Citation:

Scholz, S., J. Nichols, B. Escher, G. Ankley, R. Altenburger, B. Blackwell, W. Brack, L. Burkhard, T. Collette, J. Doering, D. Ekman, K. Fay, F. Fischer, J. Hackermüller, J. Hoffman, C. Lai, D. Leuthold, D. Martinovic-Weigelt, T. Reemtsma, N. Pollesch, A. Schroeder, G. Schüürmann, AND M. Bergen. The Eco-Exposome Concept: Supporting an Integrated Assessment of Mixtures of Environmental Chemicals. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 41(1):30-45, (2022). https://doi.org/10.1002/etc.5242

Impact/Purpose:

Prospective assessments of chemical risk are generally made by characterizing adverse effects caused by external exposures to individual chemicals. Within a real-world setting, however, organisms are simultaneously exposed to thousands of chemicals from natural and anthropogenic origins. Moreover, an assessment of risk based on external exposure may fail to represent the true risk to an organism because it does not reflect the composition and amounts of chemicals (and their biotransformation products) that are bioavailable and able to interact with internal molecular targets. Ideally, therefore, a chemical risk assessment would reflect the totality of a chemical exposure, characterized in terms of internal chemical concentrations. To better describe this internal exposure, human health researchers have developed the concept of a chemical ‘exposome.’ In this paper we consider whether the exposome concept has utility in the context of ecological risk assessment. A definition of the ‘eco-exposome’ is given, and considerations are provided for its assessment. It is proposed that targeted and non-targeted approaches for chemical analysis should be complimented by the use of targeted and non-targeted bioanalytical tools to account for undetected but toxicologically relevant chemicals and address the interplay between a chemical exposure and the organism’s response to this exposure. This expanded approach to eco-exposome assessment will provide for the possibility of applying the adverse outcome pathway (AOP) concept to help make the linkage between internal exposure and adverse effect. Analysis of the eco-exposome may also inform the development of new AOPs by indicating the presence of new chemical stressors (or bioactivities) or concern. The eco-exposome concept overlaps with several well-established concepts in ecotoxicology including aggregate exposure pathways, mixture assessment, critical body residues, biomarkers, and the AOP framework. This concept differs from current practice, however, in terms of the comprehensiveness of the assessment. While assessment of the eco-exposome can be accomplished without changes to current regulatory frameworks, application of this concept could have significant impacts on future regulations such as the development of discharge permits or environmental quality standards in the context of exposures of organisms to complex mixtures.

Description:

Organisms are exposed to ever-changing complex mixtures of chemicals over the course of their lifetime. The need to more comprehensively describe this exposure and relate it to adverse health effects has led to formulation of the exposome concept in human toxicology. Whether this concept has utility in the context of environmental hazard and risk assessment has not been discussed in detail. In this Critical Perspective, we propose—by analogy to the human exposome—to define the eco-exposome as the totality of the internal exposure (anthropogenic and natural chemicals, their biotransformation products or adducts, and endogenous signaling molecules that may be sensitive to an anthropogenic chemical exposure) over the lifetime of an ecologically relevant organism. We describe how targeted and nontargeted chemical analyses and bioassays can be employed to characterize this exposure and discuss how the adverse outcome pathway concept could be used to link this exposure to adverse effects. Available methods, their limitations, and/or requirement for improvements for practical application of the eco-exposome concept are discussed. Even though analysis of the eco-exposome can be resource-intensive and challenging, new approaches and technologies make this assessment increasingly feasible. Furthermore, an improved understanding of mechanistic relationships between external chemical exposure(s), internal chemical exposure(s), and biological effects could result in the development of proxies, that is, relatively simple chemical and biological measurements that could be used to complement internal exposure assessment or infer the internal exposure when it is difficult to measure.

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