THE DRINKING WATER REGULATION FOR ARSENIC

Arsenic (As) is a well-known human poison. Drinking water contaminated with As has been associated with a myriad of cancer and non-cancer diseases. In the US, the 1996 Safe Drinking Water Amendments put EPA on a schedule to regulate As. During this period, EPA had two National Research Council (NRC) panels to review the health effects of As. The initial one focused on bladder cancer and calculated a 1% Effctive Dose (ED01)of about 400 µg/L. Since this was only 8-fold higher than the Interim Maximum Contaminant Level (MCL) of 50 µg/L, the NRC recommended a downward revision as soon as feasible. On 1/22/01, EPA promulgated a MCL of 10 µg/L. During its review of this standard, EPA had a second NRC panel review the health data base. They stated that As was possibly more toxic than originally thought as the trivalent methylated metabolites were more toxic than arsenite and could react directly with DNA. NRC recommended a linear extrapolation from the ED01. EPA considered the health data along with costs/benefits, analytical and treatment techniques for As and on 10/31/01 announced that there would be no delay in the implementation of the As MCL of 10 µg/L. (These opinions are those of the author and not necessarily those of the US EPA.)