Grantee Research Project Results
2004 Progress Report: Pathogen Transport and Fate During Subsurface Infiltration: Integrated Laboratory and Field Study
EPA Grant Number: R829013Title: Pathogen Transport and Fate During Subsurface Infiltration: Integrated Laboratory and Field Study
Investigators: Brusseau, Mark , Gerba, Charles P.
Current Investigators: Brusseau, Mark , Gerba, Charles P. , Blanford, William
Institution: University of Arizona
EPA Project Officer: Page, Angela
Project Period: September 1, 2001 through August 31, 2004 (Extended to August 31, 2005)
Project Period Covered by this Report: September 1, 2003 through August 31, 2004
Project Amount: $519,725
RFA: Drinking Water (2000) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
The potential exposure of humans to pathogens in potable water supplies is a significant human health issue. One of the major factors influencing exposure risk is the transport and fate behavior of the pathogens in subsurface systems. A review of the literature shows that limited research has been performed on the subsurface transport and fate behavior of Cryptosporidium parvum oocysts, Giardia muris cysts, and Microsporidium Encephalitozoon intestinales spores. In addition, Cryptosporidium and Microsporidium have been shown to be resistant to chlorination, which is the primary water treatment method in the United States. Thus, although these pathogens are found in the environment, the processes that control their transport and fate from surface waters into groundwater are poorly understood.
The overall objective of this research project is to examine the transport and fate of C. parvum oocysts, G. muris cysts, and Microsporidium E. intestinales spores during subsurface infiltration (e.g. riverbank filtration, effluent recharge). The specific objectives are to:
- investigate processes influencing transport and fate of the target pathogens in model systems;
- investigate the transport and fate of target pathogens under the unsaturated conditions present during water infiltration events;
- and investigate the transport and fate of the target pathogens in a field system.
Progress Summary:
During the past year, we have conducted a series of miscible-displacement experiments with Cryptosporidium oocysts and Giardiacysts. These experiments were conducted similarly to the prior studies with Microsporidium intestinales and MS-2 coliphage. Preparation for the experiment begins with the uniform dry-packing of the column with a well-characterized, low organic matter sand or sandy soil. The column is saturated with a 0.005 N NaCl electrolyte solution. Pentafluorobenzoic acid is used as a conservative tracer to characterize the hydrodynamic properties of the packed column. Solutions containing the selected pathogen are then injected into the column, and the effluent is sampled and analyzed. Several porous media, with different mean grain diameters and grain-size distributions, were used to help investigate the role of straining on retention of the pathogens.
The results reveal that a large fraction of the spores pumped through the column were not recovered in the effluent, suggesting removal through processes such as filtration (e.g., “irreversible” attachment) and straining. The recoveries for Cryptosporidium and Giardia were significantly less than those observed for Microsporidium and MS-2. This indicates the likely impact of straining on retention of the larger pathogens. In addition, recoveries were greater for experiments conducted using a porous medium with a larger mean grain diameter compared to those obtained for experiments conducted with a smaller mean grain diameter medium. Additional experiments will be conducted to further clarify the impact of straining on retention.
It is suspected that accumulation at air-water interfaces may influence the retention and transport of pathogens in unsaturated porous media. In such cases, knowledge of the magnitude of available air-water interfacial area is critical for predicting transport behavior. This remains, however, a difficult property to quantify. We have conducted a series of gas-phase partitioning tracer tests to measure air-water interfacial areas as a function of water content for several porous media. With this data, we have developed a set of correlation equations that can be used to estimate air-water interfacial areas with knowledge of specific surface area and uniformity coefficient (grain-size distribution) of the porous medium.
We have continued work on a mathematical model to describe pathogen transport and fate in porous media. The model is being designed to incorporate multiple processes specific to pathogen transport, including rate-limited attachment-detachment, surface blockage, straining, accumulation at the air-water interface (for unsaturated conditions), and inactivation. Continuous-distribution functions are being used for attachment to account for soil-surface heterogeneity and inactivation, and to account for intra-population variability. The model has been used successfully to simulate the transport behavior observed for the pathogen miscible-displacement experiments noted above.
Future Activities:
We will continue the miscible-displacement experiments for the target pathogens. These experiments will be used to characterize the primary mechanisms influencing the retention and transport of the pathogens. We also will conduct a field experiment to examine pathogen retention and transport under more natural conditions. We will complete development and testing of the mathematical model. The model will be used to simulate the results obtained from the miscible-displacement experiments, as well as selected data sets collected from the literature.
Two presentations will be given at the upcoming national meeting of the American Geophysical Union in December 2004.
Journal Articles:
No journal articles submitted with this report: View all 9 publications for this projectSupplemental Keywords:
exposure, risk, risk assessment, health effects, ecological effects, human health, bioavailability, drinking water, watersheds, groundwater, land, soil, recharge, filtration, exposure and effects, human exposure, human health effects, human health risk, ecosystem protection, environmental exposure and risk, ecology, pathogens, infiltration, vadose zone, waste, water, environmental chemistry, fate and transport, groundwater remediation, hydrology, physical processes, Giardia, chlorination, Cryptosporidium, drinking water contaminants, drinking water treatment, Microsporidium, Encephalitozoon, Encephalitozoon intestinales, microbial risk assessment, mobility, modeling, monitoring, riverbank filtration, treatment, health, physical aspects, ecology and ecosystems, health risk assessment, microsporidia,, RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Health Risk Assessment, Fate & Transport, Risk Assessments, Physical Processes, Ecological Risk Assessment, Ecology and Ecosystems, Drinking Water, Groundwater remediation, monitoring, fate and transport, pathogens, microbial risk assessment, encephalitozoon, human health effects, chlorination, exposure and effects, other - risk assessment, exposure, modeling, cryptosporidium , encephalitozoon intestinalis, treatment, infiltration, human exposure, mobility, water quality, drinking water contaminants, drinking water treatment, Giardia, microsporidia, human health riskProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.