Organotin Release from Polyvinyl Chloride Microplastics and Concurrent Photodegradation in Water: Impacts from Salinity, Dissolved Organic Matter, and Light Exposure

Abstract

Photochemical weathering leads to degradation of microplastics and releases chemical additives, polymeric fragments, and/or byproducts. This study evaluated the release kinetics of organotin compounds (OTCs) from three different sized (10–300 μm) polyvinyl chloride (PVC) microplastics under UV- and visible light irradiation. Four OTCs, dimethyltin (DMT), monomethyltin (MMT), dibutyltin (DBT), and monobutyltin (MBT), were found to release from PVC particles after 24 h leaching in darkness ranging from 2 to 20 μg·g-PVC–1. Under UV/visible light irradiation, only DMT and DBT were detectable, whereas MMT and MBT were not detected due to rapid photodegradation. The total tin concentrations (including organic and inorganic tins) in the aqueous phase monotonically increased under light exposure. By contrast, they reached plateaus after 24 h in darkness, confirming the photodegradation of OTCs. A release kinetics model was established and correctly interpreted the microplastics size effect on the OTC release process. Finally, the impacts of salinity and dissolved organic matter (DOM) were investigated. The release and photodegradation of OTCs were both inhibited at high salinity conditions, probably due to the enhanced readsorption of OTCs on PVC microplastics and the formation of halogen radicals that were less reactive toward neutral OTCs. The presence of DOM, however, increased OTCs release probably because the excited state triplet DOM (3DOM*) formed and reacted with OTCs from PVC microplastics.

A review of microplastics aggregation in aquatic environment: Influence factors, analytical methods, and environmental implications

“…Aggregation of MPs may alter their particle sizes and surface areas, which is a key factor determining the transport of the released additives and the adsorbed contaminants (Yang et al, 2018). Compared to large aggregates, small aggregates of MPs with larger surface areas and more reactive sites may release more contaminants and degrade faster (Chen et al, 2019). For example, organotin compounds (dimethyltin and dibutyltin) were released from PVC MPs under UV and visible light irradiation, and the released content of organotin by small sized PVC MPs (10 µm) was nearly 1000-fold higher than that by large sized PVC MPs (300 µm) after 56-h UV or visible light irradiation (Chen et al, 2019).…”

Micro/nano-plastics occurrence, identification, risk analysis and mitigation: challenges and perspectives

“…Carbonyl content was seen at the maximum value of 1700–1800 cm −1 . Chen et al ( 2019 ) analyzed synthetic PVC MPs exposed to light and UV radiation using ATR-FTIR. PVC polymer has a characteristic absorption peak at 600−700 cm −1 region associated with C−Cl stretching vibration.…”

Non-Negligible Effects of UV Irradiation on Transformation and Environmental Risks of Microplastics in the Water Environment

“…The increase in salt concentration led to the high refractive index of water and salt crystals that formed on the surface of MPs; thereby, the inhibition of the MPs photo-degradation rate was caused by the reduction in the light absorption efficiency [ 42 , 66 ]. At the same time, Cl − could also effectively sequestered •OH radicals, which may weaken the promotional effect of •OH on the photoaging of MPs [ 67 ]. The research of Ranjan et al proved that PP in the terrestrial environment became fragmented within one month and was difficult to recycle, but the PP in the marine environment was less weathered and could be recycled [ 68 ].…”