Mineralisation of ¹⁴C-labelled polystyrene plastics by Penicillium variabile after ozonation pre-treatment

Large amounts of polystyrene (PS), one of the most widely used plastics in the world, end up in the environment through industrial discharge and littering, becoming one of the major components of plastic debris. Such plastics, especially the small-sized microplastics and nanoplastics, have received increasing concerns in terms of their potential environmental risks. Feasible approaches for the degradation of PS in waste materials and in the environment are highly desirable. Physicochemical pretreatments of PS may be applied to enhance biological degradation. In the present study, we synthesized ¹⁴C-labelled PS polymers, either uniformly labelled on the ring ([U-ring-¹⁴C]-PS) or labelled at the β-carbon position of the alkyl chain ([β-¹⁴C]-PS), and investigated the mineralisation of the ¹⁴C-PS polymers by the fungus Penicillium variabile CCF3219 as well as the effect of ozonation as a physico-chemical pre-treatment on the mineralisation by the fungi. Biodegradation of the ¹⁴C-PS polymers was studied in liquid medium (pH 7.5, without additional carbon substrate) with P. variabile for 16 weeks. During the incubation time, ¹⁴CO₂ was captured to calculate the mineralisation of ¹⁴C-PS and the remaining polymers were analysed by means of scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectrometry and gel-permeation chromatography (GPC). The results showed that the fungi mineralised both labelled polymers, and that the [U-ring-¹⁴C]-PS with a lower molecular weight led to a higher mineralisation rate. Ozonation pre-treatment strongly enhanced mineralisation of [β-¹⁴C]-PS. SEM analysis showed that the surface of the ozonated [β-¹⁴C]-PS became uneven and rough after the incubation, indicating an attack on the polymer by P. variabile. FT-IR analysis showed that ozonation generated carbonyl groups on the [β-¹⁴C]-PS and the amount of the carbonyl groups decreased after incubation of the [β-¹⁴C]-PS with P. variabile. GPC analysis showed that the molecular weights of the ozonated [β-¹⁴C]-PS decreased after incubation. The present data suggest that ozonation pretreatment could be a potential approach for degradation of PS waste and remediation of PS-contaminated sites.