A GLOBAL DISTRIBUTION MODEL FOR PERSISTENT ORGANIC-CHEMICALS

A nonsteady-state, multi-compartmental mass balance model of organic c ontaminant fate is presented in which the global environment is repres ented by nine sequentially arranged climatic zones. Each zone has an a ir, ocean water, fresh water, fresh water sediment, and two soil compa rtments, connected by advective and intermedia transport processes. De gradation can take place in every compartment and zone. The time, magn itude, and medium of chemical discharge is specified for each climatic zone. The seasonal variability of some key parameters such as air and ocean water temperature is taken into account. The mass balances for each of the compartments result in a system of 54 differential equatio ns, solved numerically to yield estimates of concentrations, masses, t ransport fluxes, and reaction rates as a function of time. A series of illustrative calculations studies the major factors governing the glo bal dispersion of persistent organic chemicals: (1) temperature, (2) c hemical degradability, (3) environmental descriptors such as transport rates and organic carbon contents, (4) location and amount of chemica l discharge and (5) physio-chemical properties. The calculations confi rm that condensation at low temperatures can result in elevated contam inant concentrations in the polar regions and that chemicals show dist inct global distribution patterns based on their physico-chemical prop erties. Location and medium of discharge into the environment and seve ral environmental parameters strongly influence the calculated global fate of contaminants. The factors that primarily influence pollutant e nrichment and behavior in polar regions should be studied more thoroug hly with a view to obtaining more accurate parameter values and improv ed equilibrium and rate expressions.