Location: Contaminant Fate and Transport Research2012 Annual Report
1a. Objectives (from AD-416):
Determine the relationships between manure management and populations of human pathogens and antibiotic resistant bacteria (ARB) that result in new recommendations for best management practices (BMPs); Develop effective methods and practices to protect crops from pathogen contamination; Develop management practices to minimize the transport of pathogens (e.g. E. coli O157:H7, Cryptosporidium, enterococcus, Salmonella) from concentrated dairy and beef cattle operations to water resources.
1b. Approach (from AD-416):
Conduct laboratory and field experiments to examine the important biological, chemical, and physical processes affecting the prevalence and distribution of pathogenic and antibiotic resistant bacteria on representative farms in the Santa Ana River watershed. Studies will be conducted at various scales to determine the persistence (survival) of E. coli O157:H7 in its sources on these farms and assess potential factors influencing pathogen survival in the root zone and contamination of leafy greens. Laboratory scale study will be conducted to quantify critical processes influencing the dissemination of pathogens in the watershed by runoff, streams and rivers. Factors influencing the treatment of contaminated surface waters by sand filtration will also be investigated to more fully assess its capabilities and potential weaknesses. Data obtained from these studies will be used to develop best management practices (BMPs) and low cost treatment technologies for immobilization and inactivation of pathogens from concentrated animal feeding operations (CAFOs) to water and food resources.
3. Progress Report:
Mathematical models to simulate the movement of pathogens through aquifers and soils frequently do not consider the significant influence of transients in solution ionic strength (IS) and velocity on pathogen fate. A sophisticated transport model was modified and theory was developed to mechanistically account for the transport, retention, and release of pathogens with transients in IS and velocity. The calibrated model provided a satisfactory description of the observed release behavior for a range of microbe types and sizes. Furthermore, analysis of fitted model parameters indicates that microscopic heterogeneities on the soil and/or microbe played an important role in pathogen interactions, especially for smaller sized microorganisms. This information will be of interest to scientists and engineers concerned with predicting the fate of pathogens in soils and aquifers. Data on E. coli O157:H7 persistence in major fresh produce-growing soils are limited due to the complexity in datasets generated from different environmental variables and bacterial taxa. Using the Ayasdi Iris platform, which employs Topological Data Analysis (TDA) methods, we have reconstructed the relationship structure of E. coli O157:H7 survival in 32 soils (16 organically, 16 conventionally managed soils) from California (CA) and Arizona (AZ) with a multi-resolution output. Here, we constructed our topological data using three E. coli O157, and three non- E. coli O157 strains to test their persistence in typical agricultural soils collected from 3 major fresh produce growing areas of California and Arizona. This information will be of interest to scientists and growers interested in understanding fate and survival of E. coli O157 and non-E. coli O157 in organically and conventionally managed soils.
1. Determining pathogen transport parameters on heterogeneous surfaces. The transport and retention of pathogenic microorganisms are strongly influenced by small scale variations in charge on the surfaces of the soil grains and microbes. A modeling approach was developed to predict pathogen transport parameters on these heterogeneous surfaces. Simulation results demonstrate that microbe transport parameters are complex functions that are sensitive to the size, charge, and amount of heterogeneity on the surfaces, the microbe size, the solution chemistry, and the water velocity. The findings from this study have important implications for predicting microbe transport and retention in soils and aquifers. This information will be of interest to scientists and engineers concerned with pathogen risk assessment and in the development of mitigation approaches.
2. Treatment and removal of contaminants by surface flow constructed wetland. To assess the impacts of seasonal variations and the mechanism of the wetland layout/operations on E. coli populations, we compared the genetic diversity and antibiotic resistance of the bacteria in a surface flow constructed wetlands used for treating swine waste. E. coli was enumerated and their genetic differences from samples collected from the swine house, source water, storage lagoon, storage tank, surface flow constructed wetland environment, and the final effluence using polymerase chain reaction and antibiotics resistant methods. None of the isolates were confirmed as pathogenic E. coli O157, but as other types of E. coli that are not as pathogenic as E. coli O157. Our data showed that most of the E. coli strains were without the toxin genes, but with high distribution of resistant genes. Therefore, the occurrence of E. coli with multiple resistances in the wetland is a matter of great concern due to possible transfer of resistant genes from nonpathogenic to pathogenic strains that may result in increased duration and severity of illness. This information will benefit water quality managers and scientists who are working on different best management strategies for water quality improvement.
Bradford, S.A., Torkzaban, S., Simunek, J. 2011. Modeling colloid transport and retention in saturated porous media under unfavorable attachment conditions. Water Resources Research. 47:W10503. DOI:10.1029/2011WR010812.