## 4 Discussion  
The production of bioplastics has increased in recent years and these polymers continue to enter the environment. Understanding the qualitative and quantitative impact of plastic polymers is fundamental for addressing their potential environmental pollution and their toxicological impact [36]. In this regard, the identification and quantification of bioplastic degradation products (solid microparticles and soluble compounds) and residual components, by using different analytical techniques, is a very complex challenge. Qualitative analysis of bioplastics has been performed using spectroscopic methods (i.e., fluorescence, nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR) and UV-VIS spectrophotometric techniques [37,38]), while the quantitative analysis of solid microdebris of bioplastics uses FTIR micro imaging, gas chromatography with mass spectrometry and thermal analysis [39,40,41]. The potential utility of IRMS as a complementary analytical method with respect to \"traditional\" analytical techniques for plastic analyses has been reported in our previous work [1]. In this preliminary study, carbon stable isotope analysis (\(\delta^{13}\)C) was applied. This method was used to discriminate different plastic polymers (petroleum- and plant-derived) in plastic and bioplastic materials (among which the shopping bags of Mater-Bi\({}^{\oplus}\), Novasromt), as well as for the quali-quantitative evaluation of polymers degradability in marine environments. In the present study, the same approach, i.e., the assessment of isotopic values of several polymers and some possible natural raw constituents (corn starch, potato starch and vegetable oils), was applied to identify the carbon source used to manufacture shopping bags. Among the natural sources for biopolymers production, there are C3 plants and C4 plants, which differ in photosynthetic pathways and, consequently, their carbon fingerprint. It has been demonstrated that C4 plants such as sugar cane, millet, corn and tropical grasses, using the Hatch-Slack photosynthetic cycle, have \(\delta^{13}\)C values ranging from \(-8\) to \(-20\)%, less negative respect to C3 plants (mostly dicotyledons such as wheat, rice, rye and cotton), that employ the Calvin-Benson cycle and have \(\delta^{13}\)C values ranging from \(-22\) to \(-35\)% [42]. Plant-derived plastic polymers used for food packaging, bags and bottles for drinking water showed a significant difference in isotopic values with respect to petroleum-derived plastic products ([15] and literature therein). Petroleum-derived packaging materials for food, such as shopping bags for fruits and vegetables (HDPE), were characterized by \(\delta^{13}\)C mean values of \(-33.97\pm 1.15\)%, whereas plant-derived supermarket shoppers (\"BIO\" bags) recorded \(\delta^{13}\)C mean values of \(-25.30\pm 0.70\)%, near values characteristic for C3 plants as a starch source. The different polymers analyzed, such as  
Figure 6: C=O functional groups (I\({}_{1700}\)/I\({}_{730}\)) as function of immersed time respectively for ULB (blue triangle) and LSB (red circle). PCL or PBS (Table 1), showed depleted values (from \(-27.47\) to \(-27.15\%\)) with respect to C4-derived polymers (corn starch). PCL as well as PBS are often used in biodegradable polymer blends. PCL, which is a semicrystalline linear polyester [43] produced by polymerization of \(\varepsilon\)-caprolactone commonly derived from fossil sources, received great attention in the 1980s when Novamont created a PCL/starch composite under the trademark Mater-Bi\({}^{\circleddelta}\)[44]. PBS, poly(butylene succinate-co-butylene adipate) was produced in 1990 through a polycondensation reaction of glycols with aliphatic dicarboxylic acids and their derivatives [45] and its processability and mechanical properties made it a candidate to replace other polymers such as polyethylene and polypropylene [46].