Accumulation of Heavy Metals in Agricultural Soil Irrigated by Sewage Sludge and Industrial Effluent (Case Study: Agh ghallah Industrial Estate)

Background and Industrial effluent and sewage sludge are used as fertilizer since they contain high levels of nutrient. The main pollutant in industrial effluent is heavy metals. In this study an assessment was made on the impact of industrial wastewater effluent and sewage sludge on accumulation of heavy metals in agricultural soil at Agh ghallah industrial Estate. In a descriptive-analytic study, 72 samples (sewage sludge, effluent and soil) were collected from the Industrial state. All sampling and tests were performed according to standard methods and concentration of heavy metals was determined using polarography method. To analyze the data, SPSS was used and 95% confidence intervals (P<0.05) were applied. The mean concentrations of Cd, Cu. Pb and Zn in sewage sludge were 0.53, 15.9, 1.44 and 692.7 mg/kg dw, respectively which were found to be lower than EPA standard. The concentrations of investigated heavy metals were within normal range in wastewater effluent that was discharged into surface water. The mean concentrations of metals in soil irrigated by wastewater were higher than those of the control soil. In a 10-year period, the concentration of lead and zinc increased 130 and 4 fold and cadmium and copper concentrations increased less than two-fold. There was a significant correlation between Zn and Pb in soil, sewage sludge and control soil (P<0.05). However, the concentration of Cd and Cu were not affected (P> 0.05). The concentrations of heavy metal were found lower than the maximum allowable level. Therefore, in this area, wastewater and sewage sludge could be used to irrigate agricultural lands and greenspaces in shortage of water, however, environmental regulations should be taken into account.