This flowchart, reproduced from Lecture 7, is presented here to illustrate again the dynamics and complexity of human exposure assessment (HEA) in environmental epidemiology. In the last lecture, the discussion focused on the use of human biological monitoring (HBM) in HEA. HBM has been accepted in the HEA community as the most direct measurement method for quantifying internal aggregate dose.

This lecture continues to discuss the dynamic and complex components and methodologies of HEA, but with a focus on the use of various indirect measurement methods (IMM) as tools to estimate the doses from separate routes of entry and from separate exposure media. Depending on the share they each have of the aggregate dose, not all of these separate doses need to be determined or summed.

In health risk assessment, of which HEA is a key component, the IMM approach is by far more popular than the use of HBM in assessing human exposure to environmental contaminants, primarily because the former is more practical and economical. As mentioned in Lecture 7, a knowledge of the chemical's pharmacokinetics is a prerequisite for conducting HBM. Yet such a knowledge is not always available or easily attainable. Also, collection of body fluids from humans, including urine, is considered to be quite an invasive ordeal to many people.