A SIMPLE GENERAL LIMITING LAW FOR THE OVERALL DECAY OF ORGANIC-COMPOUNDS WITH GLOBAL POLLUTION POTENTIAL

It is rigorously shown that the effective decay rate in the environmen t of a chemical is between the minimum decay rate in one of its possib le compartments and an upper value, which is the weighted-average deca y rates in all compartments. The weights are the compartments' volumes and the equilibrium concentrations that would have occurred in the co mpartment due to transport alone, with no degradation. This upper valu e is approached, in the sense of a general limiting law, if degradatio n is much slower than transport. This limiting law, together with an e stimate for the spatial range of a persistent chemical, could serve as a minimal base for exposure-based assessment of environmental risk. A s a first illustration, the result is applied to DDT and hexachloroeth ane. A broader group of chemicals will be discussed elsewhere.