The presence of hexavalent chromium, also known as chromium-6, in drinking water remains unregulated under the current provisions of the federal Safe Water Drinking Act. But that situation may change as a result of recent research showing elevated levels of chromium-6 in the drinking water supplies of 31 different cities across the United States. The U.S. Environmental Protection Agency could move to establish federal limits for chromium-6 in drinking water as early as 2012, following the completion of its own risk assessment.
This article provides background on chromium-6 in drinking water, reviews current government regulation and oversight, testing procedures and protocols for assessing levels in water, and concludes with recommendations for public water system operators addressing future chromium-6 regulations and testing requirements.
Chromium Exposure
Human exposure to chromium-6 can result from the ingestion of drinking water, which potentially facilitates the transfer of the chemical throughout the body.
Health effects related to exposure to ingested chromium-6 are presently the subject of active investigation by the EPA and other government agencies as well as private researchers. In its draft "Toxicological Review of Hexavalent Chromium" released in September 2010 for public comment, the EPA states that there is "evidence of an association between oral exposure to hexavalent chromium and stomach cancer in humans." Further, the report notes that "available evidence indicates that chromium interacts with DNA, resulting in DNA damage and mutagenesis."
A final version of the EPA's assessment was originally expected to be released in late 2011, but EPA missed the deadline.
Perhaps the most widely known case involving human exposure to drinking water containing chromium-6 was the subject of a civil suit brought against Pacific Gas and Electric (PG&E) by attorney Edward Masry and his associate Erin Brockovich in the mid-1990s. In that case, a PG&E facility in Hinkley, Calif., was found to have discharged wastewater containing high concentrations of chromium-6 into unlined ponds, which then percolated into the local groundwater. The lawsuit, settled in 1996 for a record $333 million, claimed that residents of Hinkley experienced significantly higher rates of cancer as a result of their consumption of drinking water with elevated levels of chromium-6.
Regulatory Oversight
Although the PG&E case generated significant public interest, levels of chromium-6 in drinking water have remained unregulated at the federal level. The federal Safe Drinking Water Act (SDWA), originally published in 1974 and amended as recently as January 2011, currently identifies maximum concentration levels in drinking water for more than 100 different chemicals. While concentrations of total chromium are limited to 100 µg/L (ppb), the SDWA does not specifically set concentration limits for chromium-6. Further, the EPA does not require local water systems to test drinking water supplies for chromium-6 concentrations.
At the state level, California has been the most active in efforts to establish limits for chromium-6 in drinking water and in monitoring concentration levels in local water supplies. The California Department of Public Health (CDPH, formerly the Department of Health Services) classified chromium-6 as an "unregulated chemical requiring monitoring" in 1999, and began receiving samples from local water authorities in January 2001.
Separately, the state's Office of Environmental Health Hazard Assessment (OEHHA) began efforts to establish a public health goal for chromium-6, proposing a goal of 0.06 µg/L (ppb) in September 2009. The proposed public health goal was revised downward to 0.02 µg/L (ppb) in July 2011, paving the way for the California CDPH to proceed with efforts to establish a primary drinking water standard setting a maximum contaminant level for chromium-6.
The level of interest in increased federal regulation of chromium-6 in drinking water rose dramatically in late 2010, when the non-profit Environmental Working Group (EWG) released findings from a study evaluating chromium-6 levels in public drinking water supplies in 35 selected cities across the United States. According to a report issued by the EWG, water samples from 31 of 35 cities evidenced detectible levels of chromium-6, with samples from 25 cities exhibiting levels higher than 0.06 µg/L (ppb). The average chromium concentration for all cities included in the study was 0.18 µg/L (ppb); one city in the study, Norman, Okla., had concentration levels of 12.90 µg/L (ppb).
The release of the EWG study prompted the EPA to publish recommendations in January 2011 regarding the monitoring of chromium-6 levels in drinking water by state and local drinking water authorities. The EPA's guidance includes recommendations on the frequency and process for collecting water samples for testing. It also provides detailed information on preferred laboratory testing methods for accurately assessing chromium-6 concentrations.
The EPA also pledged to release the final version of its "Toxicological Review of Hexavalent Chromium" in 2011, and to determine if additional standards and testing requirements are appropriate. In a meeting in December 2010 with a group of U.S. senators inquiring about the EPA's response to the EWG study, EPA Administrator Lisa Jackson noted that, based on the current draft risk assessment, the EPA would likely revise drinking water regulations to account for the more recent scientific findings.
At least some lawmakers are likely to keep pressure on the EPA to follow through on its commitment to strengthening chromium-6 drinking water standards. In January 2011, U.S. Senators Barbara Boxer and Dianne Feinstein introduced legislation that would set a one year deadline for the EPA to establish an enforceable limit for chromium-6 in drinking water.
