Carol Krska, BS, MS Chemical Engineering, Director of Research
To compare and assess the environmental impact of using hypochlorous acid (HOCl) to other commonly used disinfectants, one must consider the feedstock to make the product, the storage, transport, the use of the product, and finally the effluent/end product and appropriate disposal or potential pollution issues.
HOCl is a non-carbon containing aqueous solution made using purified water and a salt, typically common table salt, (sodium chloride (NaCl)). These two materials, along with some electricity and a specialized membrane, create HOCl. Potassium chloride (KCl) can also be used as the salt source. These simple, common ingredients mean making HOCl effectuates a very low environmental impact to produce as the feedstocks are quite easy to procure, store and require little pre-processing. The HOCl solution is a low concentration (in the parts per million) weakly acidic, very near neutral solution that requires no special transport or storage conditions (other than an opaque storage container to prevent exposure to uv light). It can also be made quickly and efficiently, so that excess or limited volumes are not an issue. Thus, potential supply, storage, and supply chain issues are mitigated.
Some other commonly used disinfectant products use chemistries such as quaternary amines, peroxides or bleach. These chemistries are much more complex to manufacture. They are typically made on a large scale in large chemical plants. Quaternary amines are complex multi-carbon-containing organic compounds which require a great number of chemical processing reactions to make. They require pre-processed feedstocks and can also require solvents, higher temperatures or pressures, along with additional purification steps to make. These are a quite industrialized chemical processes, requiring a chemical plant and substantial facilities to produce. Of course, quaternary amine products also have health risks and multiple efficacy issues with their use as disinfectant products Peroxides are also commonly used disinfectant products, with hydrogen peroxides-based products being among the most common. Hydrogen peroxide can be used in a low concentration but is not always effective against all pathogens, particularly some bleaching (paper, sugar, textile, etc.) processes, and it is also used as an agent in producing many other chemicals. It is produced in large scale chemical plants. Because of production methods and chemistry, hydrogen peroxide takes a lot of energy to produce. Unfortunately, approximately half the energy used in the manufacturing process is lost as heat. Much of the hydrogen peroxide is produced outside of the USA. The hydrogen peroxide solution is acidic. The pH can vary, generally between 1 and 5, depending on the manufacturing method and concentration. Also, storage and transport conditions need to be stringently controlled for concentrated solutions.
Bleach (sodium hypochlorite) solutions are commonly used for disinfectant purposes. Bleach is made in industrial chemical processing plants from liquid chlorine and caustic soda (sodium hydroxide). These feedstocks are highly dangerous chemicals to handle and transport, so exceptional care must be implemented to manufacture bleach. Additionally, the feedstocks require a significant amount of energy to produce before being converted into bleach.Most bleach is manufactured for use in industrial chemical applications (textiles, polyvinyl chloride, chemical intermediaries, etc.) Bleach solutions are caustic due to their innate chemistry, and care must be taken when using to avoid exposure to bare skin and to bleach vapors, which can result in breathing difficulties and asthma. Proper storage is crucial, as bleach can have more significant toxic properties as a concentrate. Finally, the disposal of the spent solutions needs to be addressed. HOCl has no special disposal requirements. For many applications, it is used as a mist or electrostatic spray so that a small volume of material is actually used to disinfect a space. In this case, the HOCl present in the solution reacts with the pathogen or decomposes back to water and a very minor amount of salt. HOCl in solution at concentration sufficient for disinfecting is highly compatible with the human skin biome. It's so effective and compatible that it is used in a wide range of medical settings and applications such as to clean wounds, lavage abdominal cavities during surgery, for dental rinse and for eye medicines to name just a few. It's also used in applications such as a rinse for organic produce and to maintain a pathogenfree water for swimming pools in a "salt-water chlorination " system.
Finally, it's used a multitude of veterinary applications like reducing bacteria and virus issues in large chicken houses and dairies and in water systems to eliminate biofilm and kill undesirable pathogens. Should a large volume of the HOCl solution be spilled, no special precautions to protect the environment is needed.
