From macroplastic to microplastic: Degradation of high density polyethylene, polypropylene, and polystyrene in a salt marsh habitat

As part of the degradation process, it is believed that most plastic debris becomes brittle over time, fragmenting into progressively smaller particles. The smallest of these particles, known as microplastics, have been receiving increased attention due to the hazards they present to wildlife. To understand the process of plastic degradation in an intertidal salt marsh habitat, strips (15.2 × 2.5 cm) of high density polyethylene (HDPE), polypropylene (PP), and extruded polystyrene (PS) were field deployed in June 2014 and monitored for biological succession, weight, surface area, UV transmittance, and fragmentation. Subsets of strips were collected after 4, 8, 16, and 32 weeks. After 4 weeks, biofilm had developed on all three polymers with evidence of grazing periwinkles (Littoraria irrorata). The accreting biofilm resulted in an increased weight of the PP and PS strips at 32 weeks by 33.5 and 167.0%, respectively, with a concomitant decrease in UV transmittance by ∼99%. Beginning at 8 weeks, microplastic fragments and fibers were produced from strips of all three polymers, and scanning electron microscopy revealed surface erosion of the strips characterized by extensive cracking and pitting. The results of this study suggest that the degradation of plastic debris proceeds relatively quickly in salt marshes, and that surface delamination is the primary mechanism by which microplastic particles are produced in the early stages of degradation.

J. E. Weinstein, B. K. Crocker, A. D. Gray, Environmental Toxicology and Chemistry, accepted 19 March 2016

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