Heavy Metals In Soils And Wheat Plants Near A Lead Smelter In The North China Plain

The heavy metals in soils near lead (Pb) smelters are primarily from atmosphericdeposition and tailings. Several large lead smelting plants lie in the North China Plain,however, the effect of these plants on the properties of soils in the vicinity have not been welldocumented. In this work, soil samples were collected near a lead smelter which producesabout0.3million tons of Pb and analyzed to investigate the effect of large lead smelting planton the soil properties in this region. The results were as follows,(a) The contents of the total Pb in the0-20,20-40and40-80cm layers in the soil were28.3-183,24.6-90.1and26.6-35.7mg kg-1, respectively, and the average DTPA-Pb were5.43-75.5,1.67-29.0and1.08-5.43mg kg-1. In the0-20cm layer, the pollution indexes (PI) ofall the samples <2000m to the chimney were larger than3, in the20-40cm layer, sampleswith PI>3were less than50m to the chimney.(b) The contents of the total Cd in the0-20,20-40and40-80cm layers were0.33-2.36,0.22-0.44and0.22-0.23mg kg-1, respectively, while those of DTPA-Cd contents were0.30-1.89,0.10-0.34and0.07-0.18mg kg-1, respectively. The PIs were all greater than3forsamples collected in <4795m to the chimney.(c) Significant negative correlations were for in all the four layers for DTPA-Pb and thedistance to the chimney (p<0.001), such correlations were also found for DTPA-Cd, total Pband the distance (p<0.001) in0-40cm layer, the total Pb and the distance in40-80cm layer(p<0.05), the total Cd and the distance in0-20cm layer (p<0.001).(d) Positive correlation was found between soil pH and the distance to the chimney in0-20cm layer (p<0.05). For samples collected <500m to the chimney, soil pH increased withincreasing distance to the chimney in0-40cm layers, while electrical conductivity (EC)decreased with the distance.(e) Ranges of Pb in leaf, straw, glume and grain of wheat in the vicinity of the smelterwere37.7-365,3.41-39.7,10.6-141and0.48-12.2mg kg-1, respectively, while those of Cdwere2.42-12.2,0.64-13.3,0.48-4.15and0.06-0.62mg kg-1, respectively. Judged by the limitin the standard, PI of Pb of the wheat grain were>3for samples collected in3000m to thechimney, PI of Cd of the wheat grain were>3for samples collected in1000m to the chimney, while for the grain samples collected from>2400m to the chimney, the PI of both heavymetals were <1.(f) The contents of Pb in the leaf, straw, glume and grain of the wheat correlatednegatively with the distance to the chimney (p<0.001), while the contents of Cd in the leafand glume correlated negatively to the distance (p<0.001). The Pb contents in different organsof wheat ranked leaf> glume> straw>grain, that of Cd ranked leaf> straw> glume>grain.The results of this work suggest that, the soil and wheat were already polluted by thelead smelter; the heavy metals migrate vertically in the soil profile. The lead smelting alsoaffected soil pH and EC.