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

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.

Advancing Evaluation of Microplastics Thresholds to Inform Water Treatment Needs and Risks

“…This is due to a lack of reliable toxicological data, , uncertainties in human exposure to microplastics, , and challenges in sampling and quantification. , Therefore, risk assessments are not currently able to assess health risk accurately . Furthermore, microplastics may induce health effects in different ways: (1) the effect of the microplastic particles themselves, − (2) the effect of chemicals associated with microplastics, including adsorbed/absorbed contaminants or additives, − and (3) the potential effect of attached microbial biofilm on microplastics themselves or its role in breaking down and altering the chemical makeup of microplastics. − This highlights the necessary multidimensionality of microplastics dose–response assessment to determine their overall toxic effects. Additional complexity arises because the many possible combinations of chemicals and physicochemical properties make it impossible to account for all types and sizes of plastics and their association with all regulated contaminants .…”