Heterogeneous and Photosensitized Oxidative Degradation Kinetics of the Plastic Additive Bisphenol-A in Sea Spray Aerosol Mimics

Plastics have becomeubiquitous in the world's oceans, andrecent work indicates that they can transfer from the ocean to theatmosphere in sea spray aerosol (SSA). Hazardous chemical residuesin plastics, including bisphenol-A (BPA), represent a sizable fractionof consumer plastics and have been measured consistently in air overboth terrestrial and marine environments. However, the chemical lifetimesof BPA and mechanisms by which plastic residues degrade with respectto photochemical and heterogeneous oxidation processes in aerosolsare unknown. Here, we present the photosensitized and OH-initiatedheterogeneous oxidation kinetics of BPA in the aerosol phase consistingof pure-component BPA and internal mixtures of BPA, NaCl, and dissolvedphotosensitizing organic matter. We found that photosensitizers enhancedBPA degradation in binary-component BPA + photosensitizer aerosolmixtures when irradiated in the absence of OH. OH-initiated degradationof BPA was enhanced in the presence of NaCl with and without photosensitizingspecies. We attribute this enhanced degradation to greater mobilityand thus reaction probability between BPA, OH, and reactive chlorinespecies (RCS) formed through reaction between OH and dissolved Cl- in the more liquid-like aerosol matrix in the presenceof NaCl. Addition of the photosensitizers in the ternary-componentBPA + NaCl + photosensitizer aerosol led to no enhancement in thedegradation of BPA following light exposure compared to the binary-componentBPA + NaCl aerosol. This was attributed to quenching of triplet stateformation by dissolved Cl- in the less viscous aqueousaerosol mixtures containing NaCl. Based upon measured second-orderheterogeneous reaction rates, the estimated lifetime of BPA with respectto heterogeneous oxidation by OH is one week in the presence of NaClcompared to 20 days in the absence of NaCl. This work highlights theimportant heterogeneous and photosensitized reactions and the roleof phase state, which affect the lifetimes of hazardous plastic pollutantsin SSA with implications for understanding pollutant transport andexposure risks in coastal marine environments.

Automated summary

Plastics in the ocean can transfer to the atmosphere in sea spray aerosol. Bisphenol-A (BPA), a hazardous chemical residue commonly found in consumer plastics, has been consistently measured in both terrestrial and marine air. The degradation of BPA through photochemical and heterogeneous oxidation processes in aerosols is influenced by photosensitizers and reactive chlorinespecies.