Understanding the fate of Cryptosporidium and Giardia in storage reservoirs: a legacy of Sydney's water contamination incident

Interaction Forces Drive the Environmental Transmission of Pathogenic Protozoa

“…Their respective settling velocity has been determined according to the Stokes law, taking into account the parasite diameter and its specific gravity ( Table 1). The settling velocity of unattached parasites is relatively low (e.g., 0.35 m s Ϫ1 for Cryptosporidium) (78); however, when attached to particles, the very same parasites settle faster (ϳ1.3 m s Ϫ1 ) mainly due to an increase of the apparent diameter of the objects and of their specific gravity (49,78). These parasites are likely to be associated with fecal or soil particles before entering rivers or water reservoirs, so settling may occur more or less efficiently depending on the size of particles, suggesting that some particle-attached parasites may travel along rivers (35).…”

“…It has been clearly demonstrated that mathematical models for bacteria are not suitable for predicting the fate and transport of parasitic protozoa (17,28,35). In particular, fecal indicators fail to reflect water contamination by Cryptosporidium and Giardia parasites because of the ability of oocysts and cysts to interact and aggregate reversibly with other particles, in contrast to other microorganisms (35,49). Several specific models have been successfully used for estimating protozoan loads in watersheds in some particular contexts (17,28,35).…”

A hydrodynamics-based approach to evaluating the risk of waterborne pathogens entering drinking water intakes in a large, stratified lake

“…8b) and losses due to settling were negligible. The importance of solar radiation for pathogen inactivation found is in contrast to other studies that did not consider the effect of solar radiation on pathogen infectivity (Anderson et al, 1998;Stewart et al, 2002) or those that considered settling to significantly reduce oocyst concentrations in the water column (Medema et al, 1998;Hawkins et al, 2000). Although alpine Lake Tahoe is characterized by high radiation intensities and high water clarity (i.e.…”

Estimating the risk from sewage treatment plant effluent in the Sydney catchment area

“…A further three simulations of hazardous event impacts on gastrointestinal risk are used to illustrate: 1) complete failure of the WFP during dry weather flows; 2) failure of Lake Burragorang as a barrier, caused by the short circuiting of flood waters comparable to the 1998 incident (e.g. Hawkins et al 2000 andCox et al 2003); and 3) concurrent STP bypass and high short circuiting flows. STP performance data were collected in two ways.…”

“…Lake Burragorang catchment (9,050 km 2 ) receives treated effluent from eight STPs (exceeding 600 EP) along with run-off from urban, agricultural and forested areas (Hawkins et al 2000). After heavy rainfall in 1998, elevated levels of Cryptosporidium oocysts and Giardia cysts were detected within the raw and filter water supply.…”