Christopher Wu’s research while affiliated with University of Washington Tacoma and other places

Chemical contamination is an increasingly important conservation issue in urban runoff-impacted watersheds. Regulatory and restoration efforts typically evaluate limited conventional parameters and pollutants. However, complex urban chemical mixtures contain hundreds to thousands of organic contaminants that remain unidentified, unregulated, and poorly understood. This study aimed to develop broadly representative metrics of water quality impairment corresponding to previously documented biological degradation along gradients of human impacts. Stream samples (n = 65, baseflow/rainfall conditions, 2017-2018) were collected from 15 regional watersheds (Puget Sound, WA, USA) across an urbanization gradient defined by landscape characteristics. Surface water chemical composition characterized via non-targeted high-resolution mass spectrometry (7068 detections) was highly correlated with landscape-based urbanization gradient (p < 0.01) and season (p < 0.01). Landscape-scale changes in chemical composition closely aligned with two anchors of biological decline: coho salmon (Oncorhynchus kisutch) mortality risk (p < 0.001) and loss of stream macroinvertebrate diversity and abundance (p < 0.001). We isolated and identified 32 indicators for urban runoff impacts and corresponding receiving water ecological health, including well-known anthropogenic contaminants (e.g., caffeine, organophosphates, vehicle-derived chemicals), two related environmental transformation products, and a novel (methoxymethyl)melamine compound. Outcomes support data-directed selection of next-generation water quality indicators for prioritization and evaluation of watershed management efforts intended to protect aquatic ecosystems.

Tire tread particles turn streams toxic For coho salmon in the U.S. Pacific Northwest, returning to spawn in urban and suburban streams can be deadly. Regular acute mortality events are tied, in particular, to stormwater runoff, but the identity of the causative toxicant(s) has not been known. Starting from leachate from new and aged tire tread wear particles, Tian et al. followed toxic fractions through chromatography steps, eventually isolating a single molecule that could induce acute toxicity at threshold concentrations of ∼1 microgram per liter. The compound, called 6PPD-quinone, is an oxidation product of an additive intended to prevent damage to tire rubber from ozone. Measurements from road runoff and immediate receiving waters show concentrations of 6PPD-quinone high enough to account for the acute toxicity events. Science , this issue p. 185

Stormwater runoff clearly impacts water quality and ecological health of urban receiving waters. Subsequent management efforts are often guided by conceptual models of contaminant “first flushes”, defined by disproportionate concentrations or mass loads early in the storm hydrograph. However, studies examining the dynamics of contaminant transport and receiving water hydrology have primarily focused on “traditional” stormwater contaminants and point sources, with less evaluation of chemically complex non-point pollution sources. Accordingly, we conducted baseflow and storm sampling in Miller Creek, a representative small, urban watershed in the Puget Sound region (WA, USA). We comprehensively characterized organic contaminant profiles and dynamics via targeted quantification of 35 stormwater-derived chemicals, complementary non-target HRMS analyses, and surrogate chemical metrics of ecological health. For quantified analytes, total daily baseflow loads were 0.8-3.4 g/day and storm event loads were ~80-320 g/storm (~48 h interval), with nine contaminants detected during storms at >500 ng/L. Notably, urban creek “pollutographs” were much broader than relatively sharp storm hydrographs and exhibited transport-limited (rather than mass-limited) source dynamics, with immediate water quality degradation during low-intensity precipitation and continued mobilization of contaminant mass across the entire hydrograph. Study outcomes support prioritization of source identification and focused stormwater management efforts to improve water quality and promote ecosystem function in small urban receiving waters.

Pollutants transported in urban stormwater runoff induce pervasive water quality degradation in receiving waters. To accurately characterize stormwater quality and treatment system performance across the range of possible contaminant characteristics, comprehensive multi-residue analytical methods are necessary. Here, we developed a solid-phase extraction (SPE) and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method to quantify representative stormwater-derived organic contaminants across multiple chemical classes, including vehicle-related chemicals, corrosion inhibitors, industrial chemicals, pesticides, pharmaceuticals and personal care products, and antioxidants. Extraction conditions, isotope-labeled internal standards, and LC-MS/MS parameters were optimized to enhance recovery, minimize matrix effects, and maximize selectivity and sensitivity. The developed method was sensitive (method quantification limits < 10 ng/L for > 80% of selected analytes) and accurate (mean relative recoveries in the range of 70–130%, with relative standard deviations < 25% for 77% of the analytes) for most of the analytes. The method was used to analyze samples collected from nine urban watersheds during a storm event; 62% of the 39 analytes were detected at least once at concentrations up to 540 ng/L (1,3-diphenylguanidine). Spatial trends in detection and concentration were observed for vehicle-related and industrial chemicals that correlated with vehicle traffic. Total concentrations of pesticides suggested that residential uses could be more important sources than agriculture. This study illustrates the pervasive occurrence of a wide variety of stormwater-derived chemicals in urban receiving waters and highlights the need to better understand their environmental fate and ecological implications.

