Man-made natural and regenerated cellulosic fibres greatly outnumber microplastic fibres in the atmosphere.

Atmospheric microplastics have been widely reported in studies around the world. Microfibres are often the dominant morphology found by researchers, although synthetic (i.e., plastic) microfibres are typically just a fraction of the total number of microfibres, with other, non-synthetic, cellulosic microfibres frequently being reported. This study set out to review existing literature to determine the relative proportion of cellulosic and synthetic atmospheric anthropogenic (man-made) microfibres, discuss trends in the microfibre abundances, and outline proposed best-practices for future studies. We conducted a systematic review of the existing literature and identified 33 peer-reviewed articles from Scopus and Google Scholar searches that examined cellulosic microfibres and synthetic microfibres in the atmosphere. Multiple analyses indicate that cellulosic microfibres are considerably more common than synthetic microfibres. FT-IR and Raman spectroscopy data obtained from 24 studies, showed that 57% of microfibres were cellulosic and 23% were synthetic. The remaining were either inorganic, or not determined. In total, 20 studies identified more cellulosic microfibres, compared to 11 studies which identified more synthetic microfibres. The data show that cellulosic microfibres are 2.5 times more abundant between 2016 and 2022, however, the proportion of cellulosic microfibres appear to be decreasing, while synthetic microfibres are increasing. We expect a crossover to happen by 2030, where synthetic microfibres will be dominant in the atmosphere. We propose that future studies on atmospheric anthropogenic microfibres should include information on natural and regenerated cellulosic microfibres, and design studies which are inclusive of cellulosic microfibres during analysis and reporting. This will allow researchers to monitor trends in the composition of atmospheric microfibers and will help address the frequent underestimation of cellulosic microfibre abundance in the atmosphere.

First comparison of sampler surface areas for atmospheric microfibre deposition.

Recent studies have reported on the widespread abundance of atmospheric microplastics (At-MPs) and atmospheric anthropogenic microfibres (At-AMFs) in urban and remote locations. This study sought to test whether there were differences in the quantity of deposited At-AMFs collected when comparing three different surface sampler areas (small: 0.0113 m2 (Φ = 120 mm), medium: 0.0254 m2 (Φ = 180 mm) and large: 0.0346 m2 (Φ = 210 mm)). The analysis revealed no statistically significant variation in the number of At-AMFs recorded, when data was presented in At-AMFs per m2 day-1. However, our findings indicate that for any given individual sampling event, the amount of deposition can range by ∼ 150 to 200 At-AMFs m2 d-1 even if samplers are kept relatively close together. To account for this, we would recommend that future studies collect data in duplicate or triplicate. Our results suggest that data can be compared across different sites and geographical regions-at least if comparing the overall mean and standard deviation of all samples collected. These findings are important because currently there is no standard sampler size for passive collection of At-AMFs and At-MPs.

A Simple Sample Preparation Method to Significantly Improve Fourier Transform Infrared (FT-IR) Spectra of Microplastics.

Spectroscopic analysis has become an essential part of the rapidly growing field of microplastic (MP) research. Here, we introduce a simple sample preparation method that dramatically improves results from Fourier transform infrared (FT-IR) analysis of MP and other environmental fibers. Our method provides cost-effective, reliable, high-quality spectra that achieve high-matching scores to polymer libraries. The efficacy of this method is demonstrated with two environmental datasets from Singapore and Phnom Penh that were collected while sampling for atmospheric MPs. The method developed and applied in this study is a simplification of the KBr method, where the analyzed fiber is pressed to a thickness of <10 µm; however, no KBr powder is required. For the combined dataset, 379 non-pressed fibers were analyzed with 193 (51%) returning a search score of ≥80% (chosen minimum search score threshold) and 259 pressed fibers, with 254 (98%) returning a search score of ≥80%. Direct comparisons of fibers before and after pressing show that the highest individual search score, and average search score from multiple single-point measurements, is overwhelmingly higher following our method. Our method immobilizes and improves the surface of the fiber, by creating a wider and uniform area for measurements. For FT-IR operators, this saves considerable time, improves reliability of the analysis, and, importantly, provides reproducibility of the spectra generated.