Hexavalent chromium is used beneficially in a variety of industrial applications, including surface finishing to prevent corrosion. Due to the potentially significant environmental and human health concerns that can arise, surface finishing facilities using hexavalent chromium have implemented substantial engineering and management controls to minimize potential exposures in the workplace and in the environment. Despite the success of these efforts, regulatory and policy initiatives continue to call for even more controls on the use of hexavalent chromium. Provided below is a summary of some recent actions regarding oral exposures of hexavalent chromium that could impact even further the use of hexavalent chromium in the surface finishing industry.
EPA’s IRIS Report on Oral Exposures of Hexavalent Chromium
On September 30, 2010 EPA issued a Draft Toxicological Review of Hexavalent Chromium: In Support of Summary Information on the Integrated Risk Information System (IRIS). 75 Fed. Reg. 60454 (2010). EPA’s IRIS is a human health assessment program that evaluates risk information on effects that may result from exposure to chemical substances found in the environment. In the draft IRIS report EPA proposed a new draft oral cancer slope factor and a new draft oral reference dose based on data from a National Toxicology Program (NTP) two-year drinking water study. To derive the new oral cancer slope factor EPA used a highly conservative modeling approach.
Although the NTP study demonstrated that hexavalent chromium induced cancer in rodents, the concentrations administered in the NTP study are far in excess of typical environmental exposures. These higher doses may have overwhelmed the normal protective mechanisms that are thought to limit the carcinogenic potential following ingestion. Additionally, the NTP study raised numerous questions regarding how hexavalent chromium caused tumors in animals, and how these findings in laboratory animals relate to humans (who are typically exposed at much lower levels of hexavalent chromium and have significant notable differences in gastrointestinal anatomy and physiology).
EWG Report on Hexavalent Chromium in Drinking Water
In December 2010 the Environmental Working Group (EWG) released a report on the presence of hexavalent chromium in drinking water. EWG tested drinking water in 35 U.S. cities. Hexavalent chromium was detected in 31 of the 35 cities, with concentrations ranging from 0.03 parts per billion (ppb) to 12.9 ppb. All but one of the cities had levels less than or equal to 2.0 ppb, and more than three-fourths of samples had concentrations of less than 1.0 ppb.
EPA has a drinking water standard for total chromium of 100 ppb, and California has a limit of 50 ppb for total chromium. Due to some of the technical and practical difficulties associated with distinguishing among hexavalent chromium, trivalent chromium and other chromium compounds, drinking water limits have not yet been set for hexavalent chromium. California has, however, proposed a public health goal (not a regulatory limit) for hexavalent chromium in drinking water of 0.06 ppb. California just recently issued a new recommendation that the state goal for hexavalent chromium in drinking water should be 0.02 ppb. In its report, EWG used the proposed state goal as its benchmark for risk.
The EWG report has received widespread media coverage. Some public interest groups have even accused EPA Administrator, Lisa Jackson, of failing to regulate hexavalent chromium stringently enough. In response to the EWG report, EPA issued guidance to public drinking water systems to begin monitoring for hexavalent chromium in drinking water. Additional political and policy pressure on this issue will continue to be directed at EPA.
Drinking water standards typically serve as the basis for other regulatory limits. As a result, if EPA were to set a new drinking water standard for hexavalent chromium consistent with the claims made in the EWG report, the beneficial use of hexavalent chromium in surface finishing could be significantly restricted in the future on a number of regulatory fronts.
Surface Finishing Industry Response: NASF Comments on EPA’s IRIS Report
To ensure that regulators and citizens have accurate and relevant data to make informed regulatory and risk management decisions, the NASF submitted comments on December 29, 2010 regarding EPA’s draft IRIS report and addressed the results of the EWG drinking water report. NASF requested that EPA incorporate data from a new study conducted by the American Chemistry Council (ACC) as part of EPA’s IRIS assessment for oral exposures for hexavalent chromium. The new ACC study examines the potential risks posed by exposure to lower concentrations of hexavalent chromium.
Similar to the unrealistically high concentrations of hexavalent chromium used in the NTP study, the EWG report cited the cancer incidences associated with the Hinkley, CA wells contaminated with very high levels of hexavalent chromium as evidence that the relatively low levels of hexavalent chromium found in drinking water pose a cancer risk to humans. The concentrations of hexavalent chromium in the wells around Hinkley, CA were approximately 580 ppb.
These unusually high concentrations of hexavalent chromium in the wells associated with Hinkley do not necessarily dictate that the lower concentrations of hexavalent chromium in drinking water from the EWG study (which are three to four orders of magnitude lower) would pose similar cancer risks. Furthermore, lower concentrations of hexavalent chromium are typically reduced to the less harmful form of trivalent chromium in the human stomach. Such evidence strongly suggests a potential threshold effect for lower levels of oral exposure of hexavalent chromium in humans, below which few, if any, health impacts arise.
Data from the new ACC study would be directly applicable to the potential risk associated with oral exposure to low concentrations of hexavalent chromium, and will provide very useful information for regulatory decision making. EPA should, therefore, include and consider the data and results from the ACC study in its IRIS assessment for oral exposures of hexavalent chromium to provide a high-quality, science-based human health assessment to support its regulatory activities.
Potential risks posed by oral exposure of hexavalent chromium are serious human health concerns. To this end, the surface finishing industry has implemented numerous environmental and engineering controls and good industry practices to minimize potential releases of hexavalent chromium to the environment. Before proceeding with its final IRIS assessment for oral exposure of hexavalent chromium, NASF has asked EPA to consider the critical new data from the ACC study.
NASF will continue to pursue this issue aggressively with EPA and other industry partners. If you have any questions or would like additional information on this issue, please contact Christian Richter
or Jeff Hannapel