Lead in Soils

In an attempt to assess the effect of the mandatory use of unleaded gasoline in new automobiles on Pb concentrations in highway soils, Byrd et al. (1983) determined Pb concentrations in soils along U.S. Interstate 20 in northeast Louisiana and observed that the concentrations increased from 1973 to 1974 but decreased from 1975 to 1979. They concluded that the mandatory use of unleaded gasoline had significantly reduced the Pb concentrations in soils near highways. 

When incorporated in the soil, lead is of very low mobility. Hence once contaminated, a soil is liable to remain polluted with lead. This might have adverse consequences for soil fertility if the degree of contamination is great. In addition, plants grown on lead-rich soils incorporate lead and thus the concentration of lead in crop plants may be increased slightly. These questions are explored in the following sections. 

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Lead in soil slurries Electrothermal atomic absorption spectrometry... 

Patches of conductive lead sulphide can be formed on lead in the presence of sewage. This can result in the flow of a large corrosion current . Sulphate-reducing bacteria in soils can produce metal sulphides and H2S, which results in the formation of deep pits containing a black mass of lead sulphide . Other micro-organisms may also be involved in the corrosion of lead in soil . 

Aluminium, boron, silicon Lead in soil slurries Toxic organic compounds... 

Figure 4 shows an isomap of the lead pollution in the first smelter area of the Dallas Lead Study. The round symbol in the center represents the smelter. The lines are isopleths of lead in soil in pg/g. Note the cluster of closed isopleths encircling the smelter. The large number of concentric isopleths encircling the smelter shows a steep gradient or rapid change in a short distance between a low (200 ig/g) outside and a high (3,000 pg/g) inside. 

Higher levels of lead in soil can be measured near roadways. This accumulation came from car exhaust in the past. Once lead falls onto soil, it usually sticks to soil particles. Small amounts of lead may enter rivers, lakes, and streams when soil particles are moved by rainwater. Lead may remain stuck to soil particles in water for many years. Movement of lead from soil particles into underground water or drinking water is unlikely unless the water is acidic or "soft." Movement of lead from soil will also depend on the type of lead salt or compound and on the physical and chemical characteristics of the soil. 

EPA has developed standards for lead paint hazards, lead in dust, and lead in soil. To educate parents, homeowners, and tenants about lead hazards, lead poisoning prevention in the home, and the lead abatement process, EPA has published several general information pamphlets. Copies of these pamphlets can be obtained from the National Lead Information Center or from various Internet sites, including http //www.epa.gov/opptintr/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. 

The absorption of lead in soil is less than that of dissolved lead, but is similarly depressed by meals. 

Recent studies provide evidence for rapid dermal absorption of inorganic lead in adults however, these studies have not quantified the fraction of applied dose that was absorbed (Stauber et al. 1994). The quantitative significance of the dermal absorption pathway as a contributor to lead body burden remains an uncertainty. In children who experience extensive dermal contact with lead in soil, sand, or surface water and suspended sediment (e.g., beach or shoreline exposure scenario), even a low percent absorption... 

Wolff MS Mount Sinai School of Medicine of CUNY, New York, NY Analytical support for comprehensive assessment of lead exposures body burden measures will include blood lead, plasma lead, ZPP, bone lead, representing multiple compartments for deposition of lead and widely variable rates of elimination measurement of total lead in soil extracts to validate quantitative measures National Institute of Environmental Health Sciences... 

Lead may be taken up in edible plants from the soil via the root system, by direct foliar uptake and translocation within the plant, and by surface deposition of particulate matter. The amount of lead in soil that is bioavailable to a vegetable plant depends on factors such as cation exchange capacity, pH, amount of organic matter present, soil moisture content, and the type of amendments added to the soil. Back-... 

In environmental health studies conducted near four NPL sites (plus a comparison area for each), ATSDR collected lead concentration data from both environmental media and human body fluids to estimate low-level exposure risk and to document the magnitude of human exposure to lead near those sites. Environmental samples collected at participants homes included drinking water, yard soil, house dust, and house paint body fluids collected from participants included venous blood and urine specimens. For the four sites, mean concentrations of lead in soil ranged from 317 to 529 mg/kg, and mean concentrations of lead in dust ranged from 206 to 469 mg/kg (ATSDR 1995). 

Columbia University, New York, Conducting a study to determine the NY bioavailability of lead in soils for... 

A.J. Friedland Dartmouth College, Hanover, NH Identifying sources and determining mobility of lead in soil, groundwater, and vegetation... 

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. 

Davis A, Ruby MV, Bergstrom PD. 1992. Bioavailability of arsenic and lead in soils from the Butte, Montana, mining district. Environmental Science Technology 26 461-468. 

EPA. 1996a. Bioavailability of lead in soil samples from the Jasper County, Missouri Superfund Site. U.S. Environmental Protection Agency Region 8. Document Control No. 04800-030-0161. 

Murray K, Bazzi A, Carter C, et al. 1997. Distribution and mobility of lead in soils at an outdoor shooting range. Journal of Soil Contamination 6(l) 79-93. 

NriaguJO. 1978. Lead in soils, sediments and major rock types. In Nriagu JO, ed. The biogeochemistry of lead in the environment. Part A. Ecological cycles. New York, NY Elsevier/North-Holland Biomedical Press, 15-72. 

Misra S.G., Pandey G. Evaluation of suitable extractant for available lead in soils. Plant Soil 1976 45 693-696. 

In soils, lead concentrates in organic-rich surface horizons (NRCC 1973). In one instance, only 17 mg of soluble Pb/kg was found in soils 3 days after the addition of 2784 mg of lead (as lead nitrate)/kg (NRCC 1973). The estimated residence time of lead in soils is about 20 years complete turnover in topsoil is expected every few decades (Nriagu 1978a). In forest litter, however, the mean residence time of lead is lengthy estimates range from 220 years (Turner et al. 1985) to more than 500 years (Friedland and Johnson 1985). 

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