Heavy Metal Contamination and Health Risks Assessment in Soil-Rice System Irrigated with Wastewater

Abstract

The transfer of heavy metals (HMs) was investigated from wastewater used for irrigation to soil and subsequently to rice plants (Oryza sativa L.) in Northern Pakistan, a region where rice is widely consumed. The concentrations of cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn) were measured in irrigation water, soil, and different parts of the rice plant (grain, shoot, and root) collected from various paddy fields. To assess potential health risks, daily metal intake (DIM) and the health risk index (HRI) were calculated. Heavy metal concentrations varied significantly across sampling locations. In the soil, Cd ranged from 0.1 to 0.49 mg/kg, Pb from 0.8 to 2.2 mg/kg, Cu from 4.2 to 18.2 mg/kg, and Zn from 7.0 to 25.1 mg/kg. The calculated DIM followed the order Zn < Cd < Cu < Pb, while the overall HRI for adults (0.612) and children (0.533) were below the threshold of 1. However, cadmium concentrations in the studied samples exceeded suggested permissible limits. Statistically significant differences (P < 0.05) revealed higher HM concentrations in the soil and rice crops from paddy fields irrigated with contaminated wastewater compared to a control site. The findings of this study indicate that the use of wastewater for irrigation leads to increased accumulation of HMs, particularly cadmium, in rice grains, potentially posing health risks to consumers in the region.