Chemical Analysis of Microplastics and Nanoplastics: Challenges, Advanced Methods, and Perspectives

Abstract

Microplastics and nanoplastics are currently widespread pollutants in the various compartments of the environment, so there is a need to have a good comprehension of the chemical formulation and its ecological significance. Chemistry analysis is complicated as the compound contains a complex mixture of chemical components that are small in size. The advanced methods applied here, such as Py-GC-MS, LC-MS, NanoSIMS, and AFM, exploiting their ability to offer high-resolution imaging and molecular characterization, make a promise for this field. Future research directions include making machine learning modules, developing high-speed screening equipment, and finding novel markers. Innovative chemistry remains significant in budgeting for successful and efficient measures to treat plastic pollution. This review highlights chemical analysis’s critical role in plastic pollution reduction and necessitates multi-disciplinary cooperation and knowledge sharing that is critical in advancing research.

Introduction

Microplastics and nanosized particles less than 5 mm have occurred in almost all areas, with possible more extreme environmental challenges that are widespread and complex. These tiny plastic pieces, less than 5 mm long and, in many cases, nanoplastics, are traceable from various origins, including the fragmentation of larger plastic debris, wastewater treatment plants, ship activities, and the shedding of synthetic textiles. This fact of their tiny bodies and participation, which is not limited by size and their significant number, has made them a treasured feature of Earth’s land and water environments. The environmental influence of microplastics and nanoplastics on the ocean world is multi-directional and complex. These microplastics are inhaled by an assorted group of creatures, from those at the bottom of the food chain to the giant fish, leading to similar impacts on the ecosystem (1). Plastic intake can block digestive tracts, change feeding behavior, and slow reproduction, causing problems that could threaten ecologies’ overall health and stability. In addition, microplastics and nanoplastics have the potential to pick up and deliver harmful pollutants such as heavy metals and organic contaminants as they are adsorbed and magnified by them, thus leading to the transfer of these contaminants into the food webs.

Establishing the chemical structure of microplastics and nanoplastics is critical to accurately identifying the environment’s health of the polymer used; particular types of plastics are combined with the additives and impurities that stick to the surface of plastic products, creating a complex matrix of chemical substances. Regarding microplastics and nanoplastics, understanding their content assists researchers in figuring out the particles’ origins, their travel routes, and their biological consequences. For instance, awareness of specific compounds’ characteristics enables the development of highly efficient remediation tactics that help to battle the spread of VOCs even in a regulatory framework (3). As microplastics and nanoplastics represent a critical challenge and need to address this problem, this review builds and provides a current summary of the state of chemical analysis methods. This review is undertaken to the advantage of the existing techniques being critically evaluated and their flaws and limitations being identified as the study seeks to find places for improving and innovating the methods. Not least importantly, the article aims to find innovative ways to use analytical methodologies by showcasing recent breakthroughs and discovering potential ways to tackle current difficulties.

Background

Microplastic (MP) and nanoplastic (NPL) constitute synthetic polymers occupying multiple environmental niches, including ecosystems, sediments, lithosphere, and biota. Their intrusion into drinking water and food prevented their territory from being widespread everywhere, which could lead to future public health threats (4). Pollutants, such as VOCs and PM, are key among anthropogenic contaminants due to their small size and long-term nature, making them accumulate in ecosystems, raising significant ecological and health concerns. Both biodegradation and non-biodegradation pathways may lead to the dispersion of micro-and nanoplastics in plastics, as shown in Figure 1.

Figure 1: Breakdown of microplastics and nanoplastics in water and land environments (5)

These are mainly derived from factors such as the crash of large plastic debris, industrial processes, and the wearing out of plastics-containing plastics-containing products. Their omnipresence disseminates the awareness of a pronounced necessity towards comprehensive environmental knowledge and efficient mitigation plans (7). Due to the ever-increasing number of toxins, explaining their chemical properties, biosynthetic pathways, and consequences to ecosystems and human health is necessary. Shown in the Figure as a typical microplastic, the particle’s chemical structure is drawn while the artificial polymer is emphasized.

