EPA Test Method for Residual Self-Sanitizing Activity of Dried Chemical Residues on Hard, Non-Porous Surfaces

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The residual self-sanitization (RSS) method, EPA Protocol # 01-1A, is the only method which can currently be used to substantiate long-term sanitization claims with the EPA.

It evaluates the residual sanitizing efficacy of antimicrobial products after application to inanimate, nonporous, and non-food contact hard surfaces.

This test method was initially devised by Clorox and submitted to the EPA to support claims for an innovative spray product.

For the residual self-sanitization method, surfaces are inoculated, treated with test product, allowed to dry, and then abraded under alternating wet and dry conditions which are interspersed with several re-inoculations. At the end of the study and at least 24 hours later, the ability of the test surfaces to kill 99.9% of microorganisms within 5 minutes is measured.

Summary of the EPA Residual Sanitization Test Method (Bacterial)
  • Each test substance, as well as a method-specified control substance, is tested in quadruple replicate.
  • Method-specified test microorganisms include S. aureus, and E. aerogenes, or K. pneumoniae.
  • A 48-54 hour culture of the test microorganism, with a minimum of 3 consecutive transfers and supplemented with “organic soil load” is dried onto four 1 x 1 inch glass carriers per test substance tested, as well as a replicate set of controls.
  • Each dry, contaminated carrier is then treated with the test substance and allowed to sit for at least 3 hours at 45-55% relative humidity.
  • After the minimum 3 hour dry time, each set of replicates undergoes a wear and reinoculation regimen, which takes place over 24 hours at room temperature and 45-55% relative humidity, with alternating dry and wet abrasions. Abrasion of the test surface is done by a standardized Gardco abrasion machine.
  • There are a total of 12 alternating wet-dry abrasion cycles and a total of 5 reinoculations, with a minimum of 15 minute rest times after each abrasion and a minimum of 30 minute dry times after each reinoculation.
  • After the set of abrasions and reinoculations are complete, the carriers undergo a sanitization test, performed at least 24 hours after application of the test product.
  • The sanitization test includes inoculating each treated and abraded carrier with test culture, allowing it to sit for the 5 minute method-specified contact time or less, and then neutralizing it in appropriate neutralizer.
  • To be defined as a sanitizer, the test product on the carriers (the dry chemical residual) must reduce the total number of microorganisms by at least 99.9% on the surface.
Strengths of the EPA Residual Sanitization Test Method
  • The method is quantitative allowing for clear pass/fail indication.
  • The method attempts realism by incorporating abrasion (wear) of the test surface as well as re-inoculation over the course of the test.
Weaknesses of the EPA Residual Sanitization Test Method
  • The repeat abrasion portion of the test requires considerable investment in laboratory equipment and considerable technical expertise to be performed correctly and consistently, decreasing the number of laboratories that can undertake the test and increasing the likelihood of lab-to-lab variability.
  • Due to the duration of the study and hundreds of manipulations of the test and control surfaces throughout, variability from replicate to replicate is sometimes observed.

Microchem Laboratory is one of a handful of labs in the world with skill and expertise in this particular method. If you are interested in setting up a study with the lab, simply contact us or request a price quote.