Modeling Fate and Transport of Chemicals in the Environment

Numerous models are available to simulate the fate and transport of chemicals in the environment. These models reflect the multitude of processes described above to varying degrees of complexity and accuracy. They also represent different distance scales, from local to regional to global. 

Multimedia environmental models often incorporate the concept of fugac-ity into mass balance calculations. As pioneered by Dr. Donald Mackay and described in Table 2.3, fugacity models can reflect four levels of sophistication [64]. Level III fugacity models are commonly used to describe the fate and transport of a chemical released to the environment that undergoes degradation and advective transport between compartments. One such model is described below. 

The US Environmental Protection Agency s (EPA s) EPISuite software, for example, contains a Level III fugacity model based on Dr. Mackay s EQC model [65]. EPISuite allows the user to estimate how a chemical partitions between compartments and its overall persistence in the environment. The model represents four main compartments air, water, sediment, and soil. The software essentially solves a series of equations that represent advection 

I Chemical is conserved reaches equilibrium between different phases. Indicates where a chemical is likely to partition. 

II System at interphase equilibrium chemical concentrations reduced by advection and degradation. Provides first approximation of chemical persistence. 

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