Chloroxylenol, a widely used disinfectant worldwide, has been associated with ecotoxicological hazards in aquatic environments due to its relatively high chemical stability and indiscriminate use. Scientists from the Faculty of Engineering at the Hong Kong University of Science and Technology (HKUST) have discovered a promising alternative known as 2,6-dichlorobenzoquinone (2,6-DCQ), which works more effectively against some common bacteria, fungi and viruses and can be rapidly degraded and detoxified in receiving waters.

This groundbreaking study is led by Prof. ZHANG Xiangru from the Department of Civil and Environmental Engineering at HKUST, who has been studying disinfection byproducts (DBPs) for many years. During the outbreak, Prof. Zhang noticed that chlorooxylenol is structurally similar to some halophenol DBPs previously discovered by his team, which have been shown to degrade rapidly by solar photolysis.

Inspired by the structural properties and degradability of some halophenolic DBPs, the research team was able to select an effective broad-spectrum disinfectant among DBPs that could be rapidly degraded and detoxified in receiving waters. The research team tested the efficacy of 10 different DBPs in inactivating various pathogens, including E. coli (a type of bacteria associated with colon cancer), Staphylococcus aureus (bacteria), Candida albicans (fungi), and bacteriophage MS2 (viruses). They found that 2,6-DCQ was 9 to 22 times more effective than chloroxylenol in inactivating these bacteria, fungi, and viruses.

In addition, they found that the developmental toxicity of 2,6-DCQ to marine polychaete embryos declined rapidly due to its rapid degradation by hydrolysis in seawater, even in the absence of sunlight. Two days after release into seawater, 2,6-DCQ showed 31 times lower developmental toxicity compared to chlorooxylenol.

“We found that the selected DBP showed significantly stronger antimicrobial efficacy than chloroxylenol, and its concentration and associated developmental toxicity in seawater decreased rapidly, even in the dark,” said Prof. Zhang.

He stressed the urgent need for more effective and eco-friendly disinfectants, especially in the face of the COVID-19 pandemic. “Chloroxylenol has been frequently detected in aquatic environments; for example, its concentration reached up to 10.6 μg/L in river water in Hong Kong. Toxicological studies have shown adverse effects of chlorooxylenol on aquatic organisms, including endocrine disruption, embryo mortality, and developmental defects. Chronic exposure to chlorooxylenol at environmental concentrations (~4.2 μg/L) can cause gene regulation and morphological changes in rainbow trout.”

The team’s discovery of 2,6-DCQ as a promising alternative is an important step toward meeting this global need. The results suggest that 2,6-DCQ could be used as a disinfectant in a wide range of applications, including personal care products (such as hand washes, detergents, and soaps), paints, textiles, metalworking fluids, medical scrubs, as well as household sanitation, food processing equipment, surgical instruments, and public spaces.

“This innovative study not only provides a potential solution to better support human biosecurity while prioritizing environmental sustainability, but also has important implications for the development of green disinfectants and other green industrial products by exploiting the slightly alkaline nature of seawater. For example, scientists can design and develop other industrial products, such as pesticides, pharmaceuticals, and personal care products, that can be rapidly degraded by hydrolysis in seawater,” explained Prof. Zhang.

The results of their research were published in a prestigious interdisciplinary journal Nature communicationThe research team included Dr. HAN Jiarui, currently a research assistant professor at HKUST, and Dr. LI Wanxin, currently an assistant professor at Xi’an Jiaotong-Liverpool University. Both are PhD graduates from the Department of Civil and Environmental Engineering at HKUST and were postdoctoral fellows in Prof. Zhang’s group during the study.

Looking ahead, Prof. Zhang plans to investigate the relationships between disinfection efficiency and degradability of halophenols with their molecular fingerprints using machine learning. He hopes that future studies will shed light on the further development of optimal disinfectants.