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EPA's IRIS bite -Drinking Water Health Advisories • hup://www.epa.gov/ngispgm3/iris/dwatzr.htmi:» <br />• <br />The NOAELs or LOAELs are identified from studies [hat provide information on the target <br />organ affected. A study that demonstrates adose-response relationship is prefelTed over a <br />study where only a single dose has been tested. Lethality studies are not considered for HA <br />derivation. <br />HAs are derived to protect sensitive members of the population. For the One-day and <br />Ten-day HAs, the protected individual is assumed to be a child. The child is assumed to <br />weigh f0 kg unless otherwise noted. It is also assumed that the child consumes I L of <br />water/day. For aLonger-teen exposure, HAs are calculated for both a child and an adult. It <br />is assumed that an adult weighs 70 kg and consumes 2 L of water/day. For a Lifetime <br />exposure, the HA is only calculated for an adult, since the child will not be in this exposure <br />category for a lifetime. <br />HAs are calculated according to the equation: <br />HA = (NOAEL or LOAEL) (BW) / (UF) (_ L/day) _ _ mg/L <br />where: NOAEL = No-Observed-Adverse-Effect Level <br />(the exposure in mg/kg bw/day) <br />or <br />LOAEL =Lowest-Observed-Adverse Effect Level <br />([he exposure dose in mg/kg bw/day) <br />BW =assumed body weight of protected individual <br />(10 kg child or 70 kg adult) <br />OF =uncertainty factors, based on quality and nature of data <br />L/day =assumed water consumption <br />(I L/day for child or 2 L/day for adult) <br />The uncertainty factor accounts for the inherent variability within the human population <br />and between the animal species. An uncertainty factor of 10 is used when good acute or <br />chronic human data that identify a NOAEL are the basis for the HA. If the human data are <br />of good quality, but identify a LOAEL rather than a NOAEL, then an ttncertain[y factor of <br />100 is used. An uncer- tainty factor of 100 is also used when a NOAEL from a <br />well-conducted animal study serves as the basis of the HA. If an animal study that <br />identifies a LOAEL, or an animal study of limited quality is [he basis of the HA, then an <br />uncertainty factor of 1000 is employed. Use of [he uncertainty factor is largely judgmental, <br />and may take into account the quality of the toxicological data base, the significance of the <br />adverse effect or the counterbalancing of possible beneficial effects. <br />Lifetime HAs (noncarcinogens Duly) are calculated from the Drinking Water Equivalent <br />Level (DWEL) which, in turn, is based on the unrounded RtD. DWELs are calculated from <br />the equation: <br />2 or 3 6/ I I /99 4.25 PM <br />