The assessment of particle selection and blank correction to enhance the analysis of microplastics with Raman microspectroscopy

Preparation of synthetic micro- and nano plastics for method validation studies

Microplastic (MP) pollution is a persisting global problem. Accurate analysis is essential in quantifying the effects of microplastic pollution and develop novel technologies that reliably and reproducibly measure microplastic content in various samples. The most common methods for this are FTIR and Raman spectroscopy. Coloured, standardized beads are often used for method validation tests, which limits the conclusions to a very specific case rarely observed in the natural environment. This study focuses on the preparation of reference micro- and nanoplastics via cryogenic milling and shows their use for FTIR and Raman method validation studies. MPs can now be reproducibly milled from various plastics, offering the advantages of a better representation of MPs in real environment. Moreover, this study highlights issues with the current detection methods, up to now considered as the most reliable ones for MP detection and identification. Such issues, e.g. misidentification, will need to be addressed in the future. Additionally, milled MPs were used in experiments with commercial high-resolution imaging device, enabling a possible in-situ optical detection of microplastics. These experiments represent a step forward in understanding MPs in a water sample and provide a basis for a more accurate detection and identification directly from water, which would considerably reduce the time of analysis.

Human Exposure to Ambient Atmospheric Microplastics in a Megacity: Spatiotemporal Variation and Associated Microorganism-Related Health Risk

Microplastics are found in various human tissues and are considered harmful, raising concerns about human exposure to microplastics in the environment. Existing research has analyzed indoor and occupational scenarios, but long-term monitoring of ambient atmospheric microplastics (AMPs), especially in highly polluted urban regions, needs to be further investigated. This study estimated human environmental exposure to AMPs by considering inhalation, dust ingestion, and dermal exposure in three urban functional zones within a megacity. The annual exposure quantity was 7.37 × 104 items for children and 1.06 × 105 items for adults, comparable with the human microplastic consumption from food and water. Significant spatiotemporal differences were observed in the characteristics of AMPs that humans were exposed to, with wind speed and rainfall frequency mainly driving these changes. The annual human AMP exposure quantity in urban green land spaces, which were recognized as relatively low polluted zones, was comparable with that in public service zones and residential zones. Notably, significant positive correlations between the AMP characteristics and the pathogenicity of the airborne bacterial community were discovered. AMP size and immune-mediated disease risks brought by atmospheric microbes showed the most significant relationship, where Sphingomonas might act as the potential key mediator.

Microplastics and other anthropogenic fibres in large apex shark species: Abundance, characteristics, and recommendations for future research

Microplastics and microfibres are found ubiquitously in global oceans as well as marine organisms from different trophic levels. However, little is known about the presence of microplastics and microfibres in marine megafauna, such as sharks. This study provided the first investigation of the presence of microplastics and other anthropogenic fibres (i.e., cellulose based fibres) in intestine and muscle samples of four large apex shark species in Australian coastal waters. Microplastics and other anthropogenic fibres were found in 82% of the analysed intestine samples. The mean abundance in intestine samples was 3.1 ± 2.6 particles/individual, which corresponded to 0.03 ± 0.02 particles/g of intestine, across all shark species. The size of particles ranged from 190 to 4860 μm in length with 92% being fibrous in shape and the rest fragments. FTIR spectroscopy identified that 70% of fibres were cellulose-based followed by polyethylene terephthalate (PET), while the fragments were polyethylene and polypropylene. In shark muscles, 60% of samples contained microplastics and other anthropogenic fibres, again with the majority being cellulose-based fibres followed by PET fibres. Methodological differences hinder a more comprehensive assessment of microplastic contamination across studies. Additionally, we identified some challenges which should be factored in for future studies looking at the presence of microplastics as well as other anthropogenic fibres in these large marine organisms. Overall, the findings provide first evidence of microplastics and other anthropogenic fibres not only in the intestines, but also in muscle tissues of large apex shark species.

