Unanticipated Thio-oxidation of Organophosphite Chemical Additives in PVC Microplastics Following In-Situ Weathering

30 March 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Microplastics have emerged as contaminants of concern due to their worldwide distribution and persistence. Following environmental weathering the chemical composition of microplastics may be altered by physicochemical processes. In this study, nontargeted analysis was employed to examine changes in the chemical composition of five different types of microplastics that had been subjected to 16 weeks of in-situ exposure to flowing river water. The highest number of observed peak features was associated with PVC (12,043), among which 2,086 were newly formed. It was unanticipated that three organothiophosphates, including triphenyl thiophosphate (TPTP), would have the highest abundance following in-situ exposure of PVC microplastics. The abiotic formation of organothiophosphates was confirmed via in-lab simulation trials following 6 weeks of artificial weathering. To further investigate potential reaction mechanisms, triphenyl phosphite (TPPi) and PVC microplastic particles were individually incubated along with five major sulfur species. Elementary sulfur (S8) and sulfide (S2-) were observed to be responsible for the formation of TPTP via the thio-oxidation of TPPi. This is the first known report of thio-oxidation as a transformation pathway, highlighting the importance of considering chemical transformations when conducting microplastic risk assessments.

Keywords

Organothiophosphates
Organophosphates
Nontargeted analysis
Chemical transformations
Thio-oxidation

Supplementary materials

Title
Description
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Title
Supporting Information for Unanticipated Thio-oxidation of Organophosphite Chemical Additives in PVC Microplastics Following In-Situ Weathering
Description
The supporting information provides text, tables, and figures which address: (1) Recovery trials associated with extraction procedures; (2) Identification of organophosphorus compounds by nontargeted analysis when considering PVC following in-situ exposure; (3) Organophosphorus analogues in PVC after in-situ exposure; (4) Recoveries of organophosphorus compounds; (5) Peak features detected from five types of polymers after in-situ exposure; (6) Peak features detected from five types of polymers after artificial weathering; (7) Formation of TPHP associated with 3-week thio-oxidation trials.
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