Figure 2: Chemical structure of typical microplastic and nanoplastic particles (8).

Figure 2 is designed to display the molecular structure of a nano-plastic particle, clearly illustrating that these structures are tiny in size and have a synthetic character within environmental ecosystems. What is necessary to face the obstacles of MPs and NPLs is a lot of cooperation from scientists from different disciplines and the development of innovative chemical analysis methods and environmental management techniques.

Origin of NMPs

Nanoplastics can be categorized into two popular categories, depending on the foundation. “In the crux of this article, the main NMPs are elaborately described, from industrial utilization to consumer purposes. Among the ingredients are nanoparticles and microbeads, some of which are found in personal care products, industrial cleaners, and manufacturing additives. On the contrary, a “secondary” NMP source is associated with converting more significant forms of plastics during their degradation and fragmentation in the environment and during their plastic contents’ wear and tear condition. Environmental factors, including mechanical grinding, exposure to UV, and biological breaking, contribute to the end of primary NMPs online products, which increases secondary microplastics (5). The size and shape of these particles may be affected by the parent polymer’s material and the prevailing environmental conditions to which they are subjected. Identifying which type of NMP is mainly responsible for contributions, ambient air quality, and even risks to health systems is facilitated by understanding the primary and secondary sources of NMPs. Combating the challenges associated with both conventional and novel energy sources demands an overall strategic approach that addresses their production, use, disposal regimes, and derivative measures to control unbearable environmental impacts.

Challenges in Chemical Analysis of Microplastics

Even though the chemical identification of microplastics (MPs) is tough to identify as these particles have multiple shapes and shapes, the spectrum of the environmental domains to be examined is extensive. Among the varied MPs, the monomer composition, additives, and contaminants make distinguishing the correlative chemical composition difficult. Their assortment of shapes, including spherical, fibrous, and film-like forms, offers a new dimension for analytical methods. Additionally, chemical oddities of MPs’ signatures can be formed with weathering products or sorbed contaminants, preventing a detailed examination. The stability of MPs, whether they are primary or secondary particles, is also caused by their old age, which, in the long run, affects their surface traits, which influences detecting procedures (15). The nano-scale flags of MPs, and typically nanoplasmonic, are significant problems to the conventional analytical techniques, which call for high sensitivity coupled with the ability to trace levels in complex environment samples.

The modelling of MP and nanoplastic distributions (Fig.3) in different environmental compartments graphically depicts their ubiquity while calling for much better analytical techniques to reveal the involvement of these contaminants in all holistic impacts on the environment.

Here, the CMP, the concentration of microplastics, is denoted by r, and the function influencing the environment variables is f (environmental factors). This proportion reveals the link of microfiber amounts with atmospheric factors that make the development of reliable analytical methods more imperative for microplastic pollution dynamics analysis.

Figure 3: Distribution of microplastics and nanoplastics in various environmental compartments (11).

Objectives of chemical analysis

The first goal of chemical analysis serving as the microplastics (MPs) detection tool is to characterize complex chemical composition comprehensively. The decoding process involves measuring and documenting the variances, such as polymer shapes, sizes, deliveries, weathering products, and sorbed contaminants. By clarifying these parameters, studies can learn the reasons behind the presence, character of motion, and possible ecological outcomes of MPs. Techniques such as size fractionation and FFF are recommended to achieve accuracy. In Polydispersive mixtures containing microplastic particles of different sizes, size fractionation is applied to separate the small-sized particles, making the analysis more precise (2). This undoubtedly bears a significant bearing in mind, as the dimensions of MPs within environmental samples are understood to be very different.

