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United States Department of Agriculture

Agricultural Research Service

2008 Annual Report

1a.Objectives (from AD-416)
Detection, quantification, and characterization of pathogen behavior in different environmental matrices; determine inactivation/survival rates and transport characteristics of fecal coliform and pathogens from manure sources to surface or ground water; determine sources of nonpoint fecal pollution at the Santa Ana River Watershed by bacterial source tracking technology; quantify important mechanisms influencing the transport and retention of pathogenic microorganisms in subsurface environments; adapt and improve numerical models for simulating the environmental transport and fate of pathogenic microorganisms; and develop and optimize manure and lagoon water treatment strategies to minimize the transmission of pathogenic microorganisms to food and water resources.

1b.Approach (from AD-416)
Conduct laboratory, lysimeter and field experiments to examine the important physical, chemical, and biological processes affecting the fate and transport of pathogenic microorganisms in manure-soil-water systems. Laboratory studies will determine the important processes and mechanisms affecting pathogen survival. Studies will be conducted at various scales using culture and molecular approaches to investigate pathogen movement in surface water and soil. Measurements of pathogen concentration, soil and environmental conditions will be collected to allow the simulation of pathogen transport. As new information becomes available, existing models will be improved to enhance the prediction of pathogen transport to surface water, ground water, and the environment. Coupling laboratory and field scale experiments with simulation studies, new strategies will be developed to control the movement of pathogenic microorganisms from animal feeding operations to human food and the environment. Research will be conducted in collaboration with the Food Safety Research, WRRC, Albany, CA. 5310-42000-002-00D (5/01).

3.Progress Report
Cell preparation methods influence E. coli D21g surface chemistry and transport in saturated sand The effect of cell preparation methods on the surface chemistry and retention of Escherichia coli D21g was investigated over a range of ionic strength conditions by researchers at the USDA-ARS Salinity Laboratory and the UCR. The cell preparation methods that were considered included filtration and centrifugation (at various speeds and for different durations). For a given ionic strength condition, it was found that cells prepared by filtration were more negatively charged and hydrophobic than cells prepared by centrifugation. Increasing the centrifugation speed (force imposed) or duration produced cells with a higher zeta potential (less negative) and a lower hydrophobicity. Column transport experiments for E. coli D21g were also conducted with ultra pure quartz sand and the same solution chemistries. The first-order retention rate coefficient for E. coli D21g increased with increasing speed and duration of centrifugation, and was lowest in the case of filtered cells. Moreover, the influence of cell preparation method was more pronounced in lower ionic strength solutions. Reuse of CAFO wastewater on agricultural lands Researchers at the USDA-ARS Salinity Laboratory, UCR, and the EPA reviewed our current level of understanding on the environmental impact and sustainability of CAFO wastewater reuse on agricultural lands. Specifically, they address the source, composition, application practices, environmental issues, transport pathways, and potential treatments that are associated with the reuse of CAFO wastewater on agricultural lands. This research is a component of ARS National Program 206 – Manure and ByProduct Utilization, Component 3. The mission of NP 206 is to develop cost-effective management practices, technologies and decision aids that will allow producers to capture the value of manure and other byproducts without degrading environmental quality or posing a threat to human and animal health. Our research addresses the pathogen component of this program: Pathogens and pharmaceutically active compounds in manure can be transmitted to other animals and humans through food supplies and water. Production of fresh fruit and vegetables using manure or irrigating with wastewater could be mechanisms of pathogen transfer. Research is needed to determine survival, transport, and dissemination of manure pathogens and pharmaceutically active compounds in the environment to assess risks to human and animal health and to develop appropriate control measures. Methods for sensitive detection and accurate quantification of pathogens and pharmaceuticals in complex matrices such as manure and soil will be needed.

