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

Abstract

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 because of the hazards they present to wildlife. To understand the process of plastic degradation in an intertidal salt marsh habitat, strips (15.2 cm × 2.5 cm) of high-density polyethylene, polypropylene, and extruded polystyrene were field-deployed in June 2014 and monitored for biological succession, weight, surface area, ultraviolet (UV) transmittance, and fragmentation. Subsets of strips were collected after 4 wk, 8 wk, 16 wk, and 32 wk. After 4 wk, biofilm had developed on all 3 polymers with evidence of grazing periwinkles (Littoraria irrorata). The accreting biofilm resulted in an increased weight of the polypropylene and polystyrene strips at 32 wk by 33.5% and 167.0%, respectively, with a concomitant decrease in UV transmittance by approximately 99%. Beginning at 8 wk, microplastic fragments and fibers were produced from strips of all 3 polymers, and scanning electron microscopy revealed surface erosion of the strips characterized by extensive cracking and pitting. The results 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. Environ Toxicol Chem 2016;35:1632-1640. © 2016 SETAC.

Trophic transfer of microplastics in aquatic ecosystems: Identifying critical research needs

“…Recently, it has also been shown that microplastic fragments and fibers were produced from high density polyethylene, polypropylene, and polystyrene strips after 8 weeks of exposure in an intertidal salt marsh (Weinstein et al 2016).…”

“…Microplastics (MPs) have been generally defined as plastic particles that have at least 1 dimension less than 5 mm (Andrady 2011) and can be further classified by the origin of the microplastics. Primary microplastics are intentionally manufactured to have micron-sized dimensions, whereas secondary microplastics have fragmented from a larger plastic product, eventually reaching micron-sized dimensions (Weinstein et al 2016). The presence of microplastics in the environment has been widely addressed and confirmed in both aquatic and terrestrial ecosystems (Browne et al 2011;Rillig 2012).…”

Sources and dispersive modes of micro‐fibers in the environment

“…When discarded macroplastics are exposed to the elements, microfragments can be generated in situ as a result of ultraviolet, thermal, and oxidative weathering. These processes cause embrittlement, which promotes fracturing (Weinstein et al 2016); embrittled plastics become more susceptible to physical abrasion and mechanical fragmentation (Andrady, 2011). The dispersion of these plastic particles in the environment has been well studied.…”

Analysis, Occurrence, and Degradation of Microplastics in the Aqueous Environment

“…To prevent this, additives are added during the production process, and the oxidative or photooxidative degradation of the polymer is delayed until the antioxidants are consumed. After the initial oxidation of the surface of polyolefins, the degradation could occur in several weeks but results in the formation of microplastics as possible intermediates [67]. These smaller and oxidized plastic fragments are more susceptible to microbial attack, e.g., biodegradation of PE is described for pre-oxidized fragments of the original material by Pseudomonas sp.…”