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EPA's IRI~ Site -Drinking Water Health Advisories <br />III IIIIIIIII IIII III • <br />htt p://www.epa.gov/ngi spgm3/i ri s/d water. htnw..r <br />999 <br />~~United5tatos ~~-` ~ t' ~ ~~ <br />Environmental Protection ~• f <br />Agency ~ ~-: ,~:: ~.~ ~ \ <br />Integrated Risk lnlormerion System <br />01 /17/92 <br />BACKGROUND DOCUMENT 3 <br />OFFICE OF DRINKING WATER HEALTH ADVISORIES <br />The U.S. EPA's Office of Drinking Water (ODW) develops Health Advisories (HAs) for <br />individual contaminants representing less-than-lifetime exposures of One-day, Ten-day, <br />Longer-term (an exposure of several months up to 7 years), and for Lifetime exposures. <br />The HAs are developed from data describing noncarcinogenic endpoints of toxicity. HAs <br />developed for Lifetime exposures are based on the chemical's oral Reference Dose (RID) <br />(described in Background Document lAl). HAs serve as informal technical guidance <br />levels to assist public health officials when emergency spills or contamination situations <br />occur. They are not legally enforceable and are subject to change as new information <br />becomes available. <br />The HAs represent guidance levels for drinking water exposures. The values for the <br />One-day, Ten-day and Longer-term exposure periods do not consider other sources of <br />exposure such as food or air. For each, the resulting value, in mg/L, assumes that 100% of <br />an individual's exposure comes from drinking water. The lifetime HA, calculated only for <br />an adult from a chronic study, does take into consideration other sources of exposure by <br />applying a relative source contribution (RSC). In the absence ofchemical-specific data, an <br />RSC of 10 is used for inorganic contaminants and an RSC of 20 is used for organic <br />contaminants (NAS, 1977). <br />The HAs are derived employing an approach similar [o that used [o derive RfDs in that a <br />NOAEL (or LOAEL) is divided by an uncertainty factor (UF). This value is adjusted for <br />[he body weigh[ of the protected individual and assumed daily water consumption. <br />The study selected for deriving a HA ideally employs an oral route of exposure. Therefore. <br />a study where the chemical exposure is by drinking water is ideal. Studies using dietary or <br />gavage exposure are also acceptable. Inhalation data are only used in instances where oral <br />data are not available and by applying specific assumptions used in route-to-route <br />extrapolation. <br />The data used for HA derivations are generdly from a study of comparable duration to the <br />HA time period being calculated. For aOne-day HA, the study time period should ideally <br />be from a single exposure. However, longer study durations may be acceptable if the data <br />base is limited. The Ten-day HA may be calculated from a study of less than or equal to 30 <br />days. Developmental studies invoh~ing maternal exposure during part of [he gestational <br />period have also been used. Longer-teen HAs are derived from subchronic studies where <br />animals are exposed for approximately 10%n oY their lifetime (for example. 90 days for <br />rodents). <br />1 0(3 6/ I 1 /99 425 PM <br />