DOI: 10.5285/ac6ade29-2815-4938-a93a-d84f0d322bd6
title: Microplastic abundance in Antarctic Snow samples

description: This dataset presents concentration of microplastics in snow from remote Antarctic camps: Union Glacier, Schanz Glacier and the South Pole. Refined automated FTIR techniques enabled interrogation of microplastics (including fibres) to a lower detection limit of 11 micrometers in Antarctic snow for the first time. Microplastics were pervasive (73 - 3099 MP L/1). The majority (95 percent) measured less than 50 micrometers, indicating that previous microplastic reports in Antarctica may be underestimated, due to analytical restrictions. Plastic polymer composition and concentration did not vary significantly between sites, with dominant polymers being polyamide (PA), polyethylene terephthalate (PET), polyethylene (PE) and synthetic rubber. Results indicate that even in the earth's most remote regions, humans are leaving a plastic legacy in the snow, illustrating the importance of remote, cryospheric regions as critical study sites for determining temporal fluxes in microplastic pollution. 

Funding: 
All fieldwork was supported and financed by Airbnb.
description: Snow samples were taken in December 2019 from three locations in Antarctica (Union Glacier, Schanz Glacier, and the South Pole). Union Glacier (-79.766667 S, -83.4 W) is situated at the northern edge of the Western Antarctic Ice sheet, the glacier extends 86km up to the grounding line of the Ronne-Filchner Ice Shelf. Sitting approximately 550 m above and draining into Union Glacier 30 km away is the similarly u-shaped Schanz Glacier. The Amundsen-Scott South Pole Base and field camp is 1140 km away from Union Glacier. These three sites represent different remote camps, varying in size and accessibility. Twelve sites were selected for analysis: five at Union Glacier (UG1-UG5, close to the downwind of the camp), four at Schanz Glacier (SG1-SG4, 2 km area between the tracks and the retreat), and three at the South Pole (SP1-SP3), including one at the runway (SP3) and two at 250 m intervals further from the Amundsen-Scott South Pole Base. A sample was taken at the control site chosen based on logistics as the most remote location accessible, atop an exposed ridge between the Schanz and Driscoll Glacier more than 100 m above Schanz Glacier and unlikely to be impacted by the local camp.

A shallow pit was dug using a shovel to 20-40 cm depth, and the person collecting the sample was positioned downwind of the pit. Sampling was downwind of remote camps in an attempt to quantify their contribution to the microplastic footprint in the snow. The farthest wall of each pit was then ''cleaned'' of any potential contamination from the shovel by scraping approximately 5-10cm of snow from the wall with a stainless-steel cup. The cup was acid-cleaned between each sample site. Snow samples were taken at between 20-40 cm depth, to include the variance of snow accumulation across all sites. Thus, this study assumes that sampling of this layer comprises the plastic legacy of the previous 1-2 years (Hoffmann et al., 2020; Lazzara et al., 2012). 

A sample was taken by burrowing laterally into the side of the wall using the stainless-steel cup. The first ''scoop'' of each tunnel was discarded, with all subsequent collections with the cup decanted into an 800ml stainless steel tankard (ECOtanka), which remained closed when not used and placed upwind of the sampler when being used. Each container was filled, bumping the base of the tankard to collect as much as possible, with variation in snowmelt volume recorded. Each tankard was then sealed and returned to the field laboratory for filtering.

The funnel was flushed through with ''clean water'' after filtering. In place of deionised water at the camp, ''clean water'' was produced using the ''clean snow'' supply - an area of snow sectioned off, upwind of the camp, used for generating the cooking water and shower water supply at Union Glacier. This snow was collected and twice filtered through a 0.2 micrometer Isopore (polycarbonate) to remove any possible plastic contamination. Investigation under a stereomicroscope indicated no visible microplastic or other particulate, as expected when passing through a small pore-size filter. A sample of this ''clean snow'' was taken before filtering and processed as per other samples for microplastics analyses. 

Identification of Microplastics using Fourier Transform Infrared Spectrometry 
Samples had to be removed from the silver filter and transferred onto Anodisc filters (Whatman). Three laboratory blanks were carried out to determine the possible introduction of contamination during this step and any sample loss. The transfer of samples onto new filters enabled the use of the focal plane array (FPA) and full analysis of the whole filter area using Fourier Transform infrared (FTIR) in transmission mode. Initial observations using an Olympus Stereomicroscope indicated that particles were either less than 100 micrometer or were MP fibres. We combined the method of Primpke et al., (2018) with technical advice provided by Agilent Technologies; and overlaid a 2mm thick Barium Fluoride slide on top of the Anodisc filter with on top to press the material on the surface into the focal plane.
description: All measurements were carried out using the Agilent 670 Fourier Transform Infrared (FTIR) spectrometer (Agilent Technologies, Santa Clara, CA), USA, with a cryogenically cooled mercury cadmium telluride (MCT) detector. The spectrometer was coupled to an Agilent 620 microscope with an automated XYZ-stage and 128 x 128 focal plane array (FPA) detector, cooled with liquid nitrogen. The FTIR system was continuously purged using a dry air generator (FGSR). The FTIR microscope was equipped with a 15 x IR objective lens and a 15-x visual objective lens. This stage held the sample in a bespoke filter holder enabling the transmission of infrared through the lower Cassegrain, the base of an Anodisc filter where the sample was held, and through the Barium fluoride slide of the same shape and diameter as the filter. This setup facilitated FTIR imaging of both fibres and particles (microplastics of all other morphologies) (Primpke et al., 2019, Roscher et al., 2021). 

