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188 5. POTENTIAL FOR HUMAN EXPOSURE In 1988, it was estimated that 28.1 million pounds of lead was transferred off-site rather than released The ai directly to the environment and 28 million pounds of lead were released on-site to land (see Table 5-1) dissol\ (TRI88 1990). appro) in soft In 1986, an NPL hazardous waste site was identified in Genesee County, Michigan that contained a landfill 5.4, t and nine surface impoundments. The facility had accepted sludge and residual waste from a chemical is in t warehouse as well as other hazardous wastes. Analysis of the soil, sediments, and water samples taken most s from the impoundments found lead to be present in sludge samples at a maximum concentration of compo 11.6 mg/L, in sediment samples at a maximum concentration of 4,770 mg/kg dry weight, in soil samples water at 1,560 mg/kg, and in water samples at a maximum concentration of 25 mg/L (EPA 1986d). Thirty of 97 soil samples taken at a former foundry site in Dubuque, Iowa, which was on the NPL, had lead A sign concentrations exceeding 5.0 mg/L as determined using the EP toxicity test (the maximum total lead consist concentration was 4,890 mg/kg). Most of the positive samples were from soil depths of less than 2.5 feet or oth (Mundell et al. 1989). Lead r carried Levels of lead found in most soils not impacted by paint emission sources largely reflect atmospheric solids i deposition patterns (EPA 1982a). In some soils, deterioration and removal of lead-based paint from (Getz painted surfaces are the primary sources of lead (EPA 1986a). The fa 5.3 ENVIRONMENTAL FATE precipi organic 5.3.1 Transport and Partitioning factors ion-exc In the atmosphere, lead exists primarily in the particulate form. Upon release to the atmosphere, lead soils is particles are dispersed and ultimately removed from the atmosphere by wet or dry deposition. in soil, Approximately 40-70% of the deposition of lead is by wet fallout; 20-60% of particulate lead emissions strongli from automobiles are deposited near the source. An important factor in determining the atmospheric as a re transport of lead is particle size distribution. Large particles, particularly those with aerodynamic diameters soil sur of >2 µm, settle out of the atmosphere fairly rapidly and are deposited relatively close to emission sources be imm (e.g., 25 m from the roadway after being emitted in motor vehicle exhaust), whereas smaller particles may in the be transported thousands of kilometers. The dry deposition velocity for lead particles with aerodynamic content diameters of 0.06-2.0 µm was estimated to range between 0.2 and 0.5 cm/second in a coniferous forest in bound i Sweden, with an overall particle-size weighted dry deposition velocity of 0.41 cm/second (Lannefors et al. in soil ; 1983). However, the use of an average net deposition velocity of 0.6 cm/second and an average a pH o atmospheric residence time of 10 days has been recommended by the National Academy of Sciences (NAS same PI 1980). The amount of lead scavenged from the atmosphere by wet deposition varies widely; wet deposition Ions• can account for 40-70% of lead deposition depending on such factors as geographic location and amount Plants of emissions in the area (Nielsen 1984). An annual scavenging ratio (concentration in precipitation to latter p concentration in air) of 0.18x10-6 has been calculated for lead, making it the lowest value among seven stneltinl trace metals studied (iron, aluminum, manganese, copper, zinc, cadmium), thus indicating that lead is removed from the atmosphere by wet deposition relatively quickly. Wet deposition is more important than The dog dry deposition for removing lead from the atmosphere; the ratio of wet to dry deposition was calculated conditio to be 1.63, 1.99, and 2.50 for sites in southern, central, and northern Ontario, Canada, respectively (Chan presenc( et al. 1982). Lead particles from automobile emissions are quite small (<0.1 µm in diameter) but can (CEC) c grow in size by coagulation (Chamberlain et al. 1979). Lead has been found in sediment cores of lakes and a d, in Ontario and Quebec, Canada, that were remote from any point sources of lead releases, indicating that COnditio long-range atmospheric transport was occurring (Evans and Rigler 1985). soluble 1 id the si