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

Abstract

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 N₂. 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.

Keywords:

• Wastewater treatment
• denitrification
• sulfamethoxazole
• carbon dioxide

Acknowledgments

Maverick LeBlanc, Ben LeBlanc and Christine VanZomeren are acknowledged for providing hours of assistance preparing and analyzing samples. Funding for this project was provided by a Louisiana State University Board of Regents Grant.