Assessment of Health Risk Index in Soil and Grain of Wheat Irrigated by Subsurface Drip Irrigation and Treated Wastewater in Semi-Arid Region

Constant use of treated wastewater (TWW) for irrigation over long periods may cause buildup of heavy metals up to toxic levels for plants, animals, and entails environmental hazards in different aspects. The aim of this study was to assess the effect of using a deep emitter installation on lowering the potential heavy metal accumulation in soil and wheat grain, and health risk under drip irrigation with treated municipal wastewater. A field experiment was conducted according to a split block design with two treatments (fresh and wastewater) and three sub treatments (0, 15 and 30 cm depth of emitters) in four replicates in Esfahan, Iran. Soil samples were collected before planting (initial value) and after harvesting (final value) in each year. Elemental concentrations (Cu, Zn, Cd, Pb, Cr, and Ni) in soil and grain were determined using an atomic absorption spectrophotometer. A pollution load index (PLI) showed that there was not substantial buildup of heavy metals in the wastewater-irrigated soils compared to the freshwater-irrigated soils. Cu, Pb, Cr and Zn concentrations in wheat grain were within permissible EPA limits, but concentrations of Cr was above the safe limits of EPA. In addition, concentrations of Ni in wheat grain were several folds higher than EPA standards. A health risk index (HRI) which is usually adopted to assess the health risk to hazard materials in foods showed values higher than 1 for Cd and Cu, whereas children might also be exposed to health risk of Cd, Cu and Cr. Based on aforementioned results, it can be concluded that the depth of emitter in drip irrigation does not play a significant role in the accumulation of heavy metals from TWW in our sandy loam soil.