Tracing treated wastewater in an inland catchment using anthropogenic gadolinium

The discharge of treated wastewater into natural water bodies occurs worldwide; if drinking water is then extracted downstream, there is potential for micropollutants that are not fully mineralized in the wastewater treatment process to enter municipal drinking water. In Australia, drinking water treatment is typically a mixture of basic technologies such as flocculation and slow sand filtration; technologies that are not specifically designed to remove micropollutants. However, there is little awareness in Australia of the potential risk that upstream wastewater discharges may impart to the security and quality of downstream drinking water supplies. We apply a direct inductively coupled plasma mass spectrometry technique to determine the discharge of anthropogenic gadolinium from a wastewater treatment plant in Toowoomba, Queensland, Australia, that discharges into the small (147 km2) catchment of Gowrie Creek. We then continue to measure the concentrations of this wastewater tracer as Gowrie Creek flows downstream into the Condomine River, and to a community 100 km away where drinking water is extracted. Using this tracer, we demonstrate that the community has a detectable wastewater contribution within their surface drinking water supply.