Submitted to: Water Environment Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2002
Publication Date: 3/1/2003
Citation: Darnault, C.G., Garnier, P., Kim, Y.J., Oveson, K.L., Steenhuis, T.S., Parlange, J.Y., Jenkins, M., Ghiorse, W.C., Baveye, P. 2003. Preferential transport of Cryptosporidium parvum oocysts in variable-saturated subsurface environments. Water Environment Research. 75:113-120.
Interpretive Summary: Cryptosporidium parvum (Crypto for short) is a pathogenic microorganism that can cause severe diarrhea, and can be life-threatening to people with impaired immune systems. It is waterborne and has contaminated municipal drinking water systems. The objective of this study was to determine if the transmissive form of Crypto moves through subsoil to groundwater. Vertical columns 18 cm long, one filled with glass beads, and one with an undisturbed soil core were first wetted by artificial rainfall after which Crypto contaminated calf feces was applied to the surface of the columns. After the manure application artificial rainfall was commenced, and the water leaching from the bottom of the columns was collected at particular time intervals. Each sample was assayed for Crypto. Results of the analysis indicated that a percent ranging from 0.1 to 10.4 percent of the oocysts originally applied was recovered in the drainage samples. The numbers of oocysts were, nevertheless, great enough to represent an infectious dose. The results of this study indicated that movement of Crypto through the subsoil may create a risk of groundwater contamination.
Technical Abstract: Oocysts of the protozoan Cryptosporidium parvum, when they contaminate drinking water supplies, can cause outbreaks of cryptosporidiosis, a common waterborne disease. Of the different pathways by which oocysts can occur in drinking water, one has received very little attention to date; because soils are often considered to be perfect filters, the transport of oocysts through the subsoil to groundwater is generally ignored. To evaluate its significance, three series of laboratory experiments investigated subsurface transport of oocysts. Experiment I was carried out in a vertical 18 cm-long column filled either with glass beads or silica sand under conditions known to foster fingered flow. Experiment II involved undisturbed, macroporous soil columns subjected to macropore flow. Experiment III aimed to study the lateral flow on an undisturbed soil block. The columns and soil samples were subjected to artificial rainfall and were allowed to reach steady-state. At that point, feces of contaminated calves were applied at the surface , along with a known amount of KCl to serve as tracer, and rainfall was continued at the same rate. The breakthough of oocysts and Cl-, monitored in the effluent, demonstrated the importance of preferential flow on the transport of oocysts. Peak oocyst concentrations were not appreciably delayed, compared to Cl-, and in some cases, occurred even before the Cl- peak. Recovery rates for oocysts were low, ranging from 0.1 to 10.4 percent of the oocysts originally applied on the columns. However, the numbers of oocysts present in the effluents were still orders of magnitude higher than 10 oocysts, the infectious dose considered by the FDA-CFSAN to be sufficient to cause cryptosporidiosis in healthy adults. These results suggest that the transport of oocysts in the subsurface via preferential flow may create a significant risk of groundwater contamination in some situations.