General formulation of characteristic: Time for persistent chemicals in a multimedia environment

A simple yet representative method for determining the characteristic time a persistent organic pollutant remains in a multimedia environment is prese nted. The characteristic time is an important attribute for assessing long- term health and ecological impacts of a chemical. Calculating the character istic time requires information on decay rates in multiple environmental me dia as well as the proportion of mass in each environmental medium. We expl ore the premise that using a steady-state distribution of the mass in the e nvironment provides a means to calculate a representative estimate of the c haracteristic time while maintaining a simple formulation. Calculating the steady-state mass distribution incorporates the effect of advective transpo rt and nonequilibrium effects resulting from the source terms. Using severa l chemicals, we calculate and compare the characteristic time in a represen tative multimedia environment for dynamic, steady-state, and equilibrium mu ltimedia models, and also for a single medium model. We demonstrate that fo rmulating the characteristic time based on the steady-state mass distributi on in the environment closely approximates the dynamic characteristic time for a range of chemicals and thus can be used in decisions regarding chemic al use in the environment.