1. Influence of microbial community diversity on survival of Escherichia coli O157:H7 in Soil. Survival of Escherichia coli O157:H7 in the environment is a major concern to growers and to the safety of fresh produce. The goals of ARS scientists in the Contaminant Fate and Transport Research Unit in Riverside, CA were to assess the effect of microbial community structure and diversity in two soils and determine the influence of microbial diversity on the survival of Escherichia coli O157:H7. Survival of E. coli O157:H7 was higher in sandy and autoclave soils than clay and unautoclave soils. Microbial species diversity was significantly higher in clay soil than sandy soil and this resulted in higher initial decline in population in clay soil than in sandy soil. This was consistent with our hypothesis that soil systems with reduced microbial diversity offer greater opportunities for the survival of pathogenic bacteria such as E. coli O157:H7. Therefore, information on the persistence of E. coli O157:H7 in different soil types is needed for good agronomic practices and understanding of E. coli O157:H7 survival in soil from one growing season to another. This research addresses NP 206, Component 3, problem b.

2. Modeling Microorganism Retention in Porous Media. There is a need for experimental and theoretical work that demonstrats that microorganism retention under unfavorable attachment conditions is highly dependent on the coupled influence of pore space geometry, hydrodynamics, and solution chemistry. Researchers at the USDA-ARS Salinity Laboratory and the University of California Riverside have been using and/or developing computer models to examine and improve our understanding of these factors at the pore and column scales. Pore-scale simulations demonstrated that enhanced microorganism retention occurs in the smallest regions of the pore space that are associated with multiple interfaces and zones of relative flow stagnation (grain-grain contacts and the solid-air-water triple point). A dual permeability model was refined to account for different rates of advective and dispersive transport and first-order colloid retention and release in fast and slow velocity regions of the pore space at the column scale. The developed models have provided a reasonable first approximation of the simulated pore-scale physics, and are providing scientists and engineers with an improved description of observed microorganism transport behavior at larger scales. This information is needed to help protect food and water resources from contamination by pathogenic microorganisms, and to bioremediate hazardous waste sites. The research addresses National Program 206, Component 3, Problem b.

5.Significant Activities that Support Special Target Populations

6.Technology Transfer

Number of Non-Peer Reviewed Presentations and Proceedings6

Review Publications
Bradford, S.A., Torkzaban, S. 2008. Colloid Transport and Retention in Unsaturated Porous Media: A Review of Interface-Collector, and Pore-Scale Processes and Models. Vadose Zone Journal. Vol 7:667-681

Gargiulo, G., Bradford, S.A., Simunek, J., Ustohal, P., Vereecken, H., Klumpp, E. 2008. Bacteria transport and deposition under unsaturated flow conditions: the role of water content and bacteria surface hydrophobicity. Vadose Zone Journal. Vol 7(2):406-419

Ibekwe, A.M., Kennedy, A.C., Halvorson, J.J., Yang, C. 2007. Characterization of developing microbial communities in Mount St. Helen's pyroclastic substrate. Soil Biology and Biochemistry. Vol 39:2496-2507

Ibekwe, A.M., Lyon, S.R. 2008. Microbiological Evaluation of fecal bacterial Composition from surface water through Aquifer Sand Material. Journal of Water and Health. Vol 6 No 3:411-421

Torkzaban, S., Bradford, S.A., Walker, S.L. 2007. Resolving the coupled effects of hydrodynamics and DLVO forces on colloid attachment in porous media. Langmuir. Vol 23:9652-9660

Torksaban, S., Bradford, S.A., Van Genuchten, M.T., Walker, S.L. 2007. Colloid Transport in Unsaturated Porous Media: The Role of Water Content and Ionic Strength on Particle Straining. Journal of Contaminant Hydrology. Vol 96:113-127

Torkzaban, S., Tazehkand, S.S., Walker, S.L., Bradford, S.A. 2008. Transport and Fate of Bacteria in Porous Media: Coupled Effects of Chemical Conditions and Pore Space Geometry. Water Resources Research. Vol 44:1-12

Simunek, J., Bradford, S.A. 2008. Vadose Zone Modeling: Introduction and Importance. Vadose Zone Journal. Vol 7:581-586

Last Modified: 3/28/2015
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