Salt-mediated shifts in microbial communities in benzotriazole UV stabilizer-contaminated sediments: Insights into...

The microbial community in aquatic ecosystems have received increased attention. However, information about the effect of benzotriazole UV stabilizers on microbial ecosystems in sediment remain poorly understood, particularly their combined effects with dynamic environmental factors such as salinity fluctuations. Therefore, we conducted a 45-day sediment-incubation experiment through adding salt levels (0, 0.86, and 4.30 g/L NaCl) and benzotriazole UV stabilizer-329 (UV-329) concentrations (0, 10, 50 and 100 mg/kg). As a result, UV-329 increased organic matter content, cation exchange capacity, and oxygen flux, and significantly suppressed microbial metabolic activity, as evidenced by a reduction in average well color development from 0.89 to 0.66. It also altered community composition by increasing Proteobacteria abundance from 45.8 % to 54.2 %, showing a significant positive correlation (p < 0.01). Notably, after co-exposure to UV-329 and salt stress, the metabolic activity was further decreased, and Firmicutes were identified as a feature bacterial phylum. Metabolic differences caused by co-exposure were reflected in the utilization of two amino acids (L-Phenylalanine and L-Threonine), two carboxylic acids (D-Xylose and Itaconic acid), and Tween 80 on the Biolog ECO microplate. The activities of urease, dehydrogenase, fluorescein diacetate hydrolase and adenosine triphosphate (ATP) were significantly inhibited in high-concentration co-exposure groups (p < 0.05). According to IBR_V2 model, salinity enhanced the combined toxicological effect on sediments. Partial least squares path modeling showed that UV-329 and salt stress reshaped the feature bacterial phyla by directly driving sediment properties and enzymatic activities. This study provides theoretical support for the risk of UV-329 exposure under saline conditions.