Evaluating contamination impact of wastewater irrigation to soils in Zahedan, Iran.

With respect to water crisis, using urban wastewater to irrigate urban green spaces is an upcoming strategy. The pollution of lands irrigated with wastewater is one of the upcoming challenges. The main purpose of the present study was to investigate contamination indices of soils irrigated with wastewater. In this study, field experimental method in statistical form of totally random blocks with three reiterations for considered treatments was employed. To this end, one piece of three-hectare grass irrigated with wastewater and one piece of land irrigated with well water (control sample) were selected out of the green spaces of Zahedan refinery. Then, 30 compound samples were randomly taken from the depth of 0-50 cm of three lands' soil. The refinery wastewater outlet and wall water were also sampled. Physicochemical and biological features of wastewater, wall water and soil samples irrigated with the refinery wastewater and well water were measured according to the standard methods. The obtained data were analyzed using MSTAT-C software. Based on the obtained results, the modified degree of contamination (mCd) of highly and lowly used elements in the considered soils in the experiment was less than 1, indicating a low-contamination status. PLI index of the mentioned elements in the surface soil of grass irrigated with wastewater was higher than 1 and by wall water was less than 1. The concentration of sulfur in surface soil of the two treatments under investigation was in a highly severe enrichment factor (EF ≥ 50). In addition, the concentration of nitrogen, magnesium, zinc and manganese in the surface soil of palm trees and that of manganese, copper and manganese in the surface soil of the grass irrigated with wastewater had a high enrichment factor (5 ≤ EF < 25). Geoaccumulation index (I) of sulfur in the surface soil of the pieces irrigated with wall water (control) and that of potassium in the surface soil of the grass irrigated with wastewater were in no-contamination or average-contamination statuses (0 < I ≤ 1). Other elements were in non-contaminated status (I ≤ 0) in terms of I. The results of investigation of soil contamination indices showed that the soil contamination status of the study area due to wastewater irrigation was low to medium. Therefore, periodic and more accurate monitoring of wastewater treatment plant of Zahedan can be used from this wastewater for landscapes irrigation.