Uncertainty Factor (UF) 1
Uncertainty Factor (UF) 1 : [sometimes also called Safety Factor or Modifying Factor] (a) Used in converting NOAELs / LOAELs to RfDs and generally equal 10; account for (1) intraspecies variation, (2) interspecies variation, (3) use of a RfD based on a different time period, or (4) use of a LOAEL rather than a NOAEL to develop a RfD. [AIHA, 2000: Risk Assessment Principles for the Industrial Hygienist]; (b) This term may be used in either of two ways depending upon the context (i) Mathematical expression of uncertainty applied to data that are used to protect populations from hazards which cannot be assessed with high precision. (ii) With regard to food additives and contaminants, a factor applied to the no_observed effect level to derive acceptable daily intake (ADI) (the no_observed_effect level is divided by the safety factor to calculate the ADI). The value of the safety factor depends on the nature of the toxic effect, the size and type of the population to be protected, and the quality of the toxicological information available. [Duffus, 2000: Univ. Edinburgh Med School On-line Chemical Safety Glossary]; (c) One of several, generally 10_fold factors, used in operationally deriving the RfD and RfC from experimental data. UFs are intended to account for (1) the variation in sensitivity among the members of the human population, i.e., interhuman or intraspecies variability; (2) the uncertainty in extrapolating animal data to humans, i.e., interspecies variability; (3) the uncertainty in extrapolating from data obtained in a study with less_than_lifetime exposure to lifetime exposure, i.e., extrapolating from subchronic to chronic exposure; (4) the uncertainty in extrapolating from a LOAEL rather than from a NOAEL; and (5) the uncertainty associated with extrapolation from animal data when the data base is incomplete. [IRIS, 1999: Glossary of IRIS Terms]; (d) Factors used to adjust for multiple sources of uncertainty encountered in using experimental animal data for predicting effects on humans, such as intraspecies variation, interspecies variation, synergism, and different route of exposure (i.e. oral versus inhalation). [REAP, 1995: Residential Exposure Assessment Project]; (e) One of several, generally 10_fold factors used in operationally deriving the reference dose (RfD) from experimental data. UFs are intended to account for (1) the variation in sensitivity among members of the human population; (2) the uncertainty in extrapolating animal data to the case of humans; (3) the uncertainty in extrapolating from data obtained in a study that is of less_than_lifetime exposure; and (4) the uncertainty in using LOAEL data rather than NOAEL data. [USEPA, 1995: Benchmark Dose] [USEPA, 1997a: EPA Terms of Environment] [USDOE, 2000: RAIS Glossary]
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