According to a report released Sept. 11, 2001, by the Natl. Academies, even very low concentrations of arsenic in drinking water can increase cancer risks. NAS release with link to report.
These findings are consistent with the 1999 Research Council report that found high risks of cancer at EPA's maximum allowable level for arsenic in drinking water (50 ppb at the time). In January 2001, EPA lowered its standard to 10 ppb. In March 2001, the agency put that new rule on hold and asked the Research Council to review relevant research findings from the last two years. (TipSheet, Mar. 28, 2001). According to aSept. 11, 2001 Washington Post article, EPA recently signaled that it must adopt a tighter standard.
As of Aug. 31, 2001, two other expert panels had already submitted their analyses to EPA. EPA press: Robin Woods, 202-564-7841.