STABILITY AND BACTERICIDAL ACTIVITY OF CHLORINE SOLUTIONS

OBJECTIVES: To determine the stability of sodium hypochlorite (diluted household bleach) when stored for 30 days in various types of contain ers and to determine the efficacy of low concentrations of free availa ble chlorine to inactivate test bacteria. DESIGN: Laboratory-based stu dy. Solutions. of standard household bleach were prepared using tap wa ter or sterile distilled water at dilutions of 1:100, 1:50, and 1:5. C hlorine concentrations were measured, and then the solutions were plac ed into five polyethylene containers and left at room temperature (20 degrees C) under various conditions (translucent containers with light exposure and with or without air; brown opaque container without ligh t or air exposure). Samples for chlorine and pH determinations were ta ken at time 0 and on days 7, 14, 21, 30, and 40. Bactericidal activity of chlorine solutions was assessed using the Association of Official Analytical Chemists Use-Dilution Method. Test bacteria included Pseudo monas aeruginosa, Staphylococcus aureus, and Salmonella choleraesuis. RESULTS: Chlorine concentrations at 30 days varied from the 40% to 50% range for 1:50 or 1:100 dilutions stored in containers other than clo sed brown containers to 83% to 85% for the 1:5 dilution stored in clos ed but non-opaque containers to 97% to 100% for 1:50 or 1:5 solutions stored in closed brown containers. The lowest concentration of sodium hypochlorite solution that reliably inactivated all the test organisms was 100 ppm. CONCLUSIONS: These data suggest that chlorine solutions do not need to be prepared fresh daily, as is recommended currently, a nd the lowest concentration of chlorine that reliably inactivates S au reus, S choleraesuis, and P aeruginosa is 100 ppm (Infect Control Hosp Epidemiol 1998;19:323-327).