JPI Oceans - Mikroplast - WEATHER-MIC - NGI - How microplastic weathering changes its transport, fate and toxicity in the marine environm

Our ocean receives large quantities of plastic from rivers, landfills and sewage treatment plants amongst other sources. This plastic is often fragmented into so-called microplastic, often too small to see with the naked eye. The WEATHER-MIC research project investigated the processes controlling the transport, fate and toxicity of microplastic, as it is weathered by sunlight, bacteria, wave motion, changing temperatures, and other processes. Weathering was found to be an essential factor to take into consideration when assessing the fate and hazards arising from plastic pollution in the environment. The most important weathering processes are those which either affect 1) the particle size distribution or 2) the leaching of hazardous additives. Regarding particle size distribution, important processes are biofilm-assisted aggregation of all size fractions to facilitate marine snow formation or ingestion by organisms; another is fragmentation to smaller particles that can occur rapidly in areas with heavy turbulence and lots of sunlight, like coastal areas. Further research on deep sea sediments and deep in the water column is needed, as many fate processes end with sediment accumulation, alongside colloidal microplastics accumulating in the water column. Regarding the leaching of hazardous additives, their ingestion or exposure to marine life are central to our understanding, because the chemicals in plastic are what differs them from natural particles. Thus far, chemical additives to plastic were found to be substantially more hazardous than the chemicals made from the degradation of the polymers themselves. Therefore, plastics from electronic products, which contain many additives, are more hazardous than pure plastics from food packaging, which contain little additives. Our recommendations for further research is to used field-weathered material containing known amounts of additives, and at environmentally relevant levels, in different settings, particularly at emission hot spots like coastal zones and riverine outflow areas. This will further improve the accuracy of risk assessment of plastic pollution for specific sites and conditions.

WEATHER-MIC has contributed to regulations, policies and management practices, such as the Position Paper by the Marine Strategy Framework Directive Technical Group on Marine Litter and a presentation at the UN Ocean Conference, "Multilateral science-policy processes generating the evidence to underpin SDG implementation". The project contributed with advice and exhibits to the mobile ship container-based exhibition OceanPlasticsLab. The NGI has also contributed to several public awareness campaigns include a collaboration between the Race for Water Odyssey and WEATHER-MIC. This project has led to several Masters students, including 3 MSc and 1 summer student hosted by the NGI. Methods developed to quantify microplastic in sediments have been used in commercial projects by the NGI, and is now in the catalogue of laboratory services. Several research projects within the consortium have been proposed or secured, including a follow-up, u-Path, with the entire consortium.

Understanding the hazards posed by microplastics in the sea requires understanding the changes they undergo as a result of various environmental weathering processes, like UV exposure, biofilm growth and physical stress. These processes will influence parameters such as their brittleness, density, size and surface charge, which can in turn affect their environmental fate as the microplastics undergo fragmentation, aggregation and ultimately sedimentation or mineralization. Changes that lead to fragmentation or mineralization into benign fragments or molecules will reduce potential hazards; though changes that lead to the production of problematic size fractions (e.g. that can accumulate in gills) and release toxic chemicals will increase potential hazards. Similarly, the influence on mobility of plastics and the contaminants they contain are wide-ranging. The WEATHER-MIC project assembles a multidisciplinary consortium of European experts from five institutes and four countries (UFZ Germany, ACES Sweden, NGI Norway, Fraunhofer IKTS Germany and KUL Belgium) that together will develop novel tools to tackle the complex implications of weathering of microplastics in a holistic manner. The toolbox of analytical and (eco)toxicological methods, models,and new knowledge that WEATHER-MIC seeks to establish and validate in case studies for the Baltic Sea and Oslo Harbor will consist of: -fingerprinting methods to track microplastic weathering (ACES) -mechanisms of chemical release from microplastics (ACES, UFZ, NGI) -advanced particle imaging methods to investigate size distribution and morphological changes with weathering (IKTS) -improved understanding of ecological information on the biofilm that accumulates on microplastics and its trophic transfer (ACES) hydrodynamic models to account for changes in sedimentation and transport with microplastic fragmentation-aggregation (KUL, NGI), -toxicity profiles for weathered microplastics (UFZ).