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Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors
Published on: December 6, 2018
Process-specific inhibition of sediment denitrification by metal oxide nanoparticles
Qiong Wang1, Junxiang Cui1, Xiaojing Zhang2
1Henan Collaborative Innovation Center of Environmental Pollution Control and Ecological Restoration, School of Materials and Chemical Engineering, Zhengzhou University of Light Industry, Zhengzhou, 450001, China.
Abstract:
The continuous accumulation of nanoparticles (NPs) in river sediments poses a potential threat to benthic nitrogen cycling. However, systematic comparisons of their effects on denitrification pathways driven by different electron donors are lacking. This study investigated the impacts of nZVI, nCuO, and nZnO on heterotrophic denitrification (H-DN), iron-based autotrophic denitrification (Fe-AD), and sulfur-based autotrophic denitrification (S-AD) in sediment. An integrated analysis was conducted including denitrification performance, key enzyme activities, extracellular polymeric substance (EPS) responses, microbial community structure, and functional gene abundance. Results revealed process- and particle-specific nanoparticle toxicity. H-DN was sensitive only to nZnO (11.6% reduction in nitrate removal rate). Fe-AD was sensitive to three NPs, with nZnO showing the strongest inhibition (38.7% reduction). In contrast, S-AD exhibited high tolerance. Nitrite reductase (NIR) activity reached 5.1 times that of the control, coupled with lower oxyR abundance, suggesting that sulfide-mediated passivation alleviated oxidative stress. NIR was identified as the common enzymatic target. Microorganisms defended against NP stress by increasing the protein fraction of EPS. nZnO triggered abnormal soluble microbial products (SMP) profiles across all systems, with protein/polysaccharide ratios surging to 45.0-45.3. Metagenomics revealed higher abundances of heavy-metal efflux and oxidative-stress genes in H-DN and Fe-AD under NP stress, imposing an energy trade-off between defense and metabolism; these genes were less abundant in S-AD. Gene abundance-enzyme activity decoupling further cautions that ecological risk assessments based solely on community abundance may underestimate nanoparticle toxicity.
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