# Ecotoxicological Assessment of Microplastics in Freshwater Sources--A Review
## 4 Characterization Methods for Microplastics in the Environment
### Spectroscopy-Based Methods  
FTIR allows accurate identification of polymers from their characteristic IR spectra due to the possession of specific IR spectra with distinct band patterns [85]. FTIR is the most frequently used method for MPs analysis [86]. When a plastic polymer is irradiated with IR, a certain amount of energy gets absorbed by the polymer molecule, causingmolecular vibrations that yield a characteristic IR spectrum. Vibrations depend on the polymer structure and applied irradiation wavelengths [85]. Generally, FTIR analysis is performed in mid-IR range of 4000-400 cm\({}^{-1}\)[87]. Generally, plastic materials lose weight during degradation, indicating structural changes [88]. Hence, polymer degradation may be confirmed by the analysis of its functional groups; some groups are missing or possess lower or higher peak intensity in comparison to reference FTIR spectra [15; 89]. Typical vibrational bands of PE, PP, PVC, PET, and PS are summarized in Table 2. \begin{table}
\begin{tabular}{c c c} \hline
**Polymer** & **Functional Group** & **Wavenumber (cm\({}^{-1}\))** \\ \hline \multirow{6}{*}{PE} & CH\({}_{2}\) symmetric stretch & 2918; 2850 \\  & CH\({}_{2}\) asymmetric stretch & 2919 \\  & CH\({}_{2}\) bend & 1473; 1463 \\  & CH\({}_{3}\) symmetric stretch & 1377 \\  & CH\({}_{2}\) wag & 1366; 1351;1176 \\  & CH\({}_{2}\) twist & 1050 \\  & CH\({}_{2}\) rock & 731–720 \\ \hline \multirow{6}{*}{PP} & CH\({}_{2}\) asymmetric stretch & 2919 \\  & CH\({}_{3}\) asymmetric stretch & 2951 \\  & CH\({}_{3}\) symmetric stretch & 2868 \\  & CH\({}_{2}\) symmetric stretch & 2837 \\  & CH\({}_{2}\) scissors & 1458 \\  & CH\({}_{3}\) symmetric bend, CH\({}_{2}\) wag & 1377 \\  & CH Bend, CH\({}_{2}\) twist, CH\({}_{3}\) rock & 1256 \\  & CH\({}_{2}\) twist, C-C stretch, C-H bend & 1220 \\  & CH Bend, CH\({}_{3}\) rock, C-C stretch & 1168 \\  & C-C stretch, CH\({}_{3}\) rock, CH\({}_{2}\) wag, CH twist, CH bend & 1104 \\  & C-CH\({}_{3}\) stretch, C-C stretch, CH bend & 1045 \\  & CH\({}_{3}\) rock, CH\({}_{3}\) wag, CH bend & 998 \\  & CH\({}_{3}\) rock, C-C stretch & 941 \\  & CH\({}_{3}\) rock & 937 \\  & CH\({}_{3}\) rock, CH\({}_{3}\) rock, CH bond & 899 \\  & CH\({}_{2}\) rock, C-CH\({}_{3}\) stretch & 841 \\  & CH\({}_{2}\) rock, C-C stretch, C-CH stretch & 809 \\  & CH\({}_{2}\) rock & 730; 720 \\ \hline \multirow{6}{*}{PVC} & CH\({}_{2}\) asymmetric stretch & 2904 \\  & CH\({}_{2}\) symmetric stretch & 2837 \\  & CH\({}_{2}\) wag & 1354 \\  & CH Bend & 1333; 1254; 1243 \\  & C-C stretch & 1099 \\  & CH\({}_{2}\) rock & 970; 957 \\  & C-Cl stretch & 603 \\ \hline \multirow{6}{*}{PCT} & CH\({}_{2}\) asymmetric stretch & 2969 \\  & C=O stretch & 1740–1710 \\  & CH\({}_{2}\) bend & 1470 \\ \hline \multirow{6}{*}{PCT} & CH\({}_{2}\) wag & 1370–1340 \\  & C-C-O asymmetric stretch bonded to aromatic ring & 1250 \\ \cline{1-1}  & C-O stretch & 1260 \\ \cline{1-1}  & C-O-C stretch & 1100 \\ \cline{1-1}  & aromatic in-plane CH bend & 1019 \\ \cline{1-1}  & oxy-methylene group bend & 973–898 \\ \cline{1-1}  & aromatic out-of-plane CH wag & 875 \\ \cline{1-1}  & C=O rock, C-O deformation & 795 \\ \cline{1-1}  & aromatic in-phase CH wag & 730 \\ \hline \end{tabular}
\end{table} 
Table 2: Functional groups of the most used polymers and their wavenumbers in FTIR spectra [90; 91; 92; 93]. One disadvantage of FTIR analysis is that bands of organic and inorganic impurities can overlap with polymer bands in IR spectra, hindering spectroscopic evaluation [94]. Accordingly, samples should be pretreated before analysis in order to remove moisture, which may cause interference resulting in data interpretation difficulties [15; 81]. Transmission IR spectroscopy is used for thin and transparent samples, while the reflection mode is usually employed for thick and non-transparent samples. Attenuated total reflectance FTIR (ATR-FTIR) is a common FTIR technique measuring IR spectrum of polymer's surface, or a spectrum of thick and strongly absorbing polymers [95].