Anomalous reduced sequence: Potential hazards of disinfection byproduct chlorate in reclaimed water

Chlorine dioxide is used in reclaimed water treatment technologies and generates the inorganic disinfection byproduct (DBP) chlorate (ClO₃^-) during disinfection. Currently, water quality standards for reclaimed water do not specify concentration limits for ClO₃^-. This DBP can infiltrate the soil along with reclaimed water. Ion concentrations are determined by ion chromatography. Metagenomics is used to measure and analyze the genomes of all microorganisms in soil. Results indicate that ClO₃^- remains stable in groundwater, and despite its higher redox potential (+1.21 V), it is not biologically reduced. Instead, NO₃^- with a lower redox potential (+0.94 V), undergoes significant biological reduction. Concurrently, microbial oxidative stress levels increase markedly by 133.77%, significantly stimulating the production of extracellular proteins by over 20.13% and polysaccharides by over 9.68%. Additionally, slight changes in microbial community structure are observed, including the elimination of microorganisms such as Chloroflexota, a slight decrease in species richness, and a minor increase in the regulation of genes related to amino acid metabolism by 2.56%. In terms of microbial ecological risks, ClO₃^- significantly upregulates microbial resistance gene levels by 16.15%, with microorganisms adopting two main strategies to mitigate ClO₃^- toxicity: altering target proteins or nucleic acids (51.70%) and efflux (43.41%). The relative abundance of efflux-related genes increases by 44.72%. Pathogenic bacteria show significant changes in relative abundance (over 156.52%) and community structure, with Acinetobacter junii increasing by 222.22% and Acinetobacter baumannii decreasing by 63.20%. In summary, ClO₃^- infiltrating with reclaimed water may potentially contaminate the groundwater environment. This study provides a comprehensive understanding of the interactions between ClO₃^- and soil microorganisms.