The biggest challenge to date in exposure modeling is to link exposure to uptake outside of the laboratory. A biomagnification model that was successfully applied to terrestrial biomagnification known as BIOMAG is a good example of linking exposure to uptake. The model considers target species which are top predators in significant ecosystems. The model incorporates a consideration of bioavailability (concentration in soil solution), ecology
(stochastic food chain models), toxicology (simple compartment model), and a consideration of effect based on the 'no observed effect concentration' (NOEC). Movement of the contaminant through the food chain is quantified using bioaccumulation factors (BAFs); a ratio of the concentration of contaminant in the consumer and the food that it consumed. Such approaches have been used to underpin soil standards by calculating the level of soil pollution that gives rise to the maximum tolerable risk for birds and mammals at the top of the particular food chain, and in general involves working backward through the model, starting at maximum tolerable risk. One shortfall of this and many models is controlling the sensitivity of the model especially in a situation where heterogeneity of soil contamination amplifies the variability of the model, although it is suggested that soil solution concentration should be treated as a stochastic parameter, in a similar manner to BAF. In aquatic toxicology, similar relationship can be explored by using quantitative structure-activity relationships (QSAR) in rule-based expert systems.
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