Emission of microplastics and potential mitigation measures : Abrasive cleaning agents, paints and tyre wear

According to the Marine Strategy Framework Directive 2008/56/EC (MSFD), research must be conducted on the amount, occurrence and the sources of microplastics, and on measures that can reduce the emissions of microplastics.To support the development of effective and efficient action plans by the Dutch government, RIVM published in 2014 an inventory and prioritization of land-based sources of microplastics [1].The prioritization of land-based sources was scored based on a first qualitative evaluation of three criteria: 1) volume of the emission, 2) feasibility of measures and 3) action perspectives for consumers.The current report is a follow-up study to three prioritized land-based sources: 1) abrasive cleaning agents, 2) paints and lacquers and 3) rubber tyres.The aim was to quantify emissions of microplastics from these sources in the Netherlands and to propose potential measures for reduction of microplastics.The study was announced by the Dutch government in the MSFD Programme of measures. DefinitionMicroplastics are solid, synthetic polymer particles with a size smaller than 5 mm, with a low solubility in water and a low degradation rate.Microplastics may contain non-polymeric additives, oils, fillers or other product aids.The mass of these inherent ingredients is included in the emission calculations.However, external substances or materials attached to microplastics during or after their use phase, such as road dirt to tyre wear particles, are not included in the emission calculations. DetergentsWe screened >400 (abrasive) cleaning agents of six market-leading companies and found that ten products were suspected of containing microplastics.These microplastics serve as abrasive agents.It all concerned products used to clean floors.Based on market data, it was estimated that the total emission of microplastics from abrasive cleaning agents is 2.6 tons/year, which is almost completely discharged into the sewer.Emissions to surface water are estimated to be 1.2 tons/year.The most likely measures to reduce emissions into surface water are a legal ban or the gradual, voluntary phase-out of microplastics in detergents.These are measures that need to be taken by the responsible producers. PaintsPaint particles are considered as microplastics because they have a backbone of polymers.For the building sector, a total emission of 490 tons was estimated.In respect of paints, applications in the building and shipping sector were determined to be responsible for the largest part of paint use.In the building sector, a distinction is made between professionals and do-it-yourself (DIY) consumers.The amount of plastics that are released by removal of old paint layers, by the tear and wear of paint and by the rinsing of rollers and brushes coated with water-soluble wall paints is taken in to account.Emissions to surface water are estimated to be 130 tons per year.For shipping, the removal of paint at shipyards and marinas, as well as the wear and tear during shipping are quantified.In the shipping sector, it is estimated that 200 tons of microplastics per year are released to surface water. Rubber tyresRoad transport vehicle tyres were estimated to contribute 1,800 tons of particles from tyre tread wear per year into surface water through run-off from pavements, effluents and overflows of the sewage system, and 6,200 tons per year into soil.Additionally, another 900 tons per year of fine particulate matter from tyres are released to the air, and 7,400 tons per year are captured in open asphalt concrete roads.This pertains to the wear of tyres on nine different vehicle types: such as several types of trucks, passenger cars, buses and motorcycles.Potential measures comprise innovations made to tyres and road surfaces and the collection of run-off water, consumer awareness with respect to driving behaviour, tyre pressure and wheel alignment, the proper use of summer and winter tyres, and ways to reduce vehicle kilometres. UncertaintiesThe emission estimates in this report are often based on limited information and rely partly on expert judgement.For this reason, ranges of emissions to surface water are reported.It is recommended that research be conducted in order to fill some significant knowledge gaps.Towards the end, suggestions are given in this report. MeasuresLegal, economic, voluntary and persuasive instruments for a policy to reduce microplastics were discussed and supplemented with a list of potentially product-specific viable options.The measures proposed in this study should be subjected to further socio-economic analysis to determine the effectiveness, viability and the costs and benefits of the measures.A generic measure could be the improvement of sewage treatment plants.In general, this end-of-pipe measure is less favourable than preventive source measures and measures that address the producer's responsibility.Furthermore, the current distribution of microplastics towards sewage treatment plants and removal efficiency of these plants are highly uncertain.These uncertainties must be reduced by specific research before end-of-pipe measures are introduced.