An approach for assessing human exposures to chemical mixtures in the environment

A Machine-Learning-Driven Pathophysiology-Based New Approach Method for the Dose-Dependent Assessment of Hazardous Chemical Mixtures and Experimental Validations

Environmental chemicals, such as PFAS, exist as mixtures and are frequently encountered at varying concentrations, which can lead to serious health effects, such as cancer. Therefore, understanding the dose-dependent toxicity of chemical mixtures is essential for health risk assessment. However, comprehensive methods to assess toxicity and identify the mechanisms of these harmful mixtures are currently absent. In this study, the dose-dependent toxicity assessments of chemical mixtures are performed in three methodologically distinct phases. In the first phase, we evaluated our machine-learning method (AI-HNN) and pathophysiology method (CPTM) for predicting toxicity. In the second phase, we integrated AI-HNN and CPTM to establish a comprehensive new approach method (NAM) framework called AI-CPTM that is targeted at refining prediction accuracy and providing a comprehensive understanding of toxicity mechanisms. The third phase involved experimental validations of the AI-CPTM predictions. Initially, we developed binary, multiclass classification, and regression models to predict binary, categorical toxicity, and toxic potencies using nearly a thousand experimental mixtures. This empirical dataset was expanded with assumption-based virtual mixtures, compensating for the lack of experimental data and broadening the scope of the dataset. For comparison, we also developed machine-learning models based on RF, Bagging, AdaBoost, SVR, GB, KR, DT, KN, and Consensus methods. The AI-HNN achieved overall accuracies of over 80%, with the AUC exceeding 90%. In the final phase, we demonstrated the superior performance and predictive capability of AI-CPTM, including for PFAS mixtures and their interaction effects, through rigorous literature and statistical validations, along with experimental dose-response zebrafish-embryo toxicity assays. Overall, the AI-CPTM approach significantly improves upon the limitations of standalone AI models, showing extensive enhancements in identifying toxic chemicals and mixtures and their mechanisms. This study is the first to develop a hybrid NAM that integrates AI with a pathophysiology method to comprehensively predict chemical-mixture toxicity, carcinogenicity, and mechanisms.

Experimental exposure assessment for in vitro cell-based bioassays in 96- and 384-well plates

In vitro cell-based bioassays have great potential for applications in the human health risk assessment of chemicals. The quantification of freely dissolved concentrations (C free) in in vitro assays is essential to generate reliable data for in vitro-to-in vivo extrapolation. Existing methods for the quantification of C free are limited to low-throughput microtiter plates. The present study is a proof of principle for the applicability of a solid-phase microextraction (SPME) method for the determination of C free in the peroxisome proliferator-activated receptor gamma (PPARγ) bioassay run in 384-well plates with 80 µL medium per well. The effect concentrations obtained from 384-well plates were compared with those obtained from 96-well plates in a previous study. Nominal effect concentrations obtained using 96- and 384-well plates agreed with each other within a factor of three, and freely dissolved effect concentrations agreed within a factor of 6.5. The good degree of agreement in the results from both plate formats proves the general applicability of the SPME method for the determination of C free for bioassays in 384-well plates, making the present study a first step toward exposure assessment in high-throughput bioassays.

Evaluation of biochemical, hematological, and genotoxic parameters in mice exposed to individual and combined ethoprophos and cadmium

Environmental contamination by complex mixtures of pesticides and metals is a major health problem in agriculture and industry. In real life scenarios, we are exposed to mixtures of chemicals rather than single chemicals, and therefore it is critical to assess their toxicity. The current work was conducted to assess the toxic effects of a low dose (2% median lethal dose) of ethoprophos (Etho, 0.16 mg kg^-1 bw), and cadmium (Cd, 0.63 mg kg^-1 bw); each alone or in combination on hematological, biochemical, and genotoxic parameters in male mice for one or four weeks. The tested toxicants resulted in a decline in body and organs weights, the most hematological indices, acetylcholine esterase activity, and the total protein content, while they significantly increased liver and kidney function parameters. Furthermore, they increased the mitotic index (MI), number of abnormal sperms, and chromosomes. In conclusion, Etho and Cd induce deleterious effects on all tested parameters in male mice which reflect more obvious impacts when both combined, particularly after 28 days of exposure. However, further research is needed to confirm toxicokinetic or toxicodynamic interactions between these two toxic compounds in the organisms.