High resolution mass spectrometry (HRMS) analyses provide expansive chemical characterizations of environmental samples. To date, most research efforts have developed tools to expedite labor- and time-intensive contaminant identification efforts. However, even without chemical identity, the richness of non-target HRMS datasets represents a significant opportunity to chemically differentiate samples and delineate source contributions. To develop this potential, we evaluated the use of unidentified HRMS detections to define sample uniqueness and provide additional statistical resolution for quantitative source apportionment, overcoming a critical limitation of existing approaches based on targeted contaminants. By creating a series of sample mixtures that mimic pollution sources in a representative watershed, we assessed the fidelity of HRMS source fingerprints during dilution and mixing. This approach isolated 8-447 non-target compounds per sample for source apportionment and yielded accurate source concentration estimates (between 0.82-1.4-fold of actual values), even in multi-source systems with <1% source contributions. Furthermore, we mined the non-target data to identify five source-specific chemical end-members amenable to apportionment. While additional development studies are needed to fully evaluate the myriad factors affecting method accuracy and capabilities, this study provides a conceptual foundation for novel applications of non-target HRMS data to confidently distinguish and quantify source impacts in complex systems.

Here, we developed a novel and sensitive method for the detection and quantification of metastable trenbolone and altrenogest photoproducts in agricultural receiving waters based on solid phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Primary method analytes were seven cycloaddition or photohydration transformation products of 17α-trenbolone (17α-TBOH), 17β-trenbolone (17β-TBOH), trendione (TBO), and altrenogest (ALT), which are key contributors to the fate and environmental risks of these steroidal pharmaceuticals. Because commercial analytical standards are not available, reference standards for photoproducts were generated from trenbolone or ALT with a solar simulator (˜6 h, >10 half-lives). Efficient detection of metastable photoproducts required cold and pH neutral conditions, rapid sample processing, minimal sample storage, and consideration of cationic artifacts. Method detection limits (MDLs) were 0.034-0.40 ng L-1 for parent compounds and 0.16-2.1 ng L-1 for photoproducts, sufficient for their detection in agroecosystems. Matrix suppression was observed and corrected by internal standards, and relative recovery rates were near 100% for all analytes except for 12-OH-17α-TBOH (˜75% recovery). Intra-day variation was <20% and inter-day variation <25% for all the analytes. The developed method is capable of the analysis of trenbolone, altrenogest, and their key bioactive photoproducts in agricultural receiving waters.

The hyporheic zone (HZ), located at the interface of surface and groundwater, is a natural bioreactor for attenuation of chemical contaminants. Engineered HZs can be incorporated into stream restoration projects to enhance hyporheic exchange, with flowpaths optimized to promote biological habitat, water quantity, and water quality improvements. Designing HZs for in-stream treatment of stormwater, a significant source of flow and contaminant loads to urban creeks, requires assessment of both the hydrology and biogeochemical capacity for water quality improvement. Here, we applied tracer tests and high resolution mass spectrometry (HRMS) to characterize an engineered hyporheic zone unit process, called a hyporheic design element (HDE), in the Thornton Creek Watershed in Seattle, WA. Dye, NaCl, and bromide were used to hydrologically link downwelling and upwelling zones and estimate the hydraulic retention time (HRT) of hyporheic flowpaths. We then compared water quality improvements across hydrologically-linked surface and hyporheic flowpaths (3–5 m length; ∼30 min to >3 h) during baseflow and stormflow conditions. We evaluated fate outcomes for 83 identified contaminants during stormflow, including those correlated with an urban runoff mortality syndrome in coho salmon. Non-target HRMS analysis was used to assess holistic water quality improvements and evaluate attenuation mechanisms. The data indicated substantial water quality improvement in hyporheic flowpaths relative to surface flow and improved contaminant removal with longer hyporheic HRT (for ∼1900 non-target compounds detected during stormflow, <17% were attenuated >50% via surface flow vs. 59% and 78% via short and long hyporheic residence times, respectively), and strong contributions of hydrophobic sorption towards observed contaminant attenuation.

Urban stormwater is a major threat to ecological health, causing a range of adverse, mostly sublethal effects. In western North America, urban runoff is acutely lethal to adult coho salmon (Oncorhynchus kisutch) that spawn each fall in freshwater creeks. Although the mortality syndrome is correlated to urbanization and attributed to road runoff contaminant(s), the causal agent(s) remain unknown. We applied high-resolution mass spectrometry to isolate a coho mortality chemical signature: a list of nontarget and identified features that co-occurred in waters lethal to coho spawners (road runoff from controlled exposures and urban receiving waters from two field observations of symptomatic coho). Hierarchical cluster analysis indicated that tire wear particle (TWP) leachates were most chemically similar to the waters with observed toxicity, relative to other vehicle-derived sources. Prominent road runoff contaminants in the signature included two groups of nitrogen-containing compounds derived from TWP, polyethylene glycols, octylphenol ethoxylates, and polypropylene glycols. A (methoxymethyl)melamine compound family, previously unreported in North America, was detected in road runoff and urban creeks at concentrations up to ∼9 and ∼0.3 μg/L, respectively. The results indicate TWPs are an under-appreciated contaminant source in urban watersheds and should be prioritized for fate and toxicity assessment.