# Microplastic Pollution: Chemical Characterization and Impact on Wildlife
## 2 The Chemical and Physical Characterization of Microplastics
### FTIR Microscopy
Reprinted with permission from the March/April 2014 edition of BioOptics World Copyright 2014 by PennWell. Right–Photograph of a modern FTIR benchtop microscope. Photograph provided by Thermo Fisher Scientific. **  
Figure 5: **(A,B)–FTIR spectra and optical images of MPs of various compositions. Characteristic peaks differ based upon MP composition. Figures have been reproduced from Refs. [40; 58] with permission of publishers. **  
Thus, while suspected microplastic particles can be identified visually through optical microscopy, their chemical identity is often verified using FTIR spectroscopy [59]. In the work of [PERSON] et al. [60], an FTIR microscope was used to count microplastic particles and identify their composition concurrently. This was accomplished by utilizing an FTIR system that includes a mercury cadmium telluride (MCT) detector with liquid nitrogen cooling. The authors were able to identify 15 different polymeric microplastics present in air samples collected via deposition in London. The authors also determined MP deposition rates ranging from 575-1008 microplastic particles/m\({}^{2}\)/day. The MPs observed were of various shapes, but fibers accounted for the vast majority (approx. 92% of the total). The work of [PERSON] et al. [61] demonstrates use of a more conventional experimental apparatus for FTIR spectroscopy of MPs. Herein, a micro-FTIR with a mercury cadmium telluride (MCT) detector was used to record FTIR spectra in microtransmission mode (not a microscope) because it allowed for highly sensitive observations in the mid-infrared. Samples were visually segregated and placed on KBr pellets, and the following measurement parameters were used for the microtransmission mode: spot 50 \(\upmu\)m 20 scans, 8 cm\({}^{-1}\) resolution, and 4000-550 cm\({}^{-1}\) spectral range. The apparatus allowed the authors to detect the presence of 12 different anthropogenic polymers or groups of polymers with a predominance of polyethylene, polypropylene, polyester, and acrylic fibers present within the wastewater effluent of Madrid, Spain. The work of [PERSON] et al. also reports use of a conventional attachment for FTIR analysis, the attenuated total reflection (ATR) Fourier transform infrared (ATR-FTIR) approach. After collecting microplastics from fish sampled from the Qarasu River of Iran, the ATR-FTIR sample cell was used to collect IR spectra with an average of 64 scans, at a very typical resolution of 4 cm\({}^{-1}\) from 450 cm\({}^{-1}\) to 4000 cm\({}^{-1}\)[62]. The authors determined that 94% of fish had MPs present, with polystyrene, polyethylene, and nylon being most abundant. Fibers were the most abundant particle type (85.12%), followed by fragment (12.32%), foam (0.77%), film (1.21%), and microbeads (0.56%), respectively. In another work considering water from the Tamsui River in Taiwan, [PERSON] et al. [63] concluded that microplastics are largely generated from land-based sources since MPs particle concentrations peaked after rain events. FTIR spectra of the samples were collected using the attenuated total reflection Fourier transform infrared (ATR-FTIR) microspectroscopy approach. FTIR spectra of samples were acquired with 128 scans with standard 4 cm\({}^{-1}\) resolution range of 4000-650 cm\({}^{-1}\) using a Nicolet 6700 FTIR coupled to a MIRacleTM single reflection germanium ATR cell manufactured by PIKE (Fitchburg, WI, USA). This sampling of works summarizes the use of FTIR spectroscopy for the chemical characterization of microplastic particles collected from a variety of sources. By no means should this brief overview be construed as being a comprehensive review of FTIR measurements in the field of MPs, but rather an overview of the technique and the information it provides. FTIR remains a very valuable technique for MP identification--particularly when used in microscopy mode. FTIR allows rapid (minutes) determination of the chemical composition of MP particles.