What Is Hexavalent Chromium?
Hexavalent chromium (Cr(VI)) is a form of the element chromium, which is one of the most abundant chemical elements found in the earth’s crust. There are two potential sources of hexavalent chromium in drinking water – natural sources such as rocks, minerals, and other geology, and localized industrial runoff. Typical U.S. drinking water supplies contain naturally occurring chromium.
National and international regulatory agencies have set drinking water standards to protect the public from all forms of chromium (Cr(VI) and Cr(III)) in drinking water. Cr(III), also known as trivalent chromium, can also be naturally present in drinking water and is a micronutrient that is essential for metabolism. The human body naturally detoxifies low levels of Cr(VI) into non-toxic Cr(III), no matter the source. The EPA, for example, has a drinking water standard of 100 parts per billion (ppb) for total chromium. See what various regulatory agencies have to say about hexavalent chromium here.
EPA’s Flawed IRIS Assessment for Hexavalent Chromium
EPA’s Integrated Risk Information System (IRIS) program identifies human health hazards associated with a substance. The IRIS program, however, has a troubling history of being out of step with the best available science and methods, lacking transparency, and being unresponsive to peer review and stakeholder recommendations. In August 2024, EPA released a final IRIS assessment of oral and inhalation exposure of hexavalent chromium [Cr(VI)]. The final assessment was an abrupt shift in the basis of EPA’s oral cancer slope factor (CSF) from intestinal cancer in mice (2022 draft IRIS assessment) to oral mucosa cancer in rats without any external peer review of this endpoint as the primary driver for EPA’s conclusion.
The final IRIS assessment for Cr(VI) is at odds with the findings of over 30 peer-reviewed studies, which support a threshold for effects and a non-linear, dose-dependent response. EPA’s approach and results could lead to toxicity values far lower than the average background levels of hexavalent chromium in groundwater and could lead to future regulatory action that would impose massive costs to water systems nationwide with little to no public health benefit.
Pursuant to a settlement agreement, by August 2027 EPA’s Office of Water must determine whether the existing maximum contaminant level (MCL) for total chromium should be revised in accordance with the Safe Drinking Water Act.
