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Frequently Asked Questions: Chromium in Water
Is Madison tap water safe to drink?
Yes. Madison water is routinely tested for more than 130 potential contaminants, including both regulated and unregulated substances. Our extensive testing confirms that we meet all current federal and state drinking water standards.
What is chromium 6 and why is it in our water?
Chromium 6 is an element that is commonly found at low levels in drinking water. It can occur naturally in the ground but may also enter drinking water sources, including groundwater, from historic leaks and industrial hazardous waste sites. Chromium 6 is known to be a potent carcinogen when inhaled. It was recently found to also cause cancer in laboratory mice and rats when they were exposed to high levels in drinking water. The chromium 6 found in Madison’s drinking water is believed to be naturally occurring in the ground and not due to industrial pollution.
Why are we hearing about chromium 6 now? Have chromium levels in Madison water suddenly increased?
Several factors have contributed to the current attention on chromium 6. First, recently published studies on mice and rats in the US combined with observations in China have suggested a higher risk from chromium 6 in drinking water than was previously thought.
Second, the state of California proposed a public health goal (PHG) for chromium 6, the only state to do so, as the initial step in the process of developing an enforceable water quality standard for that state. The proposed PHG of 0.06 parts per billion (recently revised downward to 0.02 ppb) provided a point of comparison for the non-profit group, the Environmental Working Group, to compare a limited number of cities from across the United States.
Public records from the state of California show that of over 7,000 drinking water sources that were tested, about one-third of them had detectable levels of chromium 6 (greater than 1 ppb). Of those sources with detectable amounts of chromium 6, the median concentration was nearly 4 ppb.
Finally, similar to the situation with other drinking water contaminants, the ability to detect trace concentrations of one part per billion, which is equivalent to one second in 32 years, or less, has outpaced the science that can provide meaning to the significance of chronic exposures to these minute levels in drinking water. Measuring total chromium levels below 1 ppb was not standard until the mid-1990s. Previously, the detection ability was in parts per million, not billion. Furthermore, few analytical labs are capable of measuring chromium 6 down to the proposed California public health goal.
Total chromium levels have been measured at Madison wells since at least the early 1970s, and the levels are relatively unchanged since that time. The techniques and the methods for measuring chromium may have changed, but the concentrations have not.
How do our rates of stomach cancer compare to the rest of the state and nation?
The level of chromium in our area's drinking water has remained steady at least since the 1970s, yet rates of stomach cancer have declined over the same period. The statewide rate of stomach cancer is well below the national average (3.8 per 100,000 people) and Dane County has the lowest rate in the state (2.5 per 100,000 people).
How do the concentrations of chromium 6 in our water compare to studies and incidents where it was found to cause cancer?
Local experts have suggested that total chromium concentrations in the 0-1 ppb range are not uncommon and are likely due to the geologic composition of the aquifer from which our drinking water is drawn. Other studies have shown that ground waters generally have a higher fraction of total chromium in the chromium 6 form while chromium 3 dominates in surface waters.
Chromium 6 was the carcinogen made famous by the movie Erin Brockovich. Hinckley, California residents were awarded a multi-million dollar settlement from Pacific Gas & Electric, a company that used chromium 6 to prevent rust in cooling tower water at its compressor station. Wastewater from the station percolated into the groundwater, affecting an area approximately two miles long and nearly a mile wide. Concentrations in groundwater monitoring wells in Hinckley have measured over 500 ppb.
What is the difference between total chromium, chromium 6, and chromium 3?
Chromium occurs in the environment and drinking water sources in two principal forms: trivalent chromium (chromium 3) and hexavalent chromium (chromium 6). The sum of all chromium in a sample is called total chromium. Chromium 3 occurs naturally in food and is an essential dietary nutrient while chromium 6 is a more toxic form of chromium.
Chromium can transform from chromium 3 to chromium 6, and vice versa, depending on the physical and chemical environment. For example, industrial releases of chromium 6 are often converted to chromium 3 after being deposited into the soil.
What is the current water quality standard for chromium?
Currently, there is no federal or state regulation for chromium 6. The federal government regulates only total chromium and the maximum contaminant level (MCL) is 100 ug/L or 100 parts per billion (ppb). When the regulation was established, it was assumed that all chromium in drinking water was chromium 6 and the MCL of 100 ppb was protective of human health.
What are the total chromium levels for Madison wells?
All Madison wells are tested annually for total chromium. The levels range from below detection to a little over 2 ppb and are relatively unchanged in the over thirty years of test results we have. These levels are well below the current regulatory limit of 100 ppb.
