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—Room Preceding page blank 181 5. POTENTIAL FOR HUMAN EXPOSURE S.1 OVERVIEW Lead is dispersed throughout the environment primarily as the result of anthropogenic activities. Environmental fate processes may transform one lead compound to another; however, lead is not degraded Ind is still available for human exposure, even though the compounds containing it vary enormously. Ibe general population is exposed to lead in ambient air, in many foods, in drinking water, and in dust. Segments of the general population at highest risk of health effects from lead exposure are preschool-age children, pregnant women and their fetuses, and white males between 40 and 59 years of age. Within these groups, relationships have been established between lead exposure and adverse health effects. Human exposure to lead above baseline levels is common. Some of the more important lead exposures occur as a result of living in urban environments, particularly in areas with high traffic flows, or near --� stationary emission sources (e.g., smelters), consumption of produce from family gardens, renovation of homes containing lead-based paint, pica (an abnormal eating habit in children), contact with interior lead aint dust, occupational exposure, secondary occupational exposure (e.g., families of workers using lead), smoking, and wine consumption. Higher than normal exposures may also occur to residents living in close proximity to NPL sites that contain elevated levels of lead. The highest and most prolonged lead exposures are found among workers in the lead smelting, refining, and manufacturing industries. the primary source of lead in the environment is anthropogenic emissions to the atmosphere. As of 1984, combustion of leaded gasoline was responsible for approximately 90% of all anthropogenic lead emissions. EPA has been phasing out the use of lead alkyls in gasoline, however, and as of 1988, auto emissions accounted for only 34% of the annual lead emissions (EPA 1990c). Atmospheric deposition is the largest source of lead found in soils. Lead is transferred continuously between air, water, and soil by natural chemical and physical processes such as weathering, runoff, precipitation, dry deposition of dust, and stream/river flow; however, soil and sediments appear to be important sinks for lead. Lead particles are removed from the atmosphere primarily by wet and dry deposition. The average residence time in the atmosphere is 10 days. Over this time, long-distance transport, up to thousands of kilometers, may take place. Lead is extremely persistent in both water and soil. The speciation of lead in these media varies widely depending upon such.factors as temperature, pH, and the presence of humic materials. Lead is �rgely associated with suspended solids and sediments in aquatic systems, and it occurs in relatively hnmobile forms in soil. dead has been found at 922 of the 1,300 NPL hazardous waste sites (HAZDAT 1992). The frequency of ttiese sites within the United States can be seen in Figure 5-1. Of these sites, 8 are located in the �otnmonwealth of Puerto Rico (not shown). S2 RELEASES TO THE ENVIRONMENT �ad is a naturally occurring element that has been found in the earth's crust and in all compartments of �S biosphere. Although both natural and anthropogenic processes are responsible for the distribution of td throughout the environment, anthropogenic releases of lead are predominant. Lead is regulated by veral federal statutes and is a priority water pollutant and a hazardous air pollutant (see Chapter 7). though combustion of leaded gasoline used to be the primary source of anthropogenic atmospheric pleases of lead, industrial releases to soil from nonferrous smelters, battery plants, and chemical plants