Abstract
Wastewater is actively used for irrigation of vegetable and forage crops in arid lands due to water scarcity and cost advantages. The objective of this review was to assess the effect of wastewater (mixture sources) reuse in irrigation on soil, crop (vegetable and forage crops), animal products, and human health. The metadata analysis of 95 studies revealed that the mean of toxic heavy metals including nickel (Ni), chromium (Cr), cadmium (Cd), lead (Pb), and zinc (Zn) in untreated wastewater were higher than the world standard limits in wastewater-irrigated regions. Although heavy metals in treated wastewater were within the standard limits in those areas, the concentration of those toxic elements (Pb, Cd, Ni, Cr, and As) exceeded the allowable limits in both soil and vegetables’ edible parts. In fact, the concentration of heavy metals in vegetables’ edible parts increased by 3–9 fold when compared with those irrigated with fresh water. Escherichia coli in wastewater-irrigated soil was about 2 × 106 (CFU g−1) and about 15 (CFU g−1) in vegetables’ edible parts (leaf, bulb, tuber and fruit) while the mean total coliforms was about 1.4 × 106 and 55 (CFU g−1) in soil and vegetables’ edible parts, respectively. For human health risk assessment, the estimated daily intake (EDI) and human health risk index (HRI) ranged from 0.01 to 8 (EDI and HRI > 1.0 associated with adverse health effects). Although the mean of EDI for heavy metals from wastewater-irrigated vegetables were less than 1, the HRI for Cd and Pb were above the limits for safe consumption. Overall, heavy metal levels in wastewater that used for irrigation of agricultural crops could be within the recommended levels by the world standards, but the long-term use of this reused water will contaminate soil and crops with several toxic heavy metals leading to potential carcinogenic risks to humans. Therefore, rigorous and frequent testing (wastewater, soil, and plant) is required in cultivated farms to prevent the translocation of heavy metals in the food chain.
Highlights
IntroductionGovernments in arid regions and the other countries with limited water resources have adopted several water management policies to sustain their water including rainwater harvesting and the reuse of wastewater in irrigation of agricultural crops [3,4]
This study shows that the estimated daily intake (EDI) values for heavy metals from vegetable crops irrigated with wastewater were higher than those
The metadata analysis showed that the concentration of heavy metals (Ni, Cd, Pb, Cr, and Zn) and microbial pathogens in untreated wastewater were higher than the world standard limits
Summary
Governments in arid regions and the other countries with limited water resources have adopted several water management policies to sustain their water including rainwater harvesting and the reuse of wastewater in irrigation of agricultural crops [3,4]. Considering the limited water resources due to changing climate and the exponential increase in population growth, the adoption of wastewater for irrigation of food crops and the sustainable conservation of water in arid land regions is inevitable [15]. Wastewater is an essential source for irrigation of agricultural crops, potential environmental and human health risk issues are linked to the reuse of this type of water due to the accumulation of heavy metals (lead (Pb), cadmium (Cd), nickel (Ni), chromium (Cr) and zinc (Zn)) and microbes (Escherichia coli) [6]. The metadata analyses included the levels of heavy metals (Pb, Ni, Cd, Cr, and Zn) and microbes (total coliforms, fecal coliforms, and Escherichia coli) in wastewater, irrigated-soil, and crops as well as human health risk
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