EFFICACY OF A COMBINED SYSTEM OF COPPER AND SILVER AND FREE CHLORINE FOR INACTIVATION OF NAEGLERIA-FOWLERI AMEBAS IN WATER

Electrolytically generated copper and silver ions (400:40 and 800:80 mu g/l) were evaluated separately and combined with 1.0 mg/l free chlorine, for their efficacy in reducing the viable numbers of Naegleria fowleri amoebas in water (pH 7.3 and 23-25 degrees C). Inactivation rates (k = log(10) reduction/min) and T-99 values (exposure time required to achieve a 99% or a 2 log(10) reduction) of the disinfectants were determined. Copper and silver alone, at ratio of 400:40 to 800:80 mu g/l caused no significant inactivation of N. fowleri even after 72 hours of exposure (k = 0.00017 and 0.00013, respectively). Addition of 1.0 mg/l free chlorine to water which contained 400:40 or 800:80 mu g/l copper and silver resulted in enhanced inactivation rates (k = 0.458 and 0.515, respectively) compared to either chlorine alone (k = 0.33) or the metals alone. Water containing 800:80 mu g/l copper and silver with 1.0 mg/l chlorine showed a T-99 value of 3.9 minutes, while chlorine alone showed a T-99 of 6.1 minutes. Enhanced inactivation of N. fowleri by a combined system of free chlorine and copper and silver may be attributed to the different mechanism that each disinfectant utilizes in inactivating the amoebas, and may suggest a synergistic effect.