Depth wise accumulation of heavy metals in sewage contaminated and uncontaminated soils
Publication Date : 17/10/2015
Continuous use of sewage irrigation on agricultural land increased the total Cd, Pb, Cr and Zn from 2.21±0.24-5.21±0.41 mg kg-1, 3.62±0.31-4.56±0.42 mg kg-1, 2.72±0.19-4.24±0.33 mg kg-1 and 67.58±2.34-88.47±3.89 mg kg-1 in surface soil (0-10 cm), respectively. A very low amount of heavy metals (Cd, Pb, Cr and Zn) were observed in (30-50 cm) depth in comparison to surface soil (0-10 cm) in all the soil examined. Similarly increased the accumulation of DTPA-extractable Cd, Pb, Cr and Zn from 0.216±0.032-0.256±0.033 mg kg-1, 0.64±0.22-0.82±0.22 mg kg-1, 0.38±0.17-0.54±0.22 mg kg-1 and 12.57±0.53-15.28±1.09 mg kg-1 in surface soil (0-10cm) respectively. A low amount of total heavy metals (Cd, Pb, Cr and Zn) were observed in 30-50 cm depth in comparison to surface soil (0-10 cm) in all the soil examined indicating low mobility of these metals down the depth. The total heavy metals (Cd, Pb, Cr and Zn) and DTPA-extractable heavy metals content of sewage contaminated and uncontaminated soils decreased with increasing soil depth. The soil organic carbon content in soils were positively and significantly correlated with DTPA-extractable Cd (r=0.98**), Pb (r=0.93**), Cr (r=95**) and Zn (r=1.00**), while clay contents showed negative impact on the extractability of these metals. Similarly correlations of total heavy metals with physical property were observed positively, while pH and clay content showed negatively impact. In uncontaminated soil, low content of heavy metals were found in comparison to contaminated soil. Under risk assessment, profile-wise study indicated accumulation of Cd, Pb, Cr and Zn below up to 50 cm. Naini contaminated soil was highly contaminated than other three sites.Thus, it may be concluded that a high concentration of extractable heavy metals in surface soils (0-10 cm) will not only reduce the plant growth but will also affect the availability of other essential elements to plants.
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