Fragmentation of plastic objects in a laboratory seawater microcosm

Jan Gerritse,A Dick Vethaak,Heather A Leslie,Lisa I Devriese,Caroline A De Tender

doi:10.1038/s41598-020-67927-1

Jan Gerritse, A Dick Vethaak + Show 3 more

Open Access

https://doi.org/10.1038/s41598-020-67927-1

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Abstract

We studied the fragmentation of conventional thermoplastic and compostable plastic items in a laboratory seawater microcosm. In the microcosm, polyurethane foams, cellulose acetate cigarette filters, and compostable polyester and polylactic acid items readily sank, whereas polyethylene air pouches, latex balloons, polystyrene foams and polypropylene cups remained afloat. Microbial biofilms dominated by Cyanobacteria, Proteobacteria, Planctomycetes and Bacteriodetes grew on the plastics, and caused some of the polyethylene items to sink to the bottom. Electrical resistances (ER) of plastic items decreased as function of time, an indication that seawater had penetrated into microscopic crevices in the plastic that had developed over time. Rate constants for ER decrease in polyethylene items in the microcosm were similar to tensile elongation decrease of polyethylene sheets floating in sea, measured previously by others. Weight loss of plastic items was ≤ 1% per year for polyethylene, polystyrene and polypropylene, 3–5% for latex, polyethylene terephthalate and polyurethane, 15% for cellulose acetate, and 7–27% for polyester and polylactic acid compostable bags. The formation of microplastics observed in the microcosm was responsible for at least part of the weight loss. This study emphasizes the need to obtain experimental data on plastic litter degradation under conditions that are realistic for marine environments.

Highlights

We studied the fragmentation of conventional thermoplastic and compostable plastic items in a laboratory seawater microcosm
polyethylene terephthalate (PET) bottles and fleece, PS coffee cups and the polylactic acid (PLA) materials were placed in the microcosm, they immediately sank to the bottom because of a higher density than seawater
Fragmentation of plastic items can be estimated with a variety of analytical techniques, based on morphological and rheological changes, or on gravimetric, scanning electron microscopy (SEM), spectroscopic or chromatographic analyses[56]

Summary

Introduction

We studied the fragmentation of conventional thermoplastic and compostable plastic items in a laboratory seawater microcosm. An estimated 13% to 32% of the total weight of buoyant plastics in the oceans consists of microplastic particles of 0.3–5 mm in size[14,21,22]. It is currently unknown how and at which rates fragmentation of plastic proceeds. Larger plastic litter items may be eaten by or cause entanglement of marine fish, birds and mammals, while the micro- and nanoplastic particles are more prone to being ingested by large, and by smaller invertebrates such as mussels and zooplankton with the potential for accumulation in food chains[19,41]. The larger specific surface area generated through fragmentation increases contact with water with faster leaching or sorption rates for chemicals and additional area for biofouling[49]

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