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Papers by Daniel Snow

Environmental Science & Technology, Mar 24, 2020

$Research paper thumbnail of Concomitant uptake of antimicrobials and \u3ci\u3eSalmonella\u3c/i\u3e in soil and into lettuce following wastewater irrigation$

The use of wastewater for irrigation may introduce antimicrobials and human pathogens into the fo... more The use of wastewater for irrigation may introduce antimicrobials and human pathogens into the food supply through vegetative uptake. The objective of this study was to investigate the uptake of three antimicrobials and Salmonella in two lettuce cultivars. After repeated subirrigation with synthetic wastewater, lettuce leaves and soil were collected at three sequential harvests. The internalization frequency of Salmonella in lettuce was low. A soil horizon-influenced Salmonella concentration gradient was determined with concentrations in bottom soil 2 log CFU/g higher than in top soil. Lincomycin and sulfamethoxazole were recovered from lettuce leaves at concentrations as high as 822 ng/g and 125 ng/g fresh weight, respectively. Antimicrobial concentrations in lettuce decreased from the first to the third harvest suggesting that the plant growth rate may exceed antimicrobial uptake rates. Accumulation of antimicrobials was significantly different between cultivars demonstrating a su...

The Science of the total environment, Jan 3, 2017

Agriculturally-dominated waterways such as those found throughout the Midwestern United States of... more Agriculturally-dominated waterways such as those found throughout the Midwestern United States often experience seasonal pulses of agrichemical contaminants which pose a potential hazard to aquatic organisms at varying life stages. The objective of this study was to characterize the developmental plasticity of fathead minnow larvae in a natural environment subject to a seasonal episodic perturbation in the form of a complex mixture of agricultural stressors. Fathead minnow larvae were maintained at the Elkhorn River Research Station for a 28-d in situ exposure to an agrichemical pulse event. Minnow larvae were sampled after 14 and 28days to characterize developmental plasticity through growth measures and relative gene expression. Concentrations of agrichemical contaminants measured in water using polar organic chemical integrative samplers and composite sediment samples throughout the 28-d exposure were quantified using gas chromatography-mass spectrometry. Elevated concentrations ...

Journal of hazardous materials, Jan 27, 2016

Although several abiotic processes have been reported that can transform antibiotics, little is k... more Although several abiotic processes have been reported that can transform antibiotics, little is known about whether and how microbiological processes may degrade antibiotics in the environment. This work isolated one tetracycline degrading bacterial strain, Stenotrophomonas maltophilia strain DT1, and characterized the biotransformation of tetracycline by DT1 under various environmental conditions. The biotransformation rate was the highest when the initial pH was 9 and the reaction temperature was at 30°C, and can be described using the Michaelis-Menten model under different initial tetracycline concentrations. When additional substrate was present, the substrate that caused increased biomass resulted in a decreased biotransformation rate of tetracycline. According to disk diffusion tests, the biotransformation products of tetracycline had lower antibiotic potency than the parent compound. Six possible biotransformation products were identified, and a potential biotransformation pa...

Journal of Environmental Quality, 2016

Journal of Environmental Quality, 2015

Environmental pollution (Barking, Essex : 1987), 2015

The Science of the total environment, 2013

Among the conventional disposal methods for livestock mortalities, on-farm burial is a preferred ... more Among the conventional disposal methods for livestock mortalities, on-farm burial is a preferred method, but the potential water quality impacts of animal carcass burial are not well understood. Typically, on-farm burial pits are constructed without liners and any leachate produced may infiltrate into soil and groundwater. To date, no information is available on temporal trends for contaminants in leachate produced from livestock mortality pits. In our study, we examined the concentrations of conventional contaminants including electrical conductivity, COD, TOC, TKN, TP, and solids, as well as veterinary antimicrobials and steroid hormones in leachate over a period of 20 months. Most of the contaminants were detected in leachate after 50 days of decomposition, reaching a peak concentration at approximately 200 days and declined to baseline levels by 400 days. The estrogen 17β-estradiol and a veterinary antimicrobial, monensin, were observed at maximum concentrations of 20,069 ng/L a...