Stability and bactericidal activity of chlorine solutions

Area of Science:

• Microbiology
• Environmental Science
• Public Health

Background:

• Sodium hypochlorite (household bleach) is a common disinfectant.
• Current recommendations often advise daily preparation of chlorine solutions due to stability concerns.
• Understanding the stability and efficacy of stored chlorine solutions is crucial for effective disinfection practices.

Purpose of the Study:

• To assess the stability of sodium hypochlorite solutions stored for 30 days in various containers.
• To evaluate the efficacy of low-concentration free available chlorine in inactivating specific bacteria.
• To determine optimal storage conditions for maintaining chlorine solution potency.

Main Methods:

• Laboratory study involving dilutions of household bleach (1:100, 1:50, 1:5) in tap or distilled water.
• Storage in different polyethylene containers (translucent, opaque brown) under varying light and air exposure conditions.
• Regular measurement of chlorine concentration and pH over 40 days.
• Assessment of bactericidal activity using the Association of Official Analytical Chemists Use-Dilution Method against Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonella choleraesuis.

Main Results:

• Chlorine concentration retention at 30 days varied significantly by container type and dilution.
• Solutions stored in closed brown containers retained 97%-100% efficacy.
• Solutions in other containers showed lower retention (40%-85%).
• The minimum effective concentration for inactivating test bacteria was 100 ppm.

Conclusions:

• Sodium hypochlorite solutions demonstrate good stability for up to 30 days when stored appropriately.
• Closed brown containers are optimal for preserving chlorine solution efficacy.
• A concentration of 100 ppm free available chlorine is sufficient to inactivate key pathogenic bacteria.