Following degradation and fragmentation of plastic litter over two years' weathering on Swedish beaches.

Plastic litter stranded on beaches is a worldwide problem. The harsh conditions, intense UV radiation, fluctuating temperatures and mechanical abrasion from wind and wave forces, should favour macroplastic degradation and increase fragmentation rate. In a field experiment, ten types of commonly found beach litter items of a variety of polymers, product categories and colours, were placed on two highly exposed beaches on the Swedish west coast. Samples were analysed after 6, 12 and 24 months of exposure, and compared to pristine, un-weathered control items, following degradation by measuring changes in chemical composition (FTIR), thermal properties (DSC), mechanical properties (tensile strength) and morphological feature of surface structure (SEM), while fragmentation was indicated from visual inspection, weight loss and analysis of discolouration. Also, after two years' exposure, only minor signs of chemical and thermal degradation and changes in surface morphology were found. Still, after 6-24 months' exposure, several litter items, including string (PE), candy paper (LDPE), plastic bag (LDPE), rope (PP), fishing net (PA), container lid (PET), Styrofoam (ESP) and beach toy (PVC) samples, demonstrated decolouration, weight loss and had already fragmented, or were brittle enough to have the potential to do so as shown by major loss (17-71%) in tensile strength. Candy paper had lost 71% of tensile strength after 12 months, and after 24 months, samples were transparent and > 50% were disintegrated. Our results highlight beach litter as source for microplastic pollution and support management with swift beach cleaning activities of heavily polluted sites to remove macroplastics before microplastics are formed.