Occurrence, characterisation and variations of microplastics and cellulose fibres in the Scottish Atlantic coastal marine environment

Student thesis: Doctoral ThesisDoctor of Philosophy (awarded by UHI)


Over the past decade, microplastics have proven to be globally ubiquitous and
widespread, and as a result are considered one of the major threats for the
environment and potentially human health. In the marine coastal environment,
microplastics have been widely studied. However, specific information about their
dynamics, behaviour and fluxes through different environmental compartments are
missing. Numerous uncertainties regarding microplastic pollution in the Scottish
marine environment persist as few studies have investigated the passage of
microplastics through the ecosystem by looking at mussels, seawater and sediment.
To contribute to the knowledge gaps regarding composition, distribution and
spatial/temporal variability in microplastics, it is necessary to consider several
environmental compartments covering a large spatial area. A tool-kit was
specifically designed to be used by citizen scientists to collect microplastics from
seawater, beach sediments and wild mussels covering ~400 km of the North and
West Scottish coastline allowing for microplastic composition and concentrations at
both spatial and temporal scales to be investigated. The results of this thesis
highlight that microplastics were found at every sampling site and in every
compartment studied, with concentrations relatively low in sediment being 60 ± 10
particles/kg d.w., whilst in water they were 1220 ± 170 particles/m-3 and in mussels
were 0.60 ± 0.12 particles/g wwt, which is similar to what has been seen on mainland
European coastlines. Microplastic characteristics and concentrations varied
between locations for all three environmental compartments ranging from 20 ± 10
to 120 ± 40 particles/kg d.w. for sediment, 700 ± 260 to 1800 ± 460 particles/m-3 for
seawater and 0.19 ± 0.05 to 1.38 ± 0.64 particles/g wwt for mussels, that were under
the influence of diverse factors (e.g. tide, wave, topography of site, proximity to river
mouth or anthropogenic activities and urbanised areas). Potential sources and
pathways were highlighted such as clothing/textile industry, tourism, sailing/fishing,
wastewater and towns for the dominant ones, but paints and road dust were also
recorded, influencing the composition of microplastics (i.e. polymer type, shape and
size) residing in the three compartments. Temporal variations of microplastic
composition and concentrations were noted for seawater and mussels (usually
winter > summer) fluctuating with seasons suggesting a combined influence of biotic
and abiotic factors (rainfall, wind, tourism). Investigations into semi-synthetic and
natural fibres found that cellulose fibres were mostly natural even though semi-synthetic fibres were also present. The
cellulose fibres dominated the particles found in mussels (60%), seawater (53%)
and in the sediment (63%). This work demonstrates that microplastics are
widespread, prevalent and dynamic pollutants, moving in a complex coastal
environment and that further studies are required to elucidate whether cellulose
fibres present the same problems that are associated with microplastics.
Date of Award15 Jun 2022
Original languageEnglish
Awarding Institution
  • University of the Highlands and Islands
SponsorsESF studentship
SupervisorBhavani Narayanaswamy (Supervisor), Neil James (Supervisor) & Andrew Dale (Supervisor)

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