Impact of Irrigation by Municipal Sewage on Accumulation of Heavy Metals in Soil

Impact of irrigation with municipal sewage on accumulation of soil by heavy metals (Fe, Mn, Cr, Pb and Cd) was investigated in two artificial stands Eldar pine (Pinus eldarica Meadow.), 1) irrigated by municipal sewage and 2) irrigated by well water in the suburban areas of Tehran. In each stand, soil profiles were dug and soil samples taken from depths of 0-15, 15-30 and 30-60 centimeter. Municipal sewage and well water were sampled daily (3 days in each month) from early June to late November. Results indicated that municipal sewage had significantly (P < 0.01) higher amounts of Fe, Mn, Cr and Pb compared to well water. Level of these heavy metals in municipal sewage was upon the internationally recommended (WHO) maximum permissible limits set for land use. Application of municipal sewage resulted in a 1.5-fold increase in the concentrations of soil Fe, Mn, Cr and Pb. These heavy metals showed their greatest values in the upper layer of soil (0-15 cm). The concentration of soil heavy metals, with the exception of Pb, was below the critical limits. Cd was not detected in water and soil samples. With regard to high concentration of heavy metals in sewage, it was concluded that the long-term use of municipal sewage in irrigation might enriched soil with heavy metals to concentrations that may pose potential environmental and health risks. Hence regulations about the utilization of sewage in irrigation should consider in order to: 1-Control the content of heavy metals that may be added to soil and 2- Minimize the risk of negative effects to ecosystem health.