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).