significantly reduced, found that median <br /> %il lead levels taken from the foundations of homes, in yards, and adjacent to the street were 700 <br />