Dethwise Distribution of Heavy Metals in Soils Receiving Sewage Sludge

Soils (Haplaquents) were studied for accumulation and mobility of heavy metals due to continuous use of sewage sludge. Extractable Pb, Cd, Zn, Cu, Mn and Fe in these soils ranged from 1.2–10.2, 0.02–0.21, 0.5–11.4, 0.3–14.5, 5.5–21.3 and 6.1–54.9 ppm with their corresponding total content of 32–86, 1.3–4.5, 10–326, 1–101, 234–654 ppm and 2.80–3.13 per cent, respectively. By and large, the maximum concentration of these metals was in surface layer of soil profile (except total Pb, Cd, Mn and Fe) which progressively decreased with increasing depth up to 45 cm and thereafter the decreasing trend was irregular. The surface soil samples nearest to sewage discharge point contained highest amount of these metals which decreased with increasing distance form the point of discharge except for total Cd; Mn and Fe. Most of these metals were significantly and negatively correlated with pH and positively with organic carbon and clay content of the soils.