The Sum of the Parts: In situ degradation and fragmentation of plastic polymers in a forested and urban stream

Inland riverine systems are major conduits of organic materials to coastal systems, and they also transport plastics that enter the ocean. Plastic materials that pass-through streams are subjected to various degradation processes that facilitate their fragmentation into microplastics (MPs). Streams, therefore, are an influential but understudied landscape feature that affects the fate and transport of MPs. Here, we investigate the in-situ degradation of common plastic polymers (e.g., low-density polyethylene, polyethylene terephthalate, and polystyrene) and their fragmentation into MPs in urban and forested streams. We deployed plastic items and a natural biodegradable polymer (cellulose) into a stream habitat for 52 weeks. SEM-EDS analysis revealed biofilm formation on each plastic item, which was mainly composed of diatoms. We found that regardless of stream habitat type, polymers produced MPs in two weeks, with polystyrene having the highest fragmentation rate (8 particles/ week).  We explored several degradation indices (carboxyl index, hydroxyl index, and vinyl index), which revealed that oxidation played a major role in plastic degradation over time. Lastly, we found that field-aged plastics can leach measurable levels of plastic-derived dissolved organic carbon, demonstrating plastics as a source of allochthonous carbon in streams that are relatively unaccounted for in carbon budget estimates. Our findings add to the knowledge gap regarding MP fragmentation in freshwater by providing real-time in situ data on the rate of polymer fragmentation and degradation in streams.

Presentation Preference: Oral

Primary Presenter: Austin Gray, Virginia Tech (austindg@vt.edu)

Authors:

Beija Gore, Virginia Tech  (beijag96@vt.edu)

Megan Gaesser, Virginia Tech  (meganeg@vt.edu)

Luisana Rodriguez Sequeira, Virginia Tech  (lrs@vt.edu)

Tessa Thibodeau, Virginia Tech  (tessathibodeau@vt.edu)

Sam Purvis, Virginia Tech  (scpurvis@vt.edu)

Allison Montgomery, Virginia Tech  (akjmontgomery25@vt.edu)

Kathryn Ouimet, Virginia Tech  (kouimet25@vt.edu)

Arianna Porter, Virginia Tech  (arianna0304@vt.edu)

Tina Dura, Virginia Tech  (tinadura@vt.edu)

Kathleen Mayer, Virginia Tech  (kathleengm@vt.edu)