As mentioned briefly in the last slide, human biomonitoring relies heavily on a good understanding of the chemical's pharmacokinetics. That is, insofar as the human biomonitoring (HBM) method is based on the determination of the chemical or its metabolite in certain biological fluids, it is essential to understand how the substance is absorbed via the human's outer boundary(ies). It is also important to know how the absorbed chemical is distributed to the body's different tissue compartments, including the fluid of which a small fraction is to be collected to serve as biomonitoring samples.

Other kinetics of equal importance are the elimination and biotransformation rates, as well as those on accumulation in the body. All of these kinetics are required in order to better appreciate the percentage expected to be recovered in the sampling fluid. A good understanding of these kinetics will also provide a better estimate for the portion of the parent compound that is expected to be biotransformed into the metabolite that is to be measured.

The confounding factors and considerations involved in HBM are numerous and have been highlighted elsewhere (see, e.g., Ashford et al., 1990; Bardodej et al., 1987; Chester, 1993; Woollen, 1993). As pointed out by Bernard and Lauwerys (1987), a decrease in the biotransformation of a chemical may be seen in persons with hepatic insufficiency, which can vary with age, sex, stress, or diseases. On the other hand, the ethical aspects and the sensitivity as well as the specificity of the analytical technique used are concerns already discussed in Lecture 4.