A systems toxicology approach to compare the heavy metal mixtures (Pb, As, MeHg) impact in neurodegenerative diseases

Conventional toxicological risk assessment methods mainly working on single chemicals that fail to adequately address the simultaneous exposure and their potential toxicity in humans. We herein investigated the toxic heavy metals lead (Pb), arsenic (As), and methylmercury (MeHg) and their binary mixtures role in neurodegenerative diseases. To characterize the toxicity of metal mixtures at the molecular level, we established a non-animal omics-based organ relevant cell model system. The obtained experimental data was refined by using the statistical and downstream functional analysis. The protein expression information substantiates the previous findings of single metal (Pb, As, and MeHg) induced alterations to mitochondrial dysfunction, oxidative stress, mRNA splicing, and ubiquitin system dysfunction relation to neurodegenerative diseases. The functional downstream analysis of single and binary mixtures protein data is presented in a comparative manner. The heavy metals mixtures' outcome showed significant differences in the protein expression compared to single metals that indicate metal mixtures exposure is more hazardous than single metal exposure. These results suggest that more comprehensive strategies are needed to improve the mixtures risk assessment in the future.

Laboratory Efficacy and Disinfection by-Product Formation of a Coagulant/Disinfectant Tablet for Point-of-Use Water Treatment

Coagulant/disinfection products (CDPs) are a point-of-use (POU) water treatment technique that can improve microbial quality, reduce turbidity, and produce a free chlorine residual (FCR), serving as a potentially effective option for decentralized water treatment in a variety of contexts, including humanitarian emergencies. A novel CDP with a sodium dichloroisocyanurate-based disinfectant was evaluated with regard to its laboratory water treatment efficacy and generation of disinfection byproducts (DBPs). The CDP water treatment performance was assessed relative to bacteriological (E. coli) humanitarian water quality objectives, World Health Organization recommendations for evaluating POU water treatment options, and available DBP regulations and guidelines. At least 4 log10 E. coli reductions, for a “highly protective” status with regard to bacterial reductions, were attained in the tested conditions. Treated waters were consistently below 10 MPN/100 mL with regard to E. coli concentrations, with the majority of samples showing no detectable E. coli. For most conditions, target FCR values were not attained. Treated water turbidity levels were mostly between 5 NTU and 10 NTU. DBP levels were below the regulatory and health-based targets for both families of DBPs studied. This study has served to identify the performance envelopes of the CDP tested under challenging conditions.

Characterizing Risk for Cumulative Risk Assessments

In assessing environmental health risks, the risk characterization step synthesizes information gathered in evaluating exposures to stressors together with dose-response relationships, characteristics of the exposed population, and external environmental conditions. This article summarizes key steps of a cumulative risk assessment (CRA) followed by a discussion of considerations for characterizing cumulative risks. Cumulative risk characterizations differ considerably from single chemical- or single source-based risk characterization. CRAs typically focus on a specific population instead of a pollutant or pollutant source and should include an evaluation of all relevant sources contributing to the exposures in the population and other factors that influence dose-response relationships. Second, CRAs may include influential environmental and population-specific conditions, involving multiple chemical and nonchemical stressors. Third, a CRA could examine multiple health effects, reflecting joint toxicity and the potential for toxicological interactions. Fourth, the complexities often necessitate simplifying methods, including judgment-based and semi-quantitative indices that collapse disparate data into numerical scores. Fifth, because of the higher dimensionality and potentially large number of interactions, information needed to quantify risk is typically incomplete, necessitating an uncertainty analysis. Three approaches that could be used for characterizing risks in a CRA are presented: the multiroute hazard index, stressor grouping by exposure and toxicity, and indices for screening multiple factors and conditions. Other key roles of the risk characterization in CRAs are also described, mainly the translational aspect of including a characterization summary for lay readers (in addition to the technical analysis), and placing the results in the context of the likely risk-based decisions.

