@article {walsh_synergy_2022,
	title = {Synergy between Sunlight, Titanium Dioxide, and Microbes Enhances Cellulose Diacetate Degradation in the Ocean},
	journal = {Environmental Science \& Technology},
	volume = {56},
	number = {19},
	year = {2022},
	note = {Publisher: American Chemical Society},
	month = {09/2022},
	pages = {13810{\textendash}13819},
	abstract = {Sunlight chemically transforms marine plastics into a suite of products, with formulation-the specific mixture of polymers and additives-driving rates and products. However, the effect of light-driven transformations on subsequent microbial lability is poorly understood. Here, we examined the interplay between photochemical and biological degradation of fabrics made from cellulose diacetate (CDA), a biobased polymer used commonly in consumer products. We also examined the influence of \~{}1\% titanium dioxide (TiO2), a common pigment and photocatalyst. We sequentially exposed CDA to simulated sunlight and native marine microbes to understand how photodegradation influences metabolic rates and pathways. Nuclear magnetic resonance spectroscopy revealed that sunlight initiated chain scission reactions, reducing CDA{\textquoteright}s average molecular weight. Natural abundance carbon isotope measurements demonstrated that chain scission ultimately yields CO2, a newly identified abiotic loss term of CDA in the environment. Measurements of fabric mass loss and enzymatic activities in seawater implied that photodegradation enhanced biodegradation by performing steps typically facilitated by cellulase. TiO2 accelerated CDA photodegradation, expediting biodegradation. Collectively, these findings (i) underline the importance of formulation in plastic{\textquoteright}s environmental fate and (ii) suggest that overlooking synergy between photochemical and biological degradation may lead to overestimates of marine plastic persistence.},
	issn = {0013-936X},
	doi = {10.1021/acs.est.2c04348},
	url = {https://doi.org/10.1021/acs.est.2c04348},
	author = {Walsh, Anna N. and Mazzotta, Michael G. and Nelson, Taylor F. and Reddy, Christopher M. and Ward, Collin P.}
}
@article {3003,
	title = {Plastic Formulation is an Emerging Control of Its Photochemical Fate in the Ocean},
	journal = {Environmental Science \& Technology},
	volume = {55},
	year = {2021},
	month = {09/2021},
	pages = {12383 - 12392},
	abstract = {Sunlight exposure is a control of long-term plastic fate in the environment that converts plastic into oxygenated products spanning the polymer, dissolved, and gas phases. However, our understanding of how plastic formulation influences the amount and composition of these photoproducts remains incomplete. Here, we characterized the initial formulations and resulting dissolved photoproducts of four single-use consumer polyethylene (PE) bags from major retailers and one pure PE film. Consumer PE bags contained 15{\textendash}36\% inorganic additives, primarily calcium carbonate (13{\textendash}34\%) and titanium dioxide (TiO2; 1{\textendash}2\%). Sunlight exposure consistently increased production of dissolved organic carbon (DOC) relative to leaching in the dark (3- to 80-fold). All consumer PE bags produced more DOC during sunlight exposure than the pure PE (1.2- to 2.0-fold). The DOC leached after sunlight exposure increasingly reflected the 13C and 14C isotopic composition of the plastic. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry revealed that sunlight exposure substantially increased the number of DOC formulas detected (1.1- to 50-fold). TiO2-containing bags photochemically degraded into the most compositionally similar DOC, with 68{\textendash}94\% of photoproduced formulas in common with at least one other TiO2-containing bag. Conversely, only 28\% of photoproduced formulas from the pure PE were detected in photoproduced DOC from the consumer PE. Overall, these findings suggest that plastic formulation, especially TiO2, plays a determining role in the amount and composition of DOC generated by sunlight. Consequently, studies on pure, unweathered polymers may not accurately represent the fates and impacts of the plastics entering the ocean.},
	isbn = {0013-936X},
	doi = {10.1021/acs.est.1c02272},
	url = {https://doi.org/10.1021/acs.est.1c02272},
	author = {Walsh, Anna N. and Reddy, Christopher M. and Niles, Sydney F. and McKenna, Amy M. and Hansel, Colleen M. and Ward, Collin P.}
}
@article {2647,
	title = {Sunlight Converts Polystyrene to Carbon Dioxide and Dissolved Organic Carbon},
	journal = {Environmental Science \& Technology Letters},
	year = {2019},
	month = {Oct-10-2019},
	abstract = {Numerous international governmental agencies that steer policy assume that polystyrene persists in the environment for millennia. Here, we show that polystyrene is completely photochemically oxidized to carbon dioxide and partially photochemically oxidized to dissolved organic carbon. Lifetimes of complete and partial photochemical oxidation are estimated to occur on centennial and decadal time scales, respectively. These lifetimes are orders of magnitude faster than biological respiration of polystyrene and thus challenge the prevailing assumption that polystyrene persists in the environment for millennia. Additives disproportionately altered the relative susceptibility to complete and partial photochemical oxidation of polystyrene and accelerated breakdown by shifting light absorbance and reactivity to longer wavelengths. Polystyrene photochemical oxidation increased approximately 25\% with a 10 {\textdegree}C increase in temperature, indicating that temperature is unlikely to be a primary driver of photochemical oxidation rates. Collectively, sunlight exposure appears to be a governing control of the environmental persistence of polystyrene, and thus, photochemical loss terms need to be included in mass balance studies on the environmental fate of polystyrene. The experimental framework presented herein should be applied to a diverse array of polymers and formulations to establish how general these results are for other plastics in the environment.},
	issn = {2328-8930},
	doi = {10.1021/acs.estlett.9b00532},
	url = {https://pubs.acs.org/doi/abs/10.1021/acs.estlett.9b00532},
	author = {Ward, Collin P. and Armstrong, Cassia J. and Walsh, Anna N. and Jackson, Julia H. and Reddy, Christopher M.}
}
