Microplastics in road dust: A practical guide for identification and characterisation

Deep-learning enabled rapid and low-cost detection of microplastics in consumer products following on-site extraction and image processing

Microplastic (MP) contamination has become a major concern in recent times, posing a significant threat to the environment and human health. Existing techniques for MP detection require access to expensive and specialized microscopy setups and often demand long turnaround time and extensive labor. Herein, we propose a simple platform for MP detection, where MPs are extracted from salt, sugar, teabag, toothpaste and toothpowder samples, and imaged using a low-cost mobile phone-based microscopy setup. The extraction process involves the isolation of MPs from their matrices using the well-established density separation technique with ZnCl2 solution (1.7 g cm-3) and hydrogen peroxide (H2O2) to oxidize organic matter. A commercially available miniaturized microscopy attachment (TinyScope, $10) is fixed on top of an ordinary cell phone camera and is used to capture about 2490 images of MPs obtained from five different product categories. The YOLOv5 deep learning model was used to detect microplastics in images. It was trained on a dataset of 1990 images, validated with 250 images, and tested on a separate set of 250 images. The presence of plastic content in the detected samples was confirmed by performing attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and the morphologies of the MPs were determined using the field-emission scanning electron microscopy (FE-SEM). Results show that the deep-learning enabled image processing approach can identify MPs with an accuracy of 98%. Overall, the fast, accurate, and affordable detection of MPs in low-resource settings can lead to the monitoring of MP content in consumer products on a more frequent basis.

Occurrence, ecological risk of microplastics in campus athletic fields runoff and their adsorption behavior towards heavy metals

The occurrence of microplastics in athletic fields and their risk of ecological pollution have attracted widespread attention. The abundance, particle size, morphology, color and type of microplastics as well as their ecological risk are conducted in five types of athletic fields runoff on a campus in Beijing. The concentration of microplastics in the stormwater runoff of the five athletic fields ranges 2433 ± 493 to 5067 ± 839 particles/L, composed of fibers, granules and fragments. Fibers microplastics (41-64%) are the most abundant in stormwater runoff samples from most athletic fields, followed by granules (26-45%), and fragments (8-18%). ATR-FTIR and micro-FTIR identify the types of microplastics in runoff from athletic fields as EPDM, SBR, PE, PP, PO, rayon, and nylon. The degree of microplastic pollution is ranked level II-III pollution, which posing potential health and ecological risks. The adsorption behavior is tested for three types of microplastic particles including ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR) and aged-SBR particles derives from athletic fields surface materials towards runoff typical heavy metals Pb and Zn. The adsorption isotherms are more in line with the Langmuir model, indicating a chemical monolayer adsorption. The maximum adsorption capacity towards Pb and Zn follow the order of EPDM (2.67 mg/g) > aged-SBR (1.50 mg/g) > SBR (0.13 mg/g), and EPDM (2.61 mg/g) > aged-SBR (1.50 mg/g) > SBR (0.56 mg/g), respectively. Aged microplastics are subjected to processes such as UV aging and weathering, the surface layer is more likely to acquire charges and adsorb metals to maintain charge balance. EPDM, SBR and aged-SBR particles all contain Ca, Zn, and Mg, which can undergo displacement reactions with Pb and Zn. FTIR results indicate that the adsorption of heavy metals may alter the surface chemical properties of microplastics, rendering them more polar. XPS results reveal that the changes in surface functional groups of EPDM are more pronounced before and after adsorption compared to SBR and aged-SBR, indicating that chemical adsorption plays a dominant role in this process. Microplastics in runoff from athletic fields is an important source of microplastic release, and the occurrence of microplastics needs to attract further attention. The adsorption of microplastics and pollutants in athletic field runoff could exacerbate their combined pollution, thus their ecological risks cannot be ignored.

Size- and shape-dependent ingestion and acute toxicity of fragmented and spherical microplastics in the absence and presence of prey on two marine zooplankton

As microplastics (MPs) are particulate pollutants, their size and shape, and the presence of prey in the media can affect their toxicity. However, the size- and shape-dependent toxicities of MPs and their prey-dependent ingestion patterns in marine zooplankton are not well understood. Thus, we investigated the ingestion and egestion patterns, and toxicity of different shapes and sizes of MPs on two marine zooplankton, Brachionus koreanus and Diaphanosoma celebensis, under different prey conditions. The ingestion assay showed that smaller MPs were ingested more frequently, regardless of their shape. However, fragmented MPs showed higher toxicity than spherical MPs of comparable size. Prey in the media reduced the uptake and toxicity of MPs in both species depending on the taxa's feeding strategy. Our findings demonstrate that the size and shape of MPs are important factors in determining toxicity and that the presence of prey should also be considered when assessing MP toxicity.

