Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2003
Publication Date: 5/15/2004
Citation: Kato, S., Jenkins, M., Fogarty, E., Bowman, D. 2004. Cryptosporidium parvum oocyst inactivation in field soil and its relation to soil characteristics: Analysis using the geographic information system. Science of the Total Environment. 321:47-58.
Interpretive Summary: Cryptosporidium parvum (Crypto for short) is a pathogenic microorganism that can cause severe and life-threatening diarrhea. One of the sources of Crypto in recreational and municipal drinking waters is dairy farms, and new-borne calves in particular. Managers of municipal watersheds and public health officials, therefore, need to understand how long Crypto can survive in the environment, especially the soil environment of a pasture or field where contaminated manure is spread. A field experiment was established on a dairy farm in western New York on which Crypto was placed in surface soil at 70 sampling points on a grid that included pastured, and corn fields, and uncultivated woodlands. The organisms were tested for their ability to be infective 60 and 120 days after being put into the soil. After 120 days, on the average, 10% of the Crypto remained infective, and in some sampling points as many as 30% of the Crypto remained infective. Soil characteristics such as soil moisture, acidity, organic matter, and temperature were not correlated with Crypto's die-off. Results of this study exemplified the non-uniformity of Crypto's die-off across a landscape, and emphasized the potential of Crypto to survive in large enough numbers in soil that could be transported by rain events to surface waters and, thus, threaten public health.
Technical Abstract: The need exists to understand the environmental parameters that affect inactivation of Cryptosporidium parvum oocysts in soil under field conditions. The inactivation of C. parvum oocysts placed in the natural environment was studied at a dairy farm in western New York State, U.S.A. Seventy sampling points were arranged in a grid with points 150 m apart using the Geographic Information Systems. The sampling points were distributed among three distinct areas: woodland, corn field, and pasture. Purified oocysts were inoculated into chambers filled with soil from each sampling point, and buried in the surface of each respective sampling point. To compare C. parvum oocyst survival with another organism known to survive environmental stresses, Ascaris suum eggs were also placed in soil contained in chambers and buried at the same sampling points as the oocysts. As controls oocysts and eggs in distilled water were also placed at each sampling point. Oocyst and egg viability, soil pH, and percent gravimetric water content were measured at all sampling points at 0, 60, and 120 day sampling periods. Soil organic content was determined for each sampling point. At 120 days after placement, mean viability of C. parvum oocysts was 10% although at a few sampling points, 30% of oocysts were still potentially infective; whereas 90% of A. suum eggs were viable at all sampling points. Statistically significant differences were not observed among the three different sampling areas, and no statistically significant predictors were found by regression analysis. Results exemplified the heterogeneity of soil parameters and oocyst viability across a landscape; such results make predictive models for C. parvum inactivation problematical. The long-term survival of C. parvum oocysts in soil under field conditions, as this study demonstrated, emphasizes their potential as a risk to contaminate surface waters.