• Under EPA’s Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005), Cr(VI) is “likely to be carcinogenic” via oral exposure based on sufficiently supported [laboratory] animal studies relevant to humans. This assessment maintains the previous conclusion (U.S. EPA, 1998) that Cr(VI) is “carcinogenic to humans” via inhalation exposure.
• This may be a synopsis of the full weight-of-evidence narrative.

Oral Slope Factor: 0.27 per mg/kg-day
Extrapolation Method: HEDs calculated using BW3/4 scaling
Tumor site(s): Gastrointestinal
Tumor type(s): Squamous cell carcinoma or squamous cell papilloma. (NTP, 2008)
Note: EPA has concluded that Cr(VI) is carcinogenic by a mutagenic mode of action. Thus, based on the EPA cancer guidelines (2005), the oral slope factor (OSF) addressing lifetime exposure includes application of age-dependent adjustment factors (ADAFs). The OSF is recommended for lifetime exposures. An adult-based cancer slope factor of 0.16 per mg/kg-day is also provided. This adult-based cancer slope factor can be used instead of the OSF when assessing cancer risk associated with exposure scenarios that don’t include early life (< 16 years of age) or when other calculations by the user are necessary (e.g., when applying ADAFs to age-specific exposure estimates).

Inhalation Unit Risk: 0.018 per µg/m³
Extrapolation Method: Linear extrapolation from LEC01 derived from Cox proportional hazard model with 5 year lag using lifetable analysis.
Tumor site(s): Respiratory
Tumor type(s): Lung cancer Note: EPA has concluded that Cr(VI) is carcinogenic by a mutagenic mode of action. Thus, based on the EPA cancer guidelines (2005), the inhalation unit risk (IUR) addressing lifetime exposure includes application of age-dependent adjustment factors (ADAFs). The IUR is recommended for lifetime exposures. An adult-based cancer inhalation unit risk of 0.011 per µg/m3 is also provided. This adult-based cancer inhalation unit risk can be used instead of the IUR when assessing cancer risk associated with exposure scenarios that don’t include early life (< 16 years of age) or when other calculations by the user are necessary (e.g., when applying ADAFs to age-specific exposure estimates).