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Browsing by Author "Hilaire, Sheldon S."

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    Oxytetracycline and Monensin Uptake by Tifton 85 Bermudagrass from Dairy Manure-Applied Soil
    Hilaire, Sheldon S.; Bellows, Barbara; Brady, Jeff A.; Muir, James P. (MDPI, 2020-03-27)
    To address concerns regarding the potential impact of antibiotic use in animal husbandry on antibiotic resistance in humans, we conducted a greenhouse-based study examining uptake of the veterinary antibiotics oxytetracycline (OTC) and monensin (MON) by Tifton 85 Bermudagrass (T85), the most commonly grown forage grass in the southeastern U.S.A. Since oxytetracycline is used in both veterinary and human medicine, its accumulation in animal products could impact human resistance to this antibiotic. Monensin is not used in human medicine but has a high potential for accumulating in the environment. Our research examined antibiotic uptake by forage grass T85, the effect of dairy manure application on its uptake, and antibiotic retention in soil. We compared unspiked, wet dairy manure to wet dairy manure spiked with MON or OTC that was soil surface applied to pots or incorporated into soil. After 6 wk, plant stem/leaf and root tissue, as well as soil samples, were assessed for antibiotic residues using enzyme-linked immunosorbent assay (ELISA). Results confirmed Tifton 85 MON and OTC uptake. Six weeks after adding the antibiotics, the greatest plant matter OTC and MON contents were 157.9 ± 70.6 and 234.4 ± 19.6 µg kg−1, respectively, and 17.6 and 369.5 µg kg−1, respectively, for soil. When spiked with OTC, manure incorporation led to decreased OTC uptake by T85 tissue. Bioaccumulation of these antimicrobials in livestock and in the environment is a potential concern for animal, environmental, and human health.
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    A spectrum of preferential flow alters solute mobility in soils
    Radolinski, Jesse; Le, Hanh; Hilaire, Sheldon S.; Xia, Kang; Scott, Durelle T.; Stewart, Ryan D. (Nature Portfolio, 2022-03-11)
    Preferential flow reduces water residence times and allows rapid transport of pollutants such as organic contaminants. Thus, preferential flow is considered to reduce the influence of soil matrix-solute interactions during solute transport. While this claim may be true when rainfall directly follows solute application, forcing rapid chemical and physical disequilibrium, it has been perpetuated as a general feature of solute transport-regardless of the magnitude preferential flow. A small number of studies have alternatively shown that preferential transport of strongly sorbing solutes is reduced when solutes have time to diffuse and equilibrate within the soil matrix. Here we expand this inference by allowing solute sorption equilibrium to occur and exploring how physiochemical properties affect solute transport across a vast range of preferential flow. We applied deuterium-labeled rainfall to field plots containing manure spiked with eight common antibiotics with a range of affinity for the soil after 7 days of equilibration with the soil matrix and quantified preferential flow and solute transport using 48 soil pore water samplers spread along a hillslope. Based on > 700 measurements, our data showed that solute transport to lysimeters was similar-regardless of antibiotic affinity for soil-when preferential flow represented less than 15% of the total water flow. When preferential flow exceeded 15%, however, concentrations were higher for compounds with relatively low affinity for soil. We provide evidence that (1) bypassing water flow can select for compounds that are more easily released from the soil matrix, and (2) this phenomenon becomes more evident as the magnitude of preferential flow increases. We argue that considering the natural spectrum preferential flow as an explanatory variable to gauge the influence of soil matrix-solute interactions may improve parsimonious transport models.