A key part of any restoration project is the proper selection, handling and use of disinfecting agents.
Controlling microbial activity — and the odors, health hazards, and secondary damages they can cause — is critical to successful restoration and cleaning.
In this article, the first of two parts, we’ll discuss the two types of disinfectants. In part 2, to be published next month, we’ll discuss the differences between disinfectants and sterilants and conclude with a few thoughts about the significance of dwell time.
Chemists often use long names to describe molecules, so people develop nicknames for them. That's why most of you know “quaternary ammonium chloride“ as “quats.”
The proper name is even longer: Diisobutylphenoxyethoxy ethyl dimethyl benzyl ammonium chloride monohydrate. Some quats are used as fabric softeners and static control agents, but this article addresses quats with antimicrobial effects.
How do quats actually kill microbes? There are several theories, but two are most widely accepted: 1) Quats attack cell membranes causing them to leak, sort of like a chemical pin bursting a germ balloon. 2) Quats disrupt enzymes that are critical to proper cell function. Using a mechanical analogy again, it's like throwing a monkey wrench into gears.
What are some advantages of quats?
Quats are a common active in many institutional and home products, even antiseptics. Advantages include:
- Very low odor
- Low toxicity compared to other actives
- Non-corrosive to metals, doesn't bleach textiles (in contrast to chlorine)
- Broad efficacy (but note that quats don't kill all germs)
- Tolerant of a wide range pH conditions making it versatile
- Can handle some organic soil load before becoming ineffective
- Bacteriostatic and fungistatic properties provide lasting effects that keep killing germs (be aware that if a product label requires re-application after a period of time, it’s likely the stasis or lasting benefits of the product are limited).
Every tool has its limitations and quats are no different. Limitations include:
- Soaps, and surfactants similar to soaps, can easily contaminate quats and inactivate them
- Hard water also inactivates quats, so they may need to be blended with a water conditioning agent
- Some quats are not readily biodegradable
- Quats must be properly diluted to maintain efficacy.
Tip: Beware of over-diluting quats. Some studies show that germs can grow in over-diluted quat solutions. Test strips are available to measure the concentration of ready-to-use quat solutions. This is a great reminder to follow label directions.
Phenol is relatively corrosive and toxic compared to quaternary compounds. Chemists have tinkered with the molecule — creating variations — to limit the molecule's dangerous properties while retaining its germ-killing characteristics. As a result, there are quite a number of phenolic-type disinfectants in the marketplace today.
The key mechanism a phenolic compound uses to kill germs is "denaturation," which is the disruption of a protein's structure.
Germs use enzymes to digest food, grow and reproduce. Enzymes are comprised of proteins as a key part of their biochemical machinery. Denaturing a protein renders it useless to the germ, and the germ can no longer grow or reproduce or digest food. Boiling an egg denatures the egg's proteins, rendering any germs harmless and making the egg easier for us to digest.
Advantages of phenolic disinfectants include:
- Phenols have broad efficacy and kill a number of germs including bacteria, virus, fungi , even tuberculosis, which is a particularly durable bacterium.
- While phenols vary widely in toxicity, one member of this group (thymol) has such low toxicity that it is used in some brands of mouthwash.
- Phenols tend to be more economical than many other disinfectant actives.
Some limitations of phenols include:
- Many versions of phenols are corrosive or irritating to skin and eyes.
- Phenols tend to have a stronger odor than other disinfectant actives.
- Phenols are inactivated by certain detergent compounds and at certain pH levels.
- As always when using an EPA-registered disinfectant, be sure to follow label directions.
Today, either quats or phenols are the primary active ingredient in most antimicrobials used in the restoration and cleaning industries.
There are alternatives. Oxygen-based disinfectants are gaining some ground, and the push for green cleaning options has resulted in the introduction of a number of products that reduce environmental impact.
But for now, quats and phenols remain our most effective tools for disinfecting the restoration job site.
Next month: Part 2: Disinfectants, sterilants and dwell time
Mike Kerner is senior scientist for Legend Brands. Kerner coordinates the development and introduction of Legend Brands chemical products, prepares technical documentation and provides technical support to customers. He has many years of experience as a senior scientist, product implementation manager and analytical chemist prior to joining Legend Brands in 2009. Kerner has an undergraduate degree in chemistry from Benedictine University in Lisle, IL and a master’s degree in chemistry from Purdue University in West Lafayette, IN.