International Journal of Marine Science, 2025, Vol.15, No.5, 245-254 http://www.aquapublisher.com/index.php/ijms 246 2 Monitoring Technology for Microplastic Pollution 2.1 Application of optical microscope and infrared spectroscopy in monitoring When detecting microplastics in environmental samples in laboratories, the traditional and basic method is optical microscopy observation and counting. Researchers usually use screens or filter membranes to collect microplastic particles in environmental media, and then use stereomicroscopes or microphotography systems to identify and count particles larger than a certain size (such as 0.3 mm). Due to the complex composition of environmental samples, it is easy to misjudge some natural fibers as plastics by visual observation alone. To improve identification accuracy, modern monitoring widely combines Fourier transform infrared spectroscopy (FT-IR) or Raman spectroscopy to identify components of suspicious microplastic particles. Microinfrared spectroscopy can quickly identify the polymer species of particles through infrared absorption peak fingerprint characteristics, and is one of the common methods for environmental microplastic monitoring (Figure 1) (Renner et al., 2019; Böke et al., 2022). When analyzing estuary and offshore water samples, particles in two particle size segments, 11 μm~500 μm and 500 μm~5000 μm were first captured by sieve filtration, and then batch scanning and identification were used by infrared microscopy technology to successfully obtain the concentration, size distribution and polymer composition information of the microplastics in the sample. Infrared spectroscopy can detect plastic particles with particle sizes of tens of microns or even smaller (Othman et al., 2023; Lim et al., 2024), but it is still difficult for nanoplastics. In addition, combined with polarization microscopy, fluorescence staining and other methods can also help improve the sensitivity of microscopy detection. Figure 1 Schematic diagram of O-PTIR spectroscopy. A pulsed tunable IR laser is collinear with the visible detection laser, and the beams are focused via dichroic mirrors (DM1-3) on the sample surface through a reflective objective (RO). When IR absorption occurs, the photothermal response of the sample surface is monitored by the visible probe laser. The reflected light passes through a beam splitter (BS), is measured by a visible detector, and the IR signal is extracted while sweeping the wavelength of the IR laser source. Raman-shifted light is simultaneously diverted to the Raman spectrometer (Adopted from Böke et al., 2022) 2.2 The potential of environmental DNA technology in microplastic detection Environmental DNA (eDNA) technology is a new environmental monitoring method developed in recent years. It refers to inferring the existence of species and environmental conditions by detecting free biological DNA
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