Disinfection of human enteric viruses in water by copper and silver in combination with low levels of chlorine

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Abstract
The efficacy of copper and silver ions, in combination with low levels of free chlorine (FC), was evaluated for the disinfection of hepatitis A virus (HAV), human rotavirus (HRV), human adenovirus, and poliovirus (PV) in water. HAV and HRV showed little inactivation in all conditions. PV showed more than a 4 log10 titer reduction in the presence of copper and silver combined with 0.5 mg of FC per liter or in the presence of 1 mg of FC per liter alone. Human adenovirus persisted longer than PV with the same treatments, although it persisted significantly less than HRV or HAV. The addition of 700 micrograms of copper and 70 micrograms of silver per liter did not enhance the inactivation rates after the exposure to 0.5 or 0.2 mg of FC per liter, although on some occasions it produced a level of inactivation similar to that induced by a higher dose of FC alone. Virus aggregates were observed in the presence of copper and silver ions, although not in the presence of FC alone. Our data indicate that the use of copper and silver ions in water systems may not provide a reliable alternative to high levels of FC for the disinfection of viral pathogens. Gene probe-based procedures were not adequate to monitor the presence of infectious HAV after disinfection. PV does not appear to be an adequate model viral strain to be used in disinfection studies. Bacteroides fragilis bacteriophages were consistently more resistant to disinfection than PV, suggesting that they would be more suitable indicators, although they survived significantly less than HAV or HRV.