Using optimized particle imaging of micro-Raman to characterize microplastics in water samples

Characterizing the chemical properties, morphologies, size, and quantities of microplastics (MPs) in water samples with high precision is critically important for understanding the environmental behaviors of MPs. Traditional detection methods, such as Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy point-by-point detection, provide worthy reference techniques but are time- and labor-consuming. We established a super time-saving and high-precision technique to characterize MPs using micro-Raman automatic particle identification (MR-API). Based on the identification of PS spheres, screen magnification, exposure time, and the number of scans are selected as crucial detection parameters for MR-API analysis, which highly affect the precision of the results. Detecting particles down to 1 μm requires magnification of the mosaic until the scale showed 200 μm. The recommended setting parameters were 83.33 or 100 ms exposure time, 20 scans, 7 mW laser power, and 1 μm image pixel size, suitable for polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), polyethylene (PE), polyvinyl chloride (PVC), and polyamide (PA) particles detection. With the complete procedure of MR-API measurements, the recovery of MPs was 61.67-90.00 %. To validate the feasibility of the MR-API, the method was used to detect samples of known plastic types (mask leachates) and unknown plastic types (urban lake). A total of 4540 particles in the sample of mask leachates consuming 35 h 50 min 43 s, and 0.92 ± 0.49 % of particles were identified as MPs. The urban river sample efficiently identified PP, PET, PE, PVC, PS, EVA, and VC/VAC MPs using this method. The detected MPs size ranged from 8.3 to 5000 μm, saving 75.03 % and 58.38 % of the time compared to the conventional micro-FTIR and micro-Raman point-by-point methods, respectively. Therefore, this method is effective for detecting MPs in the environmental samples and has excellent prospects.

M. M. Ferraz M. Microplastics analytics: why we should not underestimate the importance of blank controls

Recent years have seen considerable scientific attention devoted towards documenting the presence of microplastics (MPs) in environmental samples. Due to omnipresence of environmental microplastics, however, disentangling environmental MPs from sample contamination is a challenge. Hence, the environmental (collection site and laboratory) microplastics contamination of samples during processing is a reality that we must address, in order to generate reproducible and reliable data. Here we investigated published literature and have found that around 1/5 of studies failed to use blank controls in their experiments. Additionally, only 34% of the studies used a controlled air environment for their sample processing (laminar flow, fume hood, closed laboratory, clean room, etc.). In that regard, we have also shown that preparing samples in the fume hood, leads to more microplastics > 1 μm) contamination than preparing it in the laboratory bench and the laminar flow. Although it did not completely prevent microplastics contamination, the processing of sample inside the laminar flow is the best option to reduce sample contamination during processing. Overall, we showed that blank controls are a must in microplastics sample preparation, but it is often overlooked by researchers.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s43591-023-00065-3.

Microplastics in coastal blue carbon ecosystems: A global Meta-analysis of its distribution, driving mechanisms, and potential risks

Microplastics, as emerging pollutants, have become a global environmental concern. Blue carbon ecosystems (BCEs) are threatened by microplastics. Although substantial studies have explored the dynamics and threats of microplastics in BCEs, the fate and driving factors of microplastics in BCEs on a global scale remain largely unknown. Here, the occurrence, driving factors, and risks of microplastics in global BCEs were investigated by synthesizing a global meta-analysis. The results showed that the abundance of microplastics in BCEs has notable spatial differences worldwide, with the highest microplastic concentrations in Asia, especially in South and Southeast Asia. Microplastic abundance is influenced by the vegetation habitat, climate, coastal environment, and river runoff. The interaction of geographic location, ecosystem type, coastal environment, and climate enhanced the effects of microplastic distribution. In addition, we found that microplastic accumulation in organisms varied according to feeding habits and body weight. Significant accumulation was observed in large fish; however, growth dilution effects were also observed. The effect of microplastics on the organic carbon content of sediments from BCEs varies by ecosystem; microplastic concentrations do not necessarily increase organic carbon sequestration. Global BCEs are at a high risk of microplastic pollution, with high microplastic abundance and toxicity driving the high pollution risk. Finally, this review provides scientific evidence that will form the basis for future microplastic research, focusing on the transport of microplastics in BCEs; effects on the growth, development, and primary productivity of blue carbon plants; and soil biogeochemical cycles.

