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Cryptospondium (part 1 of 2) Page 9 of 13 �•��V Cryptosporidium oocysts have been detected in treated waters in the western United States. These values tend to be low, averaging 0.001 oocysts per liter in filtered waters and 0.006 oocysts per liter in non-�Itered waters. In waterborne outbreaks Cryptosporidium oocyst concentrations in the treated water were much higher than these values. For example, in the Carroiton, Georgia outbreak, treated water oocyst levels were 2.2 per liter. After the outbreak in Milwaukee, treated water oocysts levels reached 0.16 per liter. However, there is significant uncertainty as to how high the leveis were during the outbreak. Outbreaks have been more often associated with filtered waters than unfiltered waters, and usually wfth agricultural (particularly animal wastes) contamination of drinking water sources. In a�itration process, Cryptosporidium oocysts, Giardia cysts, other pathogens and debris are concentrated in the filters so that breakthrough of the accumulated material can increase the risk of Cryptosporidium infections. Effectiveness of Water Treatment Processes The two basic mechanisms for eliminating pathogenic organisms during water treatment are: chemical inactivation and physical removal. The former is accomplished through disinfection, and the latter through coagulation and filtration. Disinfection Chlorine is not effective for inactivating Cryptosporidium oocysts. It has been reported that oocysts exposed to undiluted household bleach (5% NaOCI) for several hours were still capable of inducing infection. Chlorine dioxide appears to be effective, but at doses far higher than would be reasonable in water treatment, especially in light of the concern over the chlorine dioxide by-products chlorite and chlorate. Ozone is effective for inactivating Cryptosporidium but requires Ct values 10 to 20 times greater than for Giardia. Ultraviolet light is effective at inactivating Cryptosporidium though at very high doses. Ct values for various disinfectants against Cryptosporidium and Giardia are presented in Table 1.3,2z,24,s4 5equential use of these disinfectants, however, results in synergestic effects. Tab/e 1 Comparative Ct Va/ues for Parasites �-�� Ct Product -, Disinfectant � Giardia Cryptosporidium Chloramine 1,230 14,400 Chlorine 80 14,400 Chlorine Dioxide 15 � 160 Ozone 0.95 5 to 10 1. Assume 2-logs inactivation and 10 2. Units in mg/I-min. Even though ozone appears to be effective for Cryptosporidium inactivation, there is a http://sfwater.org/printContent.cfin/C_ID/446/ 10/19/2004