Effect-directed analysis and beyond: how to find causal environmental toxicants

Abstract

Humans and wildlife are exposed to complex environmental mixtures. Identifying causal toxic pollutants in environmental samples remains challenging because of the high complexity of sample mixtures and the unknown nature of the potential toxicants. In the field of environmental chemistry and toxicology, this pursuit of causal toxicants leads us to the method of effect-directed analysis (EDA), an integrated method comprised of three iterative modules: (1) bioassays to guide component prioritization; (2) fractionation to reduce the mixture complexity; and (3) chemical analysis to identify the toxicants. In this commentary review, we try to provide a concise guideline for EDA beginners by summarizing good practices from successful EDA studies, categorized by sample-toxicity pair selection, efficient separation, and chemical analysis. We also discussed the practical challenges faced with current EDA practices. Based on these above, we try to provide suggestions and perspectives for future EDA studies. Specifically, we discussed the potential of applying EDA on human biological examples to identify the environmental causes of human diseases. We proposed future collaboration between environmental chemists and toxicologists, environmental health scientists, epidemiologists, physicians, and social scientists.

Emerging contaminants: A One Health perspective

“… 144 The combination of in vitro and in chemico assays with non-targeted chemical analysis represents a novel, more effective approach to identifying the bioactive/toxic contaminants in our environment. 145 , 146 …”

High-Resolution Mass Spectrometry for Human Exposomics: Expanding Chemical Space Coverage

“…86 For over two decades, EDA has been actively employed to enhance environmental monitoring (most commonly, water) and advance human exposomics. 87,88 As opposed to the many active, invasive sampling methods aiming at a broad coverage (e.g., blood), it is equally important to devise passive sampling techniques to capture exposome components in situ (often considered the "bioavailable" fraction) in both environmental monitoring 89 and biomonitoring. 90 This is especially true when samples are not easily accessible, or intermittent, longitudinal, and noninvasive monitoring is desired, e.g., in vulnerable populations such as newborns, infants, young children, and pregnant women.…”

“…The HRMS-led NTA capacity is broadly conducive to effect-based methods to identify individual drivers and modifiers of toxicity and disease. 38,87 One seminal case study is the identification of 6PPDquinone, a causative toxicant responsible for the massive acute mortality of coho salmon in seasons returning to spawn and a recurring event puzzling scientists for decades. 84 6PPDquinone is a major transformation product of 6PPD, or N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, a common antiozonant and antioxidant added to vehicle tires.…”

“…EDA utilizes sample fractionation schemes and biological/toxicity assays designed for the problems formulated at the front end before delving into chemical analysis. , The target sample matrix (and extraction), test systems, and operational readouts of MOA and toxicity are determined first to guide the downstream chemical analysis, as implemented in recent successful cases. , Since molecular mechanisms of toxicity essentially boil down to ligand binding (to target receptors), specific and sensitive protein affinity-based assays can be used for selective extraction and screening, as demonstrated by bioassays based on endoplasmic reticulum (ER) protein pulldown . For over two decades, EDA has been actively employed to enhance environmental monitoring (most commonly, water) and advance human exposomics. , …”

High-Efficiency Effect-Directed Analysis Leveraging Five High Level Advancements: A Critical Review

“…Effect-directed analysis (EDA), which combines bioassays with chemical analysis, is recognized as a potent approach for identifying causal toxicants in complex environmental samples. ,− EDA consists of five essential steps: extraction, fractionation, bioassays, chemical analysis, and identification of causal toxicants . Specifically, the sample extract undergoes a series of fractionation steps to reduce its complexity, followed by biological testing of components to filter out inactive fractions, with only active fractions subjected to target, suspect, or nontarget analysis (NTA), and ultimately, the substances that drive changes in total toxicity, known as the key toxicants, are identified and validated through multiple lines of evidence. − EDA has been extensively used to identify key toxicants in various environmental samples, such as surface water, industrial wastewater, influent and effluent of wastewater treatment plants (WWTPs), sediments, , soil, crude oil, and biota. , However, several challenges remain in the crucial steps of EDA. First, the risk of toxicant loss occurs during extraction, such as solid-phase extraction (SPE) methods for water media.…”