Copper speciation drives its reactivity, bioavailability, and toxicity in aquatic systems. In stormwater runoff and wastewater effluents, two major sources of dissolved copper to freshwater, copper exists primarily as organic complexes with dissolved organic matter (DOM). Despite evidence that DOM from stormwater and wastewater differ from that of freshwater, the specific identity of copper ligands in aquatic environments remain unclear. Consequently, current speciation models that guide Cu regulations assume humic-like DOM, leading to erroneous estimates of toxic free Cu when applied to receiving waters impacted by these waste streams. To determine how organic Cu ligands in anthropogenic sources differ from each other and from those in natural sources, we characterized organic Cu complexes found in wastewater effluent and treated stormwater. Following solid phase extraction, isolated organic copper in each sample was quantified with Liquid Chromatography(LC) coupled to an Inductively Coupled Plasma Mass Spectrometer (ICPMS) and distinct complexes were identified using the same LC coupled to a high-resolution Electrospray Ionization Mass Spectrometer (ESIMS). The results revealed greater concentrations of extractable organic copper species in wastewater effluent compared to treated stormwater. Quantification of different fractions across retention time windows from LC-ICPMS, showed that the organic copper species differed in their relative polarity. The wastewater had a significantly higher percentage (53 %) of non-polar complexes that eluted between 15-30 minutes compared to the stormwater (33 %). Additionally, a distinct Cu complex, [C₂₁H₃₀N₂O₄Cu]⁺, was identified in only wastewater using the LC-ESIMS. These results reveal molecular differences in organic Cu complexes between anthropogenic streams and indicate that dissolved copper from these sources influence Cu speciation. Ongoing research aims to identify additional complexes and compare the current results to a river receiving wastewater and stormwater. Such findings will inform ways to account for anthropogenic Cu sources within existing speciation models and to potentially improve them.

Jeffrey Nason

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