Which organic contaminants should be paid more attention: Based on an improved health risk assessment framework

The rapid growth of the pharmaceutical and chemical industries has contributed to an escalation in water pollution (Basheer, 2018). Notable pollutants encompass persistent organic pollutants (POPs), endocrine-disrupting compounds (EDCs), and antibiotics. These emerging contaminants exhibit characteristics such as a high degree of harm, widespread sources, concealed risks, environmental persistence, and intricate governance structures (Tang et al., 2021). In numerous regions, emerging contaminants in water sources are detected at concentrations as low as ng/L (Rathi et al., 2021; Wang et al., 2023; ZHAO et al., 2022). These substances have been linked to carcinogenic effects on the human body and can lead to disruptions in the endocrine system, gradual degradation of immune organ functions, a severe decline in reproductive ability, delayed neural tissue behavior, and disrupted development (Chen et al., 2023; Khan et al., 2022; Rasheed et al., 2019). Due to the involvement of various industries and the complexity of the supply chain, it is difficult to develop alternative products and technologies for emerging Contaminants. The governance of these pollutants poses significant challenges, as conventional treatment technologies are not effective in their removal (Gomes et al., 2018; Rosal et al., 2010). These pollutants can accumulate in the human body when consumed in drinking water and are metabolized slowly. Simultaneously, during the disinfection process, disinfectants undergo reactions with natural organic matter, anthropogenic pollutants, and bromides/iodides, giving rise to disinfection by-products (DBPs) (Krasner et al., 2022; Wagner and Plewa, 2017). DBPs exhibit cytotoxic, neurotoxic, mutagenic, genotoxic, carcinogenic, and teratogenic effects (Mazhar et al., 2020). Notably, certain novel DBPs, like halogenated quinones, may possess toxicity levels exceeding those of regulated DBPs, such as haloacetic acids and chloroform, by more than 1000 times (Hu et al., 2020; Wu et al., 2021). This presents a significant risk to human health.

The prioritization of screening for hazardous compounds in drinking water is crucial for effective health risk assessment and management (Zhou et al., 2019). First, they allow regulatory authorities to focus resources on monitoring and managing the most significant threats to water quality. Second, they enable the development of targeted risk assessment strategies for the identified priority pollutants. Third, by regularly updating these lists, authorities can adapt to evolving environmental challenges and emerging contaminants, ensuring that regulations and management practices remain effective in safeguarding water quality and public health.

The United States has been a pioneer in this field, publishing the Federal Government Risk Assessment: Management Process, also known as the “Red Book” by the United States National Research Council (NRC). This guidelines lets out the basic framework for conventional health risk assessment for the U.S. Environmental Protection Agency (USEPA), the Food and Drug Administration (FDA), and the Occupational Safety and Health Administration (OSHA), known as the classic “four-step” risk assessment: hazard identification, exposure assessment, dose-response evaluation, and risk characterization(National Research Council US, 1983). Pollutants are ranked based on their frequency of occurrence, toxicity, and potential for population exposure. Then, a total score is calculated for prioritization (Grimmett and Munch, 2013) To ensure the consistency in hazard identification and dose-response evaluation information for the same compounds, the USEPA created the Integrated Risk Information System (IRIS) in 1985 as a database of possible human health effects caused by compound exposures. Other international organizations and countries have also issued some technical specifications related to health risk assessment, including The World Health Organization (WHO)(Organization, 1978) and The European Union (EU)(Vermeire et al., 1997). Based on the physicochemical properties and toxicity data, the emission, distribution, and exposure level of the compound were inferred, while the risk value was calculated in combination with the toxicity data.

Conventional human health risk assessment model developed by the USEPA, which calculates risk values based on exposure dose and toxic effects, has been applied to the screening of many substances, such as fluoride (Li et al., 2018; Yousefi et al., 2018), heavy metals (Chowdhury et al., 2016; Saha et al., 2017), antibiotics(Sanganyado and Gwenzi, 2019; Shi et al., 2022), and PPCPs(Sharma et al., 2019). Conventional health risk assessment process only considers the toxic effects of compounds on humans. Ma, S. et al. put forward an exposure-activity ratio method, considering both in vitro and in vivo toxic effects as well as the potential harm of future biological effects (Ma et al., 2023). The same is true for the risk assessment framework based on toxicity quotient (Finckh et al., 2022) and comprehensive assessment based on the risk quotient model(Liu et al., 2020). In fact, the risk of a compound to human health is influenced by multiple factors. Antibiotics, for example, can be transferred to human health through (1) direct infection with antibiotics or pathogenic antibiotic resistant bacteria (ARB) and (2) horizontal transfer of antibiotic resistance genes (ARGs)(Zainab et al., 2020). Additionally, numbers of studies (Arnot et al., 2013; Liu et al., 2015; McLachlan et al., 2011; Papa et al., 2018; Wei et al., 2015) have shown that there are complex mechanisms of action when xenobiotics (defined as chemicals to which an organism is exposed that are extrinsic to the normal metabolism of that organism) enter the human body. Differences in the cumulation and metabolic pathways of certain chemicals may lead to changes in the effects of compound toxicity on human health.

Therefore, to evaluate the impact of chemicals on human health, we should not only pay attention to toxicity, but also consider its cumulation and metabolism factors. For antibiotics with low toxicity, it is more necessary to consider the influence of their resistance genes. However, the existing evaluation methods may miss some substances that have a greater impact on human health. To comprehensively assess the effects of mixed pollutants on humans beyond toxicity, this study established an improved health risk assessment framework based on conventional health risk (toxicity) assessment, which quantify (a) accumulation, (b) persistence, and (c) antibiotics resistance at different exposure levels of compounds, thereby developing a prioritization system for drinking water. To verify our ideas, we evaluated drinking water in China with our improved method and compared it with conventional methods. Based on two different screening frameworks, a prioritized list of compounds in Chinese drinking water was proposed based on the screening framework, providing guidance for drinking water regulation and quality improvement.