Environmental pathway analysis provides the link between qualification of source emissions and assessments of receptor exposure (eg. human exposure) through estimation of the ambient concentrations of contaminants in the various environmental media.Two basic techniques can be employed to investigate environmental pathways: analytic sampling programs & mathematical fate modelling. Sampling programs are costly to design & implement, therefore, computerized mathematical models of environmental processes are frequently used to generate information unavailable by other means or to estimate data (i.e. environmental conc.) that would otherwise be costly to obtain.