On the other hand, field flow fractionation (FFF) can provide powerful separation capability that works without any stationary phase. It allows different particles, considering their diffusivity in a flowing carrier fluid, to be separated; thus, fractionation of particles with their sizes, shape, or even their density becomes possible (7). This technology serves to improve the resolution mission and analysis of MP, which makes it possible to identify and characterize individual particles or populations with better accuracy.

Thermal Degradation Combined with GC/MS

With the incorporation of pyrolysis coupled with gas chromatography-mass spectrometry (GC/MS), an analytical workflow that allows for compound identification and quantification was established for plastic waste detection in samples. The thermal cracking way of plastics creates an environment where they can easily break under controlled radiation minus oxygen. The toxic compounds, including intermediate chemical products, are formed, and the analysis is done through mass spectrometry (MS). This method can help us distinguish the different chemicals on a molecular level. Pyrolysis is used to identify plastics pyrolysis products, e.g., thermal degradation analysis by pyrolysis gas-chromatography-mass spectrometry (Py-GC/MS). Py-GC/MS has been developed as a powerful analytical tool presenting four operation modes — figuratively known as single-shot analysis, double-shot analysis, evolved gas analysis (EGA-Py-GC/MS), and reactive or thermochemolytic Py-GC/MS. Short of it, all the given samples will be torched in a single go, giving an overall nature of the composition. The double-shot analysis sequence is more complicated because it involves two separate pyrolysis steps, which, unfortunately, are complicated by the difficulty in eliminating different elements from the sample (14). EGA-MS or sublimation spectroscopy is essential for tracking gas release during pyrolysis, which is very informative to the decomposition ways’ outcomes. The reacting/Thermochemolytic Pi-GC/MS technique above depends on the chemical derivatization to provide sensitivity for particular functional groups.

Figure 4: The principle of Py-GC/MS (9).

Figure 4 reveals the principle of Py-GC/MS. The stepwise process is apparent in this view, from introducing the sample to the spectrometric analysis of the pyrolysate products. This particular analytical method is known to provide high sensitivity and accurate identification of plastics and their degradation products in the environment. Thus, it’s a beneficial technique in research laboratories (8). Another advantage of this GC/MS technology is its ability to integrate with other analysis techniques for total plastic pollution characterization and the cultivation of credible strategies for mitigation.

Current Research

Empirical approaches designed explicitly for the identification and taxonomy of MPs and NPLs within environmental matrices using standard methods have been widely applied. These methods are constituted by microscopic techniques, spectroscopic processes, and chromatographic processes, each implying their strengths and restrictions. Microscopy methods, e.g., optical and scanning electron microscopy (SEM), allow for visual observation and morphological characterization of MPs and NPLs (13). Optical microscopy has higher image resolution for particles than other methods of analysis, so it is possible to identify the size and shape of particles. SEM has transmission electron microscopy for precise surface topography and composition information through electron beam scanning.

Figure 5: The use of optical microscopy in visualizing microplastics in environmental samples (13).

Spectroscopic techniques such as infrared spectroscopy by FTIR and Raman spectroscopy are crucial for chemically identifying microplastics and nanoplastics. FTIR senses molecular absorption patterns by characteristic groups in plastic polymers and operates their differentiation, thus providing better and quicker identification.

Raman spectroscopy

Molecular identification offered by Raman spectroscopy is based on the elastic scattering of light from plastic, granting both qualitative and quantitative analyzing access to plastics. The Raman spectroscopy system provides a potent analytical tool for the chemical identification of plastics and nanoplastics (MPs & NPLs) because of its molecular fingerprint feature. This non-invasive technique involves the inelastic scattering of monochromatic light by molecules, which generates distinctive Raman shifts – molecular fingerprints – that are detectable by the system (9). Using the Raman microscope, investigators can scrutinize the compositional structure of particular MPs and NPLs and identify the particles’ specific polymer types and additives. Notably, Raman spectroscopy provides qualitative analysis and quantitative determination of plastic contaminants in environmental matters.

