|NORDENHOLT, R - University Of Missouri|
|GOYNE, KEITH - University Of Missouri|
|KREMER, ROBERT - Retired ARS Employee|
|LIN, CHUNG - University Of Missouri|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2015
Publication Date: 3/1/2016
Citation: Nordenholt, R.M., Goyne, K.W., Kremer, R.J., Lin, C.H., Lerch, R.N., Veum, K.S. 2016. Veterinary antibiotic effects on atrazine degradation and soil microorganisms. Journal of Environmental Quality. 45(2):565-575. doi: 10.2134/jeq2015.05.0235.
Interpretive Summary: Veterinary antibiotics (VAs) have been utilized in U.S. animal agriculture for decades to treat and prevent animal illness and promote increased animal growth. Some of the VAs fed to animals remain intact and are present in manure applied to farmland. These biologically active compounds can affect soil microorganisms and may affect the breakdown of other agricultural chemicals in soils, such as the corn herbicide atrazine. In this study, researchers from the University of Missouri and ARS investigated the effect of two VAs (sulfamethazine and oxytetracycline) on atrazine breakdown in soil with and without manure addition. Atrazine breakdown was rapid in soils with only VAs added (no manure) and half of the added atrazine was degraded in only 5 days regardless of the type of VA or its concentration. When manure was added to the soil along with atrazine and the VAs, atrazine degraded more slowly, taking more than 20 days to degrade half of the atrazine. Additional analyses showed that atrazine, manure, and the VAs inhibited growth of some soil microorganisms, but the VAs had a minor affect compared to manure addtition on how fast atrazine breaks down in soil. Overall, the results indicated that the presence of the two VAs used in this study did not alter the fate of atrazine in soils. This work contributes to the growing base of knowledge regarding the effects of VAs on the soil environment and will benefit growers, extension personnel, and agricultural consultants by showing that VA effects on herbicide fate will likely be minor and weed control in manure fields will not be greatly affected.
Technical Abstract: Veterinary antibiotics (VAs) in manure applied to agricultural lands may change agrichemical degradation by altering soil microbial community structure or function. The objectives of this study were to investigate the influence of two VAs, sulfamethazine (SMZ) and oxytetracycline (OTC), on atrazine (ATZ) degradation, soil microbial enzymatic activity, and phospholipid fatty acid (PLFA) markers. Sandy loam soil was amended with and without 5% swine manure (w/w), 0 or 500 µg kg-1 ATZ, and 0, 100, or 1000 µg kg-1 SMZ or OTC and incubated for 96 days. The half-life of ATZ was not significantly affected by VA treatment in the presence or absence of manure. However, the VAs partially inhibited ATZ mineralization in soils without manure (25 – 50% reduction). Manure amendment decreased ATZ degradation by 22%, reduced ATZ mineralization by 50%, and increased the half-life of ATZ by >10 days. The VAs had limited adverse effects on the microbial enzymes ß-glucosidase or dehydrogenase in soils with and without manure. In contrast, manure application stimulated dehydrogenase activity and altered ATZ metabolite profiles. The PLFA markers were reduced by additions of ATZ, manure, OTC, and SMZ; adverse synergistic effects of combined treatments were noted for mycorrhizal fungi and actinomycetes. In this work, VA application altered microbial community structure but the changes did not influence persistence of the ATZ parent compound. The results demonstrate that manure application had a greater effect on ATZ degradation than the VAs, suggesting that OTC and SMZ presence in land applied manure is unlikely to alter ATZ fate within soil.