The application of tape lifting for microplastic pollution monitoring

Microplastics (MPs) are man-made polymer particles in the size range 1 μm to 5 mm. They have been proven to be present in all of Earth's environments through extensive global studies. Such studies regularly involve the isolation of MPs from water or other media using a filtration method. MPs are then commonly analysed for size and polymer type, either in situ on the filter or after removal from it by hand picking. These approaches provide the opportunity for the accidental loss of such particles and do nothing to protect the sample from contamination, whilst hand-picking from filter papers is also time consuming. The analysis frequently focusses solely on one technique and rarely facilitates the full characterisation of the MPs.

This paper sets out a workflow that addresses these shortcomings. Tape lifting (a forensic approach to particulate recovery) is at the heart of this workflow. This technique uses self-adhesive tape to recover particles of interest and results in a tape lift in which those particles are held between the tape and a sheet of suitable material. In the proposed workflow, the tape is Easylift® and the sheet is glass. Tape lifting offers significant time saving in the field, allowing more samples to be taken. It also creates a secure environment for the particles of interest and facilitates reproducible research by preserving samples for future study.

To investigate the recovery rate of MPs from filter papers using Easylift®, a simulation experiment was conducted, which tested glass fibre and cellulose fibre filter papers and ceramic and glass-frit Büchner funnels. It found that the rate of recovery of MPs from filters onto the tape had a mean of 96.4% (s n-1 = 3.5 percentage points, n = 12) with evidence that both filter type and funnel type effect that rate and that there is an interaction effect between these factors. In addition, the recovery rate from water onto the filter papers was investigated; this had a mean of 92.1% (s n-1 = 4.1 percentage points, n = 12) with no evidence that the filter type or funnel type used influenced that rate.

This paper also explores Easylift®’s attributes that facilitate the proposed workflow by enabling analysis of MPs whilst they are held within the tape lift. Easylift® is compatible with a wide range of non-destructive analytical techniques including polarized light microscopy (PLM), confocal Raman spectroscopy, fluorescence microscopy, microspectrophotometry (MSP) and hyperspectral microscopy, and this compatibility is explored in this paper. The compatibility with these techniques allows samples to be fully characterised for their morphological, optical and chemical properties, providing further information about the samples that can aid future studies that investigate source identification and the detection of MP features that may affect ecotoxicological effects.