A Preliminary Quantitative and Qualitative Investigation of Microplastic Pollution of Maltese Surface and Sub-Surface Coastal Waters

Kossari-Tarnik, E.; Bordos, G.; Prikler, B.; Gauci, A., and Deidun, A., 2024. A preliminary quantitative and qualitative investigation of microplastic pollution of Maltese surface and sub-surface coastal waters. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 1099-1103. Charlotte (North Carolina), ISSN 0749-0208. The microplastic contamination of the marine domain has become one of the most urging environmental challenges of the century. The current study aims to quantify and to characterize microplastics sampled within surface and sub-surface waters of the Maltese archipelago (central Mediterranean) through the implementation of an innovative methodology and to investigate the dynamics of such pollution over a two-year period (2022 and 2023). This survey exams different sea layers in order to determine whether different plastic polymers accumulate with increasing water depth. We have performed an experimental sampling methodology, through the modification of a Manta net trawl, normally deployed for the sampling of the surface water. An experimental sampling methodology, a horizontal tow sampling was executed by maintaining the Manta net at a stable depth (6 ±1m and 10 ±1m) at a position parallel to the surface, by setting up the perfect balance between the weight of the frame of the Manta-net and the speed of the tugboat to keep the net taut. One nearshore site from Malta which is highly influenced by anthropogenic effects was identified, and also one reference site which is more remote from these effects. The focus of this research was on the lower size range of microplastics (50-1000 µm) since the larger microplastic fragments (1000-5000µm) were almost exclusively restricted to surface samples. The highest fraction (29%) of the sampled microplastic particles were made of polyethylene, followed by acrylic (25.4%), PP (polypropylene - 23.5%) and polystyrene – PS (10.4%). Over the two years of sampling, 69% of the total number of polymer particles sampled from the two water column components were distributed within the 50-350 µm size range. The microplastic particle density of the surface waters was in the range of 0.510-7.363 particles/m3, while that at a depth of 10m was in the range of 1.090-6.600 particles/m3. The results emerging from this study are useful in bridging existing knowledge gaps (e.g. on microplastic densities within the water column) which are hindering the application of relevant European and Mediterranean environmental assessment and monitoring thresholds.