Plastic debris represents an emerging threat to the marine environment, particularly wildlife. Common belief holds that large pieces of plastic debris, “macroplastics,” break down rather quickly into many smaller pieces, “microplastics.” Microplastics have received significant attention from the research community over the last 5 to 10 years because these small pieces can be harmful to wildlife, including fish, when ingested.
While we know plastics can take 50 years or longer to fully disintegrate, we know much less about the process and timing by which plastic disintegration occurs in the marine environment. Understanding the process and speed by which plastics produce microplastics will be helpful for the general public or anyone considering marine debris removal efforts.
To document the process and timing of plastic degradation, investigators selected example products made from the three most common plastics in South Carolina intertidal marshes: trash bags (high-density polyethylene and polypropylene) and foam dinner plates (extruded polystyrene). Next, they placed multiple 1-inch by 5-inch plastic strips of each type to a custom-made structure in the marsh. They examined subsets of strips of each type after 4, 8, 16 and 32 weeks to document changes in weight, surface area, biofouling activity and fragmentation.
The results indicate that plastic debris can create microplastic particles relatively quickly in salt marshes — perhaps in as little as 8 weeks. Surface delamination of the plastic strips was the primary cause of microplastic production.
After 8 weeks, microorganisms — collectively termed biofilm — coated all plastic samples to some degree. Researchers observed that this biofilm, in turn, served as food for salt marsh periwinkle snails, which fed on the coating on the plastic strips.
The investigators speculate that most plastic debris in subtropical, intertidal salt marshes likely release microplastic particles every tidal cycle.
Weinstein, J.E., Crocker, B.K., and Gray, A. D. (2016). From macroplastic to microplastic: degradation of high-density polyethylene, polypropylene, and polystyrene in a salt marsh habitat. Environmental Toxicology and Chemistry, Vol. 35, No. 7, pp. 1632–1640.
This study was prepared as a result of work sponsored by the South Carolina Sea Grant Consortium with National Oceanic and Atmospheric Administration Award N155 (E/ER-45) as well as the state of South Carolina.
Summary compiled by Scott Baker
Photos of marsh periwinkle snails courtesy of NOAA
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