Factors influencing the formation, fate and transport of microplastic in marine coastal ecosystems

The FORTRAN project was a research collaboration between SINTEF Ocean, the University of Stellenbosch, the University of Western Cape and the South-African NGO WildOceans. The project explored the factors affecting the formation of microplastic (MP) fragments (<5 mm) from macroplastic litter items in the marine environment. Laboratory studies investigated how physical, chemical and biological conditions along the coast affect how MP is formed, degraded and transported with ocean currents. Different types of plastic were used to investigate how parameters such as chemical composition may impact on its ultimate environmental fate and to understand what environmental consequences this may have. To this end, methods for characterisation of MP were applied to investigate both physical and chemical degradation, as well as microbial growth on the MP surface. Additionally, the project investigated how the presence of chemical additives impact these processes. The project focused on the most common plastic polymers; polyethylene (PE) polyethylene terephthalate (PET), polypropylene (PP), polyamide (PA, nylon) and polyvinyl chloride (PVC). The chemical additive content in these materials varies greatly and we have used a range of particle shapes, sizes and colors in our experiments to quantify the effects of these parameters on degradation processes. A primary part of the project was to quantify how UV irradiation (simulating sunlight at different intensities), in synergy with increased temperature, degrades plastic both chemically and physically. Experiments have simulated coastal environments where particles move between being stranded (dry) and suspended at the water surface. The MP physicochemical properties monitored over the course of the experiments were mass, crystallinity, microhardness and the level of carbonyl and hydroxyl functional groups (representing oxidative degradation). All particles tested exhibited some degree of degradation, but the extent of degradation and which parameters had the greatest influence on the process varied. For example, PP was more degraded than PET when subjected to UV irradiation in air, with clear PP more significantly degraded than black PP (which may contain a UV stabilizing additive). While preliminary UV treatment in air led to the material being more resistant to further degradation in water, the opposite was the case for materials that were thermally degraded in air. Both increased temperature and UV irradiation was associated with increased levels of degradation, while PP degraded more in seawater compared to demineralized water. The project also investigated the influence of MP physicochemical properties (including additive chemical content) and primary UV degradation on microbial colonisation and biofilm formation in seawater at temperatures relevant to both Norwegian and South African coastal environments. Results show that biofilm formation is limited at lower temperatures, but there was greater microbial growth on particles with a greater content of chemical additives at increased temperatures . Furthermore, both additive chemicals and UV degradation appear to affect the microbial community settling and developing on MP. In the final stage of the FORTRAN project, experimental was used data to develop models that predict plastic and MP degradation, biofilm formation and transport in the marine environment. A hydrodynamic model that disperses simulated particles through the coastal zone to understand transport mechanisms was applied based on insights generated within the project. As part of the FORTRAN project, the WILDOCEANS Blue Crew assisted in sampling plastic nurdles from South African beaches. The Blue Crew team comprises a group of previously unemployed women who collect waste from beaches on a daily basis and prevent it from getting washed back into the ocean. Nurdles assumed to be originating from a spill of pristine pellets close to Durban 2017 have been transported across large distances around the South African coast. Chemical analysis of these nurdles has demonstrated that most are likely to have originated from the 2017 spill, but some appear to be from other sources. The nurdles identified as being from the incident was used to further validate degradation models based on laboratory experiments: FORTRAN has established a communication platform towards multiple stakeholder groups to ensure dissemination of the knowledge generated in the project. 'Noah the Nurdle' is a fictional character that, through a series of graphics, explains the fate of MP in the marine environment to followers on social media. To date, an audience of tens of thousands have been reached across our Facebook, Twitter, and Instagram platforms. WILDOCEANS also visited local schools to present the FORTRAN project and increase awareness and demonstrate the effects of marine plastic pollution in South Africa.

The FORTRAN project has contributed to advancing the understanding of environmental factors impacting plastic and microplastic particles in the marine environment. UV degradation of plastic particles has been studied through simulations of exposure conditions relevant to both the Norwegian and South-African environments. These studies have allowed us to gain a stronger understanding of the fragmentation pathways, polymer degradation and formation of smaller microplastic particles resulting from UV degradation, as well as release of plastic associated chemicals with potentially hazardous properties. Novel test systems to investigate the rate and impact of biofilm formation on microplastic particle fate in the marine environment under varying temperatures have been developed and applied within the project. These are now available for use in future projects aiming to develop empirical data for input to microplastic and plastic fate modelling, as well as towards microplastic risk assessment. The project has demonstrated the use of chemical and physical characterization techniques to track the source of environmentally released microplastics, here exemplified as plastic nurdle spills. This tool is not only applicable to the research community, but with further developments it may also be implemented by regulatory and monitoring bodies in the event of acute spill scenarios. The applicability of existing hydrodynamic modelling tools towards microplastic fate has been demonstrated through the project, and the feasibility of implementing empirical data assessed and tested. Together with the analytical tools discussed above, this will be of key importance in determining the fate, accumulation zones and potential impacts of plastic spilled at sea to aquatic organisms. The FORTRAN project has contributed to the education of twelve individuals (one postdoctoral candidate, four Masters level and three Bachelor level students, as well as two postgraduate interns) working across the diverse activities and disciplines involved in the project. Through dissemination and outreach activities targeted towards younger level school children in South-Africa, the project has created a lasting impact through its knowledge sharing activities and through the development of skills regarding environmental impacts of pollution at all levels of education. Through social media campaigns involving the fictional character "Noah the Nurdle", the project has reached tens of thousands of individuals, creating awareness about microplastic pollution and developing common societal understanding of the pathways of microplastics in the marine environment and how these materials undergo degradation to form smaller and smaller particles due to natural weathering and degradation processes.

The FORTRAN project will investigate factors influencing the formation of nano- and microplastic particles from degradation of plastic marine litter, studying their subsequent fate and transport in marine coastal ecosystems. The project will use reference materials representing the most abundant types of plastic litter found in the marine environment. To investigate the influence of plastic additive chemicals on degradation processes, the reference materials will include plastic with differing additive contents and profiles. Methods will be developed to characterise and quantify the formation of nano- and microplastic particle degradation products and additive chemical leaching. FORTRAN will study the influence of plastic physicochemical properties, including additive chemical content, on microbial colonisation and biofilm formation. The role of biofilms on the vertical and lateral dispersal and transport of microplastic will also be investigated. Finally, FORTRAN will develop a series of models to predict plastic and microplastic degradation, biofilm formation and transport in the marine environment. The models will be developed and validated using data generated within the project. State of the art analytical and imaging instruments will characterise the test materials throughout the degradation and additive leaching studies. Conceptual modelling within FORTRAN will (i) act as a basis for designing laboratory experiments, (ii) utilise data generated within the project to develop a hydrodynamic model that will disperse simulated particles through the coastal zone. In situ validation of the model output will be conducted. FORTRAN will establish a communication platform towards multiple stakeholder groups to ensure dissemination of the knowledge generated in the project. Furthermore, public engagement and increasing public awareness about the issue of marine litter and microplastic will be achieved through the activities of the Wildland Conservation Trust.