Antibiotics and the Terrestrial Nitrogen Cycle: A Review

The distribution, fate, and effects of human and veterinary antibiotics in the environment have been the subject of intense investigation for nearly two decades. Studies show that the structure and function of microbial communities in soil and sediment are modified by antibiotic exposure but the resulting impact on biogeochemical processes is poorly understood. This review summarizes the most recent data on the present use and physicochemical properties of human and veterinary antibiotics and provides an overview of their occurrence in soil and sediment. This is followed by an examination of the potential effects of antibiotics on microbial nitrogen turnover and methodological approaches to measuring the effects of antibiotics on nitrification and denitrification. Recent studies identified six major classes of antibiotics in soil and sediment, occurring at concentrations between ng·kg−1 and mg·kg−1. Among these, tetracycline and fluorquinolone antibiotics are the most resistant to degradation and leaching and may accumulate to high concentrations (mg·kg−1) in terrestrial environments. Less persistent compounds such as the sulfonamides are often detected at lower concentrations (ng·kg−1 to μg·kg−1) but their occurrence is also reported more frequently. Only 26 studies were found that investigated the effects of antibiotics on microbial nitrogen cycling. Some antibiotics had no observable effect on nitrogen redox activity in soil and sediment while others appeared to increase or decrease rates of reaction. This lack of consensus could be attributed to a number of different variables including antibiotic dose, method of antibiotic application, variations in the microbial community structure, or method of quantification. We conclude by recommending that future studies adopt a more comprehensive approach to report on changes of the microbial community structure and function as well as the short- and long-term impacts of antibiotics on the accumulation and loss of nitrogen pollutants.