Insight into the generation of toxic by-products during UV/H2O2 degradation of carbamazepine: Mechanisms, N-transformation and toxicity

Carbamazepine (CBZ) is a widely used anticonvulsant drug that has been detected in aquatic environments. This study investigated the toxicity of its by-products (CBZ-BPs), which may surpass CBZ. Unlike the previous studies, this study offered a more systematic approach to identifying toxic BPs and inferring degradation pathways. Furthermore, quadrupole time-of-flight (QTOF) and density functional theory (DFT) calculations were employed to analyze CBZ-BP structures and degradation pathways. Evaluation of total organic carbon (TOC) and total nitrogen (TN) mineralization rates, revealed carbon (C) greater susceptibility to mineralization compared with nitrogen (N). Furthermore, three rules were established for CBZ decarbonization and N removal during degradation, observing the transformation of aromatic compounds into aliphatic hydrocarbons and stable N-containing organic matter over time. Five potentially highly toxic BPs were screened from 14 identified BPs, with toxicity predictions guiding the selection of commercial standards for quantification and true toxicity testing. Additionally, BP207 emerged as the most toxic, supported by the predictive toxicity accumulation model (PTAM). Notably, highly toxic BPs feature an acridine structure, indicating its significant contribution to toxicity. These findings offered valuable insights into the degradation mechanisms of emerging contaminants and the biosafety of aquatic environments during deep oxidation.

Disentangling the coupling relationships between functional denitrifiers and nitrogen transformation during cattle-manure and biochar composting: A novel perspective

This study explored the coupling relationships between denitrifiers and N-transformation using multi-level (DNA, RNA and enzyme) and multi-aspect (abundance, diversity, structure, key community, network pattern, and functional module) analyses during cattle-manure (CM) and biochar (CMB) composting. Amino sugar-N (ASN, 0.914) and hydrolysable unknown-N (-0.724) were main organic-N components mediating NH₄⁺-N in CM and CMB, respectively. Biochar lowered nirK, nirS, and nosZ genes copies, up-regulated nir gene transcripts, and inhibited nitrite reductase (NIR) activity. For nirK-denitrifiers, Luteimonas was predominant taxa influencing NO₂^--N and amino acid-N (AAN). Unclassified_k_norank_d_Bacteria and unclassified_p_Proteobacteria regulated NO₃^--N and ASN, respectively. These three genera played crucial roles in mediating NIR activity and nosZ/nirK. For nirS-denitrifiers, Paracoccus and Pseudomonas mediated NH₄⁺-N and AAN, respectively, and they were vital genera regulating NO₃^--N, ASN and NIR activity. Furthermore, nirK-denitrifiers was major contributor to denitrification. Overall, functional denitrifiers might simultaneously participate in multiple N-transformation processes.

Contrasting impact of elevated atmospheric CO2 on nitrogen cycle in eutrophic water with or without Eichhornia crassipes (Mart.) Solms

The elevation of atmospheric CO₂ is an inevitable trend that would lead to significant impact on the interrelated carbon and nitrogen cycles through microbial activities in the aquatic ecosystem. Eutrophication has become a common trophic state of inland waters throughout the world, but how the elevated CO₂ affects N cycles in such eutrophic water with algal bloom, and how vegetative restoration helps to mitigate N₂O emission remains unknown. We conducted the experiments to investigate the effects of ambient and elevated atmospheric CO₂ (a[CO₂], e[CO₂]; 400, 800 μmol﹒mol^-1) with and without the floating aquatic plant, Eichhornia crassipes (Mart.) Solms, on N-transformation in eutrophic water using the ¹⁵N tracer method. The nitrification could be slightly inhibited by e[CO₂], due mainly to the competition for dissolved inorganic carbon between algae and nitrifiers. The e[CO₂] promoted denitrification and N₂O emissions from eutrophic water without growth of plants, leading to aggravation of greenhouse effect and forming a vicious cycle. However, growth of the aquatic plant, Eichhornia crassipes, slightly promoted nitrification, but reduced N₂O emissions from eutrophic water under e[CO₂] conditions, thereby attenuating the negative effect of e[CO₂] on N₂O emissions. In the experiment, the N transformation was influenced by many factors such as pH, DO and algae density, except e[CO₂] and plant presence. The pH could be regulated through diurnal photosynthesis and respiration of algae and mitigated the acidification of water caused by e[CO₂], leading to an appropriate pH range for both nitrifying and denitrifying microbes. Algal respiration at night could consume DO and enhance abundance of denitrifying functional genes (nirK, nosZ) in water, which was also supposed to be a critical factor affecting denitrification and N₂O emissions. This study clarifies how the greenhouse effect caused by e[CO₂] mediates N biogeochemical cycle in the aquatic ecosystem, and how vegetative restoration mitigates greenhouse gas emission.