Improving bleach's bug-killing potential


Researchers from MicroChem Lab, Inc in Euless, Texas have found that adding vinegar to standard bleach will enormously enhance its killing potential.

Sodium hypochlorite (NaOCl) in the form of laundry bleach is available in most households. The concentrate is about 5.25 to 6% 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 2,000 to 5,000 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.

At alkaline pH values of about 8.5 or higher, more than 90% 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% of the bleach is in the form of hypochlorite (HOCl). HOCl is about 80 to 200 times more antimicrobial than OCl-.
A small amount of household vinegar is sufficient to lower the pH of bleach to an acidic range.

Researchers 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% of the surfaces after 20 minutes. During the same time period the acidified solution killed all of the spores on all of the surfaces.

Recipe for killer bleach: 1 cup bleach to 1 gallon water, with the addition of 1 cup vinegar.

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First Published in July 2009

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