Polystyrene micro(nano)plastics mitigate DEHP phytotoxicity and enhance its phytoremediation by pak choi

Due to large specific surface area and great hydrophobicity, micro(nano)plastics (MNPs) can absorb organic pollutants and alter their bioavailability and phytotoxicity. This study aimed to assess the effects of polystyrene (PS, 100 nm and 8 µm) MNPs on Di-(2-ethylhexyl) phthalate (DEHP) phytotoxicity and soil remediation. Moreover, alterations of soil enzyme activities and microbial community by MNPs and DEHP were also explored. The results showed that PS-NPs and PS-MPs increased shoot height (23.5 %, 25.6 %) and root weight (8.4 %, 21.1 %) of pak choi in DEHP-contaminated soil and enhanced removal efficiency of DEHP to 65.5 % and 68.8 %, respectively. SEM results on cross-sections of pak choi roots revealed potential for MNPs to enter plants and thus affect phytotoxicity of DEHP. Speculatively, PS-NPs might alleviate DEHP stress by reducing oxidative damage and improving ionic homeostasis in pak choi, however, PS-MPs were more likely to decrease DEHP bioavailability, resulting in significant reduction in DEHP toxicity. Furthermore, presence of MNPs improved soil nutrient levels and increased relative abundance of PAEs-degrading bacteria, which might further promote plant growth and DEHP degradation. The findings provided comprehensive understanding of how MNPs influence phytotoxicity and phytoremediation of DEHP and held important implication for ecological risk assessment of MNPs and DEHP co-pollution.