Rhizodegradation of sulfamethazine and tetracycline and the associated impacts on soil microbial activities
Abstract
The use of sulfamethazine (SLF) and tetracycline (TC) to maintain animal health in swine, poultry or cattle feedlot operations results in significant application of these veterinary pharmaceuticals to the landscape during grazing or manure disposal operations. Drinking water sources contaminated by these veterinary antibiotics have raised public health concern in the US. Recent studies have demonstrated the benefits of using multi-species vegetated buffers to reduce the transport of the veterinary antibiotics. However, the fates of these antibiotics in vegetative buffers and their impact on the rhizosphere microbial activities have not been well documented. A growth chamber study was conducted to investigate the rhizodegradation of 3H-sulfamethazine and 3H- tetracycline and the relationship of degradation with soil enzyme activities in the rhizosphere of five selected plant species. The plant species included: 1) switchgrass, 2) eastern gammagrass, 3) orchardgrass, and 4) hybrid poplar. All plant treatments were grown in pots containing Mexico silt loam. Pots containing soil without plants were used as controls. Plants were grown to maturity ([approximately] 3 months), and the rhizosphere soils were collected. Radio-labelled SLF or TC was then applied to the rhizosphere soils and incubated in the dark for five weeks. Among the plant species, hybrid poplar showed the highest capability for promoting degradation of SLF in the rhizosphere. The significantly higher SLF degradation rates in poplar rhizosphere may have been associated with its high enzymatic activities. When comparing the soil enzymatic activities between the antibiotic treatments, fluorescein diacetate hydrolytic and glucosaminidase enzyme activities were significantly lower in TC treated soils than in SF treated soils. The [beta]_glucosidase activities were similar between the two antibiotics treatments. The hybrid poplar showing high rhizodegradation potential could be incorporated into buffer designs to mitigate the impacts of these two antibiotics in the environment.