Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2002
Publication Date: 10/1/2002
Citation: Bradford, S.A., Schijven, J. Release of Cryptosporidium and Giardia from Dairy Calf Manure: Impact of Solution Salinity. Journal of Environmental Science and Technology. v. 36. p. 3916-3923. Interpretive Summary: Reliable data on the environmental factors which affect the transfer of disease causing microorganisms, such as Giardia and Cryptosporidium (oo)cysts, from animal manure to water are needed to accurately assess and minimize contamination potential to surface and drinking water supplies. Studies were initiated to determine transfer behavior of naturally occurring (oo)cysts from Holstein dairy calf manure to water of various salt contents. Results from the studies indicate that the salt content is an important factor to consider when describing the manure and (oo)cysts release behavior. On the farm, higher release rates for manure and (oo)cysts are anticipated when manure is expose to rain or drinking water (low salt). Conversely, lower release rates for manure and (oo)cysts are expected when manure is exposed to animal urine (high salt). Changes in aqueous manure and (oo)cysts concentrations are also expected during the rainy season. Decreasing concentrations of manure and (oo)cysts are projected with increasing water application duration. A conceptual model to predict the release behavior of manure and (oo)cysts was presented and successfully applied the experimental data.
Technical Abstract: Studies were initiated to determine the release behavior of Cryptosporidium oocysts and Giardia cysts from dairy calf manure to waters of various salinity. Experiments were conducted by sprinkling a particular aqueous solution over a manure disk and collecting the runoff water. Effluent concentrations of manure and (oo)cysts were initially several orders of magnitude below their starting concentration in the manure, after continued application of water the concentrations gradually decreased, and then exhibited persistent concentration tailing. Solution salinity significantly affected the shape and magnitude of the manure and (oo)cyst concentrations curves. Increases in solution salinity tended to decrease the manure and (oo)cyst concentrations at a particular time. This was attributed to a stabilization of manure by compression of the double layer thickness between negatively charged colloidal material in the manure phase. Calculated release efficiencies of the (oo)cysts (relative to manure release) also decreased with increasing solution salinity. Experimental observation indicate that only the surface layer of manure was depleted of finer manure materials and (oo)cysts and that the manure will act as a long-term source of contamination. A conceptual model to describe and predict manure and (oo)cyst release rates and cumulative loading for the various solution salinities was proposed and applied to the experimental data. The calibrated model yielded a reasonable description of the experimental results.