A Raman spectrum of a piece of plastic belongs to its molecular structure and composition, thus exhibiting their difference in the case of several kinds of polymers. There is a well-illustrated Raman spectroscopy to detect microplastics in environmental samples (Figure 6).

Figure 6: Application of Raman spectroscopy in identifying microplastics (9).

Fourier-transform infrared spectroscopy (FTIR).

Fourier-transform infrared spectroscopy (FTIR) is an analytical technique that can be applied to environmental samples for material identification and characterization. FTIR (Fourier Transform Infrared Spectroscopy) produces a spectrum by causing absorption in the sample’s chemical bonds of infrared radiation. A Fourier transforms after the well-formed interferogram is given as a spectrum that carries data related to the character of the chemical bond in the sample. With this method, complicated functional groups in plastics can be simply determined, enabling an immediate characterization of the type of polymer. The FTIR spectrum of plastic, revealing the molecular structure of plastic particles, provides details on identifying the components that can be used for its analysis. The equation below represents Beer’s law, which describes the relationship between the absorption of light by a sample, its concentration, and the path length: The equation below represents Beer’s law, which describes the relationship between the absorption of light by a sample, its concentration, and the path length:

Where A is the Absorbance, b is the length of the light path, ε is the molar absorptivity, and C is the concentration.

Advanced Chromatographic techniques

Chromatographic methodology constitutes a significant part of specialized approaches utilized in the exhaustive screening of MPs and NPLs, providing critical data on these particles’ chemical composition and origins. The combination of pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) method is a powerful tool that allows to decompose the plastic samples by heat transformation plus separating and then identifying the resulting pyrolysis products using a gas chromatography coupled to a mass spectrometer. Those methods contribute to characterizing polymer conglomerates and identifying components and sources in MPs and NPLs.

The advanced liquid chromatography-mass spectrometry (LC-MS) analysis is one of the techniques used to investigate the microplastics and nanoplastics. LC-MS determines organic compounds’ composition depending on their interactions with a liquid mobile phase and a solid support phase, where the mechanism is a separation and further identification with a mass spectrometer (11). LC-MS is one of the most accurate and efficient methods of analysis. It is probably the best tool for analyzing additives, pollutants, and degradation products associated with micro-plastic particles. As these modern chromatographic methods furnish valuable data for the chemical characterization of the MPs and NPLs and environmental effects monitoring, they create a basis for developing suitable specific remediation methods.

Applications of developed methods beyond NMP research

Besides emerging techniques for studying microplastics and nanoplastics, nano-scale secondary ion mass spectrometry (NanoSIMS) and atomic force microscopy (AFM) are other available methods. NanoSIMS combines high-resolution imaging of individual grains and chemical analysis to contour down elemental compositions and distributions of grains. AFM can achieve nanometer-scale resolution mapping of mission control structures when these particles are deposited on the surfaces with nanometer-scale resolution, offering the opportunity for the detailed characterization of surface properties.

In contrast to the conventional approach, employing modern devices such as AFM brings unprecedented spatial resolution and sensitivity, making small particles and their surface properties imaginable. Besides these methods, elementary ones help to know microplastics and nanoplastics better from varying units; the adoption of new-fangled techniques will necessitate specific equipment and skills, which may be complex and, thus, costly to acquire, making them less accessible than basic approaches. Besides, their characteristics make them very important for conducting studies about microplastics and nanoplastics in samples through the environment.

Through these sensitive methods, for example, the NanoSIMS and AFM, the researcher can analyze aboriginal particles of both organic and other chemical origins, including microorganisms. Such analyzers offer resolution and elemental analysis applicable to revealing advanced particle feature data such as elemental composition, crystalline structure, and surface property. A table showing the pros and cons of each method can be added to highlight the strengths and weaknesses of each method discussed. They include factors like spatial resolution, detecting the limits, sample preparation needs, and applicability of the techniques to different particles. This would provide more research on the performance and applicability of these techniques on many types of particulate matter, including microplastics, nanoplastics, and others.