Visual characterization of microplastics in corn flour by near field molecular spectral imaging and data mining

As potential hazard to human health, microplastics have attracted increasing attention. Most current studies have addressed the characterization of microplastics from the environment. For microplastics in food, most detections focused on liquid systems such as alcohol, beverages, etc., while there has been quite rare research on microplastics in solid foods with complex matrices. Thus, this study attempted to use three molecular spectral imaging approaches, namely, Fourier transform infrared (FTIR), optical photothermal resonance infrared (O-PTIR), and confocal Raman spectral imaging, combined with chemometrics to characterize the presence of microplastics in corn flour. The results demonstrated that O-PTIR imaging can rapidly sense the presence of microplastics, but its data integrity and visualization were limited. By decomposing the image, FTIR and Raman acquired a more integral distribution. Wherein, microplastics were well depicted by Raman imaging coupled with independent component analysis. Moreover, O-PTIR imaging can quickly detect contaminants at low concentrations but with a low detection rate. Raman imaging underperformed in low-concentration samples but provided a better visualization in mid-concentration samples. Overall, the results confirmed that the visual detection of microplastics in powdered food can be realized by molecular spectral imaging coupled with data mining, which can provide a reference for the detection of microplastics in other foods.

Disposable face masks release micro particles to the aqueous environment after simulating sunlight aging: Microplastics or non-microplastics?

This study focuses on characterizing microplastics and non-microplastics released from surgical masks (SMs), N95 masks (N95), KN95 masks (KN95), and children's masks (CMs) after simulating sunlight aging. Based on micro-Raman spectrum analysis, it was found that the dominant particles released from masks were non-microplastics (66.76-98.85%). Unfortunately, CMs released the most microplastics, which is 8.92 times more than SMs. The predominant size range of microplastics was 30-500 µm, and the main polymer types were PP and PET. Compared with the whole SMs, the microplastic particles released from the cutting-SMs increased conspicuously, which is 12.15 times that of the whole SMs. The main components of non-microplastics include β-carotene, microcrystalline cellulose 102, and eight types of minerals. Furthermore, non-microplastics were mainly fibrous and fragmented in appearance, similar to the morphology of microplastics. After 15 days of UVA-aging, the fibers of the face layers had cracks to varying degrees. It was estimated that these four types of masks can release at least 31.5 trillion microplastics annually in China. Overall, this study demonstrated that the masks could release a large quantity of microplastics and non-microplastics to the environment after sunlight aging, deserving urgent attention in the future study.

Analytical methods for microplastics in the environment: a review

Microplastic pollution is a recently discovered threat to ecosystems requiring the development of new analytical methods. Here, we review classical and advanced methods for microplastic analysis. Methods include visual analysis, laser diffraction particle, dynamic light scattering, scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, thermal analysis, mass spectrometry, aptamer and in vitro selection, and flow cytometry.

Variation of microplastics in the shore sediment of high-altitude lakes of the Indian Himalaya using different pretreatment methods

Microplastics pollution is a growing environmental concern. However, microplastics studies in high altitude remote lakes are scarce. In this study, microplastics pollution was assessed in the shore sediment of three high altitude lakes in Ladakh of the Indian Himalaya, namely Pangong Lake, Tsomoriri Lake and Tsokar Lake. Sampling of lakes shore sediment was performed in August 2019. Two different pretreatment methods were implemented with sediment samples from same sites, resulting two sets of samples. One set of samples was pretreated utilizing enzymatic degradation together with Fenton reactions. Another set of samples from the same sites were pretreated with 30 % hydrogen peroxide (H₂O₂) and Fenton reaction. Enzymatically pretreated samples resulted in higher microplastics concentrations than the set of H₂O₂ pretreated samples, which indicated that microplastics concentrations in sediment samples varies even among samples from the same site and that the pretreatment procedure may impact on the reported microplastics concentrations. Considering both sets of samples, microplastic concentration was 160-1000 MP/kg dw in Pangong Lake, 960-3800 MP/kg dw in Tsomoriri Lake, and 160-1000 MP/kg dw in Tsokar Lake. Blank correction based on the limit of detection and the limit of quantification indicated that microplastics concentrations at some sites of the studied lakes are higher than the limit of detection and the limit of quantification. The findings of this study indicated that the studied lakes in the Indian Himalaya are contaminated with microplastics. In addition, the comparison of microplastics using different pretreatment methods illustrated the importance of harmonization of microplastics studies to enable a reliable comparison among microplastics data. Therefore, this study contributes towards an assessment of microplastics in the high-altitude lakes in Indian Himalaya. The findings attributed towards clearer understanding regarding the need of harmonization of pretreatment methods and demonstrated the importance of reporting complete information in microplastics research.