Size Dependence of Plastic Photochemical Lifetimes in Surface Waters

Microplastics are found floating on fresh and ocean waters. Sunlight-driven photochemistry can dissolve buoyant microplastics, removing them from the environment and producing dissolved organic carbon (DOC). However, it is unclear how photochemical lifetimes of plastics vary with particle size. We hypothesized that the increase in cross-sectional surface area to volume ratio as plastics decrease in size results in more rapid dissolution as smaller plastics receive a larger light dose per unit mass than larger plastics. To test this, samples of expanded polystyrene (EPS) and polypropylene (PP) spanning a range of sizes were irradiated floating on water in a solar simulator. A linear relationship between surface area to volume ratio and DOC accumulation rate was observed for EPS and a power relationship was observed for PP. Using these relationships, the photochemical lifetimes of plastics of different sizes were predicted. Results for macroplastics concur with general expectations that plastics take a long time to degrade, indicating that macroplastics greater than 10 cm should take almost 200 years to photochemically dissolve. However, at smaller sizes, plastics cease to meet these expectations, with 1 nm nanoplastics predicted to have lifetimes at the sea surface of 17 days for PP and 1 minute for EPS.

Presentation Preference: Oral

Primary Presenter: Aron Stubbins, Northeastern University (a.stubbins@northeastern.edu)

Authors:

Ariana Patterson, Northeastern University  (patterson.ar@northeastern.edu)

Charlotte Wiman, Northeastern University  (c.wiman@northeastern.edu)

Samuel Munoz, Northeastern University  (s.munoz@northeastern.edu)

Erin Tuttle, Assumption University  (ee.tuttle@assumption.edu)

Lixin Zhu, Northeastern University  (lixinzhu0305@hotmail.com)

Kara Lavender Law, Sea Education Association  (klavender@sea.edu)

Aron Stubbins, Northeastern University  (aron.stubbins@northeastern.edu)