Quats: Biological Toxicity
& WET Testing Failures
Protecting the Environment Against Quats
by Melissa John, Aquafix Research Scientist
All of our work here at Aquafix is guided by our mission statement: “Safer water and better lives through pioneering biosciences.” In line with this mission, we have conducted and are continuing to conduct numerous studies involving quaternary ammonium cations (QACs or quats) and their toxicity concerning wastewater microorganisms, in both aerobic and anaerobic processes. Past studies have focused on the impacts of quats on cold temperature shock and recovery, long-term toxicity, acute toxicity, and methane production via anaerobic digestion. Currently, we are concentrating on the toxicity of different quat species in wastewater and their impacts on the environment.
All About Quats
Quats are cationic detergents with antimicrobial properties, making these compounds common in cleaning products. These compounds have a central nitrogen cation with four attached groups; these groups (R groups) are used to classify the quat. Variations in these groups can affect the antimicrobial activity of the quat in terms of dose and effectiveness against microorganisms. Additionally, the length of these attached groups can affect the antimicrobial activity of quats. According to Gerba (2015), methyl group lengths of C12 through C16 typically show the greatest amount of antimicrobial activity.
The positive charge of quats is crucial to their function. It allows them to interact with the negatively charged bacterial cell membrane, puncturing it, and compromising its functionality. This disruption leads to cellular leakage, ultimately resulting in cell death, fulfilling their antimicrobial role.
Figure 1: Quat Structure (Wikidoc, 2024).
Effects of Quats on WWTPs
Figure 2: Mixed Liquor with 0 ppm quat added.
Figure 3: Mixed Liquor with 25 ppm quat added.
While quats are effective in various applications, including medical, industrial, and household cleaning; their use had increased dramatically due to the COVID-19 pandemic (Lu et al., 2024). It is estimated that approximately 75% of quats used end up in sewers and wastewater treatment plants (WWTPs) (Lu et al., 2024). Though some industries have moved away from using cleaning chemicals with “quat” in their descriptions, quats go by many names, making it hard to distinguish whether cleaning solutions have them and if they’ll cause problems for WWTPs down the pipleline. Although degradation of quats occurs in WWTPs, the process is slow and depends on factors such as the chemical structure and concentration of the quat, adsorption to biosolids, and microorganism consortia (Mohapatra et al., 2023). Consequently, quats may be released into the natural environment through wastewater effluent or land application of biosolids. Additionally, since quats serve as antimicrobial agents, they can inhibit WWTP efficacy. Our research indicates that quats can create a more turbid supernatant, hinder BOD removal, and inhibit nitrification, potentially resulting in low-quality effluent.
WET Testing
The release of quats into natural water bodies or low-quality effluent could cause WWTPs to fail their whole effluent toxicity (WET) tests. These tests, mandated by the Clean Water Act under the National Pollutant Discharge Elimination System (NPDES) of the Environmental Protection Agency (EPA), assess the toxicity of wastewater effluent samples. The goal is to ensure that the discharged effluent does not negatively impact aquatic organisms. WET testing involves exposing specific organisms (such as fathead minnows and water fleas) to various concentrations of effluent over specified time intervals to detect toxicity. In Wisconsin, two types of
Figure 4: Fathead minnow, commonly used organism for WET testing in Wisconsin. (United States Fish and Wildlife Service, 2008)
tests are required: acute and chronic. The acute test measures survivability, determining the concentration causing 50% lethality (LC50) over a short period of time (48 or 96 hours); if 50% or more of the organisms die in 100% effluent, the test fails (University of Wisconsin, 2024). The chronic test assesses the concentration affecting growth, development, and reproduction over a longer duration (7 days) to determine at what concentration fecundity is inhibited by 25% (IC25) (University of Wisconsin, 2024). If this concentration is lower than the instream waste concentration (ICW), the test fails.
Quat Effects on Biological Organisms
Quats have been shown to be lethal or inhibit growth in aquatic organisms though “oxidative stress, disruption of cell membrane or molecular defects causing apoptosis and endoplasmic reticulum stress (unfold or misfold of proteins),” either through single quat toxicity or quat mixture toxicity (Mohapatra et al, 2023). Additionally, their net positive charge allows them to strongly bind with negatively charged algal cell walls (Liang et al, 2013). This binding could make algae more sensitive than other aquatic life forms, such as fish or crustaceans, potentially resulting in a bottom-up trophic cascade that limits other aquatic life.
Given these concerns, our ongoing research aims to enhance the understanding of quat toxicity and its environmental impacts. Through this we hope to develop effective strategies to mitigate their adverse effects, including optimizing WWTP to better handle quats, ensuring that we are fulfilling our mission statement.
References
Gerba C. P. (2015). Quaternary ammonium biocides: efficacy in application. Applied and environmental microbiology, 81(2), 464–469. https://doi.org/10.1128/AEM.02633-14
Liang, Z., Ge, F., Zeng, H., Xu, Y., Peng, F., & Wong, M. (2013). Influence of cetyltrimethyl ammonium bromide on nutrient uptake and cell responses of Chlorella vulgaris. Aquatic Toxicology, 138–139, 81-87. https://doi.org/10.1016/j.aquatox.2013.04.010
Lu, Z., Mahony, A. K., Arnold, W. A., Marshall, C. W., & McNamara, P. J. (2024). Quaternary ammonia compounds in disinfectant products: Evaluating the potential for promoting antibiotic resistance and disrupting wastewater treatment plant performance. Environmental Science Advances, 3(2), 208-226. https://doi.org/10.1039/d3va00063j
Mohapatra, S., Yutao, L., Goh, S. G., Ng, C., Luhua, Y., Tran, N. H., & Gin, K. Y. (2023). Quaternary ammonium compounds of emerging concern: Classification, occurrence, fate, toxicity and antimicrobial resistance. Journal of hazardous materials, 445, 130393. https://doi.org/10.1016/j.jhazmat.2022.130393
Raver, D. (2008). Fathead minnow. USFWS National Digital Library. Retrieved August 28, 2024, from https://digitalmedia.fws.gov/digital/collection/natdiglib/id/4588.
Whole Effluent Toxicity (WET) Tests. (n.d.). Southern Lakeshore Watershed, University of Wisconsin–Madison. Retrieved August 6, 2024, from https://www.slh.wisc.edu/environmental/toxicology/whole-effluent-toxicity-tests-wet/#:~:text=What%20is%20a%20WET%20test,to%20estimate%20the%20effluent’s%20toxicity
Wikidoc. (n.d.). Quaternary ammonium cation. Wikidoc. Retrieved August 6, 2024, from https://www.wikidoc.org/index.php/Quaternary_ammonium_cation
Products to Protect Against Quats
CounterQuat
- Mitigate potential upsets and protect bacteria from toxins
- Works against Quats, PAAs, and other cleaning agents
- Great for systems with frequent cleanouts
SmartBOD
- Balanced blend of nutrients to promote flocculation and improve settling
- Great for systems with low or intermittent loading
- Lowers effluent BOD, TSS, ammonia, and phosphorous while reducing bulking
Microanalysis & Filament Origins Test Kit
- Identification of major and minor filaments
- Precise explanation of filament presence and origin
- Treatment and process recommendations
About the Author
Melissa John is a Research Scientist for Aquafix and holds a bachelor’s in environmental sciences. Melissa is the newest member to the Aquafix lab team and has been familiarizing herself to wastewater microscopy.