The following discussion of the four steps of risk assessment was 

 excerpted from "Principles of Risk Assessment: A Nontechnical 

 Review" (U.S. EPA, 1985). 



Hazard identification involves gathering and evaluating data on the 

 types of health injury or disease that may be produced by a chemical 

 and on the conditions of exposure under which injury or disease is 

 produced. It may also involve characterization of the behavior of 

 a chemical within the body and the interactions it undergoes with 

 organs, cells, or even part of cells. Data of the latter types may be 

 of value in answering the uhimate question of whether the forms of 

 toxicity known to be produced by a substance in one population 

 group or in experimental settings are also likely to be produced in 

 humans. Hazard identification is not risk assessment; we are simply 

 determining whether it is scientifically correct to infer that toxic 

 effects observed in one setting will occur in other settings (e.g., 

 whether substances found to be carcinogenic or teratogenic in 

 experimental animals are likely to have the same results in humans). 



Dose-response assessment involves describing the quantitative 

 relationship between the amount of exposure to a substance and 

 the extent of toxic injury or disease. Data are derived from animal 

 studies, or less frequently, from studies in exposed populations. 

 There may be many different toxic effects under different condi- 

 tions of exposure. 



The risks of a substance cannot be ascertained with any degree of 

 confidence unless dose-response relationships are quantified, even 

 if the substance is known to be toxic. 



Exposure assessment involves describing the nature and size of the 

 population exposed to a substance and the magnitude and duration 

 of their exposure. The evaluation could concern past or current 

 exposures, or exposures anticipated in the future. 



Risk characterization generally involves the integration of the as- 

 sessment process (hazard identification, dose-response assess- 

 ment, and exposure assessment) to determine the likelihood that 

 humans will experience any of the various forms of toxicity as- 

 sociated with a substance. (In cases where exposure data are not 

 available, hypothetical risk can be characterized by the integration 

 of hazard identification and dose-response assessment data alone.) 

 A framework to define the significance of the risk is developed, and 

 all of the assumptions, uncertainties, and scientificjudgments of the 

 preceding three steps are presented. 



IRIS is a tool that provides hazard identincation and dose-response 

 assessment inrormation, but does not provide situational information 

 on instances of exposiu-e. Combined with specific exposure informa- 

 tion, the data in IRIS can be used for characterization of the public 



The Role of IRIS in Risk 

 Assessment/ Risk 

 Management 



