Wastewater contamination of deep groundwater in Sudan, an arid developing country: Application of artificial sweeteners and antibiotics as molecular markers

A total of 27 groundwater samples, including deep-well (>100 m) samples; 8 surface water samples, including Nile River samples; 9 wastewater samples; and 2 tap-water samples were collected in Sudan and analyzed for artificial sweeteners and antibiotics. Acesulfame (ACE), an artificial sweetener, was frequently (59%) detected in groundwater samples collected in Khartoum, the highly populated capital city of Sudan, with a concentration ranging from 2 ng/L to 2,900 ng/L, and in sewage samples (~10,000 ng/L). ACE concentrations detected in the groundwater were positively correlated with the population density. No substantial amounts of ACE were detected in the Nile River at Khartoum, although high ACE levels were expected because of the large population and insufficiency of the sewage treatment system. These findings suggest that sewage generated in Khartoum is trapped in the ground rather than discharged to the Nile River, probably because the arid climate limits runoff and facilitates sewage infiltration into the ground. This contrasts with the findings reported in tropical Asian rivers. In addition, we detected ACE in deep groundwater in other arid countries, including Iran, Kenya, and Mozambique, where the available aquifers are primarily unconfined and vulnerable to the vertical infiltration of pollutants from the ground. These findings suggest that populated cities in the arid climate zone are at a high risk of deep groundwater contamination with sewage and associated chemicals. Antibiotics were widely detected in urban and rural environments. In the Nile River and the deep groundwater at Khartoum, tetracyclines, especially chlortetracycline (CTC), predominated among the 17 antibiotics measured, including sulfonamides, macrolides, and tetracyclines. CTC was detected in 65% of the samples, with a concentration range of 0.3–90 ng/L. The concentrations of sewage-derived antibiotics estimated from the ACE concentrations and the CTC to ACE ratios in sewage were much lower than those observed in the Nile River and its vicinities. Considering the usage pattern of antibiotics in Sudan, we concluded that the antibiotics were derived from veterinary use. This study demonstrated that artificial sweeteners and antibiotics combined are useful as molecular markers for investigating environmental water pollution in developing countries with highly arid climates.