An undocumented source of plastic contamination in sensitive estuarine environments.

The degradation of plastic infrastructure installed along estuaries and coastal environments may constitute a significant source of plastic contamination. This study aimed to determine the prevalence of plastic infrastructure and the extent of surface degradation of these plastics in a case study system, the Swan and Canning Estuary, Western Australia. The severity of cracks, chips, deformation, and material loss were used to estimate a novel degradation index for the plastic components on structures. The most common plastic infrastructure was decking on jetties, predominantly fibre reinforced (70 %) and co-polymer recycled (20 %) plastics. Degradation was evident at every site and varied across structures and plastic materials. The severity of degradation was likely influenced by a range of complex interacting factors such as structure age, and wet-dry cycling, alkalinity, and high temperatures that are characteristic of estuarine environments and known to exacerbate degradation of plastic materials. This study revealed plastic infrastructure was common in the case study system, structures start degrading during installation and may constitute a significant, and hitherto undocumented, source of plastic to these environments.