Emerging contaminants in wastewater, stormwater runoff, and surface water: Application as chemical markers for diffuse sources

Diffuse sources of pollution such as sewer leakages, sewer overflows, illicit discharges and stormwater runoff affect the urban surface water quality but often remain unknown. Therefore, the development of chemical markers for identifying and characterizing the origin of diffuse sources of pollution in urban surface waters is a requisite for protecting and managing urban water resources. In this study, the occurrence of 31 emerging contaminants (ECs) in untreated wastewater, treated wastewater, urban stormwater runoff, agricultural stormwater runoff, and freshwater bodies was investigated. Artificial sweeteners (ASs), pharmaceuticals and personal care products (PPCPs) were more frequently detected in the collected water samples. In raw wastewater, 21 target ECs were detected 100% in the collected samples with median concentrations ranging from 49.6 to 77,721 ng/L, while in freshwater bodies, only 13 compounds were found with detection frequency >50%. The median concentration of the majority of detected ECs in freshwater samples was below 100 ng/L. The suitability of ECs as chemical markers of diffuse sources in an urban watershed was assessed using a suite of criteria, including the detection frequency (DF), detection ratio (DR) (i.e. the ratio between median concentration and method quantification limit of a compound) and attenuation rates (i.e., biodegradation, sorption and abiotic degradation) in wastewater treatment processes. In addition, we propose a new key criterion, the concentration ratio (CR) of labile to conservative compounds, to evaluate the applicability of suitable chemical markers for source tracking. Using this new set of criteria (i.e. CR, DF, DR and attenuation rates), our analysis showed that among the investigated ECs, only acesulfame (ACE), acetaminophen (ACT), cyclamate (CYC), saccharin (SAC) were suitable as chemical markers of diffuse sources in surface waters. For caffeine (CF), N,N-diethyl-meta-toluamide (DEET), crotamiton (CTMT), triclocarban (TCC) and triclosan (TCS), their median concentration ratio to sucralose (SUC) in water bodies was consistently higher than that in raw wastewater, suggesting that these compounds might be unsuitable as chemical markers of sewage leakage in surface waters for this study area.