Health risk assessment of potentially harmful elements and dietary minerals from vegetables irrigated with untreated wastewater, Pakistan

Abstract

In the developing world, vegetables are commonly grown in suburban areas irrigated with untreated wastewater containing potentially harmful elements (PHEs). In Pakistan, there is no published work on the bioaccessibility aspect of PHEs and dietary minerals (DMs) in sewage-irrigated soil or the vegetables grown on such soils in Pakistan. Several industrial districts of Pakistan were selected for assessment of the risk associated with the ingestion of vegetables grown over sewage-irrigated soils. Both the total and bioaccessible fraction of PHEs (Cd, Co, Cr, Ni, and Pb) and DMs (Fe, Cu, Mn, Zn, Ca, Mg, and I) in soils and vegetable samples were measured. The concentrations of these PHEs and DMs in sewage-irrigated and control soils were below published upper threshold limits. However, compared to control soils, sewage irrigation over the years decreased soil pH (7.7 vs 8.1) and enhanced dissolved organic carbon (1.8 vs 0.8 %), which could enhance the phyto-availability of PHEs and DMs to crops. Of the PHEs and DMs, the highest transfer factor (soil to plant) was noted for Cd and Ca, respectively. Concentrations of PHEs in most of the sewage-irrigated vegetables were below the published upper threshold limits, except for Cd in the fruiting portion of eggplant and bell pepper (0.06-0.08 mg/kg Cd, dry weight) at three locations in Gujarat and Kasur districts. The bioaccessible fraction of PHEs can reduce the context of dietary intake measurements compared to total concentrations, but differences between both measurements were not significant for Cd. Since the soils of the sampled districts are not overly contaminated compared to control sites, vegetables grown over sewage-irrigated soils would provide an opportunity to harvest mineral-rich vegetables potentially providing consumers 62, 60, 12, 104, and 63 % higher dietary intake of Cu, Mn, Zn, Ca, and Mg, respectively. Based on Fe and vanadium correlations in vegetables, it is inferred that a significant proportion of total dietary Fe intake could be contributed by soil particles adhered to the consumable portion of vegetables. Faecal sterol ratios were used to identify and distinguish the source of faecal contamination in soils from Gujranwala, Gujarat, and Lahore districts, confirming the presence of human-derived sewage biomarkers at different stages of environmental alteration. A strong correlation of some metals with soil organic matter concentration was observed, but none with sewage biomarkers.

Heavy metal accumulation and health risk assessment in wastewater-irrigated urban vegetable farming sites of Addis Ababa, Ethiopia

“…cicla, respectively. Similar low levels were also obtained in previous studies (Itanna 1998;Liu et al 2005;Aschale et al 2015;Mekonnen et al 2015;Zia et al 2016;). The two way ANOVA test revealed significant differences by farming site, vegetable type and their interaction (Table 4).…”

“…crispa. As a result, we emphasize the differences in physiology of metal uptake, exclusion, accumulation, as well as foliage deposition and retention (Zurera et al 1987;Cui et al 2004;Zia et al 2016). …”

“…However, long-term application of partially treated or untreated wastewater could result in accumulation of heavy metals in the soil (Elgallal et al 2016). Effluents from household and industries, drainage water, atmospheric deposition, and trafficrelated emissions transported with storm water into the sewage and/or irrigation system carry number of pollutants and enrich the urban waste water with heavy metals (Saha et al 2015;Zia et al 2016;. The consumption of food crops grown in wastewater-irrigated areas is one of the principal factor contributing human exposure to pathogens.…”

“…The consumption of food crops grown in wastewater-irrigated areas is one of the principal factor contributing human exposure to pathogens. In addition, the cultivation of crops for human consumption on wastewater-irrigated soil can potentially lead to the uptake and accumulation of trace metals in the edible plant parts resulting potential risk to human (Rattan et al 2005;Xue et al 2012;Ahmad et al 2016;Zia et al 2016). Heavy metals are very harmful because of their non-biodggrdable nature, long half-lives and their high bioaccumulation potential (Duruibe et al 2007;Shah et al 2012).…”

Heavy Metals Accumulation in the Edible Parts of some Sewage Wastewater Irrigated Vegetable Crops

“…Similar results were found by Eissa (2016). The long-term use of treated and untreated wastewater in irrigation was reported to cause significant buildup of the heavy metals in the soils (Khan et al, 2008;Ullah et al, 2011;Gosh et al, 2012;Uzma et al, 2016;Zia et al, 2017). …”