Title:
Atmospheric Chemistry of Tire Wear Antioxidants: Implications of transformation product mixtures on Human and Ecosystem Health
Abstract:
Tire-wear antioxidants are used by the rubber industry to inhibit the degradation of tires. Recent research has implicated a breakdown product of a tire-wear antioxidant (N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine; 6PPD) as an acute risk to aquatic organisms, via aqueous ozonation. However, as a first step, tire-wear particles containing antioxidants are often emitted to the atmosphere, where heterogenous reactions with oxidants and other constituents may form transformation products with structures, environmental fates and toxicities that have yet to be considered. Here, a series of laboratory experiments were conducted to investigate the heterogeneous oxidation of 6PPD and N,N′-diphenyl-p-phenylenediamine (DPPD), in the presence of ozone, OH radical, and nitrogen oxides (NOX), as would occur for particulate matter (PM) in the atmosphere. The results demonstrated that the kinetics of transformation were rapid, allowing for atmospheric heterogeneous oxidation to be an important source of exposure, with at least 130 transformation products detected from 6-PPD and DPPD, many of which were previously unknown. In-silico model predictions indicated that the persistence, bioaccumulation, environmental mobility and toxicity of several of the transformation products formed were far more detrimental than the parent antioxidant, especially those formed in the presence of NOX. The laboratory data were used to constrain complex non-targeted mass spectra of ambient PM samples, confirming the presence of many of the identified transformation products in PM emitted near a major roadway and within the greater suburban region. Most importantly, we demonstrate that the transformation product mixtures can trigger potent inflammatory responses and cell death in human macrophage cells. These effects far exceed those of the parent antioxidants even at low concentrations, while 6PPD-Q, a known driver of aquatic toxicity, failed to elicit similar cytotoxicity or inflammation. The results have important implications for airborne exposure, downwind deposition, and mitigation for a future expected to be dominated by Electric vehicles.
Bio:
John Liggio is a Senior Research Scientist in the Air Quality Research Division, Environment and Climate Change Canada (ECCC). He completed his Ph.D. in 2004 with the Department of Chemistry & Centre for Atmospheric Chemistry at York University followed by 4 years of post-doc at ECCC. Currently, John leads several major ECCC field programs and laboratory-based studies, including the Oil Sands Monitoring (OSM) program, Chemical Management Plan (CMP) program and downstream oil and gas, methane and VOC research programs. His research interests include emission studies such as Oil sector greenhouse gases, wildfire, urban emissions etc, understanding the processes of formation and evolution of smog and secondary organic aerosol, transformation and fate of persistent pollutants, Chemical ionization Mass Spectrometry methods development and many more. He is a member of various national and international science advisory groups such as the World Meteorological Organization (WMO) science advisory group and the Senior Science Advisory Council (ECCC).