Human health risk assessment associated with the reuse of treated wastewater in arid areas

Qatar produces more than 850,000 m(3)/day of highly treated wastewater. The present study aims at characterizing the effluents coming out of three central wastewater treatment plants (WWTPs) of chemical pollutants including metals, metalloids and antibiotics commonly used in the country. Additionally, the study is assessing human health risks associated with the exposure to the treated wastewater (TWW) via dermal and ingestion routes. Although the origin of domestic wastewater is desalinated water (the only source of fresh water), the results show that the targeted parameters in TWW were within the international standards. Concentrations of Cl, F, Br, NO3, NO2, SO4 and PO4, were 389, <0.1, 1.2, 25, <0.1, 346, and 2.8 mg/L, respectively. On the other hand, among all cations, metals and metalloids, only boron (B) was 2.1 mg/L which is higher than the Qatari guidelines for TWW reuse in irrigation of 1.5 mg/L. Additionally, strontium (Sr) and thallium (Tl) were detected with relatively high concentrations of 30 mg/L and 12.5 mu g/L, respectively, due to their natural and anthropogenic sources. The study found that the low concentrations of all tested metals and metalloids do not pose any risk to human health. However, Tl presents exposure levels above the 10 % of oral reference dose (HQ = 0.4) for accidental oral ingestion of TWW. The results for antibiotics show that exposure for adults and children to TWW are far below the admissible daily intakes set using minimum therapeutic dose and considering uncertainty factors. Treated wastewater of Qatar can be used safely for irrigation. However, further investigations are still needed to assess microbiological quality.