Evaluating the fate, effects and mitigation measures for microplastic fibre pollution in aquatic environments

MICROFIBRE investigated the environmental fate and behaviour of microfibres (MFs) and their ingestion and toxicological effects on aquatic species under freshwater and marine conditions. Study materials were synthetic fibres (polyacrylic, PAN; polyamide, PA; polyester, PES) and wool (natural reference). MF uptake, excretion and effects were studied in freshwater, marine temperate and marine polar species. Fate studies Degradation: UV degradation (simulated sunlight) depended on polymer type. PA, PES and wool MFs exhibited surface changes after 14 d, followed by fragmentation after <2 weeks (PES), <2 months (wool) and <5 months (PA). PAN MFs remained mostly unaltered after 9 months. Degradation was similar in fresh and seawater. A range of PES degradation products leached during exposure. Mechanical abrasion caused no observable changes in MFs over 9 months. Long term hydrolysis of PES fleece was studied in fresh- and seawater with and without shaking with sand for up to 24 months at 55, 65 and 75 °C. No significant physical wear was detected and only a small degree of hydrolysis was detected, indicating PES MFs are quite stable in aquatic environments without UV exposure. Degraded reference materials: An accelerated (<3 h) alkaline hydrolysis degradation method was developed to generate reproducible and controllable degradation in PES MFs. Degradation is determined by measuring product formation and visual changes using SEM. Partially degraded PES fibres are a key reference material for fate and effects studies. Sedimentation studies: Fate studies also included assessment of the sinking rates of the MFs with different lengths (60 µm & 3 mm) in freshwater and seawater. A novel method using a silhouette camera was developed to identify sinking fibres and measure their individual speed. No significant differences due to fibre length, polymer composition or salinity were observed in a preliminary study. Associated chemicals: Non-target screening identified >16,000 compounds in PES, PA, PAN and wool MFs, representing additives, production chemicals and degradation products. UV-stabilisers (bisphenols and benzophenones) were present in all MFs and leached into aqueous media. While these rapidly UV-degrade, other identified additives may be more persistent. MF interaction with persistent organic pollutants (POPs) was also investigated. Wool sorbed significantly more POPs than synthetic MF, where the order of sorption capacity was PA>PES>>PAN. Uptake & Effect Studies Algae: Effects of PES, PA and wool MFs (60 and 3000 µm) and MF leachates were studied in the marine microalgae Isochrysis galbana. Population size decrease indicated polymer- and size-related effects. High MF concentrations induced growth effects, while PES leachates increased biomass. MF leachates did not affect photosynthetic efficiency, but the relative carbohydrate content shifted from glucose-like to cellulose-like compounds. Marine zooplankton: Exposure of the copepod Calanus finmarchicus to 60, 100, 300, 1000 and 3000 µm PAN MFs led to preferential uptake of ~60 µm MF by copepodites and up to 85 µm MFs in adults. Adult C. finmarchicus showed selective ingestion of PES MFs over PA and wool MFs, but all MFs were excreted at the same rate with no signs of accumulation. Selective uptake of synthetic MF, but not wool, reduced algal ingestion in a dose-dependent manner, with adverse impacts on lipid accumulation. PES-exposed copepods exhibited delayed development and increased mortality. Adult arctic copepods (C. hyperboreus) exhibited unlimited egestion of MFs, with the number of MFs per faecal pellet ranked PES>PA>wool. Faecal pellets of copepods exposed to synthetic MFs were longer and altered in shape compared to unexposed and wool-exposed copepods. For both species, ingestion rate=egestion rate. Freshwater zooplankton: The toxicity of different polymer types (PS, PA and PES) and shapes (beads, fibres and fragments) was investigated using a Daphnia magna reproduction test. Preliminary results suggest fragments elicit higher reproductive toxicity than fibres of the same polymer, but no difference in reproduction was observed between PA and PES MFs. Mitigation MICROFIBRE investigated which yarn and textile properties influence MF release from domestic washing machines. Washing machines at a commercial laundry service were fitted with a filtration system to collect MFs from wastewater. SINTEF also contributed to an international Cross-Industry Agreement that developed a harmonised test method for measuring release of MFs during washing. Three workshops were held in 2018, 2019 & 2020. Workshop 1 created a common understanding of the processes and parameters that cause and affect MF release from textiles. Workshop 2 applied Fuzzy Cognitive Mapping and Scenario Development for identifying key research needs, solutions and policy options for MF pollution. Workshop 3 mapped out targeted focus areas for mitigation actions.

MICROFIBRE has developed novel methods, including an internationally recognised standard, that are already being adopted by the research community, as well as novel partially degraded microfibre (MF) reference materials. Results from MICROFIBRE have been communicated to and taken up by organisations including the International Council for Exploration of the Seas, the EU MSFD WGML, the Norwegian Environment Agency, the Arctic Monitoring and Assessment Programme and the OECD. In the longer term, knowledge from MICROFIBRE will contribute to the development of new practices and policy related to MFs and microplastic. Importantly, the strong involvement of a range of clothing producers throughout the project has ensured that the knowledge from MICROFIBRE is being used directly to try and mitigate MF release through changes in textile production. In addition, filtration technologies developed within the project have been implemented at a commercial laundry company to reduce MF emissions.

The MICROFIBRE project will investigate the uptake and impact of microplastic fibres (MPFs), develop and apply laboratory methods for simulating environmental MPF degradation, and establish a decision support framework for polymer material selection with low environmental impacts. To reflect the ubiquitous nature of MPF pollution, the project will focus on freshwater, temperate marine and polar marine ecosystems. The fate and effects of MPFs will be studied using environmental conditions and species representing these ecosystems, including species from different trophic levels and a broad range of acute and sublethal endpoints. MICROFIBRE will bridge the current gap between laboratory assessment using commercially available feedstock plastic materials and the degraded plastic materials that dominate aquatic environments. Degraded MPFs will be generated using simulated UV and physical weathering of pristine reference materials in the laboratory. The role of degradation on the adsorption of persistent organic pollutants to MPFs and the implications for subsequent toxicity will also be investigated. To help identify potential mitigation measures, factors influencing the release of MPFs from synthetic clothing during washing will be studied. The project design aims to provide a basis for conducting comparisons between species, effects, ecosystems and MP degradation, with the goal of establishing a framework for enabling stakeholders (e.g. industry, consumers and regulators) to make informed material selections with low environmental impacts. The project brings together three of the key actors and stakeholders (research, industry and NGOs) in addressing and understanding the implications of microplastic fibre (MPF) emissions to inland and marine waters. By bringing together such a broad stakeholder group, MICROFIBRE represents a unique opportunity to go beyond fundamental research and apply the knowledge generated to initiating the first steps in mitigating the problem.