Investigating the toxicological effects of aged nanoplastics (NPs) in soil is critical, as UV irradiation may exacerbate their ecological toxicity by altering surface properties and enhancing interactions with the soil. Here, we investigated the effects of different concentrations of pristine and aged polystyrene (PS) and carboxylpolystyrene (PSC) NPs on lettuce and soil properties. Both pristine and aged NPs inhibited pigment synthesis and lettuce growth. The maximum growth inhibition rates of leaf (root) biomass were 10.2 % (23.4 %) and 32.7 % (45.3 %) for pristine PS and PSC (50 mg center dot L- 1) and 26.7 % (35.9 %) and 43.1 % (57.8 %) for aged PS and PSC (50 mg center dot L- 1), respectively. NPs induced excessive reactive oxygen species (ROS) production in the leaves and roots, antioxidant defense mechanisms, and oxidative damage, which was more pronounced with aged NPs. ROS accumulation gradually increased with aging time and concentration of NPs, which inhibited photosynthesis and decreased biomass. At the same aging duration, exposure to either pristine or aged NPs significantly reduced soil pH. Compared to the control, neither pristine nor aged NPs altered the composition of dissolved organic matter, whereas aged PSC induced a significant increase in the intensity of soluble microbial byproducts; this was attributed to differences in soil acidity and alkalinity. Low concentrations of pristine and aged NPs increased the Chao 1 index in soils, exhibiting hormesis, and altered relative microbial abundances. Pristine and aged PS/ PSCs promoted microbial oxidative phosphorylation, carbon fixation pathways in prokaryotes, and the tricarboxylic acid cycle. The results provide critical insights into the impacts of NPs on plant and soil microbial growth.

Nanoplastics (NPs), identified as emerging pollutants, pose a great risk to environment and global public health, exerting profound influences on the prevalence and dissemination of antibiotic resistance genes (ARGs). Despite evidence suggesting that nano-sized plastic particles can facilitate the horizontal gene transfer (HGT) of ARGs, it is imperative to explore strategies for inhibiting the transfer of ARGs. Currently, limited information exists regarding the characteristics of environmentally aged NPs and their impact on ARGs propagation. Herein, we investigated the impact of photo-aged NPs on the transfer of ARG-carrying plasmids into Escherichia coli (E. coli) cells. Following simulated sunlight irradiation, photo-aged nano-sized polystyrene plastics (PS NPs) exhibited multiple enzyme-like activities, including peroxidase (POD) and oxidase (OXD), leading to a burst of reactive oxygen species (ROS). At relatively low concentrations (0.1, 1 mu g/mL), both pristine and aged PS NPs facilitated the transfer of pUC19 and pHSG396 plasmids within E. coli due to moderate ROS production and enhanced cell membrane permeability. Intriguingly, at relatively high concentrations (5, 10 mu g/mL), aged PS NPs significantly suppressed plasmids transformation. The non-unidirectional impact of aged PS NPs involved the overproduction of ROS (center dot OH and center dot O-2(-)) via nanozyme activity, directly degrading ARGs and damaging plasmid structure. Additionally, oxidative damage to bacteria resulted from the presence of much toxic free radicals, causing physical damage to cell membranes, reduction of the SOS response and restriction of adenosine-triphosphate (ATP) supply, ultimately leading to inactivation of recipient cells. This study unveils the intrinsic multienzyme-like activity of environmentally aged NPs, highlighting their potential to impede the transfer and dissemination of ARGs.