RESPONSE OF PERIPHYTON IN AQUACULTURE WATER TO SULFAMETHOXAZOLE STRESS AND ITS DEGRADATION

The extensive use and accumulation of sulfamethoxazole (SMX) in the aquaculture contributed to its residues in aquaculture water, which may cause various negative impacts on the aquatic ecological environment. Furthermore, periphyton is a common micro-ecosystem in water bodies composed of autotrophs and heterotrophs, including algae, fungi, bacteria, protozoa, metazoans, extracellular polymers (EPS) and debris, etc. Nevertheless, there is a lack of research on the impact of SMX on the growth and development of periphyton and its purification function in aquaculture water. In this survey, the effect of SMX on periphyton was researched in simulating aquaculture water, and the response of periphyton to SMX was explored through the biomass and total antioxidant capacity of the periphyton. The removal effect and the main degradation intermediates of SMX by periphyton were investigated by high-performance liquid chromatography (HPLC) and ultra-performance liquid chromatography quadrupole-time-of-flight mass spectrometry (UPLC-QTOF-MS). This research demonstrated that under 5 and 10 mg/L SMX, the secretion of extracellular polymer (EPS) of the periphyton increased by 31.3% and 21.5% compared with the control group, and the antioxidant capacity diminished by 20.6% and 31.8%, but there was no significant difference in biomass accumulation. It showed that SMX decreased the total antioxidant capacity of the mature periphyton, their oxidative systems were damaged, and more extracellular polymers were secreted to enhance tolerance to SMX. The results of the removal experiment indicated that the periphyton would promote the reduction of SMX, and the removal rate of SMX at 1 g/L was 25.10% on the 14th day. It is supposed that SMX was used by periphyton as a carbon source to promote biodegradation and shorten the half-life of SMX degradation. Thus, periphyton had a certain potential for SMX bioremediation in aquaculture water. The main routes of SMX biodegradation by the periphyton are the cleavage and activation of the sulfonamide group (N-S bond) and the amine group (-NH₂) on the benzene ring. The primary degradation intermediates were N4-acetyl-SMX, p-Benzoquinoneimine, Desulphone-SMX and Desamino-SMX. Among these degradation products, N4-acetyl-SMX, p-Benzoquinoneimide and Desamino-SMX were fewer toxic than SMX, and Desulphone-SMX was somewhat more toxic than SMX. The research provides theoretical support for assessing the ecological risk of SMX in aquaculture water and the engineering application of periphyton to remove SMX.