The vast production and use of plastics for the past 70 years has led to the release of microplastics throughout the environment and, as a result, into the food and water sources consumed daily by humans and animals. To better understand microplastic-related toxicity in both the environment and human health, accurate analytical methods such as atomic force microscopy (AFM) are crucial.
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Due to the widespread production of plastics throughout the world, these synthetic polymers have accumulated to unprecedented levels within the environment. In particular, microplastic particles have been detected in a wide range of shapes, polymers, sizes, and concentrations in various types of environments, ranging from freshwater and agroecosystems to food and drinking water supplies.
What are Microplastics?
Microplastics are synthetic solid particles or polymeric matrices that have either a regular or irregular shape. Typically, microplastics are within the size range of one micrometer (µm) to five millimeters (mm) and originate through primary or secondary manufacturing sources.
Environmental and Health Effects of Microplastics
The effects that microplastics have on both human and environmental health is not fully understood; however, these effects can often be categorized as either physical or chemical effects.
Whereas the physical effects of microplastics are directly related to the size, shape, and concentration of microplastics, the chemical effects of microplastics are due to the hazardous chemicals that comprise these particles.
In addition to the additives and polymeric raw materials that derive from the plastic source, microplastics also consist of chemicals that these particles have absorbed from their environment.
The additives found in microplastics vary greatly, as they can be used to enhance the performance of the plastic product to improve their resistance to various environmental factors such as temperature, light radiation, mold, bacteria, and humidity.
Despite the advantages that these additives provide to the plastic product, many of them are toxic; thus, their ability to contaminate soil, air, and water sources is of significant concern.
Some of the most concerning additives that can be found in plastics and, subsequently, microplastics include bisphenol A (BPA), phthalates, heavy metals, and flame retardants.
Conventional Methods to Analyze Microplastics
To gain a better understanding of the health and environmental impact of microplastics, several analytical procedures have been adopted to extract, isolate, identify, and quantify these particles within various environmental sources.
The identification of microplastics, for example, is a critical aspect of the analytical process, as these particles can come in a wide range of sizes, shapes, and polymer types, thereby increasing the difficulty of accurately identifying them in different environmental matrices.
When microplastics are identified based on their physical characteristics alone, several microscopy techniques can be used, including dissecting, polarized, fluorescence, scanning, and atomic force microscopy (AFM). Comparatively, the chemical characterization of microplastics can be achieved through spectroscopic techniques and thermal analytical methods.
AFM for Microplastic Analysis
AFM, which is often combined with either infrared (IR) or Raman spectroscopy, is a widely used analytical tool for microplastic analysis.
When coupled with IR or Raman spectroscopy, AFM can also provide information on the chemical composition of a sample.
AFM uses a thin probe that interacts with the sample’s surface. In addition to providing images at nanometer (nm) resolutions, AFM probes can also be operated in both contact and non-contact modes with samples.
In one recent International Journal of Molecular Sciences study, researchers utilized AFM in nanochemical PeakForce Tapping mode to visualize the uptake and distribution of polystyrene spherical microplastics present within humans in fibroblasts.
This nanomechanical mode in AFM enables researchers to obtain quantitative measurements on various sample characteristics such as modulus and adhesion after image acquisition.
Furthermore, since AFM is not considered to be suitable to probe the internal parts of biological entities, the incorporation of this nanomechanical mode overcame this traditional limitation of AFM.
The researchers assessed the effects of polystyrene microplastic particles on cellular morphology while providing information on the shape and size of the microplastics, as well as the extent of their penetration into the human fibroblasts.
The researchers did not need to use any fluorescent labels, allowing them to directly analyze microplastics in cell cultures. The researchers hypothesized that this analytical approach could also help detect microplastics within human cells after fixation.
References and Further Reading
Akhatova, F., Ishmukhametov, I., Fakhrullina, G., & Fakhrullin, R. (2022). Nanomechanical Atomic Force Microscopy to Probe Microplastics Uptake and Distribution. International Journal of Molecular Science 23(2); 806. doi:10.3390/ijms23020806.
Campanale, C., Massarelli, C., Savino, I., et al. (2020). A Detailed Review Study on Potential Effects of Microplastics and Additives of Concern on Human Health. International Journal of Environmental Research and Public Health 17(4); 1212. doi:10.3390/ijerph17041212.
Shim, W. J., Hong, S. H., & Eo, S. E. (2017). Identification methods in microplastic analysis: a review. Analytical Methods 9. doi:10.1039/C6AY02558G.