An explicit review and proposal of an integrated framework system to mitigate the baffling complexities induced by road dust-associated contaminants

Road dust-associated contaminants (RD-AC) are gradually becoming a much thornier problem, as their monotonous correlations render them carcinogenic, mutagenic, and teratogenic. While many studies have examined the harmful effects of road dust on both humans and the environment, few studies have considered the co-exposure risk and gradient outcomes given the spatial extent of RD-AC. In this spirit, this paper presents in-depth elucidation into the baffling complexities induced by both major and emerging contaminants of road dust through a panorama-to-profile up-to-date review of diverse studies unified by the goal of advancing innovative methods to mitigate these contaminants. The paper thoroughly explores the correlations between RD-AC and provides insights to understand their potential in dispersing saprotrophic microorganisms. It also explores emerging challenges and proposes a novel integrated framework system aimed at thermally inactivating viruses and other pathogenic micro-organisms commingled with RD-AC. The main findings are: (i) the co-exposure risk of both major and emerging contaminants add another layer of complexity, highlighting the need for more holistic framework strategies, given the geospatial morphology of these contaminants; (ii) road dust contaminants show great potential for extended prevalence and severity of viral particles pollution; (iii) increasing trend of environmentally persistent free radicals (EPFRs) in road dust, with studies conducted solely in China thus far; and (iv) substantial hurdle exists in acquiring data concerning acute procedural distress and long-term co-exposure risk to RD-ACs. Given the baffling complexities of RD-ACs, co-exposure risk and the need for innovative mitigation strategies, the study underscore the significance of establishing robust systems for deep road dust contaminants control and future research efforts while recognizing the interconnectivity within the contaminants associated with road dust.

Occurrence and characteristics of microplastics in soils from greenhouse and open-field cultivation using plastic mulch film

There is a major knowledge gap concerning the extent of microplastic pollution in agronomic regions of China, which represent a plastic use hotspot. In order to clarify the amendment of agronomic region and plastic film mulching mode to microplastics distribution, the characteristics of microplastics distributed in agricultural soils from three typical regions (Beijing (BJ), Shandong (SD), and Xinjiang (XJ)) with two plastic film mulching modes (greenhouse (G) and conventional field-based film mulching (M)) in China were investigated. Microplastics weight and their response to planting regions were also evaluated in this study. The result showed that the average abundance of microplastics in soils from BJ, SD, and XJ was 1.83 × 104 items kg-1, 4.02 × 104 items kg-1, and 3.39 × 104 items kg-1, and the estimated weight of microplastics per kg of dry soils was 3.12 mg kg-1, 5.63 mg kg-1, and 7.99 mg kg-1, respectively. Microplastics in farmland were mainly of small particle size (50 to 250 μm), with their abundance decreasing with increasing particle size. Among the microplastics detected, polyethylene and polypropylene were the two dominant types present, accounting for 50.0% and 19.7%, respectively. The standard total effect of planting regions on microplastic number and weight was 31.8% and 32.3%, and plastic film mulching modes (G vs. M) could explain 34.4% of the total variation of microplastic compositions with a contribution rate of 65.6% in this study. This research provides key data for an assessment of the environmental risk of microplastics and supports the development of guidelines for the sustainable use of agricultural plastic film. Further, it is necessary to quantify and assess the contribution of other different plastic sources to microplastics in soil. Big data technologies or isotope tracer techniques may be promising approaches.

Quantification and Chemical Characterization of Plastic Additives and Small Microplastics (<100 μm) in Highway Road Dust

Road dust is one of the environment's most important microplastic and plastic additive sources. Traffic vehicles and the wear of tires can release these emerging contaminants, which can be resuspended in the air and washed off by stormwater runoff. In this study, a concurrent quantification and chemical characterization of additives, plasticizers, natural and non-plastic synthetic fibers (APFs), and small microplastics (SMPs, <100 µm) in samples of highway road dust (HWRD) was performed. The sampling procedure was optimized, as well as pretreatment (extraction, purification, and filtration) and analysis via micro-FTIR. The average length of the SMPs was 88 µm, while the average width was 50 µm. The highest abundance of SMPs was detected in HWRD 7 (802 ± 39 SMPs/g). Among the polymers characterized and quantified, vinyl ester and polytetrafluoroethylene were predominant. APFs' average particle length was 80 µm and their width was 45 µm, confirming that both of these emerging pollutants are less than 100 µm in size. Their maximum concentration was in RD7, with 1044 ± 45 APFs/g. Lubricants and plasticizers are the two most abundant categories, followed by vulcanizing agents, accelerators, and pre-vulcanizing retarders derived mainly from tires. A potential relationship between APFs and SMPs in the different seasons was observed, as their concentration was lower in summer for both and higher in winter 2022. These results will be significant in investigating the load of these pollutants from highways, which is urgently necessary for more accurate inclusion in emission inventories, receptor modeling, and health protection programs by policymakers, especially in air and water pollution policies, to prevent risks to human health.