# Microplastics in Water Resources: Threats and Challenges
## 5 Methods for Determining Microl plastics
### Optical Microscopy Method  
Optical microscopes and stereomicroscopes are effective tools in microplastics analysis because of their ability to provide high-resolution images and the capability to employ various imaging techniques. The advantages of this method include the rapid identification and assessment of the morphology of microplastics, which is crucial to understanding their source, distribution, and environmental impact [122; 123]. Optical microscopy is useful for a quick preliminary assessment of samples for the presence of microplastics. The low complexity of the method allows multiple samples to be evaluated without the need for  
Figure 4: Number of scientific publications searched by the ScienceDirect portal tool using the keywords FTIR + microplastic, Nile Red + microplastic, LDIR + microplastic by year [121].  
special preparation. For example, in the case of water samples, simply filtering the sample and examining the filter under a microscope is often sufficient. However, there are some disadvantages associated with this method. Optical microscopy is not sufficient for identifying the chemical composition of microplastics, which is essential to understanding the potential hazards to organisms and the environment. A comprehensive analysis of the size distribution and type of material helps to find correlations between these characteristics and the impact of MPs on the environment [118]. In addition, identifying microplastics of very small sizes, especially those smaller than 20 \(\upmu\)m, can be challenging. Much depends on the skills and experience of the researcher conducting the examination [124]. Human error is a significant limitation of optical microscopy, particularly when distinguishing microplastics from organic or mineral particles. Studies, such as [PERSON] et al. (2015) [125], have demonstrated that misidentification rates can range from 10% to 60%, depending on the sample type and the researcher's expertise. These error rates were determined by comparing the results of optical microscopy with those of Raman spectroscopy, which is a more accurate and reliable method for identifying microplastics [125]. Therefore, human error cannot be completely eliminated. Under microscopic magnification, microplastic particles can exhibit various morphological features, making their identification difficult. These microscopic particles often assume various shapes and structures, making them similar to other small organic or mineral fragments. In a microscopic image, microplastics often resemble tiny grains of sand, fibers, or plant fragments. They can also be similar to microorganisms, such as phytoplankton [126]. Due to their small size, microplastics can be difficult to distinguish from natural environmental components, further complicating the identification process [127]. As a result, optical microscopy is often used as part of more advanced analyses, such as FTIR or Raman spectroscopy (RS), which allow for the identification of the type of plastic material [128]. Therefore, detecting MPs visually using a microscope can be prone to errors, leading to quantitative overestimation or underestimation [125]. Despite these limitations, optical microscopy remains a widely used method in microplastic research because of its simplicity, speed, and effectiveness in identifying larger particles. When used in conjunction with other advanced analytical techniques, this tool enables a more comprehensive analysis of the composition and characteristics of microplastics.