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Water: Chromium in Drinking Water

EPA’s recommendations for enhanced monitoring for Hexavalent Chromium (Chromium-6) in Drinking Water

EPA began a rigorous and comprehensive review of the health effects of chromium-6 following the 2008 release of toxicity studies by the Department of Health and Human Service's National Toxicology Program. In September, 2010, EPA released a draft of the scientific human health assessment (Toxicological Review of  Hexavalent Chromium) for public comment and external peer review. When this human health assessment is finalized EPA will carefully review the conclusions and consider all relevant information to determine if a new standard needs to be set.

In the interim period, EPA is providing the following guidance to water systems on how they may monitor for chromium-6 in addition to the monitoring they are required to perform for total chromium. EPA believes that monitoring for chromium-6 will enable public water systems (PWSs) to: better inform their consumers about the levels of chromium-6 in their drinking water, evaluate the degree to which other forms of chromium are transformed into chromium-6 in their drinking water and assess the degree to which existing treatment is affecting the levels of chromium-6.

Enhanced Monitoring

Why is EPA seeking assistance from water systems to understand chromium-6 levels? If we're not sure what a safe level is at this stage, why monitor now?
It is possible that a lower, more stringent regulatory level for chromium will be considered in the future. Given that possibility, it will be extremely helpful to EPA, states, and utilities to prepare now by gaining a better understanding of the span and scope of the issue. EPA strongly recommends that utilities think proactively in terms of gaining a better understanding of the nature and sources of chromium-6 and how they might be addressed in the future.

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Should my water system conduct enhanced monitoring for chromium-6?
Given the emerging public health information, EPA has provided guidance to public water systems on how systems could enhance chromium monitoring through additional chromium-6 sampling and analysis. The Agency encourages water systems to consider the following recommendations and to determine how your system might enhance drinking water monitoring for chromium-6.

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Is EPA requiring water systems to perform chromium-6 monitoring through the Unregulated Contaminant Monitoring Rule (UCMR)?
The third Unregulated Contaminant Monitoring Regulation (UCMR 3) requires many public water systems to monitor for 28 contaminants including chromium-6. For more information about the UCMR 3 see https://water.epa.gov/lawsregs/rulesregs/sdwa/ucmr/ucmr3/index.cfm The UCMR 3 requires many but not all public water systems to monitor chromium-6 for a 1 year period. EPA encourages those systems not required to conduct monitoring under the UCMR3 to voluntarily monitor for chromium-6. This monitoring will enable systems and their customers to better understand the impact that chromium-6 has on their drinking water.

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Where should water systems collect samples?
Chromium is complex in its behavior in drinking water systems as it may occur in water systems in both the chromium-3 and chromium-6 forms. Under distribution system conditions-- in the presence of an oxidant such as chlorine -- chromium-3 can be transformed into the more toxic chromium-6 form. Existing treatment processes such as conventional treatment may be effective in removing chromium-3, but not chromium-6. To understand the fate of incoming chromium-6 in raw water supplies or transformed chromium-6 from chromium-3 following conventional treatment and disinfection, EPA recommends that systems collect samples at the locations listed below.
    Intake or well locations: EPA recommends that water systems collect samples of untreated water at the intake or well. Systems with multiple intakes and wells should identify sampling points that result in a representative sample of the utilized source waters to account for the multiple sources and seasonal variation in sources. Chromium data at entry points can serve as a guide for identifying the corresponding source water intakes and wells, which should preferably be targeted for monitoring.

    Entry points to the distribution system: EPA recommends that systems with drinking water treatment processes also collect samples at the point that treated water enters the distribution system. Systems with multiple entry points should collect samples from representative entry points to the distribution system.