Dioxin risk assessment: mechanisms of action and possible toxicity in human health

Dioxin-like compounds (DLCs) have been classified by the World Health Organization (WHO) as one of the most persistent toxic chemical substances in the environment, and they are associated with several occupational activities and industrial accidents around the world. Since the end of the 1970s, these toxic chemicals have been banned because of their human toxicity potential, long half-life, wide dispersion, and they bioaccumulate in the food web. This review serves as a primer for environmental health professionals to provide guidance on short-term risk assessment of dioxin and to identify key findings for health and exposure assessment based on policies of different agencies. It also presents possible health effects of dioxins, mechanisms of action, toxic equivalency factors (TEFs), and dose-response characterization. Key studies related to toxicity values of dioxin-like compounds and their possible human health risk were identified through PubMed and supplemented with relevant studies characterized by reviewing the reference lists in the review articles and primary literature. Existing data decreases the scope of analyses and models in relevant studies to a manageable size by focusing on the set of important studies related to the perspective of developing toxicity values of DLCs.

Integrated ecological risk assessment of dioxin compounds

Current ecological risk assessment (ERA) schemes focus mainly on bioaccumulation and toxicity of pollutants in individual organisms. Ecological models are tools mainly used to assess ecological risks of pollutants to ecosystems, communities, and populations. Their main advantage is the relatively direct integration of the species sensitivity to organic pollutants, the fate and mechanism of action in the environment of toxicants, and life-history features of the individual organism of concern. To promote scientific consensus on ERA schemes, this review is intended to provide a guideline on short-term ERA involving dioxin chemicals and to identify key findings for exposure assessment based on policies of different agencies. It also presents possible adverse effects of dioxins on ecosystems, toxicity equivalence methodology, environmental fate and transport modeling, and development of stressor-response profiles for dioxin-like chemicals.

Exposure to multiple metals from groundwater-a global crisis: geology, climate change, health effects, testing, and mitigation

This paper presents an overview of the global extent of naturally occurring toxic metals in groundwater. Adverse health effects attributed to the toxic metals most commonly found in groundwater are reviewed, as well as chemical, biochemical, and physiological interactions between these metals. Synergistic and antagonistic effects that have been reported between the toxic metals found in groundwater and the dietary trace elements are highlighted, and common behavioural, cultural, and dietary practices that are likely to significantly modify health risks due to use of metal-contaminated groundwater are reviewed. Methods for analytical testing of samples containing multiple metals are discussed, with special attention to analytical interferences between metals and reagents. An overview is presented of approaches to providing safe water when groundwater contains multiple metallic toxins.

Understanding the mismatch between the demands of risk assessment and practice of scientists--the case of Deca-BDE

This review describes how a mismatch between the knowledge produced by scientists and the evidence demanded by regulators has emerged, and how society has struggled to find definitive answers to questions of safety, for an important flame retardant chemical in current use - Deca-BDE. This has involved two key disciplines: analytical chemistry and toxicology. Within the chemistry, a lack of standardized methodologies among scientists has resulted in a persistent yet largely undeclared failure to replicate results within the discipline. Within the toxicology, the quest for innovative, curiosity-driven research by university scientists in preference to using validated standard protocols, designed to promote consistency within the risk assessment process, has prompted questions about the credibility and relevance of scientific findings. Yet scientific laboratories have compelling reasons to do things the way they do in the cause of producing new knowledge, pointing to a sustained gap between the aims and practices of research scientists and those of risk management. A more rigorous scientific process that treats different elements of input data as discrete pieces of evidence is needed to ensure that science rather than politics will always define chemical safety.