A new study led by researchers at the Wuhan Botanical Garden of the Chinese Academy of Sciences, has found that the coexistence of heavy metals and antibiotics in aquatic environments poses a serious threat to critical nitrogen transformation processes and the overall multifunctionality of constructed wetlands (CWs).

Over an 84-day period, the research team systematically examined the combined impacts of copper (Cu) and three common antibiotics—sulfamethoxazole (SMZ), doxycycline (DC) and ciprofloxacin (CIP)—on wetland ecosystems.

The study demonstrated that elevated Cu levels, especially when paired with SMZ, suppressed denitrification and anammox processes while boosting nitrous oxide (N₂O) emissions. Under the same concentration of antibiotic stress, the addition of high-dose Cu induced a shift in the microbial community: it reduced microbial diversity and increased the abundance of dominant phyla such as Proteobacteria.

Microbial co-occurrence networks were far more susceptible to the effects of DC and CIP than to SMZ. Antioxidant enzyme activities and malondialdehyde levels showed pollutant-specific responses, which varied according to both Cu dosage and antibiotic type. Low-dose Cu was found to enhance the multifunctionality of wetland ecosystems, but this positive effect was negated under high copper stress—particularly when combined with DC.

These findings highlight that the persistent co-accumulation of heavy metals and antibiotics can simultaneously alter the structure, ecological processes and multifunctionality of wetland ecosystems. They also underscore that such impacts are directly linked to Cu concentration and antibiotic type.

Recently published in Journal of Environmental Management, the study was funded by the National Natural Science Foundation of China and the Hubei Provincial Key Research and Development Program.

A diagram illustrating the pathway by which combined pollutants alter nitrogen transformation and multifunctionality in wetlands. (Image by MA Lin)