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 exposometo 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.
We describe a method for the individual measurement of
simultaneously occurring, unimolecular, site-specific
“microequilibrium” constants as in, for example, prototropic
tautomerism and zwitterionic equilibria. Our method
represents an elaboration of that of Nygren et al.
(Anal.
Chem. 1996, 68, 1706−10), which thereby
becomes
generalized and improves the accuracy. Specifically,
by
making spectral measurements as a function of temperature, we demonstrate the ability to determine
site-specific
microenthalpies unambiguously. Analysis proceeds via
multivariate nonlinear regression modeling of, for example, the Gibbs−Helmholtz relation. Additional
determinations of macroscopic equilibrium constants as a
function of temperature, in combination with the previously determined microenthalpies, in turn enables the
determination of all remaining site-specific thermodynamic parameters, i.e., microentropies, micro free energies, and/or microequilibrium constants, and moreover
allows us to resolve and measure the spectra of tautomeric
isocoulombers. To our knowledge, we have hereby devised the first such universally applicable and accurate
measurement method on record.
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