ICS Magazine

Biocides Redefined

April 12, 2007


Q: Has there been a change in the way that IICRC S500 refers to biocides?
A: The simple answer to your question is yes. Prior to the S500 Third Edition, the IICRC S500 Standard and Reference Guide for Professional Water Damage Restoration referred to biocides as chemicals that are used to kill microorganisms and those that retard or suppress growth as antimicrobials (Editor’s Note: the following revisits and updates information originally published in September 2005).

Biocides are sometimes referred to as bactericides or fungicides when they are designed to kill bacteria and fungi, respectively. In addition, antimicrobials are sometimes referred to as bacteriostats or fungistats when they are designed to inhibit growth of bacteria or fungi. If you break down the term biocide into its prefix and suffix, you come up with “bio-,” which means life and “-cide,” which means kill. Therefore, they are life killers. The suffix “-stat” means stasis or static. Often the products referred to as fungistats only inhibit microbial growth and do not necessarily kill fungi. They maintain a static environment.

These definitions are consistent with the American Conference of Governmental Industrial Hygienists (ACGIH) publication entitled Bioaerosols: Assessment and Control. Note the following quotes from this publication:

“Biocides are toxic chemicals or physical agents capable of killing or inactivating one or more groups of microorgan-isms, that is, vegetative bacteria, mycobacteria, or bacterial spores; vegetative fungi or fungal spores; parasites; or vi-ruses.” (16.1.1)

Biocides tend to be aqueous solutions [e.g., alcohols (ethyl, isopropyl), hydrogen peroxide, aldehydes (formaldehyde, glutaraldehyde), phenolic compounds, quaternary ammonium compounds (cationic detergents), halogens (chlorine, iodine, and bromine compounds)]. Biocides are generally aqueous and once they are applied or evaporate, they are no longer effective.

“Antimicrobial agents are chemical formulations incorporated into or applied onto a material or product to suppress vegetative bacterial and fungal growth as it occurs (Table 16.1). Such compounds may be used to retard microbial growth in potential sources. Typically, antimicrobial agents are incorporated into products during manufacture (e.g., carpet material, ceiling tiles, and air filters). Additionally, antimicrobial agents are often included in products (e.g., paints, coatings, and sealants) that are applied to various building and equipment surfaces.” (16.1.2)
“Bacteriostatic agent: chemical agent that suppresses or retards bacterial growth on direct contact with the treated material.
Fungistatic agent: chemical agent that suppresses or retards fungal growth on direct contact with the treated material.” (Table 16.1)


Antimicrobials are often metallic compounds that continue to leave a residue that has prolonged effectiveness. Some are chemically bound so that they can be added as ingredient in paint, plastic or fiber production. Some antimicrobial fibers are used in garments and flooring materials.

In the Third Edition of the S500 it was decided by the S500 Consensus Body to use the United States Environmental Protection Agency’s (USEPA) definitions. The S500 Third Edition Reference Guide makes the following statement:

Definition and Regulation
Antimicrobials are substances used to destroy (biocides) or suppress growth (growth inhibitors/static agents) of microorganisms (i.e., bacteria, viruses, or fungi) on inanimate objects, surfaces, and materials. The United States Environmental Protection Agency (USEPA) Antimicrobials Division registers and regulates antimicrobial products (which the Agency refers to as a pesticide) under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). Some jurisdictions require commercial applicators of antimicrobial products to be licensed, certified, or to be specially trained.

Another well-respected publication has similar definitions as the ACGIH publication, Disinfection, Sterilization, and Preservation by Seymour S. Block. While this book does use similar terms, it also refers to biocides as antimicrobial in several instances. A biocide is defined as “a substance that kills all living organisms, pathogenic or nonpathogenic.” A bacteriostat is defined as “an agent, usually chemical, that prevents the growth of bacteria but does not necessarily kill them or their spores.” Finally, an antimicrobial agent is defined as “any agent that kills or suppresses the growth of microorganisms.”

This last definition is somewhat consistent with the way that the Environmental Protection Agency (EPA) refers to biocides and antimicrobials. Interestingly, the EPA also refers to both biocides and antimicrobials as pesticides. On the EPA Web site under the heading “What are Antimicrobial Pesticides?” it states “Antimicrobial pesticides are substances or mixtures of substances used to destroy or suppress the growth of harmful microorganisms whether bacteria, viruses, or fungi on inanimate objects and surfaces.” In some states you might be required to have a pest control applicator’s license in order to apply these products legally in your customers’ homes.

I understand the desire to change to the EPA terminology. However, the change to the USEPA terminology is going to be confusing to the reader. For example, we will be referring to quaternary ammonium chloride (quats) as a biocide and as an antimicrobial or pesticide.