Transport of Cryptosporidium parvum oocysts through disparate agricultural soils

The presence of Cryptosporidium parvum oocysts in source waters is a cause of major public health concern for drinking-water treatment plants. The oocysts occurring in the feces of livestock can be disseminated horizontally via runoff during storm events and contaminate surface waters. Soils are often the initial barrier to subsurface transport of Cryptosporidium parvum oocysts which receive oocyst-laden manure from grazing livestock. However, rainfall events can cause rapid vertical movement of oocysts through preferential flow paths in the soils leading to ground water contamination. A systematic study was undertaken to assess the efficacy of three disparate agricultural soils (two tropical, variable-charge soils of volcanic origin from Hawaii and a humic, quartz-rich temperate soil from Illinois) to remove Cryptosporidium parvum oocysts and oocyst-sized microspheres in batch and flow-through columns.;To test the effect of soil mineralogy on oocysts transport, saturated flow-through column experiments were conducted by packing the three agricultural soils and injecting oocysts and microspheres. The results showed that oocysts were transported through preferential flow paths in high-clay, high-iron tropical soil from Hawaii and humic-rich quartz dominated temperate soil from Illinois. Transport through volcanic-ash soil collected from the island of Hawaii was highly reversible because of high soil organic matter content.;The effects of dissolved organic carbon (DOC) on oocysts and microspheres transport through these soils were assessed in a subsequent phase of this study. DOC in form of natural organic matter enhanced the removal of oocyst-sized colloids (microspheres and oocysts), whereas surfactants lowered the removal efficiency of oocysts and microspheres. The transport potentials of oocysts and microspheres were affected differentially by the physicochemical properties of the soils. Whereas oocysts transport was more strongly affected by soil mineralogy, microspheres transport was much more sensitive to the nature of DOC.