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Title: INFLUENCE OF SOIL TYPE AND BOVINE MANURE ON FATE AND TRANSPORT OF CRYPTOSPORIDIUM PARVUM OOCYSTS IN SOIL

Author
item ROUHI, S - N VA SOIL/WATER CONS DIST
item KUCZYNSKA, EWA - USDA/FAS
item SHELTON, DANIEL

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2000
Publication Date: 12/1/2000
Citation: N/A

Interpretive Summary: Cryptosporidium parvum is a widespread protozoan parasite afflicting numerous mammalian species, including humans. Several outbreaks of cryptosporidiosis have occurred in the past decade, the most severe in Milwaukee, WI where over 400,000 people were infected C. parvum is a particularly serious health threat to immuno-deficient individuals (e.g., AIDS, cancer patients) because there are no effective treatments for the disease. An important mode of transmission to humans is believed to be via contaminated drinking water or recreational waters. Beef/dairy animals are widely believed to be a major source of contamination because of their numbers and distribution, incidence of infection, and extent of oocyst excretion. Potential mechanisms of water contamination include surface transport of oocysts from land-applied manures or fecal excretion, or vertical transport via preferential flow to groundwater. These studies were econducted to assess oocyst decomposition rates in soils and to investigate variables affecting vertical transport. Experiments were conducted with packed soil cores to simulate tilled soil. Results indicate that the rates and extent of oocyst leaching are dependent on the interactive effects of manure, soil structure, water infiltration, and time. In general, oocysts do not appear to be readily transported through tilled soils.

Technical Abstract: Experiments were conducted to assess C. parvum oocyst decomposition rates in soils and to investigate variables affecting transport. Oocyst recoveries decreased rapidly with time in loam and sandy loam soils, indicating that oocysts decompose. Attempts to estimate decomposition rates were complicated by adhesion of oocysts to soil particles. Data from mpacked soil cores (simulating tilled soil) indicate that rates/extent of oocyst leaching are dependent on the interactive effects of manure, soil structure, water flux (infiltration), and time. Negligible oocyst leaching was observed with purified oocysts. Bovine manure enhanced oocyst transport; the extent of transport was, in decreasing order: coarse sand, loam, sandy loam. Manure simultaneously inhibited water flux by occluding soil pores; the extent of inhibition was dependent on soil structure. To simulate field drainage conditions, a slight suction was applied to some cores. Suction resulted in higher water fluxes in sandy loam and loam cores. An inverse relationship was observed between water flux and oocysts leached in sandy loam and loam cores. Analysis of oocyst distributions in cores revealed that greater oocyst infiltration into the core profile occurred under suction conditions; in the absence of suction, the majority of oocysts remained near the soil surface. Oocysts leached decreased approximately exponentially on consecutive days after application. These studies indicate that oocysts are not readily transported through tilled soils.