AUTHORS: Kutz SM, Landeen LK, Yahya MT, and Gerba CP

PUBLICATION REF: Proceedings of the Fourth Conference on Progress in Clinical Disinfection. State University of New York, Bighamton, New York, April 11-13, 1988

PURPOSE OF STUDY:
Although chlorination is the traditional method of disinfecting swimming pools, hot tubs, and cooling towers to prevent outbreaks of illness due to pathogenic bacteria, viruses, and protozoa, high levels of chlorine can cause eye and skin irritation was well giving rise to a noticeable chlorine odor. The authors evaluated electrolytically generated copper: silver ions alone and in combination with low levels of free chlorine as an alternative method of reducing the bacterial population in water.

MATERIALS AND METHODS:
The test medium was local well water which was subjected to chemical analysis, filtering, and pH stabilization and used at room temperature. Suspensions of the following organisms were prepared: Escherichia coli, Legionella pneumophila, Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella TYPHII, Klebsiella terrigena, and Streptococcus faecalls. Approximately 1 ml of the selected bacterial suspension was added to 99 ml of test medium containing (1) copper: silver ions in a concentration of 400 ug/liter copper to 40 ug/liter silver, (2) free chlorine (0.2 mg/liter) alone, or (3) a combination of copper: silver ions and free chlorine (quantities as above). Cultures were incubated and the bacterial colonies enumerated, after which statistical analysis were performed.

RESULTS:
The bacteria tested were inactivated more rapidly in a solution in which electrolytically generated copper and silver ions were added to low levels of chlorine than where either method was used separately. Some organisms were more resistant to treatment than others. In the experiments with Salmonella typehi and Klebsiella terrigena no viable cells were recovered after 30 seconds of exposure to either chlorine alone or to the combined regimen, indicating equal effectiveness when resistance to disinfection is low. On the other hand, Legionella pneumophilia titers decreased more than 5 log 10 values after 7 minutes of exposure to free chlorine (0.2 mg/liters) alone for the same length of time. Similarly, E. coli numbers were reduced by 4.2 log 10 by the combination regimen but by less than 3 log 10 after extended exposure to the copper: silver method without chlorine.

CONCLUSIONS:
The use of electrolytically generated copper and silver ions in combination with low levels of free chlorine proved an effective method of killing a wide range of pathogenic bacteria under controlled test conditions. Such bacteria are of potential concern in swimming pools and cooling towers.