Finally, the EPA has proposed changes to its Unregulated Contaminant Monitoring Regulation 3 (UCMR 3) requiring the monitoring of contaminants using EPA and/or consensus analytical methods. As published in the Federal Register in March 2011, proposed changes would include chromium-6 among the list of contaminants under UCMR 3 subject to assessment monitoring by public water systems. No decision about the proposed UCMR 3 changes was available at the time this white paper was being prepared.
Monitoring, Testing
As previously noted, the EPA issued recommendations in January 2011 for public water systems regarding enhanced monitoring measures for chromium-6 in drinking water. While the agency evaluates what additional monitoring and testing measures should be implemented, this guidance represents the best framework currently available for the assessment of chromium-6 content by public water systems.
The EPA's guidance includes recommendations in the following areas:
- Preferred sampling locations
- Sampling frequency
- Laboratory assessment methods
Preferred Sampling Locations
To ensure the most accurate sampling results, the EPA recommends collecting samples from the following locations:
- Intake/well locations: Samples should be collected at the intake or well location so that untreated water can be evaluated. Systems with multiple intakes, wells or other entry points should collect samples from representative entry points to a distribution system, so that data can be used to identify corresponding water sources with concentrations of chromium-6.
- Entry points to the distribution system: Samples should also be collected at the points at which treated water enters a distribution system. Again, systems with multiple entry points should collect samples from representative entry points. The number of entry points sampled will likely depend on the number of treatment facilities, as well as the historical levels of chromium concentrations in treated water.
- Distribution system: Finally, samples should be collected at various locations within the distribution system, with special attention to those locations considered to represent the "maximum residence time." The number of sample locations within a distribution system will depend on the number of entry points, proximity of entry points to each other and overall size of the distribution system.
Sampling Frequency
The EPA recommends that public water systems that rely on surface water sources, such as lakes and streams, collect samples for assessment at least once every three months. This frequency is necessary to capture variations in the levels of chromium-6 that may occur in source waters. Public water systems that rely on ground water sources should be sampled once every six months. To the extent practical, water samples should be collected from all specified locations on the same day.
Laboratory Assessment Methods
The EPA currently recommends the use of a modified version of EPA Method 218.6, "Determination of Dissolved Hexavalent Chromium in Drinking Water, Groundwater and Industrial Wastewater Effluents by Ion Chromatography," for analyzing drinking water samples for chromium-6 content. The modified method includes a lower eluent flow rate, longer reaction coil and larger injection volume, which combine to significantly increase the sensitivity of an assessment. As such, the modified method allows for the detection of chromium-6 concentrations as low as 0.02 µg/L (ppb), consistent with California's proposed public health goal, and for reporting concentrations as low as 0.06 µg/L (ppb).
Recommendations for Selecting a Testing Laboratory
While the increased federal regulation of chromium-6 appears likely, there are presently no requirements specifically limiting chromium-6 content in drinking water. Further, California is the only jurisdiction in the United States that currently requires the monitoring of drinking water for chromium-6. Due to the absence of regulations regarding chromium-6, most laboratories serving the drinking water analytical market do not include this contaminant in their scope of services, making it difficult for public water systems to identify testing laboratories that are both equipped and technically qualified to assess drinking water samples to emerging concentration limits.
While there are a number of laboratories that possess the instrumentation required to conduct chromium-6 analysis consistent with the modified requirements of EPA Method 218.6, many of these laboratories are routinely testing for higher, i.e., less sensitive, concentrations of chromium-6 in wastewater, and therefore may not have the knowledge or experience to test to the level of sensitivity required for drinking water assessment.
As such, public water systems should exercise care when selecting a testing laboratory to perform testing for chromium-6 in drinking water, and conduct the necessary due diligence to ensure that their selected laboratory possesses the requisite equipment and technical expertise. Testing laboratories certified by an accrediting authority to conduct testing to an approved ion chromatography method (such as EPA Method 300.0, SM 41108, or ASTM D4327) and which have expertise in drinking water testing should be given priority over other laboratories. Taking these steps can help ensure accurate testing results and minimize wasted time and expense.
About the Author: Hank Lambert is General Manager, Global Food and Water Businesses, for Underwriters Laboratories. He UL in November 2010, bringing extensive food industry general management, supply chain management and business building experience. He is focused on leveraging UL's brand equity and business model into the food supply chain and food safety business, as well as driving the growth of UL's water quality and water systems business.
Editor's Note: This article is for information purposes only, and is not intended to convey legal advice regarding the laws and regulations discussed above.
The article was based on a white paper entitled "Hexavalent Chromium: A Review of Regulations and Testing Procedures" published by Underwriters Laboratories. For a copy of the full white paper and to learn more about UL's capabilities, contact Nathan Trowbridge, customer experience manager, at [email protected].
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