Plastic losses to the environment can occur at all stages of plastic production, use and disposal. Once in the environment, plastics occurs in a variety of shapes, sizes and polymers, including dynamics such as accumulation on beaches, breakdown from macro- to microplastics, and uptake in biota. Addressing plastic pollution requires reliable indicators, i.e. measurable parameters that represent plastic pollution or certain aspects of it. This study has analysed existing indicators along the plastic value chain and in the environment, including frameworks aiming at circular economy and plastic reuse and recycling.
The main part of plastic losses is macroplastic, with an important source being the mismanagement of plastic waste, including plastic littering. Thus, the degree of mismanaged plastic waste would be a relevant indicator, but it is difficult to measure directly. Indirect determinations may be possible and have been outlined. Several environmental indicators have been established, which can be used in a complementary way, e.g. covering macro- and microplastics and representing different environmental media. Guidelines have been developed to ensure harmonized approaches. However, uncertainties in determinations remain, in addition to large fluctuations in the environment. For all types of indicators, high uncertainties will affect the power of time series in a way that significant trends will be difficult to detect.
Downstream indicators in the environment are badly connected with upstream indicators in the plastic value chain. An important microplastic component lost in the value chain is tyre abrasion, but this is no typical indicator in the marine environment. Originally, due to the large rubber component in tyre wear, these particles were not considered as microplastics. Furthermore, they may be retained in the terrestrial or freshwater environment and reach the marine environment in smaller quantities. There have also been methodological obstacles and challenges. On the other hand, lost and abandoned fishing gear is an important pollution type in the marine environment, but scarcely recognized in upstream leakage processes. Consistency is also hampered by a lack of harmonization in reporting units and upscaling practices. The report also includes some suggestions of potentially relevant new indicators, such as container losses, ghost nets and microplastics in wastewater.