Influence of thermooxidative degradation on the in situ fate of polyethylene in temperate coastal waters

Polyethylene is a commonly used polymer in plastic products and is often found as marine litter. Nevertheless there is limited knowledge about what happens to the material when it ends up in the sea. Polyethylene films were therefore thermally oxidised to four different levels of degradation. The films were then placed in stainless-steel cages in the sea off the Swedish west coast for 12 summer weeks. Subsamples were analysed with respect to biofouling, degradation and buoyancy. All levels showed a continued oxidation in the field. The pre-degraded films started fragmenting and the non-degraded films showed a decrease in tensile strain. All levels showed increased biofouling with higher presence of filamentous algae and bryozoans on pre-degraded materials. The density (kg·m−3) of the films was seen to increase slightly, and the apparent density for the pre-degraded films (density of the films with biofilm) showed a strong increase, which resulted in sinking. [Display omitted] •Films of polyethylene (PE) were predegraded to four levels and placed in the field•During the 12 weeks in the field all levels showed continuous oxidation•An indication of a bio-assimilation of highly oxidised PE was observed•Biofilm formation increased and was higher for predegraded PE•Predegraded PE fragmented and started sinking