title: Effect of various environmental factors on the viability of Cryptosporidium parvum oocysts.
abstract: OBJECTIVE
  To evaluate individual and combined effects of temperature (4, 18 and 25 degrees C), pH (7 and 10), ammonia (5 and 50 mg l(-1)) and exposure time (1, 2, 4 and 6 days) on the viability of Cryptosporidium parvum oocysts in water.
  
  
  RESULTS
  The viability of oocysts was evaluated using the fluorogenic vital dyes assay (4',6-diamidino-2-phenylindole and propidium iodide). All the factors analysed (temperature, pH, ammonia and exposure time) and their interaction were statistically significant (P < 0.005). Exposure of oocysts to pH 10 for 6 days at 25 degrees C reduced oocyst viability from approximately 80% to 51%. Similarly, the exposure of C. parvum oocysts to 5 mg NH(3) l(-1) and 50 mg NH(3) l(-1) for 4 days reduced their viability from between approximately 80% to 41.5% and 14.8%, respectively.
  
  
  CONCLUSIONS
  The interaction between pH, temperature and exposure time may have adverse effects on the survival of C. parvum oocysts in water. Low concentrations of ammonia, as commonly found in alga-based wastewater systems, over a long period of time can produce high C. parvum oocyst inactivation rates.
  
  
  CONCLUSIONS
  This study provides relevant data on the inactivation of C. parvum oocysts in alga-based wastewater-treatment systems in the northwest of Spain.
authors.affiliation: Environmental Research Institute, University of León, León, Spain. rreit@unileon.es
authors.forename: R
authors.initials: R
authors.lastname: Reinoso
authors.forename: E
authors.initials: E
authors.lastname: Becares
authors.forename: H V
authors.initials: HV
authors.lastname: Smith
mesh_terms: D000641:Ammonia; D000818:Animals; D002470:Cell Survival; D016785:Cryptosporidium parvum / Q000502:physiology*; D004202:Disinfectants; D006863:Hydrogen-Ion Concentration; D033661:Oocysts; D013030:Spain; D013696:Temperature; D013995:Time; D014871:Water Microbiology; D018508:Water Purification / Q000379:methods*
chemical_list: D004202:Disinfectants; D000641:Ammonia