title: Stability and bactericidal activity of chlorine solutions.
abstract: OBJECTIVE
  To determine the stability of sodium hypochlorite (diluted household bleach) when stored for 30 days in various types of containers and to determine the efficacy of low concentrations of free available chlorine to inactivate test bacteria.
  
  
  METHODS
  Laboratory-based study. Solutions of standard household bleach were prepared using tap water or sterile distilled water at dilutions of 1:100, 1:50, and 1:5. Chlorine concentrations were measured, and then the solutions were placed 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 light or air exposure). Samples for chlorine and pH determinations were taken 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 Pseudomonas 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 closed brown containers to 83% to 85% for the 1:5 dilution stored in closed 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, and the lowest concentration of chlorine that reliably inactivates S aureus, S choleraesuis, and P aeruginosa is 100 ppm.
authors.affiliation: Division of Infectious Diseases, University of North Carolina School of Medicine, Chapel Hill 27599-7030, USA.
authors.forename: W A
authors.initials: WA
authors.lastname: Rutala
authors.forename: E C
authors.initials: EC
authors.lastname: Cole
authors.forename: C A
authors.initials: CA
authors.lastname: Thomann
authors.forename: D J
authors.initials: DJ
authors.lastname: Weber
mesh_terms: D002713:Chlorine / Q000737:chemistry; D004203:Disinfection; D004355:Drug Stability; D004356:Drug Storage; D008826:Microbial Sensitivity Tests; D012973:Sodium Hypochlorite / Q000737:chemistry; D012996:Solutions
chemical_list: D012996:Solutions; D002713:Chlorine; D012973:Sodium Hypochlorite