Soil Pollution along the Surface Runoff in Southern Tehran

High concentrations of heavy metals in soil are toxic to plants, animals, and human beings. The present study was performed in the region in the south of Tehran, which is exposed to pollutants and where the runoff from urban areas is being extensively used for irrigation. Soil samples were collected from 8 stations. The soil distillation method was used to extract heavy metals from the samples and their concentrations were determined using atomic absorption to decide whether the concentrations of such heavy metals as Pb, Cd, Zn, Cu, and Ni exceeded hazardous limits requiring protective measures to be taken. Results showed that the concentration gradients of all the parameters studied increased in the north-south and west-east directions. The average concentrations of Pb, Ca, Zn, Cu, and Ni were 61.12, 1.42, 61.07, 25.85 and 29.22 mg/kg, respectively, in the northern stations, and 76.40, 2.62, 172.05, 69.85 and 37.40 respectively, in the southern stations. Comparison of±43.7, respectively, in the southern stations. Comparison of the two northern and southern areas revealed that the two northern and southern areas revealed that the northern areas were in contact with more surface runoff, which might have been the cause for the wider distribution of heavy metal concentrations in this region. Moreover, the runoff passing through the deepest parts of the southern region and the extensive application of the flow for irrigation could have caused the higher accumulation of heavy metals in this region. Our findings also indicated that it is necessary to treat surface runoff and to avoid runoff application for irrigation as measures for preventing environmental pollution.