A closed analytical formula for the characteristic spatial range of persistent organic pollutants

In order to use mobility as a criterion for priority setting amongst environmental chemicals the characteristic spatial range of a substance has been introduced. Roughly spoken, the spatial range is the typical distance a chemical can travel before degradation — after release from a point source in an isotropic environment with the same average geo-chemical properties as the earth. The present contribution starts with a formal definition of spatial ranges in terms of exposure. Then a simple isotropic model of global circulation is set up in analogy to previous unit-world models, covering global long-range transport and (pseudo-)first-order degradation. Afterwards, the model is solved analytically, and a closed formula for spatial range is obtained. The formula is then evaluated for a selection of representative environmental chemicals. The characteristic spatial ranges thus obtained are identical with results obtained by M. Scheringer on the basis of a more detailed computer model. It is stressed that the present result allows for a classification of environmental chemicals with respect to spatial range simply by inserting known measurable quantities into a given formula. The whole approach was designed to make the assessment procedure as workable as possible.