Mining soil lead concentrations

Soils around the Pb-Zn Port Pirie smelter in the semi-arid region of South Australia were found to contain 2,220 mg/kg Pb (about 3 km away from the mine) (Cartwright et al., 1976). Lead concentrations decreased to 140 mg/kg at a distance of 16 km and were further reduced to 32 mg/kg at 33.5 km. In tailing piles of the Leadville mining area of Colorado, U.S., Pb concentrations ranged from 6,000-10,000 mg/kg (Brown et al., 1999). XAFS spectroscopy showed that 50% of the total Pb occurred as adsorbed... 

O Day PA, Carroll SA, Waychunas GA (1998) Rock-water interactions controlling zinc, cadmium, and lead concentrations in surface waters and sediments, U.S. Tri-State Mining District. I. Molecular identification using X-ray absorption spectroscopy. Env Sci Tech 32 943-955 O Reilly S, Strawn DG, Sparks DL (2001) Residence time effects on arsenate adsorption/desorption mechanisms on goethite. Soil Sci Soc Am J 65 67-77... 

Cadmium is found in low concentrations in most soils and waters. It is produced as a by-product of zinc and lead mining and smeltering. Industrial use of cadmium has led to a dramatic increase in environmental problems caused by this element. Cadmium is used in semiconductors, nickel-cadmium batteries, electroplating, polyvinyl chloride (PVC) manufacturing, and control rods for nuclear reactors. The most important sources for aquatic contamination are active and inactive lead-zinc mines, land application of sewage sludge, zinc-cadmium smelters, effluents from plastic and steel production, and wastewaters from the production of nickel-cadmium batteries and electroplating (Zuiderveen, 1994). 

Only limited work has been done on the bioaccessibility of metals in windborne mine waste and tailings material, and so much must be inferred. Mullins and Norman (1994) analyzed the size distribution, metal content, and metal extraction by simulated biofluids (lung, gastric, intestinal) of surface materials (soils) collected from several mine waste piles in the Butte, Montana, district. They found that the concentrations of arsenic, cadmium, copper, manganese, and lead were commonly greatest in the smallest size fractions (<4.7 pm) of the waste dump material. The percentage of metals leached from the hne fraction was quite variable, but not in any consistent way, between different metals, different dumps, and different extraction fluids. 

Although ion retention by soils can cause elemental deficiencies, it also prevents excessive or toxic concentrations in most soil solutions. The evolution of life took advantage of the naturally low concentrations in water and low plant availability higher concentrations evolved as toxic. Table 2.4 shows the natural soil contents of ions that are generally harmless. The upper values are conservative estimates of soil contents that might lead to toxicity. All soils contain the toxic elements, even in amounts that are mined as ores, and these concentrations do not necessarily harm plants or groundwater. 

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