Spatio-temporal variability of microplastics in sea surface waters along the west coast of Scotland

Abstract

Microplastic pollution continues to rise with increased plastic production and waste generation worldwide, causing damage to ecosystems and disrupting ecological functions. As microplastics have been detected in all oceans from surface waters to deep sea sediment, methods for microplastics quantification and characterisation have been applied globally to study patterns in occurrence and variation. The spatial and temporal distribution of microplastics in the marine environment differs based on the sources of input and the hydrodynamics of a given region. Along the west coast of Scotland, numerous sea lochs and islands impact the movement and dispersal of microplastics. Based on the surface water microplastic surveys conducted by Marine Directorate, four west coast Scottish Marine Regions were identified to contain microplastic hotspots and further evaluated for spatial and temporal patterns of microplastic variation. The results of this study revealed microplastic abundance increased over time with the mean abundance across the west coast regions rising from 9,077 MPs kmֿ² in 2017-18 to 15,851 MPs ² in 2023-24. There was a fluctuation in abundance following the COVID-19 lockdown as the mean abundance across the west coast was 1,688 MPs kmֿ² in 2021-22, potentially reflecting a decrease in anthropogenic activity. Both spatial and temporal patterns on the west coast of Scotland revealed microplastics were predominantly classified as fragments, primarily white/clear in colour, and mainly composed of polyethylene or polypropylene; moreover, this corresponds with single-use plastics which are mainly produced with polyethylene and polypropylene polymers. The West Highlands and Argyll marine regions were primarily impacted by plastic litter from the aquaculture and fishing industries, resulting in an increased occurrence of black polyethylene microplastics and paint fragments over time. Separately, the Solway marine region exhibited a higher proportion of polystyrene foam beads compared to other regions which may be connected to fishing or offshore activities. Lastly, the Clyde marine region maintained hotspots at the top of Loch Long and exhibited the largest prevalence of microbeads, demonstrating the input from wastewater effluent and freshwater systems passing through the urban areas of the region. Altogether, this study identified the main accumulation zones of surface water microplastics and potential pathways of input primarily sourced from maritime activity, ALDFG, aquaculture, and wastewater effluent.

Datum der Bewilligung	6 Mai 2026
Originalsprache	English
Gradverleihende Hochschule	University of the Highlands and Islands
Betreuer/-in	Bhavani Narayanaswamy (Supervisor)