Litter in Urban Areas May Contribute to Microplastics Pollution: Laboratory Study of the Photodegradation of Four Commonly Discarded Plastics

Plastic litter in the urban environment has been identified as a source of microplastics and stormwater a pathway for its transportation to freshwater and marine environments. However, few studies exist on the potential for litter to contribute to microplastics in a land-based system. This laboratory-based study involves simulation of the weathering of four polymers [low-density polyethylene (PE-LD), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET)] in a land-based environment using accelerated photodegradation with three exposure times. Microplastics generated were quantified with Fourier transform infrared spectroscopy and identified using a spectra reference library. The results showed differences in release patterns and number of particles produced. For LD-PE, no clear pattern of UV-degradation was demonstrated, because the number of particles released from exposed and unexposed (control) samples was in the same order of magnitude. PS and PET showed similar patterns, where the number of particles released increased with exposure duration. The numbers of particles detected were, on average, 1, 8, and 31 particles/cm2 for PS and 3, 3, and 16 particles/cm2 for PET for exposures of seven, 28, and 56 days, respectively. PP produced the largest number of particles after 28 days exposure (ca. 58 particles/cm2) which then decreased after 56 days (ca. 21 particles/cm2). It was hypothesized that the number of particles increased with exposure time and that the generated particles then further fragmented into pieces of undetectable particle size (<10 μm).