An initial screening of antibiotic effects on microbial respiration in wetland soils

Antibiotics are biologically active compounds that are routinely detected in the environment and usually associated with treated wastewater discharge. Due to their high biological activity, antibiotics may have more environmental impacts than other pharmaceuticals. Wetlands are often used to treat or polish wastewater, with the goals of reducing nutrient and carbon loading into the environment. Nitrogen and carbon processing in wetlands is largely associated with microbial activity, however impacts to microbial activity due to antibiotic loading into treatment wetlands is relatively unknown. Two wetland soils (mineral and peat) were individually spiked with ciprofloxacin, sulfamethoxazole or tetracycline ranging from 1-1000 ppb to examine effects on microbial mediated evolution of CH4, CO2 and N-2. The antibiotics both positively and negatively affected microbial respiration (a proxy for microbial activity) rates in the two wetland soils depending on soil properties and concentration. Sulfamethoxazole reduced CO2 and N2O respiration rates at higher concentrations (500, 1000 ppb) in the mineral soil. However, the CO2 rates recovered within 48 hours, while N2O suppression continued through the end of the incubation. Ciprofloxacin and sulfamethoxazole also demonstrated the ability to suppress respiration at low spiking concentrations (1, 50 ppb) for several treatments. The results demonstrate the ability of antibiotics to impact soil respiration at environmentally relevant concentrations. Parameters that appear to affect the impacts of antibiotics were sorption, length of exposure and soil carbon content. Future studies are needed to provide further insight into antibiotic effects to microbial community structure.