Chromium is an element naturally found in water. Chromium in drinking water supplies can arise from natural (i.e. geologic) and man-made (i.e. anthropogenic) sources.  In 2008, The National Toxicology Program (NTP) reported that very high levels of hexavalent chromium [Cr(VI)] in drinking water caused certain cancers in laboratory rodents. The extremely high concentrations of Cr(VI) – sufficient to turn the water yellow – that caused cancer in rodents in the NTP study are thousands of times higher than most U.S. drinking water supplies and hundreds of times higher than the current EPA chromium drinking water standard. To better understand how Cr(VI) causes cancer in the rodents, a multidisciplinary multi-institutional research project was created. The project, called the Cr(VI) Mode of Action (MOA) Research Study, investigated the underlying mechanism of carcinogenesis in rodents initiated by Cr(VI) in drinking water. Importantly, this research provides information to help address the question of whether the trace levels of Cr(VI) present in many U.S. drinking water supplies pose any cancer risk to humans. Key objectives of the Cr(VI) MOA study were to i) better understand how Cr(VI) causes cancer in rodents (e.g., mutagenic or non mutagenic mode of action) and ii) provide data and analyses to assist regulators in setting drinking water standards for Cr(VI). This website provides a repository for data related to the Cr(VI) MOA Research Study and additional information resources related to Cr(VI).

About Us

The Cr(VI) MOA Research Study team involves a versatile group of highly qualified scientific experts from many different organizations. The organizations involved specialize in areas such as risk assessment, benchmark dose modeling, toxicology, histopathology, genomics, mutational analyses, and cytogenetics. read more

Research Project

The Cr(VI) MOA team conducted two 90-day drinking water studies using the same strains of rats and mice used in the NTP study (2008) in order to further investigate the underlying MOA of the observed tumors in the 2-year NTP study. To ensure the studies were of the highest quality and appropriate for providing the data needed for understanding the Cr(VI) MOA, these studies were subject to extensive and multiple peer review processes organized by Toxicology Excellence for Risk Assessment (TERA). Resulting data from the Cr(VI) MOA studies are available to the public. read more

Study Data

To provide transparency and objectivity regarding study data, the Cr(VI) MOA Research Study team has made major study reports and raw data files available for download by individuals or organizations interested in analyzing Cr(VI) on their own. Scientists interested in downloading these data must log in, or register if you are a new user. read mores


The Cr(VI) MOA research team has published its findings related to these studies in multiple peer-reviewed scientific journals, several of which have received awards from the Risk Assessment Specialty Section of the Society of Toxicology (SOT). Additionally, the team has presented results at scientific conferences such as the Society of Toxicology and ToxForum.  read more


Several resources related to levels of Cr(VI) in drinking water as well as human health risk assessments and toxicological reviews are available.  read more