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 follows the EPA’s Interim Residual Self-Sanitization Protocol # 01-1A and Guidance for Products Adding Residual Efficacy Claims.
It evaluates the residual disinfectant efficacy of antimicrobial products after application to inanimate, nonporous, and non-food contact hard surfaces.
This is the only EPA-approved method that can be used to substantiate a 24-hour residual sanitizer claim. Claims for a shorter or longer duration, should be addressed with the EPA prior to coordinating testing with Microchem Laboratory. Products with this claim are continuously active and can provide efficacy between regular cleaning and disinfection.
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 5 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)
- The product or products (test substance) being evaluated for efficacy along with the method-specified control substance, are tested in quadruple replicate on 1 x 1 inch glass carriers or stainless-steel carriers. EPA currently allows for liquid formulations or spray products. For towelette products, please consult with the EPA in advance.
- Method-specified test microorganisms for the residual sanitization test method include Staphylococcus aureus (ATCC6538) and Klebsiella aerogenes (ATCC 13048), or Klebsiella pneumoniae (ATCC 4352).
- 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 test and control carriers.
- The dry, inoculated carriers are treated with the test substance and control substance and allowed to dry for at least 3 hours or until completely dry at room temperature and ~45-55% relative humidity.
- After the minimum 3-hour dry time, each set of test and control replicates undergo 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 using a standardized Gardco abrasion machine.
- A residual sanitization test requires 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 abrasion and reinoculation wear regimen is complete, the carriers undergo a sanitization (RSS) 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 Study Sponsor’s requested contact time, and then neutralizing it in the appropriate neutralizer. The parallel control carriers are treated in the same manner as in the test carriers.
- To obtain a bacterial residual sanitizer claim, the product(s) should achieve ≥ 3-log reduction in ≤5 minutes when compared to the control-treated test surfaces.
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.