    Distribution System: EPA recommends that systems collect representative samples from locations within the distribution system. Since chromium-3 can transform into chromium-6 in the distribution system due to the presence of an oxidant such as chlorine, it is desirable that systems monitor for chromium-6 at locations considered to represent the maximum residence time, which is consistent with the monitoring goals for disinfection byproducts. The number of locations to consider for sampling within the distribution system will depend on the number of entry points, the relational proximity of entry points and the overall size of the distribution system. EPA also recommends that systems collect samples at a subset of 10 or fewer distribution system locations where they currently sample under the disinfection by-products rule stages 1 and 2, and that systems not disinfecting consider collecting samples from a subset of 10 or fewer locations where they typically sample under the total coliform rule .

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How frequently should samples be collected?
EPA recommends that water systems with surface water sources collect samples quarterly to capture the variation that may occur in the levels of chromium-6 in source waters. EPA recommends that ground water systems be sampled twice per year. EPA recommends that systems collect samples from each of the locations listed above on the same day.

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Is EPA requesting water systems to submit chromium-6 monitoring data?
EPA is not requesting chromium-6 data be submitted, but the Agency is open to receiving any information regarding occurrence and treatment of drinking water contaminants.

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Who should I call if I have questions about EPA's recommended enhanced monitoring for chromium-6?
Contact EPA via email at the Safe Drinking Water Hotline website or call the Safe Drinking Water Hotline at 1-800-426-4791 (Monday through Friday, 10:00 a.m. to 4:00 p.m. Eastern Time).

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Laboratory and Method

What analytical method is appropriate to measure chromium-6?
EPA recommends that laboratories use EPA Method 218.7, "Determination of Hexavalent Chromium in Drinking Water by ion Chromatography with Post-Column Derivatization and UV-Visible Spectroscopic Detection" (Version 1, November 2011), available for download at: https://water.epa.gov/scitech/drinkingwater/labcert/upload/EPA_Method_218-7.pdf.

This method is based on a modified version of EPA Method 218.6, "Determination of Dissolved Hexavalent Chromium in Drinking Water, Groundwater and Industrial Wastewater Effluents by Ion Chromatography" (Rev. 3.3, 1994; www.nemi.gov), which were outlined in Dionex Corp. Application Update 144 "Determination of Hexavalent Chromium in Drinking Water by Ion Chromatography" found at www.dionex.com/en-us/webdocs/4242-AU144_LPN1495.pdf and also in Metrohm USA Inc.'s IC Application Work AW US6-0152-012001 found at http://info.metrohmusa.com/hexachrome/downloads/HexachromebyIC.pdf. By following EPA Method 218.7, laboratories are capable of attaining a detection limit as low as 0.005 micrograms per liter µg/L (ppb) and can support a reporting limit of 0.03 µg/L (ppb). Any equivalent ion chromatographic system from any manufacturer with comparable hardware that can generate this performance and meet the quality control requirements in Section 9.0 of EPA Method 218.7 may also be used.

Links to non-EPA sites do not imply any official EPA endorsement of, or responsibility for, the opinions, ideas, data or products presented at those locations, or guarantee the validity of the information provided.

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How can I find a laboratory to analyze chromium-6?
If a public water system is having difficulty finding a laboratory that offers chromium-6 analysis, there are several state certified laboratories in California that are familiar with the modified EPA Method 218.6.  The California list of laboratories is posted at Certified laboratories for Testing Chromium-6 in Drinking Water.At present the list includes about 20 commercial labs. The California reporting level for chromium-6 is 1 ppb but each laboratory will have its own method reporting level, which may be lower. Public water systems soliciting for laboratory support from California certified laboratories should ask about the capability to support a chromium-6 suggested reporting limit of 0.03 ppb. EPA has learned that most laboratories are capable of a much lower reporting limit.

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What additional quality control measures are important?
Section 9 of EPA Method 218.7 includes necessary quality control measures for the method. Any laboratory conducting chromium-6 analysis using this method must meet these quality control requirements to report valid data. Laboratories should also supply the following information for quality control purposes:
    • Supporting analytical quality control data with observations.
    • Calibration validation data.
    • Demonstration of accurate and precise lab fortified blank measurements at the expected minimum reporting level (0.03 ppb).

