Dose-Response Assessment 



After the potential hazard associated with each contaminant of con- 

 cern is characterized, the relationship between dose of a substance and 

 its biological effect is determined. Dose-response data are used to 

 determine the toxicological potency of a substance, a quantitative 

 measure of its potential to cause a specified biological effect. The 

 concepts of exposure, dose, dose-response relationship, and 

 toxicological potency are discussed in the following sections. 



The concepts of exposure and dose, as defined below, are central to 

 risk assessment: 



• Exposure: Contact by an organism with a chemical or physical 

 agent 



• Dose: The amount of chemical uptake by an organism over a 

 specified time as a consequence of exposure. 



The "ingested dose," or amount of chemical ingested, is distinct from 

 the "absorbed dose." For the oral route of exposure, the absorbed dose 

 is the amount of chemical assimilated by absorption across the lining 

 of the gastrointestinal system. Exposure level or exposure concentra- 

 tion is used to denote the concentration (mg/kg wet weight) of con- 

 taminant in edible tissue of fish or shellfish. As shown below, the 

 absorbed dose is estimated from food consumption rate, the exposure 

 concentration, and an absorption coefficient (see Exposure Assess- 

 ment). 



The form of the dose-response relationship for carcinogens is assumed 

 to be fundamentally different from that for noncarcinogens (U.S. 

 Office of Science and Technology Policy 1985). Examples of general 

 dose-response relationships are shown in Figure 2. The lack of a 

 demonstrated threshold in dose-response relationships for car- 



Exposure and Dose 



Dose-Response 

 Relationships 



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