On aspects of the dynamic behavior of persistent chemicals in a multimedia environment related to exposure-based hazard assessment

The present research study focuses on the analysis and characterization of certain aspects of the dynamic behavior displayed by persistent chemicals in a multimedia environment (chemodynamics), which is jointly determined by the inherent physicochemical properties of the chemical substance under consideration, as well as underlying environmental processes such as degradation in different phases/media (soil, water and air) coupled with intermedia transport (interphase mass transfer). In particular, dynamic multimedia environmental models are considered with constant source terms describing steady chemical release/discharge rates into various environmental media of interest, and key risk-related aspects of the dynamic behavior of persistent chemicals are analyzed using perturbation theory techniques under conditions where degradation rates in different media are considerably slower than intermedia transport rates. Under the above conditions, the problem of defining physically meaningful and practical quantitative measures of overall persistence of chemicals in a multimedia environment is revisited, given its role as a key exposure-based indicator within all major chemical risk assessment frameworks, and a proof is provided that rigorously establishes equivalence between two important and popular persistence measures, namely the characteristic time at steady state and the inverse of the associated chemodynamics overall decay rate (slowest chemodynamic mode).