Session: Presidential Symposium: Plastics and the Oceans: Chemistry for the Journey Ahead:

Understanding and predicting the fate and transport of marine plastic debris is key to mitigating its negative environmental consequences, but challenging due to insufficient data of the processes that control its environmental lifetimes. Photodegradation is one key process that leads to fragmentation of macroplastic debris into microplastic particles, and ultimately to dissolution and mineralization of plastic material. To date, much of the understanding of photochemical processes for marine plastics comes from laboratory studies of pure polymers conducted under ideal conditions. However, plastic consumer products in the ocean may behave differently due to varying formulation (i.e., base polymer plus additives) or the growth of biofilms on their surfaces. Our objective was therefore to determine to what extent the development of biofilms screens light from plastic debris, potentially inhibiting its photodegradation rates. To this end, we collected five different consumer plastic film products composed of polyethylene (PE) or polyethylene terephthalate (PET) that are used in everyday life and commonly found among marine plastic debris, including shopping bags, packaging materials, and plastic drinking bottles. Along with films of the pure polymers PE and PET, we incubated the products in outdoor seawater mesocosms for six weeks, tracking the development of biofilm formation on their surfaces using a crystal violet-based staining protocol. Simultaneously, we measured the transmittance of light through the combined plastic and biofilm samples. We observed that a substantial amount of light was screened by these naturally-formed biofilms, independent of the plastic product. However, products containing UV-absorbing monomeric constituents (aryl-groups in PET) or additives (TiO₂ in a number of plastic film products) showed much less relative light screening by biofilms compared to the light absorbed by these plastic products. These results demonstrate that biofilms can screen light and influence the photochemical fate of marine plastic debris, but the formulation of the plastic products must be considered to accurately account for this fate-controlling process.

Christopher Reddy

Appearances