Cleaning Chemicals for Biohazard Cleanup
By Cole Barnett, (ASU Bio-Engineering Student & AZ-BIO Fall 2020 Intern)
At AZ-Bio, we utilize a variety of chemicals, solutions, and mixtures to effectively clean and disinfect the wide range of situations we come up against. This report/article aims to explain the scientific mechanisms as well as the safety aspects of the primary active ingredients in the chemicals we use. These include bleach, benzalkonium chloride, thymol, hydrogen peroxide, alcohol, and various surfactants.
Understanding the chemistry of how and why surfactants work is crucial to understanding the processes that many of these chemicals use to kill the bacteria, viruses, and fungi that are harmful to humans which we want to kill in our cleaning processes.
Most molecules can be described as being either polar or nonpolar; these two types of molecules do not like to mix at all. Oil and water is a classic example of this phenomenon. No matter how much one stirs or attempts to mix the two liquids, they will always separate back into being two distinct liquids because oil is nonpolar and water is polar. Polar molecules can mix with other polar molecules, as can nonpolar with nonpolar, but they normally will not mix with each other. Another word used to indicate polar properties is hydrophilic (meaning water-loving since it will mix with water), and another word to indicate nonpolar properties is hydrophobic (meaning water-fearing). Examples of hydrophilic substances include those that will dissolve in water such as sugar or salt. On the other hand, oil, grease, wax, and gasoline are examples of hydrophobic substances that can mix with each other, but not with water. (“Chemical Polarity”)
Surfactants are especially useful molecules because they are amphiphilic (meaning both-loving) and have both polar and nonpolar parts. This means they can break down the barrier between polar and nonpolar substances so that they may begin to mix together with the surfactant as the mediator (“Surfactant”). This is why when one’s hands are greasy with oil from an engine or from fatty food, no matter how much it is scrubbed with water, one always needs soap to get it off.
Soap is a common surfactant that will have the nonpolar side…
…of its molecules stick to the oil on one’s hands, and when they are put under running water, the polar side of the soap molecules will stick to the water and drag the oil along with it off the hands, leaving the hands clean. This is why Dawn dish soap is one of the cleaning supplies we utilize most often because it has the ability to cut through all greases and oils and makes them easy to wash away. All soaps and detergents are surfactants, or a mixture of surfactants, that are often diluted into a cleaning solution (“Detergent”). Surfactants are the main ingredient in grease-cutting cleaning supplies like Krud Kutter, and they are commonly found in all-purpose disinfectants to help clean up oils (“Safety Data Sheet – Krud Kutter”, Section 3).
The common alcohols ethanol and isopropyl alcohol are examples of amphiphilic molecules that can mix in both water (like in alcoholic drinks) and oils (like in gasoline which is commonly sold as containing 10% ethanol). In fact, since these alcohols are very readily available, safe to use, and have disinfectant properties of their own, they are used in some of our cleaning products to dissolve oils like thymol into the product. (“Ethanol”, “Isopropyl alcohol”).
Special Cleaning Chemicals for Biohazard Cleanup
The molecule 2-isopropyl-5-methylphenol, also known as thymol, is isolated from the oil of the common thyme plant. It kills bacteria, viruses, and fungi by interacting with their cells’ plasma membrane, which is highly crucial to their survival. This cell membrane has both polar and nonpolar layers, which means that neither hydrophilic nor hydrophobic substances can pass through it. This makes it extremely effective in keeping unwanted molecules outside of the cell and keeping cell components inside the cell. Thymol has some surfactant-like properties that enable it to infiltrate the membrane. By disrupting the natural state of this crucial membrane which separates the inside of bacteria, viruses, and fungal cells from the outside, it causes holes in the membrane to form, which in turn causes them to leak their vital organelles and proteins outside their bodies, effectively killing them (Xu et al., par. 7).
Thymol is unique among the chemicals we use because it is completely natural in its origin and it is almost completely non-toxic to humans and environments. It is rated by the EPA as safe to use on food surfaces (“Bioesque Botanical Disinfectant”) and to use without gloves or other PPE (“BotaniClean Disinfectant”).
Listed on many household all-purpose cleaners and disinfectants as alkyldimethyl- benzylammonium chloride, but known more succinctly as benzalkonium chloride, this molecule works similarly to thymol to kill bacteria, viruses, and fungi by disrupting the cell membranes. Unlike thymol, however, this molecule is charged, which makes it even more powerful in its ability to make holes in the membranes and kill harmful microorganisms (“Benzalkonium chloride”). This comes at a cost, though, because this chemical is dangerous to aquatic life, can cause skin irritation, and can be damaging if the eyes are exposed to it (“Safety Data Sheet – Shockwave”).
The active ingredient in this common household cleaner is sodium hypochlorite, and although this molecule itself is not very useful, it breaks down to release chlorine which is an extremely reactive and extremely corrosive disinfecting agent. When chlorine comes into contact with bacteria, viruses, or fungi, it reacts with their cells to break them down and kill them (“How Bleach Works”).
This makes bleach extremely powerful as a disinfection agent, but also hazardous to humans and dangerous for household surfaces and fabrics. It can burn skin and damage eyes on contact, and the fumes given off by the evaporation of bleach, which include the highly toxic chlorine gas, are dangerous to the nose, lungs, and eyes (“Bleach Fact Sheet”). Bleach may also be dangerous for the environment as chlorine from runoff or residue is able to form hazardous compounds which can persist for long periods of time (“Risk Assessment Report on Sodium Hypochlorite Environmental Part”).
Bleach should also never be mixed with any chemicals containing ammonia (like Windex, Shockwave, CDC-10, or even urine) or any type of acid (like vinegar or muriatic acid). It is usually recommended that one does not mix bleach with any other cleaning chemical because in many cases, bleach will react with the chemical and release chlorine gas directly into the air (“Bleach Fact Sheet”).
Hydrogen Peroxide is another well-known chemical compound that has effective disinfection properties. Its chemical formula is H2O2, not to be confused with the formula for water, H2O. Hydrogen peroxide is very unstable, and it is therefore highly reactive. Upon decomposing in the presence of other materials, it decomposes into an extremely reactive molecule called the hydroxyl radical which will react with and kill bacteria, viruses, and fungi (“Hydrogen peroxide”).
Since hydrogen peroxide is so unstable, it is kept in brown bottles because even light can cause it to decompose into water and oxygen gas. The shelf-life of a bottle of hydrogen peroxide is up to 3 years, but once the bottle is opened, its shelf-life diminishes to a maximum of 6 months, and high temperatures can cause it to break down even sooner (Helmenstine).
Although it may be highly reactive, this chemical is however much safer for the environment and less hazardous to humans than bleach. Unlike bleach, residual or runoff hydrogen peroxide will only break down to form water and oxygen gas which are non toxic byproducts. Hydrogen peroxide is, however, a fire hazard as its reactions can release heat and oxygen gas simultaneously, creating an ideal recipe for a fire and can cause flammable substances to spontaneously combust (“Safety Data Sheet – Hydrogen Peroxide 35%”, Sections 5, 10).
We have written many articles on Biohazard cleanup here on our AZ-BIO Cleanup and Restoration Blogs