# Ecotoxicological Assessment of Microplastics in Freshwater Sources--A Review
## 4 Characterization Methods for Microplastics in the Environment
### Chromatography-Based Methods  
Pyr-GC-MS is a destructive but efficient method for structural MPs identification, focused on pyrolytic degradation of the sample (only 5-200 ug) and analysis of byproducts. Polymer (sub-)type(s) and organic additives can be efficiently identified according to their mass [76]. However, the number and morphology of MPs cannot be encountered and determined, respectively, thus requiring the combination with microscopy methods (e.g., visual inspection by BM or PLM and/or SEM).  
Thermal extraction-desorption Gas Chromatography-Mass Spectrometry (TED-GC-MS) is a two-step analytical method ideally suited for the analysis of polymers and their degradation intermediates. The primary step includes the thermal decomposition of sample (performed in the thermogravimetric analyzer, TGA), followed by the collection of resulting gaseous products on a solid-phase adsorber. Thereafter, the adsorbent is analyzed by TED-GC-MS [103]. The method does not require preselection of MPs as in the case of Pyr-GC-MS [76].  
High-performance liquid chromatography (HPLC) can be also applied for MPs identification in environmental water systems. However, MPs particles must be dissolved prior to the analysis using organic solvents. Tetrahydrofurane and hexafluoroisopropanol are solvents used for PS and PET, respectively [15], while other polymers (PE, PP, and PVC) are commonly analyzed on GC-MS.  
To conclude, there are several options to perform the characterization of MPs in the environment; however, as MPs may vary in chemical composition, size, density, and shapes, as well as they are present in various water matrices, a unique method does not exist. The above methods have some advantages over another regarding the particular MPs targeted property; however, if a thorough analysis is required, a combination of methods have to be applied. For example, visual inspection by the naked eye is always a good choice as the first step; however, a visual inspection cannot be the only method. It has to be combined with more powerful inspection techniques, e.g., SEM-EDS if the size, shape, and morphology of MPs are targets of inspection. Furthermore, in order to confirm whether observed particles all belong to MPs or not, FTIR and its more advanced analogs, or more powerful, but more expensive technique, Raman analysis is required. However, both have their disadvantages; e.g., in FTIR moisture causes interference, while fluorescence may occur in the case of Raman analysis. Regardless, both methods would provide fingerprinting of present plastic materials regarding their composition. The methods based on chromatography coupled with mass spectroscopy may provide more insights into additives in MPs samples, besides their core plastic materials, which may be effectively identified by FTIR or Raman, which is rather important when monitoring MPs degradation and potential adverse effects that may be originated by present additives/intermediates. Hence, although the preparation of samples is often more complicated and analysis lasts longer than with FTIR or Raman, methods based on chromatography are highly required in MPs characterization as well. Thus, further development of currently existing methods or completely new ones for MPs identification and characterization is highly necessary due to their ubiquitous presence in the environment, as well as to provide a reliable assessment of ecological risks of MPs on aquatic organisms.