An additional quality control measure is to test replicate samples to evaluate the accuracy and precision of recoveries from field sample matrix fortified with chromium-6. This can be accomplished by preparing and analyzing lab fortified sample matrices or matrix spike samples with the companion lab fortified sample matrices duplicate or matrix spike duplicate sample.

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What is an appropriate holding time for chromium-6 samples?
EPA Method 218.7 prescribes a sample holding time for properly collected and stored samples of no more than 14 days.

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What treatment methods can be used for removing chromium-6 from drinking water?
Chromium-6 in water can be treated in one of two ways:
    • direct removal of chromium-6, or
    • reduction of chromium-6 to chromium-3, followed by removal of chromium-3.

A bench-scale study sponsored by the American Water Works Association-Water Research Foundation identified four technologies which are most promising for application by drinking water systems. These technologies include: anion exchange, coagulation and precipitation of reduced chromium-3, adsorption via sulfur modified iron media, and membrane treatment such as nanofiltration and reverse osmosis.  The bench-scale study report is available at http://www.waterrf.org/Search/Detail.aspx?Type=2&PID=2814&OID=91042F.  

While there are no full-scale treatment systems operating in the United States specifically for chromium-6 removal, two technologies [reduction/coagulation/filtration and single use weak base anion exchange (WBA)], have been demonstrated using pilot-scale systems in the city of Glendale, Calif.. Pilot-scale evaluation and cost analysis continue using the demonstration facilities in Glendale, Calif. More information about the Glendale, Calif., evaluations is available at http://www.waterrf.org/Search/Detail.aspx?Type=2&PID=3167&OID=91193.

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Will conventional treatment remove chromium from water?
Conventional treatment, coagulation and filtration, can remove chromium-3 from water, but not chromium-6.

A treatment profile survey of water systems treating surface water showed that conventional treatment was able to remove between 40 percent and 100 percent of total chromium from water.  The treatment profile survey is available at http://www.waterrf.org/Search/Detail.aspx?Type=2&PID=2759&OID=91044F.

Removal of chromium-6 by conventional treatment -- coagulation or lime softening followed by filtration -- was also investigated in bench-scale tests. The study's authors observed that chromium-6 was not removed by alum or ferric coagulation or by lime softening. They attributed the low rate of removal to the high solubility of chromate and dichromate ions.

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Does chromium-3 convert to chromium-6 in the drinking water distribution system?
If there are oxidants (including disinfectants) in the distribution system, chromium-3 can be expected to be partially or completely oxidized to chromium-6. A Water Research Foundation study evaluated the effects of free chlorine, chloramines, potassium permanganate, and hydrogen peroxide in the oxidation of chromium-3 to chromium-6. Free chlorine could oxidize 50 to 65 percent of chromium-3 to chromium-6 at neutral or low pH conditions. The presence of other ions and natural organic matter reduces the oxidation effectiveness of free chlorine on chromium-3. Chloramines and potassium permanganate also oxidized chromium-3 to chromium-6 in this study.  The study report is available at http://www.waterrf.org/Search/Detail.aspx?Type=2&PID=2814&OID=91042F.

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If EPA decides to revise the regulation that includes chromium 6 in drinking water, what is the process the agency will follow?
Prior to EPA making any decisions about revising the chromium drinking water regulation, EPA must issue its final human health assessment for chromium-6. More information regarding EPA's current schedule for the chromium-6 assessment is available at https://cfpub.epa.gov/ncea/iristrac/index.cfm?fuseaction=viewChemical.showChemical&sw_id=1114  

EPA will carefully review the final assessment and consider all other relevant information to determine if a new drinking water regulation for chromium-6 or a revision to the current total chromium standard is warranted. 

More information about the EPA's drinking water regulatory process is available at the EPA website https://water.epa.gov/lawsregs/rulesregs/regulatingcontaminants/basicinformation.cfm.

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