Quaternary amines can present a problem, as their residue is long lasting. The European Union has regulations in place for maximum level of quaternary amines on and in their fresh fruits and vegetables. In the US, there have been publications concerning how to remove quaternary amines from wastewater (usually via sedimentation) to prevent formation of nitrosamines which, according to the FDA, is a potential carcinogenic material. In general, when quaternary amines are used to disinfect surfaces, they should be followed with a rinse. pg. 3 Copyright 2022. Emerald Prairie Health. All Rights Reserved. www.EmeraldPrairieHealth.com 10601 W. 79th Street, Shawnee, KS 66215 Hydrogen peroxide decomposes to water and oxygen, so except for the case of frequent or high volume use (such as mopping floors) which can cause lead to high exposure, there is no longlasting impact with its use in very low concentrations. However, many disinfectant formulations contain more than just hydrogen peroxide and water, so they must be evaluated and assessed on an individual basis for their ultimate final environmental impact. Bleach in concentration sufficient for effective disinfection is a caustic solution which must have extreme care taken when using to not mix with acids or ammonia compounds or risk creating highly toxic chlorine or chloramine gasses. Furthermore, bleach can react with other materials in the water/waste stream to create organo-chloride compounds, including dioxins and furans, which persist long term in the environment and can be harmful to both marine life and soil.
 Block MS, Rowan BG. Hypochlorous Acid: A Review. J Oral Maxillofac Surg. 2020;78(9):1461-1466. doi:10.1016/j.joms.2020.06.029, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7315945/
 Cody, Charles; Martin, N. Ben, USPatent US569629A
 McInnes, Mark, Disinfectant Pros and cons: Hydrogen Peroxide vs. Quats, Cleaning and Maintenance Management, https://www.cmmonline.com/articles/disinfectant-pros-and-cons-hydrogen-peroxide-vs-quats
 CDC, Chemical Disinfectants, Guideline for Disinfection and Sterilization in Healthcare Facilities (2008), /www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html
 Quaternary Ammonium Compounds, Laboratory Animal Medicine (Third Edn.) 2015 https://www.sciencedirect.com/topics/neuroscience/quaternary-ammonium-compounds
 Mollenkamp, Becky, “What is quat binding and why it must be prevented,” Cleanlink magazine, www.cleanlink.com/hs/article/What-Is-Quat-Binding-And-Why-It-Must-Be-Prevented--18491
 Scranton, Alex, “what are quats and why are they on our list,”8 May 2018, https://www.womensvoices.org/2018/05/08/what-are-quats-and-why-are-they-on-our-list/
 Perumal PK, Wand ME, Sutton JM, Bock LJ. Evaluation of the effectiveness of hydrogen-peroxide-based disinfectants on biofilms formed by Gram-negative pathogens. The Journal of Hospital Infection. 2014 Aug;87(4):227-233. DOI: 10.1016/j.jhin.2014.05.004. PMID: 24957804. https://pubmed.ncbi.nlm.nih.gov/24957804/
,Hargreaves, Justin S J; Chung, Young-Min, et al, “Minimizing energy demand and environmental impact for sustainable NH3 and H2O2 production-A perspective on contributions from thermal, electro-, and photo-catalysis, Applied Catalysis A: General, Volume 594, H25 March 2020, 117419, https://www.sciencedirect.com/science/article/pii/S0926860X20300120
 Blog post, https://techiescientist.com/ph-of-hydrogen-peroxide/
 National Center for Biotechnology Information. PubChem Compound Summary for CID 784, Hydrogen peroxide. https://pubchem.ncbi.nlm.nih.gov/compound/Hydrogen-peroxide. Accessed Apr. 25, 2022.
 Pedziwiater, Paulina, et al, “Decomposition of hydrogen peroxide,” University of Technology, Lodz Poland, Acta Innovations, ISSN 2300-5599, no 26: 45-52 https://www.proakademia.eu/gfx/baza_wiedzy/461/nr_26_45- 52_2_2.pdf
 Bach, Julie; Varatharajan, Jenenee, Bleach (Sodium Hypochlorite) Manufacturing Process, https://whatisbleach.weebly.com/manufacturing-process.html
 “Manufacturing Process of Bleach,” Glo writers, https://glowriters.com/manufacturing-processes-ofbleach/#:~:text=The%20raw%20materials%20for%20making%20household%20bleach%20are,salt%2C%20comes% 20from%20either%20mines%20or%20underground%20wells.