Reliable thermal mass quantification of PVC – an ongoing challenge

Abstract Thermal analysis of micro- and nanoplastics (MNPs) is a well-established complementary method to spectroscopic techniques, enabling simultaneous quantification of synthetic polymers at trace levels. However, pyrolysis is complex and prone to interferences. As the MNP composition in environmental samples is unknown, pyrolytic signals attributed to specific homopolymers often contain degradation products from copolymers and formulations, sharing the same polymer building blocks. Thus, results need to be reported as polymer clusters (C-). However, depending on marker specificity, residual organic matrix like natural polymers, especially refractory substances, and even unrelated synthetic polymers, can compromise quantification. Polyvinyl chloride (PVC), a common polymer, is a prominent example. Its thermal degradation mainly yields chlorine-free, partially alkylated aromatics dominated by benzene and naphthalene derivatives, which lack specificity. This study evaluated the applicability of PVC pyrolysis markers, including naphthalene and methylnaphthalene, across diverse (chlorinated) synthetic and natural polymers, including soot. All polymers released these markers. Alternative indicators like dihydro- and tetrahydronaphthalene showed slightly improved but still insufficient specificity. Thus, no definitive C-PVC marker was identified. Semi-quantitative estimates of C-PVC may be feasible in less complex or well-characterized environments. Its accurate quantification in complex matrices, where residual organic matrix is unavoidable, even after severe pretreatment, remains problematic. This requires critical reassessment of C-PVC data in environmental and biological samples. If organic residues cannot be fully excluded, thermal C-PVC. quantification should be avoided or supported by complementary methods. As a compromise, a broader C-PVC* cluster that includes refractory polymers like soot or black carbon, is suggested, provided other organics (e.g. natural fibers) have been effectively removed during preprocessing. Graphical Abstract