Future Directions

In the future, we expect further development of tools for MPs and NPLs analysis, and it is just the beginning of how plastic pollution can be better investigated and managed. Integrated ML and AI algorithms open new ways for the machine-learning-driven and optimal data-analysis processes automation. With ML and AI, these patterns can be found, particle types can be classified and classified, and predicting environmental impacts through MPs and NPL chemical and morphological characteristics is not impossible. Moreover, high-throughput screening techniques will assist in the detection of large sample sets, and therefore, the analysis would be fast and comprehensive. However, it will help compare the plastic levels across different environmental compartments. Standardization and robustness methods are the basic requirements for the results obtained with the same precision and reproducibility. By setting up the procedures and testing the reliability of methods, researchers can achieve higher credibility and thus be able to compare data across studies.

Then, the detection and investigation of specific markers for identifying plastic sources, ingredients, and their degradation products in the environment will undoubtedly advance our capability to trace the origins and paths of MPs and NPLs. By discovering profitable chemical signatures belonging to a specific type of plastic and an identified degradation process, researchers might understand plastic pollution pathways better and thus assess the environmental risks. Interdisciplinary collaboration and knowledge sharing are indispensable components for propelling the progress of microplastics and nanoplastics analysis in ongoing research. Establishing a network among chemists, biologists, and engineers from different disciplines, like environmental science and engineering, through interdisciplinary research will help pool diverse skills in the fields and ensure that complex ecological issues related to plastic pollution are tackled comprehensively (12). Furthermore, it is necessary to consider the knowledge exchange taking place between academics, industry, and policymakers for the applied outcomes of research works on plastic pollution control and management. The interdisciplinary exchange of knowledge contributes much to communication and collaboration. Thus, it plays a prominent role in the innovation process and is based on evidence.

Conclusion

In conclusion, an analysis of microplastics or nanoplastics chemically brings along its difficulties, such as myriad composition, small size, and widespread circumstances. On the other hand, there are advanced methods like Py-GC-MS, LC-MS, NanoSIMS, and AFM, using which high-resolution imaging, elemental analysis, and molecular characterization can be done to give promising solutions to organic characterization. These modalities can allow us to overcome some constraints and better grasp plastic pollution in the environment. This research and innovation in chemistry will be critical in the final eradication of plastic pollution and the production of efficient mitigation systems. Identifying the root cause of the problem and applying new sophisticated analytical approaches is pivotal to the future because of lower plastic pollution risks.

