Dust, lead from leaded gasoline

Most lead used by industry comes from mined ores ("primary") or from recycled scrap metal or batteries ("secondary"). Human activities (such as the former use of "leaded" gasoline) have spread lead and substances that contain lead to all parts of the environment. For example, lead is in air, drinking water, rivers, lakes, oceans, dust, and soil. Lead is also in plants and animals that people may eat. See Chapter 3 for more information on the physical and chemical properties of lead. Chapter 4 contains more information on the production and use of lead. 

Soil Pb is an important pathway of human Pb exposure (Mielke Reagan 1998). Empirical evaluation between soil Pb and BPb indicated a strong positive and nonlinear association between soil Pb and BPb (Mielke et al., 2007a). The soil Pb footprint of New Orleans indicates that in the case of public and private properties an enormous disparity exists between the inner- city and outlying areas of New Orleans that cannot be attributed to older Pb-based paint alone dust Pb from the previous use of lead additives to gasoline provide a better explanation between... 

Of the six heavy metals discussed in this chapter, Pb has been studied extensively with respect to the environmental effects. Clair Patterson, the father of environmental Pb studies, in one of his many major publications concerning the global Pb cycle (Patterson and Settle, 1987), noted that during pre-industrial times Pb in the troposphere originated from soil dusts and volcanic gases. In modern times (1950-1980) the proportion of natural Pb in the atmosphere is overwhelmed by the industrial sources of smelter emissions and automobile exhausts. Lead air pollution levels measured near our Nation s roadways decreased 97% between 1976 and 1995 due to the consequence of the Clean Air Act that eliminated leaded gasoline which interfered with the performance of catalytic converters. 

A second factor may be emergence or existence of a floor to further atmospheric Pb emission declines in certain locales. For example, modeled estimates indicate that 90% of the atmospheric Pb particulate loading in California is attributable to reentrainment of leaded roadway dusts from roadways contaminated over past decades by leaded gasoline combustion and fallout (Harris and Davidson, 2005). Lankey et al. (1998) noted that resuspension accounts for 40% of Pb emissions in the South Coast Air Basin of CA, while a much higher fraction of 75% was reported for lead resuspension in an Armenian city (Kurlgian et al., 2002). 

Illustrative household dust lead amounts, as concentrations or loadings, reported in the United States and the United Kingdom are contained in Table 6.27. Levels by both metrics are quite high, ranging in time from the 1970s to the late 1990s. This persistence of interior dust lead content extends into later years after leaded gasoline was removed from vehicular fuel. 

As noted earlier, 108(a)(2) of the CAA as amended in 1974 and administrative action by the EPA Administrator in early 1976 led to designation of lead as a criteria pollutant. A criteria pollutant requires air quality criteria developed through an air quality criteria document that becomes the basis for setting primary and secondary NAAQS. Criteria pollutants at the time of the CAA mostly covered significant emissions from mobile sources—cars, trucks, buses, etc.— but with phaseout of leaded gasoline, there was more focus on stationary sources and those postdepositional pathways compartments for lead such as roadside dusts. 

Lead-based paiat ra buildings, interiors and exteriors Lead food cans Lead gasoline and dust Lead water pipes Soil Oil, coal, combustion and solid waste Metal refining, smelting, and manufacturing processes emissions Emissions from alkyl lead manufacturers Lead battery manufacturers and recyclers Portland cement manufactnring Painted surfaces weathering... 

The study of ambient air lead concentrations has also shown the significant correlation between the combustion of leaded gasoline and soil lead concentrations. The EPA has noted that air lead concentration decreases as you travel from the center of a city and that soil lead levels are a direct function of the deposition of ambient air lead (see EPA reports for 1986). The contribution of leaded gasoline emissions and soil lead levels to interior house dust is evident in studies showing that lead in house dust is related to exterior lead levels (Chaney, 1989). 

One of the important factors in determining the contribution of lead in soil and dust to lead levels in children is bioavailability (Chaney, 1989). Factors influencing how much lead in soil and dust ingested by children may be absorbed into the blood stream include the physical and chemical properties of the lead, particle size, and the nutritional status of the particular child. Lead from leaded gasoline emissions are predominately small particles and therefore readily bioavailable to children (Chaney, 1989). The bioavailability of lead in paint varies with particle size and the type of lead compound present in the paint (e.g., lead carbonate, lead sulfate). 

One can compare the biomarker-based risk derived for lead with population-based biomonitoring results. Data from NHANES 2000-2001 can be used to estimate the number of children in the United States who have increased blood lead (CDC 2005). Blood lead in U.S. children declined dramatically after the removal of lead from gasoline—from a median of 15 pg/dL in 1978 to 2 pg/dL in 1999 (Rogan and Ware 2003). Nonetheless, an estimated 1.6% of U.S. children 1-5 years old had blood lead greater than 10 pg/dL in 1999-2002, according to NHANES data (CDC 2005). The major exposure sources of lead for U.S. children are deterioration of lead-based paint and the resulting dust and soil contamination (CDC 2005). 

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