Health risks of heavy metal exposure and microbial contamination through consumption of vegetables irrigated with treated wastewater at Dubai, UAE

Abstract

The shortage of fresh water is a major problem throughout the world, but the situation is worst in the arid and semiarid regions. Therefore, reuse of nonconventional water resources such as treated wastewater (TWW) is a common practice to irrigate field crops, vegetables, and forestry sectors. The present study was conducted to evaluate the significant impact of different heavy metals such as copper (Cu), iron (Fe), chromium (Cr), and zinc (Zn) on the soil and leafy, root, and fruit vegetables following irrigation with TWW through subsurface drip irrigation. Our results indicate that iron (Fe) was highest in lettuce followed by spinach, and Zn and Cr were second and third most abundant element in the different vegetables. Eggplant and radish showed the lowest concentrations of various heavy metals. A significant difference was observed in transfer factor (TF) among vegetables, and highest TF_soil-veg was observed for Fe in lettuce and the lowest for Cr in eggplant. Estimated daily intake (EDI) was the lowest in adults and highest in children. Target hazard quotient (THQ) of Cu, Zn, and Fe being < 1.0 appears relatively safe in all the tested vegetables. Risk index (RI) values showed that heavy metals were lower than 1.0 and hence lower risk for human. The combined HI values for Cu, Zn, Cd, Cr, and Pb were substaintionaly higher 12.8 and 9.21 after consumption of lettuce and carrot. So, consumption of these vegetables should be avoided after irrigation with TWW. Spinach exhibited maximum total coliform loading, while ecological risk was negligible due to sandy nature of soil type. Health risks to human could be reduced through proper selection of suitable vegetables, time of maturity, and consumed organs (leaf, fruit, or root part). Appropriate should be followed to decontaminate the microbial load in order to avoid any risks to human health (both adults and children).

Keywords: Health risk index; Heavy metals; Microbial contamination; Subsurface irrigation; Target hazard quotient; United Arab Emirates; Vegetable contamination; Wastewater reuse.