In a recent review published in the Environmental Science and Technology Journal, researchers presented an overview of quaternary ammonium compounds (QACs), highlighting their environmental and human health concerns.
Study: Quaternary Ammonium Compounds: A Chemical Class of Emerging Concern. Image Credit: asiandelight/Shutterstock.com
QACs are chemicals present in a wide array of products, including preservatives, antimicrobials, disinfectants, sanitizers, air fresheners, pesticides, herbicides, hair sprays, hand wash, lotions, body washes, and wipes.
The use of QAC products has especially increased during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak, primarily due to their antimicrobial properties and the ban on active ingredients such as triclosan in body washes enforced by the United States Food and Drug Administration (US FDA) in 2016.
Increased exposure to QAC has multiple effects on the ecosystem and human well-being, which could inform policy-making and encourage using safer alternatives after evaluating their risk-benefit ratios.
About the review
In the present review, researchers summarized existing data on QACs, including their sources, properties, pharmacodynamics, pharmacokinetics, and effects on the environment and humans.
Introduction to QACs: sources and properties
Given the extensive spectrum of applications, exposure to QACs is common, and their effects must be assessed. QAC products, such as cleaners, dispensers, personal care, furniture, clothing, and their use in various settings such as homes, offices, schools, hospitals, and food services, facilitate human exposure via contaminated dust ingestion, aerosolized QAC inhalation, and dermatological absorption.
Environmental sources of QACs include wastewater, biosolids, water, soil, sediments, and food. An individual may be exposed to QAC by touching disinfected hard surfaces, unintended hand-to-mouth contact (enabling the ingestion of QACs in dust and surface residues), or dermal absorption of QACs present on the hand following surface-to-hand contact.
The low hydrophobicity and high solubility in water enable QACs to be abundantly present in wastewater systems and water, and the positive charges on QACs facilitate absorption by anionic solids such as clay mineral compounds that are present in abundance in sediment and soil.
In addition, the low QAC volatility reduces volatilization losses from indoor surfaces, enabling QAC persistence.
The permanent positive charges and nonaqueous phase sorption increase the half-life of QACs, particularly those with longer side chains, in soil.
In addition, QACs can divide into multiple, thin organic film layers on indoor surfaces to be protected from swift heterogeneous oxidative processes.
Adverse effects of QACs on the human and environmental health
QAC exposure can result in acute as well as chronic toxicological effects in vulnerable aquatic organisms such as freshwater and marine/estuarine algae, Daphnia magna, and larval Chironomus tentans (a freshwater midge), Pimephales promelas (a fathead minnow), and Brachydanio rerio (zebrafish).
In humans, excessive exposure to QACs has several dermal, respiratory, reproductive, metabolic, and immunological effects. In addition, QACs can impair mitochondrial function.
Concerning microbes, sublethal concentrations of QAC enhance antimicrobial resistance among Serratia marcescens, Pseudomonas aeruginosa, and Salmonella species through horizontal gene transfer and mutations, increasing lipid production and enhancing the activity of intrinsic features such as spores.
Oral exposure to QACs, where they have moderate bioavailability, subjects them to first-pass metabolism.
QAC compounds form complexes with bile acids via ion pairing and are actively transported to various tissues of the body through organic cation transporters, p-glycoproteins, and thiamine transporters. Subsequently, QACs are eliminated via the fecal route (the main route).
Following inhalation, QACs enter the lungs, which have high bioavailability, bypass hepatic first-pass metabolism, and enter the systemic circulation. In the blood, QACs are plasma protein-bound and have short half-lives due to QAC partitioning to tissues of the heart, kidney, spleen, and lungs.
In the liver, QAC compounds get oxidized by cytochrome P450 (CYP) enzymes and undergo beta-oxidation. Following systemic circulation in the blood and renal filtration and secretion, QACs are eliminated in small amounts in urine.
QAC exposure can cause cutaneous irritation, inflammation, corrosion, and burns. Exposure to QACs in cleaning and disinfection products can increase inflammatory cytokine levels in the lungs and lead to work-associated asthma. In addition, QAC exposure can elevate chronic obstructive pulmonary disease (COPD) development risks.
In animal studies, QAC exposure was immunosuppressive and reduced clinical signs of autoimmunity.
Concerning the reproductive system, exposure to QAC may result in infertility, antagonize the effects of estrogen, decrease ovulation, and increase post-implantation losses among women. In males, QAC may decrease sperm count and motility.
Further, QACs inhibit cholesterol synthesis and mitochondrial oxidative phosphorylation. QAC exposure may also impair embryological development, lead to neural tube defects, and increase embryonic death.
However, the ovicidal, spermicidal, embryocidal, and ovicidal effects have not been reported in mice and must be investigated in humans.
Based on the review findings, QAC compounds, present in a wide variety of products used regularly, can adversely affect the ecosystem and humans.
Further research is required with comprehensive QAC assessments to improve our understanding of QACs, inform policy-making, and re-evaluate and/or revise regulations, addressing the probable consequences of QAC use.