Heavy Metals and Microbes Accumulation in Soil and Food Crops Irrigated with Wastewater and the Potential Human Health Risk: A Metadata Analysis

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.

Risk assessment of heavy metals in soil and simultaneous monitoring in wheat irrigated with groundwater and treated wastewater and its long-term effects for residents of adjacent regions

“…28 HQ ¼ EDI RfD (4) where RfD referred to the reference dose. The hazard index (HI) to estimate the hazards of different heavy metals was calculated using eqn (5).…”

“…3,4 According to 42 countries, there is a total of 8.4 million hectares of irrigated land available for directly treating or raw wastewater. 5 Since raw wastewater contains many substances such as nutrients, pathogens, organic compounds, and heavy metals, it can be a threat for the environment and human health. Unfortunately, despite physical, chemical, and biological treatments, significant amounts of heavy metals such as Cr, Cd, Ni, Pb, and Zn as well as other contaminants remain in discharged effluents.…”

Heavy Metal Contamination in Vegetables and Their Toxic Effects on Human Health

“…As arsenite-inducing protein clustering was found and proved to be concentrationdependending, heavy metals may cause proteins to aggregate. The clusters also comprised a diverse ranging of proteins with roles linked to metabolism, protein portable, synthesis of protein, and protein stability [71][72][73][74][75]. After exposing to equi-toxic quantities of cadmium, arsenite, as well as chromium (Cr(VI)), Saccharomyces cerevisiae (budding yeast) cells gathered aggregated proteins, and the outcome of heavy metals on protein aggregation was altered in this direction: arsenic > cadmium > chromium [76][77][78][79][80].…”

Phytoremediation Potential of Selected Ornamental Woody Species to Heavy Metal Accumulation in Response to Long-Term Irrigation with Treated Wastewater

“…The use of TWW in agriculture and forestry might cause the deterioration and contamination of the soil [17,18]. Plant features, soil, and environmental factors are known to have an impact on the bioavailability of these metals [19,20].…”