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In the more conventional usage, health risk assessment (RA) as an organized quantitative process consists of four key components. As first formalized by the National Research Council (1983), these four components are: (1) hazard identification; (2) dose-response assessment; (3) exposure assessment; and (4) risk characterization. To identify health problems and set health priorities, we need to assess the risk involved or anticipated. Risk is defined as the likelihood or potential that an adverse outcome would occur. It is thus fair to argue that a health risk cannot be assessed if the hazard or cause involved is uncertain to us. This is why RA usually starts with hazard identification. Sometimes the underlying cause, though already identified, may not be at all biologically clear to us. To be able to assess the risk, we need to be assured at least that the presence or absence of an agent (or a factor) would or would not cause the health hazard. Better still, the risk would be more assessable or easily mitigated, if there were available a (quantified) dose-response relationship between the adverse health effect and the etiologic agent (or factor) in question. It is also rather intuitive that no assessment of the health risk would be useful or necessary, if current or anticipated human exposure to the agent were found to be minimal. Risk characterization, the last step in RA, is where the adverse health effect is to be associated quantitatively as well as qualitatively with a population’s exposure to the etiologic agent at issue.