This report presents an inventory of land-borne sources of microplastics that may end up in sea. Microplastics are particles smaller than 5 mm and may enter the food chain. Sources can be products, production process or routes along which they are transported via rivers to the sea. Subsequently these sources are prioritized. Based on the prioritization policy plans can be developed to reduce the amount of microplastics in the environment. More research is required to underpin and specify measures. Five criteria were used for the prioritization: volume of the emission, essentiality of the source, possibility of quick win measures, social perception and presence of alternatives for the consumer.
High priority was assigned to sources of secondary microplastics, i.e. microplastics that result from fragmentation of larger plastics. Plastic debris, which consists largely of packaging materials and disposable products is the most important source of microplastics (score 8-9 on a scale from 1-10). Other secondary microplastic sources with a relatively high score (score 6-7) are fibres and clothing, roadway runoff (including tire dust), dust from construction places, agricultural plastic and input from abroad via the rivers Rhine, Meuse and Scheldt. Also waste water, sewage sludge and compost received a relatively high score (score 6), because they contain primary as well as secondary microplastics from a variety of sources with emissions to the sewer system, such as households that emit fibres through the washing machine and microbeads used for personal care and cosmetic purposes.
For the primary microplastics, which are intentionally added to products for specific functions, the highest priorities were assigned to cosmetics and pigments and paints (score 7), followed by abrasive cleaning agents (score 6).
A complete socio-economic analysis could not be performed on short notice because of limited availability of data. Moreover, the impacts of microplastic exposure for man and environment are not clear. The priorities were assigned based on the Dutch situation by expert judgement offered by representatives of RIVM, Deltares, Rijkswaterstaat and the Dutch Pollutant Release and Transfer Register.