EPA response to Chromium Report … reading between the lines

The EPA has responded to the report by the Environmental Working Group (EWG) which indicated that chromium-6 was potentially present at unacceptably high levels in a significant majority of city water supplies tested.  In the EPA press release responding to the EWG study, two major points were made: (1) that EPA already regulates total chromium and (2) that the EPA is currently reviewing the “new science on chromium-6[.]” Regarding the first point, the numbers put forth in the EWG study suggest that the EPA limit on total chromium is insufficient to mitigate the risks associated with chromium-6.  The EWG report implies a need for limiting chromium-6 to 0.06 parts per billion (ppb) while current EPA standards limit total chromium to 100 ppb.  The EPA’s total chromium test includes all forms of chromium including forms that are used by the body in metabolism.  This means that when the fraction of chromium-6 as a portion of total chromium tested is high there may be significant potential for toxic effects from water the EPA now considers safe.  With a study suggesting that this potentially dangerous chemical is currently in US drinking water and a longstanding understanding that chromium-6 is toxic, the EPA would be wise to move quickly in determining the safe exposure level for this compound.