Heavy Metal In Farming Soils Near A Lead Smelter In The North China Plain

Metal smelting is one of the main sources of soil heavy metal pollution, in recent years, heavy metal pollution of soil near smelting plants are becoming more and more serious in China. Several large lead (Pb) smelting plants lie in the North China Plain, leading to environmental pollution with heavy metals in the vicinity of these plants. Thus, it is necessary to investigate the total and available contents and their spatial distribution of heavy metals in soil in this region.Soil samples of 0-20 cm layer were collected from two transects, which are 1000 m and 2500 m away to the north of a lead smelting plant in the North China Plain. Soil was analyzed for DTPA-extractable, total and ammonium nitrate (AN)-extractable heavy metals; pH and electrical conductivity (EC) were also determined. The results indicated that:i) Ranges of DTPA-extractable nickel (Ni), copper (Cu), lead (Pb), zinc (Zn) and cadmium (Cd) of the samples were 0.125-0.653, 0-0.523, 1.07-5.48, 7.18^-133, 1.11-4.47 and 0.250-2.35 mg kg^-1, respectively.ii) Median values of the total content of Ni, Cr, Cu, Pb, Zn, and Cd were 33.0, 118, 21.7, 96.9, 79.5 and 5.00 mg kg^-1, respectively, those of Cd, Pb and Cr were 78.1, 4.80 and 2.40 times of the corresponding background values, those of Ni, Zn and Cu were 1.30, 1.22 and 1.01 times of the background values. Calculation of the pollution index (PI) indicated that the pollution of these two transects were both in serious polluted range. iii) AN-extractable contents of Cu, Zn, Pb, Cr and Ni ranged 0.021-0.310, 0-0.320, 0.241^-1.023, 0.030-0.878 and 0.167-0.587 mg kg^-1, respectively.iv) Soil pH of all the samples ranged 7.26-8.63, averaged 8.18, EC ranged 0.1000-0.2045 mS cm^-1, averaged 0.1342 mS cm^-1.v) Spatial distribution analysis indicated that higher contents of DTPA-extractable and total Pb and Cd were found in samples near the smelter; contents of DTPA-extractable and total Pb and Cd decreased non-linearly as the distance to the smelter increased; samples near the smelter had lower pH and higher EC. Meanwhile, samples with low pH and high EC and total Cr were also found in the far most samples. These results indicate that the lead smelter is the pollution source of Cd and Pb in local soils, resulting in serious pollution of these two metals in local soils with high risk. The lead smelting also results in acidification and increase of EC of local soil. Soil heavy metal pollution reaches a distance of more than 2.8 km away from the smelting plant.