Sodium hypochlorite (NaOCl) in the form of laundry bleach is available in most households. The concentrate is about 5.25 to 6 percent NaOCl, and the pH value is about 12. Sodium hypochlorite is stable for many months at this high alkaline pH value.
"Laundry bleach is commonly diluted about 10 to 25-fold with tap water to about 2000 to 5000 parts per million of free available chlorine for use as an environmental surface disinfectant, without regard to the pH value of the diluted bleach. However, the pH value is very important for the antimicrobial effectiveness of bleach," says Norman Miner, a researcher on the study.
At alkaline pH values of about 8.5 or higher, more than 90 percent of the bleach is in the form of the chlorite ion (OCl-), which is relatively ineffective antimicrobially. At acidic pH values of about 6.8 or lower, more than 80 percent of the bleach is in the form of hypochlorite (HOCl). HOCl is about 80 to 200 times more antimicrobial than OCl-.
"Bleach is a much more effective antimicrobial chemical at an acidic pH value than at the alkaline Ph value at which bleach is manufactured and stored. A small amount of household vinegar is sufficient to lower the pH of bleach to an acidic range," says Miner.
Miner and his colleagues compared the ability of alkaline (pH 11) and acidified (pH 6) bleach dilutions to disinfect surfaces contaminated with dried bacterial spores, considered the most resistant to disinfectants of all microbes. The alkaline dilution was practically ineffective, killing all of the spores on only 2.5 percent of the surfaces after 20 minutes. During the same time period the acidified solution killed all of the spores on all of the surfaces.
"Diluted bleach at an alkaline pH is a relatively poor disinfectant, but acidified diluted bleach will virtually kill anything in 10 to 20 minutes," says Miner. "In the event of an emergency involving Bacillus anthracis spores contaminating such environmental surfaces as counter tops, desk and table tops, and floors, for example, virtually every household has a sporicidal sterilant available in the form of diluted, acidified bleach."
Miner recommends first diluting one cup of household bleach in one gallon of water and then adding one cup of white vinegar.
MicroChem Lab can be found online at www.microchemlab.net
The American Society for Microbiology (ASM) is the largest single life science society, composed of over 42,000 scientists, teachers, physicians, and health professionals. Its mission is to promote research and training in the microbiological sciences and to assist communication between scientists, policymakers, and the public to improve health, economic well-being, and the environment.
Further information on the ASM Biodefense Research Meeting can be found online at www.asmbiodefense.org.
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.