Laserfiche WebLink
192 <br /> 5. POTENTIAL FOR HUMAN EXPOSURE <br /> 5.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT ased on <br /> pie in <br /> 5.4.1 Air 5 gg/L <br /> !tom-• <br /> Lead levels in the ambient air have been monitored in a number of remote, urban, and nonurban areas finking v <br /> of the United States and other countries (EPA 1986a). Atmospheric lead concentrations vary widely but hat in 15 <br /> usually decrease with vertical and horizontal distance from emission sources; they are generally 0.3-0.8 rinking <br /> times lower indoors thati outdoors, with an average ratio of 0.5. Levels of lead in ambient air range from ad the u <br /> 7.6x10'5 Ag/m3 in remote areas such as Antarctica (Maenhaut et al. 1979) to >10 'Ug/m3 near stationary <br /> sources such as smelters, with an average annual concentration of below 1.0 Ag/M3 for urban monitoring d level <br /> sites. Unusually high levels may be found in areas of high traffic density and in confined places, such as ffice buil <br /> parking garages and tunnels, where leaded auto exhaust is found. Monitoring data from a composite of Drrosive <br /> 147 sampling sites throughout the United States indicate that the maximum quarterly average lead level 3n create <br /> in urban air during 1984 was 0.36 gg/m3 and 0.2-0.4 ug/m3 in 1986 (EPA 1988f, 1989h). Between 1979 <br /> and 1983, atmospheric lead concentrations in precipitation in Minnesota decreased from 29 to 4.3 gg/L at survey <br /> urban locations and from 5.7 to 1.5 gg/L at rural locations, indicating a reduction in lead emissions of rvice Cc <br /> more than 80%. This reduction resulted primarily from the decreased use of leaded gasoline (down 56%n) Id <br /> ctic pip <br /> and the use of more efficient emission controls on other sources (Eisenreich et al. 1986). solder <br /> ucet fixt <br /> In the 1960s, the National Air Surveillance Network (NASN) was established to monitor ambient air )ne-third <br /> quality levels of total particulate solids and trace metals, including lead, at sites in larger American cities. <br /> In 1981 some old sites were eliminated and new ones were added to give 139 urban sites for air monitoring ,4.3 Sc <br /> purposes. In 1988, the average lead concentration for all 139 sites was 0.085 gg/m3, well below the <br /> National Ambient Air Quality Standard of 1.5 ug/m3 that has been recommended for lead (EPA 1990c). le nature <br /> In 1988, the average concentration of 18 point-source sites was 0.4 11g/m3, clown from 2.9 ug/m3 in 1979, 10 to 3C <br /> and the average concentration for urban sites was 0.1 gg/m3, down from 0.8 11g/m3 in 1979 (EPA 1990c). eposition <br /> This was thought to be caused by decreased use of leaded gasolines. f soil leas <br /> timated <br /> 5.4.2 Water els, alth <br /> a smelt( <br /> Lead has been monitored in surface water, groundwater, and drinking water, and in sediments throughout houses <br /> the United States and other countries. The concentration of lead in surface water is highly variable d in su: <br /> depending upon sources of pollution, lead content of sediments, and characteristics of the system (pH, lant (tak( <br /> temperature, etc.). Mean levels of lead in surface water measured at 50,000 surface water stations upped of <br /> throughout the United States are 3.9 gg/L (based on 39,490 occurrences) (Eckel and Jacob 1988), although aping ti <br /> levels as high as 890 gg/L have been measured (EPA 1986a). Lead is estimated to be present in sea water 4edian lea <br /> at approximately 0.005 gg/L (EPA 1982x). Lead concentrations in surface water are higher in urban areas le small t <br /> than in rural areas (EPA 1982a). an 50 Al <br /> osure ii <br /> Sediments contain considerably higher levels of lead than corresponding surface waters. The average lead <br /> content of river sediments is estimated to be approximately 20,000 pg/g,whereas the average level in coastal tidies car <br /> sediments is approximately 100,000 gg/g (EPA 1982a). Surface sediment concentrations in Puget Sound 4 Baltimo <br /> ranged from 13 gg/g to 53 gg/g (Bloom and Crecelius 1987). An analysis of sediments taken from 10 lakes �M have <br /> in Pennsylvania indicated that the elevated lead values were not derived from leaching of lead from the �a►related <br /> native rocks as a result of acid deposition, but rather originated from anthropogenic lead deposition �4er-city a <br /> (probably from automotive emissions) on the soil surface and subsequent runoff of soil particulates into 4 the in <br /> the lake (Case et al. 1989). �linneapol: <br /> b� lead le <br /> X' <br />