Transport of Cryptosporidium parvum oocysts in soil columns following applications of raw and separated liquid slurry

The potential for transport of viable Cryptosporidium parvum oocysts through soil to land drains and groundwater was studied using simulated rainfall and intact soil columns which were applied raw slurry or separated liquid slurry. Following irrigation and weekly samplings over a four week period, C. parvum oocysts were detected from all soil columns regardless of slurry type and application method although recovery rates were low (<1%).

Soil columns with injected liquid slurry leached 73% and 90% more oocysts compared with columns with injected and surface applied raw slurry, respectively. Among leachate samples containing oocysts, 44/72 samples yielded viable oocysts as determined by a dye permeability assay (DAPI/PI) with the majority (41%) of viable oocysts found in leachate from soil columns with added liquid slurry.

The number of viable oocysts was positively correlated (r=0.63) with the total number of oocysts found. Destructively sampling of the soil columns showed that type of slurry and irrigation played a role in the vertical distribution of oocysts, with more oocysts recovered from soil columns added liquid slurry irrespectively of irrigation status.

Further studies are needed to determine the effectiveness of different slurry separation technologies to remove oocysts and other pathogens, as well as whether application of separated liquid slurry to agricultural land may represent higher risks for ground water contamination as compared to application of raw slurry.