Biocides and the S520

April 9, 2008
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Q: Why does the IICRC S520 Mold Remediation Standard forbid the use of biocides?

A: The S520 (First Edition) does not prohibit the use of biocides on mold-remediation projects. Rather, it discusses the limitations of what the application of such products can accomplish. Because of these limitations, it was decided that the physical removal of molds is a more effective approach.

Section 4.4 of the Standard states:

(Principles: Contamination Removal)
“Physically removing mold contamination is the primary means of remediation. It is highly recommended that mold contamination be physically removed from the structure, systems and contents to return them to Condition 1 status. Attempts to kill or encapsulate mold generally are not adequate to solve the contamination problem.”


The principles of biocide use endorsed by the S520 are drawn directly from “ACGIH Bioaerosols: Assessment and Control.”

(Chapter 10 of the Reference Guide, page 119)
“15.2 Remediators must carefully consider the necessity or advisability of applying biocides … The goal of remediation programs should be removal of all microbial growth. This generally can be accomplished by physical removal of materials supporting active growth and thorough cleaning of non-porous materials. Therefore, application of a biocide would serve no purpose that could not be accomplished with a detergent or cleaning agent.”

“16.2 Biocide use should not be considered if careful and controlled removal of contaminated materials is sufficient to address a problem.”

“16.2.4 Biocide application is not recommended in the restoration of water-damaged indoor environments except where they have suffered extensive sewage backup. Widespread pollution from raw sewage represents a significant health risk from a variety of infectious agents, and biocides may help to control and contain these agents during the restoration process…”


In addition to the above comments quoted in the S520, “Bioaerosols: Assessment and Control” goes on to state that:

15.4 Remediators must carefully consider the necessity and advisability of applying biocides when cleaning microbially contaminated surfaces [see 16.2.3]. The goal of remediation programs should be removal of all microbial growth. This generally can be accomplished by physical removal of materials supporting active growth and thorough cleaning of non-porous materials. Therefore, application of a biocide would serve no purpose that could not be accomplished with a detergent or cleaning agent.

Consistent with these principles, the S520 discourages the use of biocides. Chapter 7 of the Reference Guide, page 82, states, “Biocide application is discouraged and is not considered effective for mold remediation.” However, the S520 also recognizes that, “there may be specific instances where professional judgment dictates that biocides be applied.” The Reference Guide goes on to discuss situations where deviation from removal processes might be appropriate, stating:

“The Principles of Mold Remediation (Sections 4.3 and 4.4 of this Standard) state that mold must be controlled at its source. Further, it is highly recommended that mold be physically removed during remediation, and that attempts to kill or encapsulate it are inadequate remediation measures. At the same time, these principles recognize that unique circumstances may arise and that biocides and encapsulants may be considered in specific situations.”

Nowhere in the S520 does it state that biocide use is never appropriate. Rather, in agreement with “ACGIH Bioaerosols: Assessment and Control,” it recognizes the fact that biocides are not effective at solving mold contamination problems and requires physical removal of contaminants. It leaves the door open for biocide use in unusual situations, on a case-by-case basis.

So when would biocide use be appropriate on a mold-remediation project? Killing mold only eliminates its ability to grow in or on a host. There remains the possibility of allergic and toxigenic reactions to the exposure to dead molds. In order for molds to colonize a human host, it generally requires that the individual’s immune system not be functioning competently. While the application of a biocide to remediated surfaces may not be effective, there might be a desire to attempt to kill those molds that might be potentially pathogenic. Most molds found in contaminated buildings are not pathogenic.

In a recent article entitled “Effect of plasterboard composition on Stachybotrys chartarum growth and biological activity on spores” (Murtoneimi, T et al Applied Environmental Microbiology), it was noted that, “Spores collected from all wallboards exhibited cytotoxicity to macrophages. Biocide application did not reduce fungal growth; however, spores collected from biocide treated board exhibited the highest degree of cytotoxicity.” The implication is that biocide-treated drywall with Stachybotrys chartarum growth was more toxic that if it had not been treated with a biocide. In addition, the mold spores were still viable. Additional research is needed to determine whether the application of a biocide to mold growth triggers mycotoxin production as a defense mechanism.

In addition, there is some belief that biocide application on Category 1 water projects might be appropriate as a preventative against other microbial growth. The primary purpose of such an application is to control bacterial growth when drying is delayed, with the possibility of limiting mold germination and growth. Since the purpose is not to deal with existing mold contamination but rather to prevent it, such use in no way contradicts the S520. In a case where a property has been subjected to a Category 3 water intrusion and there is a subsequent mold problem, it would be appropriate to apply biocides for the purpose of remediating the concurrent bacterial problem.

The viewpoints presented in this article are my personal opinions and not an official position of the IICRC, the IICRC S520 Standard Committee or the S520 Edit Committee. (Note: At the time of writing this response, the IICRC has not yet released the S520 Standard and Reference Guide for Professional Mold Remediation (Second Edition) and therefore, my responses are based upon the S520 (First Edition).

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