LEAD 355 CHAPTER 5. POTENTIAL FOR HUMAN EXPOSURE 5.1 OVERVIEW Pb and Pb compounds have been identified in at least 1,287 and 46 sites, respectively, of the 1,867 hazardous waste sites that have been proposed for inclusion on the EPA National Priorities List (NPL) (ATSDR 2019). However, the number of sites evaluated for Pb is not known. The number of sites in each state is shown in Figures 5-1 and 5-2, respectively. Of these 1,287 sites for Pb, 1,273 are located within the United States, 2 are located in the Virgin Islands, 2 are located in Guam, and 10 are located in Puerto Rico (not shown). All the sites for Pb compounds are only in the United States. Figure 5-1. Number of NPL Sites with Lead Contamination LEAD 356 5. POTENTIAL FOR HUMAN EXPOSURE Figure 5-2. Number of NPL Sites with Lead Compound Contamination • Pb is an element found in concentrated and easily accessible Pb ore deposits that are widely distributed throughout the world. • The general population may be exposed to Pb in ambient air, foods, drinking water, soil, and dust. For adults, exposure to levels of Pb beyond background are usually associated with occupational exposures. • For children, exposure to high levels of Pb are associated with living in areas contaminated by Pb (e.g., soil or indoor dust in older homes with Pb paint). Exposure usually occurs by hand-to- mouth activities. • As an element, Pb does not degrade. However, particulate matter contaminated with Pb can move through air, water, and soil. • Atmospheric deposition is the largest source of Pb found in soils. Pb 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 Pb. • Pb adsorbs strongly to most soils, which limits the rate of leaching of Pb from soil. Soil acidity (pH) is the most important factor affecting solubility, mobility, and phytoavailability of Pb in soil. LEAD 357 5. POTENTIAL FOR HUMAN EXPOSURE Other conditions that increase Pb mobility in soils are reducing conditions (low redox potential; for example, anoxia) and high chloride content. Pb is dispersed throughout the environment primarily as the result of anthropogenic activities. In the air, Pb is in the form of particles and is removed by rain or gravitational settling. The solubility of Pb compounds in water is a function of pH, ionic strength, and the presence of humic material. Solubility is highest in acidic water. Soil and sediment are an important sink for Pb. Because Pb is strongly adsorbed to soil, very little is transported through runoff to surface water or leached to groundwater except under acidic conditions. Anthropogenic sources of Pb include the mining and smelting of ore, manufacture and use of Pb-containing products, combustion of coal and oil, and waste incineration. Many anthropogenic sources of Pb, most notably leaded gasoline, Pb-based paint, Pb solder in food cans, Pb-arsenate pesticides, and shot and sinkers, have been eliminated or are regulated. Pb compounds released to the environment may be transformed to other Pb compounds; however, Pb is an element and cannot be destroyed or degraded. Because Pb does not degrade over time, deposits of Pb in the environment by current and former uses leave their legacy as higher concentrations of Pb in the environment. These deposits can continue to be a source for potential Pb exposure (e.g., soil particles containing Pb also may be resuspended and redeposited). Plants and animals may bioconcentrate Pb, but Pb is not biomagnified in the aquatic or terrestrial food chain. The general population may be exposed to Pb in ambient air, foods, drinking water, soil, and dust. Segments of the general population at highest risk of health effects from Pb exposure are preschool-age children and pregnant women and their fetuses. Other segments of the general population with an increased exposure include individuals living near sites where Pb was produced or disposed. Some of the more important Pb exposures have occurred as a result of living in urban environments, particularly in areas near stationary emission sources (e.g., smelters); renovation of homes containing Pb-based paint; pica (the compulsive, habitual consumption of nonfood items); contact with interior Pb paint dust; occupational exposure; and secondary occupational exposure (e.g., families of workers in Pb industries). Higher exposures may also occur to residents living in close proximity to NPL sites that contain elevated levels of Pb. The primary source of Pb in the environment has historically been anthropogenic emissions to the atmosphere. In 1984, combustion of leaded gasoline was responsible for