| Autor: |
Redman ZC; Department of Chemistry, College of Arts and Sciences, University of Alaska Anchorage, 3211 Providence Dr., Anchorage, Alaska 99508, United States., Begley JL; Department of Chemistry, College of Arts and Sciences, University of Alaska Anchorage, 3211 Providence Dr., Anchorage, Alaska 99508, United States., Hillestad I; Department of Chemistry, College of Arts and Sciences, University of Alaska Anchorage, 3211 Providence Dr., Anchorage, Alaska 99508, United States., DiMento BP; Department of Chemistry, College of Arts and Sciences, University of Alaska Anchorage, 3211 Providence Dr., Anchorage, Alaska 99508, United States., Stanton RS; Department of Chemistry, University of California, Riverside, California 92521, United States., Aguaa AR; Department of Chemistry, University of California, Riverside, California 92521, United States., Pirrung MC; Department of Chemistry, University of California, Riverside, California 92521, United States., Tomco PL; Department of Chemistry, College of Arts and Sciences, University of Alaska Anchorage, 3211 Providence Dr., Anchorage, Alaska 99508, United States. |
| Abstrakt: |
The photochemical degradation pathways of 6PPD-quinone (6PPDQ, 6PPD-Q), a toxic transformation product of the tire antiozonant 6PPD, were determined under simulated sunlight conditions typical of high-latitude surface waters. Direct photochemical degradation resulted in 6PPDQ half-lives ranging from 17.5 h at 20 °C to no observable degradation over 48 h at 4 °C. Sensitization of excited triplet-state pathways using Cs + and Ar purging demonstrated that 6PPDQ does not decompose significantly from a triplet state relative to a singlet state. However, assessment of processes involving reactive oxygen species (ROS) quenchers and sensitizers indicated that singlet oxygen and hydroxyl radical do significantly contribute to the degradation of 6PPDQ. Investigation of these processes in natural lake waters indicated no difference in attenuation rates for direct photochemical processes at 20 °C. This suggests that direct photochemical degradation will dominate in warm waters, while indirect photochemical pathways will dominate in cold waters, involving ROS mediated by chromophoric dissolved organic matter (CDOM). Overall, the aquatic photodegradation rate of 6PPDQ will be strongly influenced by the compounding effects of environmental factors such as light screening and temperature on both direct and indirect photochemical processes. Transformation products were identified via UHPLC-Orbitrap mass spectrometry, revealing four major processes: (1) oxidation and cleavage of the quinone ring in the presence of ROS, (2) dealkylation, (3) rearrangement, and (4) deamination. These data indicate that 6PPDQ can photodegrade in cool, sunlit waters under the appropriate conditions: t 1/2 = 17.4 h tono observable decrease (direct); t 1/2 = 5.2-11.2 h (indirect, CDOM). |
