Anthropogenic microfibres and other microplastics in the sediments and soils of a small, moorland reservoir (Burrator, southwest England)

Little is known about the sources, transport and fate of anthropogenic microfibres (AMFs) and other microplastics (MPs) in dammed reservoirs. The aim of this study was to determine the concentrations, characteristics and pathways of anthropogenic particles in sediments and soils from a small, upland reservoir (Burrator, southwest England) and its influent and effluent river. Surface and subsurface (5 cm) sediments and soils were collected and characterised for organic matter and key geochemical (Ca, Fe and Rb) and anthropogenic (Pb and Zn) elements. AMFs and MPs were isolated from samples by flotation in ZnCl₂ and analysed microscopically; a selection was subject to polymer identification using Fourier Transform infrared spectrometry. AMFs of mm-dimensions were dominant and were constructed of natural cellulosics, semi-synthetic cellulosics (mainly rayon) and petroleum-based polymers (mainly polyester); other MPs were petroleum-based fragments. Total dry weight concentrations ranged from ~ 1150 items kg⁻¹ to 30,000 items kg⁻¹ but, overall, were not significantly different between sediment and soil and the surface and subsurface. Concentrations of AMFs and MPs were not related to organic matter content of sediment-soil or to Ca, Fe or Zn, but inverse correlations were observed between fibre length and elemental measures of the clay-size fraction (Rb) and anthropogenic atmospheric deposition (Pb). Our findings suggest that the principal source of particles to the system is diffuse, atmospheric deposition that occurs directly on soil and the reservoir surface and indirectly through catchment drainage. This results in a dominance of relatively high-density AMFs in sediments as low-density fibres escape with the outflow, and the occurrence of low-density MP fragments (polypropylene) in soils that have an additional (e.g., littering or road traffic) source.