Effect of Sewage Irrigation on the Accumulation of Heavy Metals in Soil and the Associated Health Risks

Water crisis as one of the fundamental problems in arid and semi-arid regions like Iran, has pushed for more use of urban waste in agricultural sector. In order to assess the consequences of urban wastewater application in agricultural practices, concentrations of heavy metals zinc, copper, cadmium, lead, chromium and nickel in the soil and corn seeds were studied. We also focused on pollution accumulation, plant transfer risk and health risk. For this, three farm soil textures were used for surface irrigation, irrigation with saline water, waste water and those irrigated for 6 years in Qom Province. Wastewater application decreased cadmium and lead and increased concentration of other metals. The maximum increase in concentration was seen for nickel (mg/L7) and the minimum for copper (mg/L 2.31), respectively. The soil accumulation index for Chrome and nickel was larger than other elements. In addition, the mean transfer indices in corn effluent treatment were 4.03, 3.03, and 0.15 for cadmium, lead and Chrome respectively. Also, Cr, Cd and Cu in corn grains irrigated with wastewater was higher than the permissible limit for human consumption. Pb Risk Index in Corn for all consumers and cadmium risk factor for children was greater than 1. According to the results, it seems that the health risk factor offers a more conservative estimate of the risk of heavy metals compared to its standard subject to further studies.