Physical-chemical properties are used to quantify a chemical's behaviour in an evaluative environment.
Three types of chemicals are treated in this model: chemicals that partition into all media (Type 1)
, involatile chemicals (Type 2),
and chemicals with zero, or near-zero, solubility (Type 3). The Level I Model assumes a simple, evaluative, closed environment with user-defined volumes and densities for the following homogeneous environmental media (or compartments): air, water, soil, sediment, suspended sediment, fish and aerosols.