Charged polystyrene microplastics inhibit uptake and transformation of ¹⁴C-triclosan in hydroponics-cabbage system

Since the outbreak of COVID-19, microplastics (MPs) and triclosan in pharmaceuticals and personal care products (PPCPs) are markedly rising. MPs and triclosan are co-present in the environment, but their interactions and subsequent implications on the fate of triclosan in plants are not well understood.

This study aimed to investigate effects of charged polystyrene microplastics (PS-MPs) on the fate of triclosan in cabbage plants under a hydroponic system.

¹⁴C-labeling method and liquid chromatography coupled with quadrupole/time-of-flight mass spectrometry (LC-QTOF-MS) analysis were applied to clarify the bioaccumulation, distribution, and metabolism of triclosan in hydroponics-cabbage system. The distribution of differentially charged PS-MPs in cabbage was investigated by confocal laser scanning microscopy and scanning electron microscopy.

The results showed that MPs had a significant impact on bioaccumulation and metabolism of triclosan in hydroponics-cabbage system. PS-COO^-, PS, and PS-NH₃⁺ MPs decreased the bioaccumulation of triclosan in cabbage by 69.1 %, 81.5 %, and 87.7 %, respectively, in comparison with the non-MP treatment (control). PS-MPs also reduced the translocation of triclosan from the roots to the shoots in cabbage, with a reduction rate of 15.6 %, 28.3 %, and 65.8 % for PS-COO^-, PS, and PS-NH₃⁺, respectively. In addition, PS-NH₃⁺ profoundly inhibited the triclosan metabolism pathways such as sulfonation, nitration, and nitrosation in the hydroponics-cabbage system. The above findings might be linked to strong adsorption between PS-NH₃⁺ and triclosan, and PS-NH₃⁺ may also potentially inhibit the growth of cabbage. Specially, the amount of triclosan adsorbed on PS-NH₃⁺ was significantly greater than that on PS and PS-COO^-. The cabbage biomass was reduced by 76.9 % in PS-NH₃⁺ groups, in comparison with the control.

The uptake and transformation of triclosan in hydroponics-cabbage system were significantly inhibited by charged PS-MPs, especially PS-NH₃⁺. This provides new insights into the fate of triclosan and other PPCPs coexisted with microplastics for potential risk assessments.