Abstract
BackgroundWastewater irrigation for vegetable production is a highly prevalent practice in Addis Ababa and a number of articles have been published on wastewater-irrigated soils and vegetables contaminated with heavy metals. However, to the best of our knowledge, an insight into assessment of human health risks associated with the consumption of vegetable crops grown on wastewater-irrigated soils is non-existent in the city. Long-term effect of wastewater irrigation on the build-up of heavy metals in soils and selected vegetable crops in Addis Ababa urban vegetable farming sites (10) was evaluated. By calculating estimated daily intakes (EDIs) and target hazard quotients (THQs) of metals, health risk associated with the consumption of the analyzed vegetables was also evaluated.ResultsThe heavy metal concentrations in irrigation water and soils did not exceed the recommended maximum limits (RMLs). Moreover, Cd, Co, Cr, Cu, Ni and Zn concentrations in all analyzed vegetables were lower than the RML standards. In contrast, Pb concentrations were 1.4–3.9 times higher. Results of two way ANOVA test showed that variation in metals concentrations were significant (p < 0.001) across farming site, vegetable type and site x vegetable interaction. The EDI and THQ values showed that there would be no potential health risk to local inhabitants due to intake of individual metal if one or more of the analyzed vegetables are consumed. Furthermore, total target hazard quotients (TTHQs) for the combined metals due to all analyzed vegetables were lower than 1, suggesting no potential health risk even to highly exposed local inhabitants.ConclusionsThere is a great respite that toxic metals like Pb and Cd have not posed potential health risk even after long term (more than 50 years) use of this water for irrigation. However, intermittent monitoring of the metals from irrigation water, in soil and crops may be required to follow/prevent their build-up in the food chain.
Highlights
Wastewater irrigation for vegetable production is a highly prevalent practice in Addis Ababa and a number of articles have been published on wastewater-irrigated soils and vegetables contaminated with heavy metals
There is a great respite that toxic metals like Pb and Cd have not posed potential health risk even after long term use of this water for irrigation
Across the ten sampling sites, the metals concentrations were far below the recommended maximum limit for irrigation water set by FAO (Ayers and Westcot 1985)
Summary
Wastewater irrigation for vegetable production is a highly prevalent practice in Addis Ababa and a number of articles have been published on wastewater-irrigated soils and vegetables contaminated with heavy metals. To the best of our knowledge, an insight into assessment of human health risks associated with the consumption of vegetable crops grown on wastewater-irrigated soils is non-existent in the city. Long-term effect of wastewater irrigation on the build-up of heavy metals in soils and selected vegetable crops in Addis Ababa urban vegetable farming sites (10) was evaluated. Long-term application of partially treated or untreated wastewater could result in accumulation of heavy metals in the soil (Elgallal et al 2016). 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). Several researchers reported that serious health problems may develop as a result of excessive accumulation of heavy metals and even essential trace elements such as Cu and Zn in human body (Oliver 1997; Jarup 2003; Kabata-Pendias and Mukherjee 2007; Luo et al 2011; Khan et al 2015)
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