Antibiotics and heavy metals often coexist in water environments, and the complex compounds can easily form, however, the combined pollutants on nitrogen removal performance is little known in wetlands.

Researchers from Wuhan Botanical Garden and Institute of Hydrobiology investigated the combined toxicity of heavy metals and antibiotics on nitrogen(N) removal performance, nitrous oxide (N₂O) emission, N metabolism-related enzymes, functional genes, and microbial communities in ecological ditches using metagenomic analysis. Cadmium (Cd) and Doxycycline (DC) were selected as model pollutants.

The exposure duration of mixed Cd/DC influenced the N removal performance of ecological ditches, and the degree of deterioration was the highest with the addition of Cd (5 mg L^-1 ) and DC (50 mg L^-1 ). A high DC concentration addition (50 mg L^-1 ) under Cd stress could increase N₂O emissions and lactate dehydrogenase (LDH) release, while the increasing Cd concentration at 1 mg L^-1 DC stress decreased N₂O emissions. Combined pollutants of Cd and DC severely inhibited critical enzymes involved in the glycolysis pathway.

These findings provide new insights into N reduction and N₂O emissions control in ecological wastewater treatment systems exposed to combined heavy metals and antibiotics.

This work was supported by the National Natural Science Foundation of China and the Natural Science Foundation of Hubei Province in China. Associate professor MA Lin is the first author and Professor LIU Wenzhi is the corresponding author.

The relevant research results have been published in Journal of Cleaner Production entitled “Low-level cadmium alleviates the disturbance of doxycycline on nitrogen removal and N₂O emissions in ditch wetlands by altering microbial community and enzymatic activity”.

 Nitrogen metabolic process in the ecological ditch microcosms exposed to Cd and DC (Image by MA Lin)