The Tire Wear Compounds 6PPD-Quinone and 1,3-Diphenylguanidine in an Urban Watershed.

Prompted by a recent report that 6PPD-quinone (6PPD-q), a by-product of a common tire manufacturing additive that is present in road runoff, is toxic to coho salmon (Oncorhynchus kisutch), extracts of water samples collected from an urban river were re-analyzed to determine if this compound was present in stormwater-influenced flows. In addition, extracts were analyzed for 1,3-diphenylguanidine (DPG), which is also used in tire manufacturing. Samples were originally collected in the fall of 2019 and winter of 2020 in the Greater Toronto Area of Canada from the Don River, a highly urbanized watershed in close proximity to several major multi-lane highways. These target compounds were analyzed using ultra-high pressure liquid chromatography with high resolution mass spectrometric detection with parallel reaction monitoring. Both 6PPD-q and DPG were detected above limits of quantification (i.e., 0.0098 µg/L) in all extracts. Maximum concentrations for 6PPD-quinone of 2.30 ± 0.05 µg/L observed in the river during storm events exceeded the LC50 for this compound for coho salmon (i.e., > 0.8 µg/L). In composite samples collected at intervals throughout one rain event, both compounds reached peak concentrations a few hours after initiation of the event (i.e., 0.52 µg/L for DPG and 2.85 µg/L for 6PPD-q), but the concentrations of 6PPD-q remained elevated above 2 µg/L for over 10-h in the middle of the event. Estimates of cumulative loads of these compounds in composite samples indicated that kg amounts of these compounds entered the Don River during each hydrological event, and the loads were proportional to the amounts of precipitation. This study contributes to the growing literature indicating that potentially toxic tire-wear compounds are present at elevated levels and are transported via road runoff into urban surface waters during rain events.

Application of photocatalytic ozonation with a WO3/TiO2 catalyst for PFAS removal under UVA/visible light.

This research evaluates photocatalytic ozonation for removing 5 PFAS (PFOA/PFHxS/PFBS/6:2 FTS/GenX) from water using a WO3/TiO2 catalyst under UVA-visible radiation. Four catalysts of varying WO3 content (0/1/3/5 wt%) were synthesized by sol-gel and characterized by XRD, TEM, STEM-EDS, HAADF-STEM, adsorption/desorption N2 isotherms, and DRS-UV-vis. 5 wt% WO3/TiO2 was the optimal composition based on physicochemical properties and photocatalytic activity tests with methylene blue. PFAS degradation showed that photocatalytic ozonation inefficiently degraded PFAS with WO3/TiO2 under UVA-visible light after 4 h (ΣPFAS removal 16 %, [range 4 %-26 %]). Photocatalysis had comparable removal to photocatalytic ozonation, photolysis and ozone photolysis showed lower removal, and ozonation had no effect. Microtox analysis showed the initial acute toxicity was no longer detectable after photocatalysis and photocatalytic ozonation treatment. Low PFAS removals under tested conditions require that future work evaluate different catalysts or treatment conditions, while disparities between tested PFAS removals demonstrate the need to evaluate multiple compounds. ENVIRONMENTAL IMPLICATION: The research presented in this manuscript involves the preparation and characterization of WO3/TiO2 catalysts used, for the first time, to remove multiple PFAS in water via photocatalytic ozonation. This manuscript supports the development of a catalytic process for the elimination of hard to degrade environmental pollutants, provides new knowledge on aspects of photocatalytic processes, and provides insights on environmental pollution abatement.

A review of ecotoxicity reduction in contaminated waters by heterogeneous photocatalytic ozonation.

The widespread deterioration of our water systems requires new wastewater treatment technologies to ensure environmental protection. Conventional wastewater treatments were not designed for, and are therefore ineffective, at removing contaminants of emerging concern (CECs) such as pharmaceuticals, personal care products, pesticides, and industrial chemicals. Furthermore, treatment processes capable of breaking down CECs may produce toxic transformation products more harmful than the parent chemicals. Heterogeneous photocatalytic ozonation provides a promising option with high degradation and mineralization of organic compounds. The aim of the present paper is to review ecotoxicity reduction in water treated by heterogeneous photocatalytic ozonation as a measure of process viability. The discussion investigates changes in toxicity based on a variety of toxicity tests performed to evaluate potential effects on ecosystems, the types of catalysts and radiation sources used, the nature of the target contaminants, and the type of water matrix treated. Acute toxicity testing, TiO2 catalysts, and mercury-vapour lamps including blacklights were dominant in the reviewed studies, investigated in 86%, 84% and 79% of the papers, respectively. Pharmaceuticals were the main group of chemicals treated and the water matrices used were predominantly pure water and secondary effluent. Overall, the findings of these studies provide evidence that photocatalytic ozonation is an efficient process to remove persistent organic compounds while, most of the time, not increasing the toxicity of the effluent (as reported by 86% of the studies). Due to the wide variation in experimental set-ups, no clear correlation between reaction conditions and toxicity was determined, however, V. fischeri acute toxicity assays and chronic/sublethal tests appeared most sensitive to transformation products. Future studies need to a) incorporate multiple toxicity tests to produce a more reliable and inclusive ecotoxicity assessment of treated effluent and b) investigate immobilized catalysts and energy efficient radiation sources (i.e. solar and LEDs) for industrial applications.