References

1. Allen, S.; Allen, D.; Karbalaei, S.; Maselli, V.; Walker, T. R. Micro(Nano)Plastics Sources, Fate, and Effects: What We Know After Ten Years of Research. Journal of Hazardous Materials Advances2022, 6, 100057. https://doi.org/10.1016/j.hazadv.2022.100057.
2. Cárdenas-Alcaide, M. F.; Godínez-Alemán, J. A.; González-González, R. B.; Iqbal, H. M. N.; Parra-Saldívar, R. Environmental Impact and Mitigation of Micro(Nano)Plastics Pollution Using Green Catalytic Tools and Green Analytical Methods. Green Analytical Chemistry2022, 3, 100031. https://doi.org/10.1016/j.greeac.2022.100031.
3. Fang, C.; Luo, Y.; Naidu, R. Microplastics and Nanoplastics Analysis: Options, Imaging, Advancements and Challenges. TrAC Trends in Analytical Chemistry2023, 166, 117158. https://doi.org/10.1016/j.trac.2023.117158.
4. Ivleva, N. P. Chemical Analysis of Microplastics and Nanoplastics: Challenges, Advanced Methods, and Perspectives. Chemical Reviews2021, 121 (19), 11886–11936. https://doi.org/10.1021/acs.chemrev.1c00178.
5. Janani, R.; Bhuvana, S.; Geethalakshmi, V.; Jeyachitra, R.; Sathishkumar, K.; Balu, R.; Ayyamperumal, R. Micro and Nano Plastics in Food: A Review on the Strategies for Identification, Isolation, and Mitigation through Photocatalysis, and Health Risk Assessment. Environmental Research2024, 241, 117666. https://doi.org/10.1016/j.envres.2023.117666.
6. Jiménez-Skrzypek, G.; Ortega-Zamora, C.; González-Sálamo, J.; Hernández-Sánchez, C.; Hernández-Borges, J. The Current Role of Chromatography in Microplastic Research: Plastics Chemical Characterization and Sorption of Contaminants. Journal of Chromatography Open2021, 1, 100001. https://doi.org/10.1016/j.jcoa.2021.100001.
7. Liu, W.; Zeng, M.; Li, Y.; Chen, G.; Wen, J.; Wang, J. Deciphering the Research of Micro(Nano)Plastics: An in-Depth Bibliometric Expedition into Ecotoxicological Impacts and Research Trends. TrAC Trends in Analytical Chemistry2024, 172, 117608. https://doi.org/10.1016/j.trac.2024.117608.
8. Parolini, M.; Ortenzi, M. A.; Morelli, C.; Gianotti, V. Emerging Use of Thermal Analysis in the Micro(Nano)Plastics Exposure Assessment. Current Opinion in Toxicology2021, 28, 38–42. https://doi.org/10.1016/j.cotox.2021.09.007.
9. Picó, Y.; Barceló, D. Analysis of Microplastics and Nanoplastics: How Green Are the Methodologies Used? Current Opinion in Green and Sustainable Chemistry2021, 31, 100503. https://doi.org/10.1016/j.cogsc.2021.100503.
10. Piyathilake, U.; Lin, C.; Bundschuh, J.; Herath, I. A Review on Constructive Classification Framework of Research Trends in Analytical Instrumentation for Secondary Micro(Nano)Plastics: What Is New and What Needs Next? Environmental Pollution2023, 335, 122320. https://doi.org/10.1016/j.envpol.2023.122320.Pramanik,
11. B. K.; Pramanik, S. K.; Monira, S. Understanding the Fragmentation of Microplastics into Nano-Plastics and Removal of Nano/Microplastics from Wastewater Using Membrane, Air Flotation and Nano-Ferrofluid Processes. Chemosphere2021, 282, 131053. https://doi.org/10.1016/j.chemosphere.2021.131053.
12. Shi, H.; Frias, J.; El-Din H. Sayed, A.; De-la-Torre, G. E.; Jong, M.-C.; Uddin, S. A.; Rajaram, R.; Chavanich, S.; Najii, A.; Fernández-Severini, M. D.; Ibrahim, Y. S.; Su, L. Small Plastic Fragments: A Bridge between Large Plastic Debris and Micro- & Nano-Plastics. TrAC Trends in Analytical Chemistry2023, 168, 117308. https://doi.org/10.1016/j.trac.2023.117308.
13. Silva, A. L. P.; Silva, S. A. M.; Duarte, A.; Barceló, D.; Rocha-Santos, T. Analytical Methodologies Used for Screening Micro(Nano)Plastics in (Eco)Toxicity Tests. Green Analytical Chemistry2022, 3, 100037. https://doi.org/10.1016/j.greeac.2022.100037.
14. Winiarska, E.; Jutel, M.; Zemelka-Wiacek, M. The Potential Impact of Nano- and Microplastics on Human Health: Understanding Human Health Risks. Environmental Research2024, 118535. https://doi.org/10.1016/j.envres.2024.118535.
15. Thompson, J. R.; Crooks, R. M. Electrokinetic Separation Techniques for Studying Nano- and Microplastics. Chemical Science2022, 13 (43), 12616–12624. https://doi.org/10.1039/d2sc04019k.