Freshly fallen snow with full of microplastics: A scientific research in Riga central and peripheral area, Latvia.

Abstract:Atmospheric transportation can be an essential pathway for microplastics (MPs), yet the understanding of the abundance, composition and morphological characteristics of the air-transported MPs remain limited.In this study, we sampled freshly fallen snow at six locations around Riga in Latvia, covering land uses of urban, rural, and remote regions (Figure 1): i) Central market (CM) at Riga Central Market, ii) Old town (OT) at Doma Church Square, iii) Parking lot (PL) at Spice Home Parking, iv) Suburb (SB) at Pavasara str. 4, v) City roof (CR) at about 50 m high on Latvian Academy of Science building and vi) Gauja National Park (NP). Samples were collected 8 – 9 December 2021. 20 L stainless steel buckets and a metal shovel were used to collect the samples. To minimize contamination, plastic tools were avoided except rubber boots and gloves. The collected snow was taken to the laboratory and kept at room temperature (22 – 23°C) until it melted. After measuring the volume of the melted snow, it was filtered through 10 µm mesh stainless steel filters. MPs were extracted from the collected particles through enzyme treatment, oxidation, and density separation (Chand et al., 2021; Simon et al., 2018). The extracted particles were analysed by FPA-µFTIR imaging, and the obtained hyperspectral images were analysed by siMPle for MP identification. Laboratory processes were conducted in a clean fume hood and only cotton lab coats were worn in the lab.MPs were detected in all snow samples, covering 16 polymer types. The most common polymers were polyester, polypropylene (PP), polyvinyl chloride (PVC), polyethylene (PE), and polyamide (PA). The results showed a large variation in MP concentration between the sites (Figure 1), among which Central market had the highest MP accumulation with 2497±755 items L-1, followed by Parking (1278±394 items L-1) and Old town (1233±57 items L-1). The order was the same when quantifying MP mass. Though also located in the urban area, snow on the City roof had significantly fewer MPs (95±19 items L-1) than other urban snow samples. This indicates that the snow had collected much of its MP while falling the last few meters or while lying on the ground. The least contaminated snow was found in Gauja National Park, which is remote from the urban area.This concludes that the MP snow contamination closely depends upon the human activities as well as strongly affected by the local sources. Figure 1: MP particle concentration (above) and MP mass concentration (below) in the analysed samples from different sampling locations ReferencesChand, R., Rasmussen, L.A., Tumlin, S., Vollertsen, J., 2021. The occurrence and fate of microplastics in a mesophilic anaerobic digester receiving sewage sludge, grease, and fatty slurries. https://doi.org/10.1016/j.scitotenv.2021.149287Simon, M., van Alst, N., Vollertsen, J., 2018. Quantification of microplastic mass and removal rates at wastewater treatment plants applying Focal Plane Array (FPA)-based Fourier Transform Infrared (FT-IR) imaging. Water Res. 142, 1–9. https://doi.org/10.1016/j.watres.2018.05.019