Degradation of sulfonamides in aquaculture wastewater by laccase-syringaldehyde mediator system: Response surface optimization, degradation kinetics, and degradation pathway.

As a new type of environmental pollutant, environmental antibiotic residues have attracted widespread attention, and the degradation and removal of antibiotics has become an engaging topic for scholars. In this paper, Novozym 51003 industrialized laccase and syringaldehyde were combined to degrade sulfonamides in aquaculture wastewater. Design Expert10 software was used for multiple regression analysis, and a response surface regression model was established to obtain the optimal degradation parameters. In the actual application, the degradation system could maintain a stable performance within 9 h, and timely supplement of the mediator could achieve a better continuous degradation effect. Low concentrations of heavy metals and organic matter would not significantly affect the degradation performance of the laccase-mediator system, making the degradation system suitable for a wide range of water quality. Enzymatic reaction kinetics demonstrated a strong affinity of sulfadiazine to the substrate. Ten degradation products were speculated using high-resolution mass spectrum based on the mass/charge ratios and the publication results. Four types of possible degradation pathways of sulfadiazine were deduced. This work provides a practical method for the degradation and removal of sulfonamide antibiotics in actual sewage.

Effects of moxifloxacin and gatifloxacin stress on growth, photosynthesis, antioxidant responses, and microcystin release in Microcystis aeruginosa.

Moxifloxacin (MOX) and gatifloxacin (GAT) are fourth-generation fluoroquinolone antibiotics that are frequently detected in surface water environments and pose a threat to aquatic organisms. However, research into their toxicity to Microcystis aeruginosa, a cyanobacterium, has thus far been limited. In the present study, we investigated the effects of these antibiotics on M. aeruginosa growth, photosynthesis, oxidative stress, and microcystin (MC) release. The results of the 96 h EC50 values of MOX and GAT were 60.34 and 25.30 µg/L, respectively, and the risk quotients calculated indicated that these antibiotics could pose considerable ecological risks at actual environmental concentrations. Photosynthetic fluorescence intensity was shown to decline markedly, and Fv/Fm significantly decreased without any evidence of recovery, suggesting that the organism's photosystems were irreversibly damaged. Chlorophyll a and carotenoid content decreased, whereas the ratio of carotenoids to chlorophyll a increased, indicating that carotenoids were less susceptible to damage than chlorophyll a. The reactive oxygen species and malondialdehyde content significantly increased, as well as the superoxide dismutase and catalase activities, indicating that exposure caused serious oxidative stress. Additionally, MC release increased. These results demonstrate that the environmental risks posed by MOX and GAT should be given serious consideration, particularly as their use is increasing.