Hexavalent Chromium (Cr-6)

Increased interest in levels of hexavalent chromium (Cr-6) in drinking water typically arises following reports about the occurrence of this metal in the nation’s drinking water. There is much uncertainty about the significance of very low levels of Cr-6 in drinking water so we are providing the following facts to keep our customers informed about the issues regarding Cr-6 and WSSC’s actions

What is chromium and where do you find it?

Chromium is a naturally occurring metal.  It is also used industrially in steel making, metal plating, leather tanning, paints, dyes, and wood preservatives.  It is discharged by industrial facilities such as coal burning power plants. Some household plumbing fixtures with chrome plating or stainless steel components may also release hexavalent chromium in the water.  Chromium is most commonly present in the environment in three forms:  trivalent, hexavalent, and the solid metal form.  Trivalent chromium is an essential micro-nutrient in the human diet and generally not considered toxic.  Hexavalent chromium is known to pose human health risk at a certain level.  A new Environmental Protection Agency (EPA) risk assessment, not finalized yet, is looking into the human health risk from hexavalent chromium exposure at the very low levels typically found in drinking water.

Is hexavalent chromium allowed in drinking water?

Hexavalent chromium, also known as chromium-6, is currently regulated under the EPA's  Safe Drinking Water Act only as a component of “total chromium”.  The allowable level (or Maximum Contaminant Level, MCL) for total chromium is 100 parts per billion (ppb). 

In 2014, California became the first state to regulate hexavalent chromium at an MCL of 10 ppb. This standard applies only to water systems in the state of California.  California initially established a Public Health Goal (PHG) of 0.02 ppb in 2011 based solely on data of health effects over a lifetime of daily exposure.  Why is the final MCL standard 500 times higher than the PHG?  The MCL was selected as close to the PHG as economically and technologically feasible, taking into account other factors including available treatment and analytical technologies and the cost of monitoring and treatment.

Does WSSC monitor for hexavalent chromium?

Currently, the EPA does not require that hexavalent chromium be separately tested in drinking water.  However, it does require that we monitor total chromium, which includes hexavalent chromium along with other harmless forms of chromium.  Total chromium levels in WSSC water are routinely less than 2 ppb, 50 times less than the EPA limit.  These results are reported to our customers annually, along with other required water quality test results, via our Water Quality Report.

In light of the concerns raised in 2011, WSSC began voluntarily monitoring for hexavalent chromium at various points within our system.  Sampling points included the source water we take into our Potomac and Patuxent Water Filtration Plants, treated water at those plants and a variety of public locations in our service area.  All data from those tests have been made available to regulators and our customers through our website, and we will keep those results online.

Here is a table showing the results of our hexavalent chromium monitoring.  Results to date indicate a very low level presence of hexavalent chromium when it is detected above the minimum reporting limit.  The average level detected since 2011 is 0.101 ppb, about 100 times lower than California’s MCL.

 

Potomac WFP Source

Potomac WFP

Tap

Bethesda

Piscataway

Patuxent WFP Source

Patuxent WFP

Tap

Colesville

Bowie

/High Bridge

February 2011

ND

ND

0.068

0.073

ND

ND

ND

ND

March 2011

0.071

0.074

ND

ND

ND

ND

ND

ND

April 2011

0.054

ND

0.098

0.100

ND

0.062

0.074

0.095

May 2011

0.110

0.093

0.100

0.150

0.053

0.057

0.130

0.120

June 2011

0.190

0.093

0.220

0.280

0.038

0.052

0.056

0.180

July 2011

0.220

0.049

0.036

0.022

0.270

0.160

0.200

0.065

August 2011

0.140

0.098

0.210

0.270

0.028

0.034

0.038

0.160

September 2011

0.067

0.080

0.140

0.190

0.039

0.042

0.051

0.110

October 2011

0.072

0.120

0.130

0.180

ND

0.029

0.058

0.100

November 2011

0.100

0.100

0.100

0.160

0.027

0.033

0.042

0.090

December 2011

0.100

0.110

0.110

0.130

0.039

0.043

0.057

0.087

January 2012

0.086

0.084

0.083

0.120

0.022

0.030

0.036

0.080

April 2012

0.090

0.077

0.087

0.100

0.024

0.033

0.047

0.072

July 2012

0.066

0.200

0.180

0.240

0.025

0.034

0.070

0.100

October 2012

0.067

0.130

0.150

0.170

ND

ND

0.029

0.067

January 2013

0.072

0.093

0.084

0.170

0.024

0.024

0.051

0.084

April 2013

0.048

0.048

0.076

0.110

0.027

0.035

0.052

0.095

August 2013

 

0.160

 

0.210

 

0.046

 

0.120

October 2013

 

0.140

 

0.200

 

0.032

 

0.100

January 2014

 

0.096

 

0.130

 

ND

 

0.080

April 2014

 

0.140

 

0.170

 

0.054

 

0.110

October 2014

 

0.200

 

0.240

 

0.029

 

0.100

January 2015

 

0.094

 

0.120

 

0.022

 

0.055

March 2015

 

0.085

 

0.100

 

0.050

 

0.110

May 2015

 

0.074

 

0.170

 

0.048

 

0.110

July 2015

 

0.220

 

0.280

 

0.042

 

0.180

October 2016

 

0.100

 

0.220

 

ND

 

0.110

January 2016

 

0.094

 

0.082

 

ND

 

0.050

April 2016

 

0.120

 

0.160

 

0.042

 

0.069

July 2016

 

0.250

 

0.300

 

0.032

 

0.100

ND – not detected.

Do studies in animals translate into harmful levels for humans?

The 2010 draft EPA risk assessment relied largely on the health-effects studies conducted by administering high dosages of hexavalent chromium to animals.  Some researchers in the scientific community have raised concerns about extrapolating animal health effects data obtained at very high hexavalent chromium levels to humans at ultra-low levels found in drinking water.  That’s because the saliva and the human stomach have some capacity to “detoxify” hexavalent chromium by reducing it to harmless, trivalent form.  This is the most significant issue that must be addressed before the risk assessment is finalized.

EPA is currently working on revising its draft risk assessment for hexavalent chromium in drinking water which was released in 2010.  This risk assessment is supposed to provide a scientific basis for deciding whether hexavalent chromium in drinking water requires regulation, and if so, at what levels.  This assessment (which should be based on sound science) is necessary for drinking water utilities like WSSC to proceed in a way that protects the health of our customers.

If the EPA decides to regulate very low levels of hexavalent chromium, how much will it cost to reach those levels?

The only treatment technologies known to effectively remove hexavalent chromium are reverse osmosis and anion exchange, both of which are prohibitively expensive.  With the tremendous financial constraints most utilities are already facing with failing infrastructure, it is highly questionable whether these additional costs to customers are justifiable given their limited presumed benefit and also the potential household sources of hexavalent chromium (e.g., plumbing fixtures).

Can I use a home filter to provide protection from potential impact of hexavalent chromium?

The home treatment device that would be most suitable for removing hexavalent chromium is reverse osmosis.  However most home filters are only certified to perform to the existing standards (i.e., total chromium of 100 ppb), which is far above the typical levels of hexavalent chromium in drinking water.  Thus, it is uncertain how much of hexavalent chromium can be removed by these units.  Hexavalent chromium is not volatile, so boiling the water is not an effective way to reduce its level.

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