Acceptable Intake for Subchronic Exposure

Acceptable Intake for Subchronic Exposure (AIS) An estimate similar in concept to the subchronic RfD. but derived using a less strictly defined methodology. Subchronic RfDs have replaced AISs as the Agency s preferred alues for use in e ahiating potential noncarcinogenic health effects resulting from subchronic exposure to a chemical. 

Verification of Uncertainty Factors. As summarized in several publications, uncertainty factors are currently recommended to estimate acceptable intakes for systemic toxicants (1,13,18). The selection of these factors in general reflects the uncertainty inherent with the use of different human or animal toxicity data (i.e., the weight of evidence plays a major role in the selection of uncertainty factors). For example, an uncertainty factor of less than 10 and perhaps even 1 may be used to estimate an ADI if sufficient data of chronic duration are available on a chemical s critical toxic effect in a known sensitive human population. That is to say that this ideal data base is sufficiently predictive of the population threshold dose therefore, uncertainty factors are not warranted. An overall uncertainty factor of 10 might be used to estimate an acceptable intake based on chronic human toxicity data and would reflect the expected intraspecies variability to the adverse effects of a chemical in the absence of chemical-specific data. An overall uncertainty factor of 100 might be used to estimate ADIs with sufficient chronic animal toxicity data this would reflect the expected intra- and interspecies variability in lieu of chemical-specific data. However, this overall factor of 100 might be used with subchronic human data in this case the 100-fold factor would reflect intraspecies variability and a subchronic exposure extrapolation. 

---