Grantee Research Project Results
Final 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. , 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 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, cryptospordium and microsporidium have been shown to be resistant to chlorination, which is the primary water treatment method in the U.S. 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 goal of the proposed research is to examine the transport and fate of Cryptosporidium parvum oocysts, Giardia muris cysts, and Microsporidium Encephalitozoon intestinales spores during movement through subsurface environments. The specific objectives are:
- Investigate the processes influencing transport and fate of the target pathogens in natural soil materials.
- Investigate the transport and fate of the target pathogens under variably saturated conditions.
- Investigate the transport and fate of the target pathogens in a field system.
- Develop and test a multi-process mathematical model for simulating transport of pathogens in porous media.
Summary/Accomplishments (Outputs/Outcomes):
The retention and transport of microsporidium Encephalitozoon intestinales spores in two water-saturated sandy porous media was investigated in this study. The initial breakthrough of the spores in the column effluent occurred essentially simultaneously with that of a non-reactive tracer, indicating no significant velocity enhancement. A large fraction (45-73%) of the spores injected into the columns was not recovered in the effluent, indicating removal from solution through colloid retention processes of attachment and/or straining. The relative significance of attachment and straining to total retention was evaluated in additional experiments. An experiment was conducted with a sieved coarse fraction of porous media for which straining is unlikely to be of significance based on the relative diameters of the spores and porous-medium pores. The spore recovery for this experiment was similar to the recoveries obtained for microsporidia transport in the unsieved parent porous medium. An additional experiment was conducted with a subsample of the coarse fraction that was acid-washed to reduce potential surface attachment sites. Spore recovery was complete for this experiment. These results suggest surface deposition was the primary removal mechanism in our system. This conclusion is supported by the results of an experiment wherein deionized water was flushed through a column that was previously flushed with electrolyte solution. The effluent spore concentrations were observed to increase upon injection of deionized water, indicating re-mobilization of spores upon a change in water chemistry. The measured data was successfully simulated using a mathematical model incorporating colloid filtration. The results of this study suggest that the transport of microspordia in sandy porous media is governed by established colloid-transport processes. See publication #1 for more information.
The role of straining and deposition in the retention and transport of Cryptosporidium parvum oocysts in natural soils was examined in this study. A series of miscible-displacement experiments were conducted using two sandy soils and a model sand that differed in physicochemical properties. A coarse sieved fraction of one of the soils (Vinton) was used to further investigate retention mechanisms. Less than 1% of the oocysts injected into the columns packed with finer soil were recovered in the effluent, indicating significant removal from solution through attachment and/or straining. The recovery was higher (10-33%) for the experiments conducted with the coarser media. The transport of Cryptosporidium was compared to that of two other protozoa, Giardia lambia and Microsporidium Encephalitozoon intestinales. Effluent recoveries correlated inversely with the size of the microorganism. The relative significance of attachment and straining to total retention of Cryptosporidium was evaluated in supplementary experiments where the retention by deposition was minimized by using one of the following experimental conditions for the original and coarse-sieved Vinton media: a zero ionic strength background solution, base/acid washed soil, or reduced hydraulic residence time. For all three treatments, oocyst recoveries were similar to the baseline experiments for both the original and coarse-sieved Vinton media. These results suggest that straining was the primary removal mechanism for these soils. See publication #6 for more information.
We have conducted a series of experiments to examine the retention and transport behavior of cryptosporidium oocysts and giardia cysts in natural sandy soils under variably saturated conditions, such as that associated with waste water application to land (wastewater recharge). One set of studies employed large columns (1, 2 meters). Recoveries of both pathogens were less than 1%. A controlled field study was conducted using a large in-situ lysimeter facility. The recovery of cryposporidium oocysts was again less than 1%. This work is described in manuscripts #7 and #8, which are in review and in preparation, respectively.
Considerably more research has been conducted on virus transport in comparison to that of protozoa. Thus, we have conducted experiments with bacteriophage PRD-1 and MS-2 to establish data sets with which to evaluate and compare the observed protozoa transport behavior. For example, for a common soil and similar conditions, the recoveries during miscible-displacement experiments for bacteriophage were higher than those for the three protozoa. Based on these and other results, bacteriophage may be expected generally to exhibit more conservative transport behavior in comparison to the three protozoa. This suggests that environmental land use controls (e.g., setback distances for well-head protection) designed based upon virus transport behavior may be sufficient for giardia, cryptosporidia, and microsporidia. See publications #2, #4, and #5 for more information.
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. However, this remains 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. This information should be useful for helping to predict retention behavior of pathogens. See publication #3 for more information.
We have developed a mathematical model to describe pathogen transport and fate in porous media. The model was 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 rate functions were used for attachment/detachment, to account for soil-surface heterogeneity and for intra-population variability of surface properties. The model has been used successfully to simulate the transport behavior observed for the pathogen miscible-displacement experiments noted above. This work is described in manuscripts #9 and #10, which are in the final stages of preparation.
In summary, in this project we have examined the transport behavior of Cryptosporidium parvum oocysts, Giardia cysts, and Microsporidium Encephalitozoon intestinales spores in natural soil materials under both saturated and variably saturated conditions. The results indicate that the transport of all three pathogens is significantly influenced by retention processes, including attachment/detachment and straining. Straining appears to be of particular importance for Cryptosporidium and Giardia. All three protozoa exhibit greater retention than that of commonly studied bacteriophage. We have developed a multi-process mathematical model to simulate the transport of microorganisms in geochemically heterogeneous porous media. The information generated from this study will help improve our understanding of protozoa transport in subsurface environments.
Journal Articles on this Report : 5 Displayed | Download in RIS Format
Other project views: | All 9 publications | 5 publications in selected types | All 5 journal articles |
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Blanford WJ, Brusseau ML, Yeh TCJ, Gerba CP, Harvey R. Influence of water chemistry and travel distance on bacteriophage PRD-1 transport in a sandy aquifer. Water Research 2005;39(11):2345-2357. |
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Brusseau ML, Oleen JK, Santamaria J, Cheng L, Orosz-Coghlan P, Chetochine AS, Blanford WJ, Rykwalder P, Gerba CP. Transport of microsporidium Encephalitozoon intestinales spores in sandy porous media. Water Research 2005;39(15):3636-3642. |
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Cheng L, Chetochine AS, Pepper IL, Brusseau ML. Influence of DOC on MS-2 bacteriophage transport in a sandy soil. Water, Air, and Soil Pollution 2007;178(1-4):315-322. |
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Chetochine AS, Brusseau ML, Gerba CP, Pepper IL. Leaching of phage from Class B biosolids and potential transport through soil. Applied and Environmental Microbiology 2006;72(1):665-671. |
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Peng S, Brusseau ML. Impact of soil texture on air-water interfacial areas in unsaturated sandy porous media. Water Resources Research 2005;41(W03021), doi:10.1029/2004WR003233. |
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Supplemental Keywords:
pathogens, exposure, risk, risk assessment, health effects, ecological effects, human health, bioavailability, drinking water, watersheds, groundwater, land, soil, recharge, filtration,, RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Water, Waste, Ecosystem Protection/Environmental Exposure & Risk, Health Risk Assessment, Environmental Chemistry, Fate & Transport, Risk Assessments, Physical Processes, Ecology and Ecosystems, Ecological Risk Assessment, 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.