In this report, the NRC’s Subcommittee to Update the 1999 Arsenic in  Drinking Water Report reviews the available toxicological, epidemiological, and risk assessment literature that has been published since the 1999 report. The  subcommittee reviewed data for dose-response assessment and risk estimation;  assessed whether the most recent EPA analysis is adequate for estimating an effective dose for a 1% response; determined whether EPA’s analysis  appropriately considers and characterizes the available data on the mode of action of arsenic and the information on dose-response and uncertainties when assessing the public-health impacts; and determined whether EPA’s risk estimates for 3, 5, 10, and 20 ìg/L of arsenic are consistent with available scientific information, including information from new studies.