Why doesn't the EPA require testing of chromium 6?
When the total chromium standard was established in 1992, chromium 6 was classified as a carcinogen for inhalation (an occupational hazard associated with inhaling chromium dust in metal processing facilities) but not for consumption in drinking water. At that time, it was believed that any chromium 6 ingested in drinking water was converted to chromium 3 by stomach acid. However, recent studies on mice and rats have raised questions about this earlier assumption. The EPA is currently reviewing the science to determine (1) if water utilities should be required to test for chromium 6 in addition to total chromium, and (2) whether the drinking water standard for total chromium should be adjusted, or whether a new standard should be established for chromium 6.
Why is the EPA reviewing its current standard for chromium?
New research on mice and rats and data collected from China suggest that chromium 6 in drinking water may cause stomach cancer in humans.
Do any water utilities currently test for chromium 6?
In January 2011, Madison began a comprehensive monitoring program for chromium 6. Other utilities in the state, including Milwaukee, Watertown, and Beloit, have tested for chromium 6 or are planning to do so. Outside of California, where monitoring is required if the total chromium concentration tests above 1 ppb, few if any utilities likely tested for chromium 6 before this year.
What is the Madison Water Utility doing about the issue?
The water utility has begun voluntarily testing all its municipal wells. During 2011, two samples will be collected from each source (well) with additional samples collected out in the distribution system.
The Water Utility Board is drafting a letter to US EPA Administrator Lisa Jackson, urging her agency to establish a regulatory standard and to require routine monitoring by water utilities across the country.
Finally, the utility is awaiting the outcome of the toxicological review currently being performed by the EPA. This review will establish whether a new regulatory standard should be created or the current total chromium standard should be modified.
How often will Madison water be tested for chromium, and where can I find the results?
The water utility began voluntarily testing for chromium 6 earlier this year and plans to test each well twice this year. In addition, a number of samples will be collected in the distribution system. Monitoring is planned for February, June, and September. Test results will be reported on our website, madisonwater.org, and through the Drinking Water Quality listserv, which you can join at https://my.cityofmadison.com/.
What is the difference between a public health goal and a water quality standard?
A public health goal (PHG) is the level of a contaminant in drinking water that does not pose a significant risk to health. Establishing a PHG is the first step in the process of developing an enforceable water quality standard, which is usually called the maximum contaminant level (MCL). Public health goals reflect the risk associated with long-term exposure and should not be used to estimate risks from short-term or acute exposure.
Public health goals are the estimated “one in one million” lifetime cancer risk level. This means that for every million people who drink two liters of water a day for 70 years, no more than one person would be expected to develop cancer from the exposure to that particular contaminant in drinking water. This “one in one million” risk level is widely accepted by doctors and scientists as the “negligible risk” standard.
The enforceable water quality standard (MCL) for a particular contaminant is set as close to the PHG as is economically and technically feasible. In some cases, the PHG and MCL are set at the same level; however, in other cases, the MCL is greater than the PHG since the “best available technology” is not able to reduce a potential contaminant below this level or it is cost prohibitive to do so with the available technology.
Are pitcher-style filters effective at removing chromium from drinking water?
Pitcher-style filters are most effective at removing impurities that impart a taste or odor to the water. Often, consumers find that they improve the taste by removing the chlorine. However, they are generally not effective at removing dissolved metals like chromium, lead, or manganese.
Are there any available filters that can remove chromium 6 from my drinking water?
Two technologies that have been shown to reduce chromium in water are ion exchange and reverse osmosis. If you are considering a home treatment unit, be sure the unit is certified to remove the contaminants you are concerned about. Two independent certifying organizations, NSF International and the Water Quality Association, provide lists of treatment devices they have certified.
Should I buy a reverse osmosis filter to filter my tap water?
Filtering is not necessary and we do not recommend it. However, some consumers might decide to filter their water for additional peace of mind. Reverse osmosis filters are effective at removing chromium; however, they remove all minerals including the ones that create a crisp, refreshing taste. All that is left is water--a tasteless substance. As with all filters, if you decide to purchase one, be sure that it is rated to remove the contaminant of concern, and that you maintain the filter according the manufacturer’s recommendations. Filter maintenance typically involves periodically replacing a cartridge filter. When deciding on a particular model, you should consider the anticipated maintenance costs and the frequency with which the cartridge must be replaced in addition to the unit cost.
Where can I find more information about chromium 6?
Websites of the following organizations provide additional information on chromium 6 in drinking water with links to more information:
United States EPA – Chromium in Drinking Water
California EPA – Public Health Goal for Hexavalent Chromium