[PHNUTR-L] Vinegar increases killing power of bleach

[Kathrynne Holden, MS, RD]

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Public release date: 17-Feb-2006
http://www.eurekalert.org/pub_releases/2006-02/asfm-vik021306.php

Contact: Jim Sliwa
jsliwa at asmusa.org
202-942-9297
American Society for Microbiology

Vinegar increases killing power of bleach

Adding white vinegar to diluted household bleach greatly increases the 
disinfecting power of the solution, making it strong enough to kill even 
bacterial spores. Researchers from MicroChem Lab, Inc. in Euless, Texas, 
report their findings today at the 2006 ASM Biodefense Research Meeting.

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.
-- 
Kathrynne Holden, MS, RD < fivestar at nutritionucanlivewith.com >
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