|
Title: Association of Cryptosporidium with bovine faecal particles and implictions for risk reduction by settling within water supply reservoirs. Authored by: Brookes, J.D., Davies, C., Hipsey, M.R. and Antenucci, J.P. Abstract:
Artificial cow pats were seeded with Cryptosporidium oocysts and subjected to a simulated rainfall event. The runoff from the faecal pat was collected and and different particle size fractions were collected within settling columns by exploiting the size-dependent settling velocities.
Particle size and Cryptosporidium concentration distribution at 10cm below the surface was measured at regular intervals over 24 hours. Initially a large proportion of the total volume of particles belonged to the larger size classes (>17 μm) however, throughout the course of the experiment, there was a sequential loss of the larger size classes from the sampling depth and a predominance of smaller particles (<17 μm) Cryptosporidium concentration at 10cm depth did not change throughout the experiment.
In the second experiment samples were taken from different depths within the settling column. Initially 26% of particles were in the size range 124-492 µm, however, as these large particles settled there was an enrichment at 30 cm after one hour (36.5% - 49.3%). There was a concomitant enrichment of smaller particles near the surface after 1h and 24h. For Pat1 there was no difference in Cryptosporidium concentration with depth after 1h and 24h. In Pat2 there was a difference in concentration between the surface and 30 cm after 24h, however, this could be explained by the settling velocity of a single oocyst. The results suggested that oocysts are not associated with large particles, but exist in faecal runoff as single oocysts and hence have a low (0.1m day-1) settling velocity. The implications of this low settling velocity on Cryptosporidium risk reduction within water supply reservoirs was investigated through application of a three-dimensional model of oocyst fate and transport to a moderately sized reservoir (26 GL). The model indicated that the role of settling on oocyst concentration reduction within the water column is between one and three orders of magnitude less than that caused by advection and dilution depending on the strength of hydrodynamic forcing.
Reference: Brookes, J.D., Davies, C., Hipsey, M.R. and Antenucci, J.P., 2006, Association of Cryptosporidium with bovine faecal particles and implictions for risk reduction by settling within water supply reservoirs., Journal of Water and Health, , 4 (1): 87-98 Keywords: Cryptosporidium, cow pats, pathogens, oocyst, risk assessment |
Publications options:
Browse by year: |
