GIS Based Chemical Fate Modeling: Principles and Applications

Chapter 2

Basics of Chemical Compartment Models and Their Implementation with GIS Functions

2.1 Introduction

Fate and transport models are tools used to describe how chemicals spread in the environment. They consist of a mathematical representation of the processes that a chemical undergoes when it is released, which can be grouped as follows:

1. Chemical phase partitioning.

2. Chemical reactions.

3. Transfer among different environmental media (air, water, soil, sediments, vegetation, biota).

4. Transport within a medium.

Mathematical representations may be derived on empirical bases (i.e., some best-fit trend line that interpolates experimental data) or may be physics-based (i.e., derived from first principles—the established axioms that are considered laws of physics). In reality, practically all physics based equations used in environmental modeling introduce, at a certain point, some empirically derived parameterization and would better be termed mediating models as discussed in Chapter 1. Hereafter we refer to models derived from the axioms of classical physics without excessive empirical parameter fitting as physics based, for the sake of simplicity, keeping in mind that the contrast with purely empirical models is sometimes blurred. Having in mind this distinction, we observe that chemical partitioning is usually represented through empirical models by introducing appropriate partition coefficients. An introductory but extensive discussion of chemical partitioning in ...