Soil, lead

Preventive Measures. The intake uptake biokinetic model (lUBK) projects the impact of lead in the environment on blood lead. This model assumes conservatively high levels of intake and cannot account for chemical speciation, thus over-predictions of blood lead levels often occur. Nonetheless, because of the allegations of the impact of blood lead and neurobehavioral development, blood lead levels in children are being reduced adrninistratively to below 10 //g/dL. In order to do so, soil leads are being reduced to a level of between 500—1000 ppm where remediation is required. 

Usually the annual variations in the specific resistance of the soil lead only to small changes in the current circuit resistance so that adjustment of the protection... 

House dust. Houses are enclosed spaces and tend to accumulate dust from the outside. There are also internal sources of house dust. The concentration ratio [MJhouse dust/[M]soil has a mean of 0.33 (standard deviation = 0.09) for the ten elements Mn, Fe, La, Sm, Hf, Th, V, Al, Sc and Ce suggesting that around 33% of house dust is soil (93). The concentration ratio for the two surface dusts, [M]house dust/[M]street dust is >1 for the elements Cu, Co, As, Sb, Zn, Cd, Au, Cl and C suggesting these elements also have an internal component. All of these elements, as well as Pb and Br, are enriched in house dust relative to their concentrations in soil. Lead and bromine originate mainly from outside the house, and probably from street dust and motor vehicle emissions and, in the case of lead, from paint. When the concentrations of lead in house dust are very high this generally signifies an internal source of lead paint, especially in older houses. 

Table I indicates the sample size and population estimates of preschoolers by study area and stratum. Though all strata for the Dixie site are shown, at the Dixie site the configuration and location of the major traffic artery in relation to the smelter site did not allow analysis of the contribution of vehicular traffic to soil lead. The contribution of the smelter to soil lead levels was possible at the RSR site and the reference site.

Table VIII. Medians of Soil Lead (ppm) by Distance, Traffic, and Study Area...

Phytoremediation in the root zone. Proteins and enzymes produced by the plant can be exuded by the roots into the rhizosphere. These plant products target contaminants in the surrounding soil, leading to precipitation or immobilization in the root zone. This mechanism within phytostabilization may reduce the fraction of the contaminant in the soil that is bioavailable. 

Accumulation of cadmium in agricultural soils leads to increased cadmium uptake by crops and vegetables, grown for human consumption.17... 

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. 

Numerous observations of non-linear relationships between PbB concentration and lead intake in humans provide further support for the existence of a saturable absorption mechanism or some other capacity limited process in the distribution of lead in humans (Pocock et al. 1983 Sherlock et al. 1984, 1986). However, in immature swine that received oral doses of lead in soil, lead dose-blood lead relationships were non-linear whereas, dose-tissue lead relationships for bone, kidney and liver were linear. The same pattern (nonlinearity for PbB and linearity for tissues) was observed in swine administered lead acetate intravenously (Casteel et al. 1997). These results suggest that the non-linearity in the lead dose-PbB relationship may derive from an effect of lead dose on some aspect of the biokinetics of lead other than absorption. Evidence from mechanistic studies for capacity-limited processes at the level of the intestinal epithelium is compelling, which would suggest that the intake-uptake relationship for lead is likely to be non-linear these studies are discussed in greater detail in Section 2.4.1. 

Adult subjects who ingested soil (particle size less than 250 im) from the Bunker Hill NPL site absorbed 26% of the resulting 250 pg/70 kg body weight lead dose when the soil was ingested in the fasted state and 2.5% when the same soil lead dose was ingested with a meal (Maddaloni et al. 1998). There are no reported measurements of the absorption of soil-bome lead in infants or children. Additional evidence for a lower absorption of soil-bome lead compared to dissolved lead is provided from studies in laboratory animal models. In immature swine that received oral doses of soil from one of four NPL sites (75 or 225 ig Pb/kg body weight), bioavailability of soil-bome lead ranged from 50% to 82% of that of a similar... 

People living near hazardous waste sites may be exposed to lead via ingestion of contaminated water or soils or by inhalation of lead particles in the air. For people not living in the vicinity of hazardous waste sites, the major route of exposure to lead is ingestion, particularly of lead-contaminated water, food, soil, lead-based paint chips, or dusts (the latter two are particularly relevant to children in lower-income urbanized populations). For occupationally exposed individuals, the predominant route of exposure is the inhalation of lead particles with oral ingestion also important in many cases. 

The primary source of lead 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 lead emissions. EPA phased out the use of lead alkyls in gasoline, however, and by 1990, auto emissions accounted for only 33% of the annual lead emissions (EPA 1996h). Use of lead additives in motor fuels was totally banned after December 31, 1995 (EPA 1996f). The ban went into effect on February 2, 1996. Atmospheric deposition is the largest source of lead found in soils. Lead is transferred... 

Lanphear et al. (1996a, 1996b, 1997, 1998b) studied factors affecting PbB levels in urban children and found the following independent predictors of children s PbB levels dust lead loading in homes, African-American race/ethnicity, soil lead levels, ingestion of soil or dirt, lead content and condition of painted... 

Outdoor lead dust was found to be a more potent contaminant of children s hands than indoor lead dust at day care centers in New Orleans boys, in general, had higher hand lead levels than girls. The conclusions were based on lead analysis of hand wipe samples taken before and after children played outdoors at four different day care centers (a private inner-city site, a private outer-city site, a public inner-city site, and a public outer-city site). The private inner-city site had a severely contaminated outdoor play area with measured soil lead concentrations ranging from 287 to 1,878 mg/kg. The outdoor play area at the public inner-city site, where children exhibited the lowest hand lead measurements of any site in the study, had been completely paved over with concrete or rubberized asphalt and had well-maintained equipment (Viverette et al. 1996). 

Aschengrau A, Beiser A, Bellinger D, et al. 1994. The impact of soil lead abatement on urban children s blood lead levels Phase II results from the Boston lead-in-soil demonstration project. Environ Research 67 125-148. 

Baltrop D, Strehlow CD, Thorton I, et al. 1974. Significance of high soil lead concentrations for childhood lead burdens. Environ Health Perspect 7 75-82. 

Chaney RL, Mielke HW, Sterret SB. 1989. Speciation, mobility and bioavailability of soil lead. Environ Geochem Health 9 105-129. 

EPA. 1996i. Urban soil lead abatement demonstration project. United States Environmental Protection Agency. Office of Research and Development, Washington, D.C. EPA/600/P-93/001af. 

Mielke HW, Dugas D, Mielke PW Jr, et al. 1997a. Associations between soil lead and childhood blood lead in urban New Orleans and rural Lafourche Parish of Louisiana. Environ Health Perspect 105(9) 950-954. 

Schmitt MDC, Trippler DL, Wachtler JN, et al. 1988. Soil lead concentrations in residential Minnesota as measured by ICP AES. Water Air Soil Pollut 39 157-168. 

Pbs=soil lead concentration PbD=dust lead concentration Pbw=water lead concentration PbA0=outside air lead concentration PbAI = inside air concentration PbF=food lead concentration T=relative time spent... 

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