Enhancing the Detectable Chemical Space in an Effluent-Dominated Stream: Non-Target Analysis Reveals Potential Rapid In Situ Product Formation

Effluent-dominated streams are increasingly common in temperate regions and have potential for adverse ecological and human health effects. Nontarget analysis (NTA) using high resolution mass spectrometry (HRMS) is an emerging approach to examine complex chemical mixtures in the environment. Here, we leveraged archived samples previously analyzed for 154 target contaminants in a well-studied temperate region effluent-dominated stream and compared target results with suspected compounds from NTA. NTA enhanced the detectable chemical space by 20 times compared to target analysis alone. Target analysis was biased toward larger mass contaminants compared to the compounds detected with NTA, indicating that target analysis was not fully representative of the compound distribution for the effluent-impacted waters. Hierarchical cluster analysis exposed clusters of compounds significantly upregulated at the effluent/stream mixing zone, revealing evidence of a novel phenomenon wherein transformation product and/or metabolite formation appears to occur rapidly in situ. Additionally, an exposure-driven NTA retrospective analysis uncovered upregulation of 7endocrine-disrupting compounds that may explain prior bioassay results. These findings have urgent implications for ecosystems and downstream communities experiencing de facto wastewater reuse conditions. NTA offers enhanced characterization of complex mixtures in effluent-dominated streams and can reveal novel mixture dynamics otherwise masked when employing target analysis alone.