From the discussions on the exposure scenarios presented in the last four slides, it is clear that there are at least two approaches to estimating the total daily exposure to a chemical. One approach is to first identify the key exposure components (inhalation, dermal, onsite, offsite, etc.). The exposures from these key routes or sources would then be estimated separately and indirectly. Indirect measurements of human exposure to environmental contaminants are often accomplished through use of the chemical's concentrations in the air, water, soil, food, foliage, and the like. These types of measurements will be the focus of discussion in Lecture 8.

Another approach is to estimate the daily exposure of the test population (more) directly through use of a biological monitoring type study on human volunteers. Biological monitoring, or biomonitoring for short, of human exposure typically involves the measurement of the internal dose, which is often estimated indirectly by measuring the chemical, or one of its metabolites, in a biological medium such as blood, expired air, or urine.

Although the biomonitoring approach presumes a direct measurement method, the internal dose so derived technically is still through indirect estimation. This is because the (total) internal dose so derived is always based upon the amount of the chemical measured with correction for the percentage expected to be recovered in the body medium used. If a metabolite were monitored, then additional correction would be needed to account for the portion of the parent compound that is expected to be biotransformed into that metabolite.