Inactivation of Legionella pneumophila by combined systems of copper and silver ions and free chlorine.
The aim of this study was to evaluate the efficacy of copper and silver ions and of free chlorine in different combinations and concentrations (0.4 to 0.8-0.04 to 0.08 mg/l Cu(2+) Ag(+); 0.4 to 0.8-0.04 to 0.08-0.2 mg/l Cu(2+) Ag(+) Cl; 0.4 to 0.8-0.04 to 0.08-2 mg/l Cu(2+) Ag(+) Cl; 0.4 to 0.8-0.04 to 0.08-4 mg/l Cu(2+) Ag(+) Cl; 2-20 mg/l Cl), in inactivating Legionella pneumophila in drinking and distilled water after a contact time of 24-hours. Treatment with chlorine alone at 20 mg/l concentration was found to be the most effective treatment leading to complete killing of bacteria within 4 minutes in all water samples. On the other hand, at 2 mg/l concentration complete inactivation was obtained after 3 hours. The association of copper and silver ions at concentrations of 0.4-0.04 mg/l was found to be less effective and live bacteria could still be identified in all water samples after a 24 hour contact time. When testing copper and silver ions in combination, at concentrations of 0.8-0.08 mg/l and different combinations of the three disinfectants, results varied according to the various concentrations and type of water. The combination of copper and silver with 2 mg/l of chlorine was found to be more effective than 2mg/l of chlorine alone; a synergistic effect can therefore be hypothesized. The physical and chemical properties of drinking water, in particular its chlorine content, may have affected the water disinfection process when disinfecting agents were used in low concentrations. In conclusion, this study confirms the efficacy of shock hyperchlorination in the inactivation of Legionella pneumophila. However, the combination of free chlorine with metal (copper and silver) ions may represent a valid option for reducing the concentration of disinfectants to safer levels for human health and avoiding damage to water distribution systems especially in facilities such as hotels and hospitals.
Pianetti
Anna
A
Toxicological, Hygienic and Environmental Sciences Institute, University of Urbino Carlo Bo, Urbino, Italy. anna.pianetti@uniurb.it
Sabatini
Luigia
L
Citterio
Barbara
B
Sisti
Elivio
E
Pierfelici
Lucia
L
Bruscolini
Francesca
F
D002713:Chlorine / Q000494:pharmacology*; D003300:Copper / Q000494:pharmacology*; D004203:Disinfection / Q000379:methods*; D006801:Humans; D007477:Ions; D016952:Legionella pneumophila / Q000187:drug effects*; D012834:Silver / Q000494:pharmacology*; D013997:Time Factors; D014871:Water Microbiology; D014881:Water Supply
D007477:Ions; D012834:Silver; D002713:Chlorine; D003300:Copper