In the previous lectures of this series, particularly Lectures 1 through 4, health risk assessment (RA) was described as an important health science discipline having close linkages with public health, toxicology, and epidemiology. Risk characterization (RC), on the other hand, was mentioned repeatedly as the fourth and final step in the RA paradigm initially developed by the National Research Council (NRC, 1983). Literally, RC is the process or effort that involves characterizing the health risk of concern, using information gathered from hazard identification (HI), dose-response assessment (DRA), and human exposure assessment (HEA). Since a risk cannot be characterized until and unless it has been assessed at least qualitatively, RA thus technically can also be considered as a component of RC.

In accordance with the Risk Characterization Handbook published by USEPA (2000a), RC is "the final, integrative step of risk assessment" that "conveys the risk assessor's judgment as to the nature and existence (or lack) of human health or ecological risks." The Risk Characterization Handbook also reiterates NRC's paradigm, saying that HI, DRA, HEA, and RC are the four key steps in RA. In that sense, RC is indeed part of the RA process.

In short, RC is and isn't part of RA because the latter has multiple connotations in protecting human health. As a public health discipline, RA goes beyond the process required to quantifying health risk. Yet in its simplest term, RA can be construed as that quantification step subject to RC.