Filters were scanned in quarters, with each quarter measuring approximately 14mm x 14mm allow a small overlap between scans when stitching together the data. The FPA detector enabled each quarter to be scanned, acquiring a mosaic of spectra (Primpke et al.,2017, 2020a). This was calibrated with an XYZ stage allowing the exact coordinates at the end of the scan to be used to accurately identify the start of the next scanning area, covering the complete area of each filter (diameter of 25mm, area 625mm2). The collection of multiple mosaics meant each sample took approximately 13 scannable hours spread over 2.5 days.
description: Best practice anti-contamination measures were taken in each laboratory. As the field laboratory was set up for the field campaign, it was thoroughly cleaned, and air conditioning remained off for the campaign. Footfall within the laboratory was restricted to the researcher, and cotton laboratory coats were worn. All instruments and containers were acid-washed before first use and were covered with aluminium foil during processing. At the British Antarctic Survey Laboratory - Cambridge, aluminium foil was used during filtering, and glass lids were used during the drying process. A bespoke Perspex shield was fitted around the FTIR stage to prevent airborne contamination during infrared analysis. The laboratory was thoroughly cleaned, and surfaces were wiped down with an ethanol dilution between each sample processing and analysis. Procedural blanks were taken to measure the introduction of contamination at any of these stages and recovery tests, to measure the loss of sample during processing. 

A contamination library was also built. For this, fibre samples were collected from the garments worn by each person in the field and the laboratory, with particles from additional possible sources of plastic pollution also collected from the field camp. These samples were analysed using attenuated total reflection using a mobile Agilent FTIR. Spectra were collected and measured against the existing spectral reference library using the siMPle software. Hierarchical cluster analysis was carried out according to Primpke et al. 2018 using the Hellinger Distance for the calculation of the resemblance matrix (Primer 6 and Permanova, Primer-E) was performed to identify the primary polymer composition of these samples by their similarity to existing database entries and inform, post-hoc, on possible sources of contamination. 

Procedural blanks were run in triplicate. Two separate sets of blanks were carried out. The first type, the ''full procedural blank'', replicated the complete procedure from collection to analysis, as per all other snow samples. A separate ECOtanka was used to collect 250ml of 0.2 micrometer filtered ''clean water'' and was processed in the same manner, i.e., filtering onto a silver filter in the field laboratory and subsequently transferred onto an Anodisc filter for FTIR analysis. Each blank was carried out on the same day the samples were processed in the field laboratory (n=3). In addition, a secondary set of procedural blanks was taken to inform about contamination introduced during the transference step from silver filter to Anodisc. These blanks, ''laboratory blanks'', replicate the procedure carried out in the Cambridge Laboratory, using 200 ml of 0.2 micrometer filtered Milli-Q water, filtered onto a silver filter and subsequently removed using 50ml of Milli-Q water onto an Anodisc and 10ml of 30 percent Ethanol to help remove any residual filtrate. 

To determine the final ''normalised concentration'' presented in the results, the concentration of each polymer type was averaged from the three ''full procedure'' blanks and subtracted from each raw sample concentration. The concentration recorded in the lab blank was used only to inform what proportion may have been introduced in the laboratory. Furthermore, the fraction likely introduced during field processing is determined by subtracting the ''lab result'' from the ''full result''.

Recovery tests were designed to determine whether there was any substantial material loss during the transference step from silver filter to Anodisc. These recovery tests were carried out in triplicate, using Nylon fibres stained with Nile Red and had a uniform diameter of 16 microns, and cut to a length of 250 microns. A fluorescent microscope was used to count fibres once dry. Following this, the sample was enclosed in its case. It was shaken to mimic the disturbance of the sample within the case that was potentially encountered during transit. The sample was then removed, filtered onto the Anodisc filter, and counts made again. For both counts, photographs were also taken across the entire filter to validate counts. In addition, one of the recovery tests was subsequently analysed using FTIR to compare the manual counts with those counted by the software. Average laboratory blank nylon fibres (n=3) were subtracted from the final count.