Microscopy and elemental analysis characterisation of microplastics in sediment of a freshwater urban river in Scotland, UK

Abstract

Understanding of the sources, fate, and impact of microplastics (MPs, < 5 mm) remains limited, particularly in freshwater environments, while limited comparability across available surveys hinders adequate monitoring and risk assessment of these contaminants. Here, the distribution of microscopic debris in an urban river close to the marine environment in the West of Scotland was investigated to assess concentration and distribution of primary and secondary MPs. Also, the efficiency of light and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) was evaluated for characterisation and quantification of MPs sized 2.8 mm–11 μm. Bank sediment samples were collected twice from the River Kelvin in Glasgow and were size-fractionated and processed for extraction of MPs by density separation. Sample MPs spiking and use of procedural blanks allowed the influence of processing on field data quality to be considered. Total abundances were 161–432 MPs kg −1 dry sediment, with fibres as the dominant type, comprising > 88% of total counts. Nevertheless, fibres in blanks suggest potential contributions from atmospheric contamination. Moreover, fibres concentrated mainly in fractions < 0.09 mm suggesting that their fate may be influenced by drivers of fine sediment dynamics in rivers. While no primary MPs were observed, metallic and glass pellets were present in high abundances in settled material and could be easily misidentified by visual inspection, demonstrating that compositional analysis is needed to avoid analytical errors from MP misidentification and overestimation. SEM-EDS allowed for a quick screening of plastic vs non-plastic pellets and improved identification of smaller fragments, whereas more advanced techniques are needed for proper identification of fibres. This study is the first to report on MPs in freshwater rivers in Scotland and suggests that diffuse sources of pollution may be delivering secondary MPs to the river. Their sources, fate, and risk in these systems will thus warrant further attention. Electronic supplementary material The online version of this article (10.1007/s11356-019-04678-1) contains supplementary material, which is available to authorized users.

Microplastic fluxes in a large and a small Mediterranean river catchments: The Têt and the Rhône, Northwestern Mediterranean Sea

“…Scheurer and Bigalke (2018) found microplastics in 90% of the 29 floodplain soils analyzed across Switzerland, with concentrations ranging from 0 and 593 MPs kg −1 , correlated with the population of the catchment. Blair et al (2019) observed and 432 MPs kg −1 within two samples along the River Kelvin in Glasgow (UK), with fibers as the dominant shape (> 88%).…”

“…In Europe, only few studies investigated MPs in river shore sediments (Klein et al, 2015;Scheurer and Bigalke, 2018;Blair et al, 2019) using a similar methodology (surface samples, NaCl gravity separation, oxidation of natural debris and FTIR verification). Klein et al (2015) monitored shores along the Rhine and one of its major tributaries, the Main River, at a larger (~40 km) spatial scale than we did and with only a single sampling period.…”

A methodological approach of the current literature on microplastic contamination in terrestrial environments: Current knowledge and baseline considerations

“…SEM provides a highmagnification image of MPs, aiming for a structural false positive discrimination. When coupled with energy-dispersive spectroscopy (SEM-EDS), determination of the elemental composition is enabled (Blair et al, 2019). The lack of strong C signal in elemental spectra suggests a non-synthetic particle.…”

Microplastics in the sediment of Lake Ulansuhai of Yellow River Basin, China

“…More broadly, they are distinguished as small plastic particles (primary source) and plastic debris (secondary source) (Frias, Otero, & Sobral, ; Moore, ). Primary microplastics comprise the plastic granules manufactured as product precursors for cosmetics, detergents, personal care products, and other industrial uses (Blair, Waldron, Phoenix, & Gauchotte‐Lindsay, ; Hidalgo‐Ruz, Gutow, Thompson, & Thiel, ). Secondary microplastics are produced by photolysis and hydraulic friction and exist as plastic debris, scales, fibers, and pellets of plastic waste from artificially discarded plastic waste such as beverage bottles, plastic bags, and fibers from synthetic textiles (Browne et al, ; Duis & Coors, ).…”