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