Submitted to: American Society of Tropical Medicine and Hygiene
Publication Type: Abstract Only
Publication Acceptance Date: 11/28/1999
Publication Date: N/A
Technical Abstract: Cryptosporidium parvum oocysts pose a threat to municipal water supplies. Because their non-point sources are in terrestrial ecosystems data on oocyst inactivation kinetics in soils under variable conditions will improve risk assessment models. The objective of this study was to determine inactivation rates o freshly purified oocysts inoculated into three soil types, a silt clay loam, a silt loam, and a sand loam. Soils were maintained at three water potentials, -0.33, -5, and -15 bars, and incubated at -10, 4, 20, and 30 deg. C. Replicate sentinel chambers contained each soil. The sentinel chambers were designed to equilibrate rapidly with the external environment into which they are placed. Each replicate sentinel chamber was injected with a quantity of distilled water (minus inoculum volume) per each soil water potential, inoculated with 2 million oocyst, and buried in bulk soil corresponding to each water potential. The bulk soil was in plastic containers that were sealed and weighed on a regular schedule to maintain constant water content over the course of the experiment, which was terminated after 156 days. There were three replicate bulk containers per treatment. At several sampling times sentinel chambers were removed from the bulk soil, oocysts were extracted, and assayed for viability with a dye permeability assay. Preliminary statistical analysis of data indcated that the two extreme temperatures, - ff10, and 30 deg. C, and the most negative water potential, -15 bars, significantly incrreased rates of oocyst inactivation. The analysis indicated that inactivation of oocysts was significantly greater in the sand loam than the silt or clay soils.