09/03 - 2015 Excellence in Environmental Engineering and Science Competition Winners

American Academy of Environmental Engineers and Scientists annual competition

2015 Grand Prize - University Research

Influence of Selected Land Application Strategies on the Fate and Transport of Antimicrobials and Antimicrobial Resistance Genes in the Agricultural Environment

Entrant: Department of Civil Engineering University of Nebraska - Lincoln and Agricultural Research Service, US Department of Agriculture.
 Persons in Charge: Xu Li and Shannon Bartelt-Hunt

Entrant Profile

This project was a collaborative effort between the University of Nebraska – Lincoln (UNL) and USDA-Agricultural Research Service (ARS).

Chartered in 1869, UNL is the state's land-grant university. As a public research university, UNL is listed by the Carnegie Foundation within the "Research Universities (very high research activity)" category. ARS is the principal in-house research agency of the USDA. ARS is charged with extending the nation's scientific knowledge and solving agricultural problems affecting Americans every day. ARS has more than 2,200 permanent scientists working on approximately 1,100 projects at more than 100 locations nationally.

Dr. Xu Li, assistant professor in the Department of Civil Engineering at UNL, has studied the fate and transport of antimicrobial resistance genes in agricultural systems, including soil, water, and livestock waste management structure. Dr. Shannon Bartelt-Hunt is an associate professor in the same department and has investigated the fate and transport of antimicrobial compounds in agricultural and municipal systems. Dr. Daniel Snow, director of the UNL Water Sciences Laboratory, has developed several methods for instrumental analysis of veterinary pharmaceuticals associated with livestock wastes.

Dr. John Gilley of ARS has extensive experience in conducting small-scale runoff simulations to evaluate contaminant transport following land application of livestock manures. Dr. Bryan Woodbury is a research agricultural engineer at the U.S. Meat Animal Research Center near Clay Center, NE. His research specialty is livestock waste management.

Stacey Joy and Bhavneet Soni were the graduate students working on the project. David Parker and David Marx also helped with the project.

Complexity of the Problem

Because of its high organic matter and nutrient contents, livestock manure is often land applied as a soil conditioner. Links between the presence of antibiotics and antibiotic resistance genes (ARGs) in livestock manure and the environmental occurrence of these constituents in soil and water are uncertain, due in part to a lack of quantitative studies documenting these links. In addition, little is known about the temporal trends of antibiotics and ARGs in soil following land application of manure and the effects of commonly used agricultural conservation practices on the movement of antibiotics and ARGs in runoff from manure-amended fields. Without this information, it is challenging for livestock producers and environmental engineers to 1) estimate the amount of antibiotics and ARGs remaining in soil over time and 2) predict the loadings of antibiotics and ARGs in agriculture runoff.

Demonstration of a Comprehensive and Integrated Approach

This project focused on antibiotics and ARGs in swine manure. Multiple aspects of manure land application strategies were tested to determine their influences on the fate and transport of antibiotics and ARGs in soil and in runoff. First, three commonly used land application methods (i.e., broadcast, injection, and incorporation) were tested. Then, narrow grass hedges planted immediately downslope from manure-amended land were investigated for their effectiveness to reduce the transport of antibiotics and ARGs in runoff. Finally, the effects of time elapsed between manure application and rainfall was investigated to determine the effects of application timing.

Plot tests were employed in the field to better simulate the real world scenario. With at least three plots for each treatment combination, we were able to test the statistical significance of our findings. Antibiotics and ARGs in both soil and runoff were quantified using state of the art methods. Results were synthesized to provide a comprehensive evaluation of the impacts of various land application strategies on the fate and transport of antibiotics and ARGs in the agricultural environment.

Quality and Importance of This University Research

Pork production is a significant agricultural enterprise in the U.S., with the majority of producers located in the Midwest and North Carolina. This study provides swine producers and environmental engineers with information concerning best management practices for manure land application. Our cumulative related work has resulted in five papers published or accepted for publication in peer-reviewed journals such as Environmental Science and Technology1, Science of the Total Environment2, Journal of Environmental Quality3, and Transaction of the American Society of Agricultural and Biological Engineers4, 5.

Originality and Innovation

Little is known about how commonly used agricultural practices may influence the fate and transport of antibiotics and ARGs in the field. Our study showed that injection and incorporation methods lead to lower total mass of antibiotics and lower levels of ARGs in runoff than did broadcast1. The impacts of the land application methods on the fate of antibiotics in soil depended on the compounds' susceptibility to photodegradation. When manure slurry was stored under anaerobic condition, chlortetracycline and tylosin decayed following first-order reaction kinetics with a half life of 1 day and 10 days, respectively2. The corresponding chlortetracyline and tylosin resistance genes decreased 1 to 3 orders of magnitude in relative abundance over the course of 40 days. Finally, our results show that narrow grass hedges were effective in reducing tylosin and its corresponding resistance gene erm(B) in agricultural runoff3. This project provided new information on the effectiveness of various land application strategies on the fate of antibiotics and ARGs in soil as well as their movement in runoff following land application of swine manure.

This project was built on our previous studies on this topic. In previous studies, we quantified the levels of antibiotics and ARGs in the liquid and solid phases of livestock waste management structures6, and discovered the occurrence of ARGs in extracellular DNA matrices in livestock wastes7.

Project Contribution to Social or Economic Advancement

The project provided key information on the environmental fate and transport of antibiotics and ARGs in soil and runoff following land application of swine manure slurry. This information is critical in developing land application strategies that can be implemented in the field to reduce the potential for public health concern.