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

Reina M Blair,Vernon R Phoenix,Susan Waldron,Caroline Gauchotte-Lindsay

doi:10.1007/s11356-019-04678-1

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.

Highlights

Plastic production and subsequent pollution are global environmental concerns
A handful of freshwater studies have included use of blanks as verification, but when reported, they were considered negligible compared to those observed in field samples (Dris et al 2015; Horton et al 2017a) or determined to be non-plastic (Hurley et al 2018)
While MP pollution research is experiencing rapid development, research remains largely skewed towards marine systems with limited information for freshwater river compartments

Summary

Introduction

Plastic production and subsequent pollution are global environmental concerns. Global plastic generation has exhibited an upwards trend since the 1950s, reaching 335 million tonnes in 2016, a 10% increase from 2015 levels (Plastics Europe 2017). Environ Sci Pollut Res (2019) 26:12491–12504 approximately 6300 million metric tonnes of plastic waste created until 2015, of which only 9% was recycled (Geyer et al 2017). Of recent concern is microscopic plastic debris commonly referred to as microplastics (MPs), typically less than 5 mm in size (GESAMP 2015), a formal definition and lower limit have not been established (Blair et al 2017). They are divided, broadly, into primary or secondary types (GESAMP 2015), though these definitions are not standardised. The contribution of different sources to overall MP loadings to the environment and the relative importance of primary and secondary types remains poorly understood (Duis and Coors 2016; GESAMP 2015)

Methods

Results

Conclusion