Size-dependent influences of nanoplastics on microbial consortium differentially inhibiting 2, 4-dichlorophenol biodegradation

Nanoplastics (NPs), as a type of newly emerging pollutant, are ubiquitous in various environmental systems, one of which is coexistence with organic pollutants in wastewater, potentially influencing the pollutants' biodegradation. A knowledge gap exists regarding the influence of microbial consortium and NPs interactions on biodegradation efficiency. In this work, a 2,4-dichlorophenol (DCP) biodegradation experiment with presence of polystyrene nanoplastics (PS-NPs) with particle sizes of 100 nm (PS) or 20 nm (PS) was conducted to verify that PS-NPs had noticeable inhibitory effect on DCP biodegradation in a size-dependent manner. PS at 10 mg/L and 100 mg/L both prolonged the microbial stagnation compared to the control without PS-NPs; PS exacerbated greater, with PS at 100 mg/L causing a noticeable 6-day lag before the start-up of rapid DCP reduction. The ROS level increased to 1.4-fold and 1.8-fold under PS and PS exposure, respectively, while the elevated LDH under PS exposure indicated the mechanical damage to cell membrane by smaller NPs. PS-NPs exposure also resulted in a decrease in microbial diversity and altered the niches of microbial species, e.g., they decreased the abundance of some functional bacteria such as Brevundimonas and Comamonas, while facilitated some minor members to obtain more proliferation. A microbial network with higher complexity and less competition was induced to mediate PS-NPs stress. Functional metabolism responded differentially to PS and PS exposure. Specifically, PS downregulated amino acid metabolism, while PS stimulated certain pathways in response to more severe oxidative stress. Our findings give insights into PS-NPs environmental effects concerning microflora and biological degradation.