Quantifying the occurrence, attenuation mechanisms, and implications of contaminants of emerging concern in a temperate-region wastewater effluent-dominated stream

Wastewater effluent-dominated streams are becoming increasingly common worldwide due to a changing climate and population growth. These systems represent ‘worst-case scenarios’ for evaluating and predicting aquatic responses to effluent-derived contaminants of emerging concern (CECs; e.g., biologically active pharmaceuticals) because high levels of pollutants are continuously discharged into a relatively small water system. Thus, to better understand the dynamics and potential impacts of CECs, I conducted a comprehensive assessment of CECs in a temperate-region wastewater effluent-dominated stream for 2 years via high-resolution field sampling, complementary laboratory batch tests and modeling approaches. Our work demonstrated 1) variable inputs over multiple years and differential in-stream attenuation of individual compounds generate evolving complex mixture exposure conditions for biota, with implications for interactive effects; 2) sorption to sediment was the predominant attenuation process that drove differential attenuation (rather than biodegradation or photolysis forming products in-stream), and field attenuation rates were 10-fold greater than laboratory tests; 3) the majority of 20 CECs can pose medium to high risks to local ecological systems (i.e., algae, invertebrates, fish within the stream) under all-flow conditions expected; 4) the predicted concentrations of CECs mixtures after joining the Iowa River, as well as the measured concentrations in the drinking water treatment plant influent and effluent, were below the human health benchmark concentrations, indicating minimal risks to humans. Our comprehensive assessment of complex exposure mixture dynamics and impacts of CECs can be generalized to other effluent-dominated systems in temperate regions critical for de facto water reuse and sustainable water resources management.