approximately 90% of all anthropogenic Pb emissions. The United States gradually phased out the use of Pb alkyls in gasoline, and by 1990, auto emissions accounted for only 33% of the annual Pb emissions (EPA 1996b). Use of Pb LEAD 358 5. POTENTIAL FOR HUMAN EXPOSURE additives in most motor fuels was totally banned after December 31, 1995 (EPA 1996a). The ban went into effect on February 2, 1996. The ban did not include off-road vehicles, including aircraft, racing cars, farm equipment, and marine engines. Pb additives are still used in fuels for piston driven airplane engines and it continues to be commercially available for other off-road uses. Atmospheric deposition is the largest source of Pb found in soils. Pb 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 Pb. Pb 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. The speciation of Pb in these media varies widely depending upon such factors as temperature, pH, and the presence of humic materials. Pb is largely associated with suspended solids and sediments in aquatic systems, and it occurs in relatively immobile forms in soil. 5.2 PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 5.2.1 Production The most important mineable Pb ore is galena (PbS), which is commonly associated with other minerals, typically zinc ores. Anglesite (PbSO4) and cerussite (PbCO3), formed by the weathering of galena, are two other important Pb minerals. Pb is processed from ore to refined metal in four steps: ore dressing; smelting; drossing; and refining. Ore dressing involves crushing, grinding, and beneficiation (concentration) (King et al. 2014). Since 1998, U.S. production of Pb has shifted to the domestic secondary Pb industry (USGS 2014). Since 2014, primary Pb metal has not been produced in the United States (USGS 2016). The Doe Run Resources Corporation operated the last domestic primary Pb smelter-refinery facility in the United States at Herculaneum, Missouri and it was closed at the end of 2013. Pb-acid batteries are the dominant source of recoverable Pb scrap, accounting for nearly 100% of all secondary Pb (USGS 2016, 2019). Domestic mines produced 368,000 metric tons of recoverable Pb in 2014, a more than 11% increase from 2013. Nearly all of the secondary Pb produced in 2014 was by 7 companies operating 12 plants in Alabama, California, Florida, Indiana, Minnesota, Missouri, New York, Pennsylvania, Tennessee, and Texas (USGS 2016). Secondary (recycled) Pb, derived from mainly scrapped Pb-acid batteries, accounted for all of the domestic refined Pb production in 2014. Due to plant closings, U.S. production LEAD 359 5. POTENTIAL FOR HUMAN EXPOSURE of secondary refined Pb decreased in 2014 by 11% to 1.02 metric tons, from 1.5 metric tons in 2013 (USGS 2016). World mine production of Pb was 4.91 million metric tons in 2014, a decrease of 9% from 2013. The United States accounted for approximately 8% of global mine production in 2014. The United States ranked third in global mine production behind China and Australia, which accounted for 49 and 15%, respectively. World production of refined Pb (primary and secondary) was 10.6 million metric tons in 2014. China produced about 45% of global refined Pb in 2014 with the United States as the second leading world producer of refined Pb, accounting for 10% (USGS 2016). In 2017 and 2018 worldwide mine production of Pb was reported as 4.58 and 4.40 million metric tons, respectively (USGS 2019). As in previous years, China was the dominant producer accounting for nearly half of the world production. Manufacturers and importers of Pb metal and selected Pb compounds are listed in Table 5-1. These data are from EPA’s Chemical Data Access Tool (now called Chemical Data Reporting [CDR]), which provides information on chemicals submitted to the EPA under the Toxic Substance Control Act that are manufactured or imported into the United States. Manufacturing volumes for more recent years are not available in the CDR as most manufacturers have withheld these data as confidential business information; however, as in previous years, the U.S. Geological Survey (USGS) reported total Pb mined in the United States in its Minerals Commodity summaries and these data for 2015–2018 are provided in Table 5-2. According to the USGS, five Pb mines located in the state of Missouri along with five mines in Alaska, Idaho, and the state of Washington accounted for all domestic Pb mine production (USGS 2019). Table 5-1. U.S. Manufacturers of Lead Metal and Selected Lead Compounds Domestic manufacturing Company Location (pounds/year) Lead 5n Plus Inc.