Comparative study on degradation of PVC microplastics under four processes: mechanism, pathway and toxicological assessment

In this study, the degradation properties of typical microplastic polyvinyl chloride (PVC) treated by Sole peroxymonosulfate (Sole PMS), Sole ferrate (Sole Fe(VI)), Sole solar light (Sole SL) and solar light activated peroxymonosulfate and ferrate (SL/PMS/Fe(VI)) were investigated. The Cl⁻ released from the treated PVC of the four processes (e.g., Sole PMS, Sole Fe(VI), Sole SL and SL/PMS/Fe(VI)) was 1.87, 2.17, 15.62 and 23.36 mg/L, respectively (SL intensity = 1.70 W/cm², [PMS] = 10 mM, [Fe(VI)] = 5 mM). Moreover, the oxidation and dehydrochlorination of PVC occurred after the treatment under the above four processes. Compared to virgin PVC, the norfloxacin (NOF) and sul1 adsorption on degraded PVC were enhanced. The adsorption of sul1 on degraded PVC under Sole PMS, Sole Fe(VI), Sole SL and SL/PMS/Fe(VI) processes was 2.76, 3.18, 63.62 and 202.21 copies/g, respectively, which was higher than that in the control group (2.67 copies/g). The release of MP-derived dissolved organic matter (MP-DOM) was promoted, and the fluorescent composition and concentration of MP-DOM were changed after treatment by the above four processes. The Sole PMS, Sole Fe(VI) and Sole SL processes mainly produced alkanes, esters and alcohols, while alkanes, esters, aldehydes and phenols were generated in the SL/PMS/Fe(VI) process. Possible degradation pathways of PVC were proposed, and the degradation products were evaluated as “toxic” or even “very toxic” based on quantitative structure-effect relationship. Compared with Sole PMS, Sole Fe(VI) and Sole SL processes, the filtrates from PVC treated by SL/PMS/Fe(VI) showed the lowest mortality rate on zebrafish embryos. The results of this study contribute to the understanding of the PVC degradation under different processes and the possible ecological impacts of degraded PVC and degradation products.