Arsenic, Inorganic

Noncancer Assessment

Reference Dose for Oral Exposure (RfD) (PDF) (29 pp, 186 K) Last Updated: 09/01/1991

System RfD (mg/kg-day) Basis PoD Composite UF Confidence
Cardiovascular, Dermal 3 x 10 -4 Hyperpigmentation, keratosis and possible vascular complications NOAEL : 8 x 10-4
3 Medium


Reference Concentration for Inhalation Exposure (RfC) (PDF) (29 pp, 186 K)
Not assessed under the IRIS Program.


Cancer Assessment

Weight of Evidence for Cancer (PDF) (29 pp, 186 K) Last Updated: 06/01/1995

WOE Characterization Framework for WOE Characterization
A (Human carcinogen) Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1986)
  • Based on sufficient evidence from human data. An increased lung cancer mortality was observed in multiple human populations exposed primarily through inhalation. Also, increased mortality from multiple internal organ cancers (liver, kidney, lung, and bladder) and an increased incidence of skin cancer were observed in populations consuming drinking water high in inorganic arsenic.
  • This may be a synopsis of the full weight-of-evidence narrative.

Quantitative Estimate of Carcinogenic Risk from Oral Exposure (PDF) (29 pp, 186 K)

Oral Slope Factor: 1.5 per mg/kg-day
Drinking Water Unit Risk: 5 x 10-5 per µg/L
Extrapolation Method: Time- and dose-related formulation of the multistage model
Tumor site(s): Dermal
Tumor type(s): Skin cancer (Tseng, 1977; Tseng et al., 1968; U.S. EPA, 1988)

Quantitative Estimate of Carcinogenic Risk from Inhalation Exposure (PDF) (29 pp, 186 K)

Inhalation Unit Risk: 4.3 x 10-3 per µg/m3
Extrapolation Method: Absolute-risk linear model
Tumor site(s): Respiratory
Tumor type(s): Lung cancer (Brown and Chu, 1983a,b,c; Lee-Feldstein, 1983; Higgins, 1982; Enterline and Marsh, 1982)

Program Outlook Details

Public Assessment Materials Date
Problem Formulation Materials/IRIS Assessment Plan Nov-2012
Preliminary Assessment Materials/Systematic Review Protocol May-2019
Public Comment Oct-2023
External Peer Review Dec-2023
Post Final Assessment TBD

Note: Any future dates displayed in the table above should be considered estimates and are subject to change. Once the external peer review is complete, estimated dates for release of the final assessment will be published. For the latest information on the status of this assessment, please refer to the IRIS Program Outlook. To access assessment documents, meeting materials or other supporting documents related to this assessment, visit the Chemical Documents tab. For more information about the development process, visit the IRIS Process page.

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