Do nano-plastics inhibit the removal of polycyclic aromatic hydrocarbons in constructed wetlands?

Constructed wetlands (CWs) are commonly used as a final barrier for polycyclic aromatic hydrocarbons (PAHs) removal, but nano-plastics (NPs) accumulation could significantly affect their performance. Whether NPs enhance or inhibit PAHs removal in CWs remains debated, and the mechanisms involved are still unclear. Here, the effects of NPs on the treatment of typical PAHs (naphthalene (NPT)) in CWs were investigated by analyzing EPS adsorption function, microbial dynamics and virulence factor genes (VFGs) changes. The presence of 100 and 1000 μg/L NPs enhanced NPT removal by 114.1 % and 77.6 %, furthermore, 55.4 % and 48.2 % of the added NPs were simultaneously removed. Correspondingly, 19.8 % and 17.6 % higher NPT content was accumulated in substrate. The addition of NPs increased EPS content by over 219.6 %, enhancing the affinity of NPT. Under NPs influence, genes that related to NPs degradation (e.g. styA, phaA, ubiH) and NPT degradation (e.g. nahAc, nahB, nahC) were significantly upregulated. Key genes in the PPP and TCA cycle were also enhanced (e.g. prpC, kgd, sdhB), providing energy and oxidative stress resistance for contaminant removal. The addition of 100 μg/L NPs reduced adhesion-related VFGs by 11.0 % and increased microbial immune regulation by 19.6 %, suggesting higher risk and stress adaptation. Therefore, the accumulation of NPs enhances NPT removal performance, while the increased concentration of NPs should be raised potential risk in CWs.