Volume 43 Number 8
Chromium: The Risk & The Fix
With heightened awareness of the health effects of chromium contamination and the resultant public concern, especially in California, chromium has become a "hot" topic in the water treatment industry. Chromium as a water contaminant has been known for many years. The U.S. Environmental Protection Agency (USEPA) chromium regulation went into effect in 1992 and limits all forms of chromium to below 100 micrograms per liter (ug/L) or parts per billion (ppb). Chromium is present in the environment in several forms. The most common and naturally occurring form is trivalent chromium—Cr(III). Other forms in the environment are present primarily from industrial processes and include hexavalent chromium—Cr(VI)—and metallic chromium—Cr(0). Cr(III) is an essential nutrient required for normal metabolism of sugars, proteins and fats.
Of the three most common forms, hexavalent chromium—also known as chromium 6—is the most toxic. Most filmgoers will recall this is the contaminant that caused the wide variety of negative health reactions among residents of Hinckley, Calif., where Pacific Gas & Electric used the chemical in its gas compressor plant. The tragedy was the story behind the movie "Erin Brockovich," that earned Julia Roberts an Academy Award.
Forms of exposure
For the general population, the most likely route of Cr(III) exposure is by eating foods that contain chromium. Cr(III) occurs naturally in many fresh vegetables, fruits, meat, yeast and grains. On average, adults in the United States take in an estimated 60 ug of chromium per day from food. An intake of 50-200 ug of Cr(III) per day is recommended for adults as an essential nutrient. At much higher levels, ingestion of Cr(III) may begin to cause health problems. Death from acute ingestion of chromium has been documented at 600,000 ug to 2,300,000 ug for an 80-kilogram (or 176-pound) adult.
Chromium has been recognized as an airborne health contaminant in industry and has been regulated for dust exposure by the Occupational Safety & Health Administration (OSHA) since 1974. There are three avenues for chromium to enter the body: inhalation, ingestion and skin exposure. The adsorption rate is dependent on the route of exposure and the form of chromium. Cr(VI) is adsorbed much faster than Cr(III) through inhalation and ingestion. Inhalation of chromium is the primary route of exposure in documenting long-term health effects. Very little chromium enters the body through healthy skin as it's a very effective barrier to many chemicals. Ingestion of chromium is a major route for acute, short-term exposure. Chromium isn't stored in the body like some other metals and is usually flushed out of the body within 24 hours.
Ties to cancer
Chromium is known to cause cancer by inhalation of dust or chromium-containing fumes only. Cr(VI) compounds have been associated with lung cancer in factory workers and have caused cancer in laboratory animals. The U.S. Department of Health and Human Services has determined that certain Cr(VI) compounds are known human carcinogens. The International Agency for Research on Cancer (IARC) has reached the conclusion that Cr(VI) is carcinogenic to humans based on sufficient evidence in laboratory studies. The USEPA has determined that Cr(VI) is a human carcinogen by inhalation and has also determined that there is insufficient information at this time to determine whether ingestion of Cr(VI) and Cr(III) in any form are human carcinogens. Studies are under way to determine the chronic health effects of Cr(VI) when ingested.
Naturally occurring chromium concentrations in drinking water are generally very low, less than 2 ug/L. Industrial sites, landfills, or busy roadways all may contribute to concentrated chromium compounds in the water supplies. The USEPA has set the maximum contaminant level of Cr(III) and Cr(VI) allowed in drinking water at 100 ug/L. The California Office of Environmental Health Hazard Assessment (OEHHA) set a public health goal for total chromium at 2.5 ug/L in 1999 and is working on setting a final Cr(VI) health goal.
Setting the standards
The ANSI/NSF standards for drinking water treatment units (DWTUs) address chromium removal for several technologies. Standard 53 covers most capacity limited technologies for the reduction of both Cr(III) and Cr(VI). Standards 58 and 62 address chromium reduction for reverse osmosis (RO) and distillation technologies. In these standards, the influent challenge is comprised of 1/2 Cr(III) and 1/2 Cr(VI) for a total concentration of 300 ug/L. The products tested must remove both forms of chromium through the entire test to below the maximum drinking water level (MDWL) of 100 ug/L.
The most common technology available for point-of-use (POU) chromium reduction is an RO system. Currently, over 130 NSF-certified systems from 35 different manufacturers meet the criteria. RO is a very efficient technology for chromium reduction and achieves reductions well below the MDWL of 100 ug/L. Distillation is also a very effective technology for chromium reduction with over 30 certified systems. Distillation also typically reduces the levels of chromium well below the MDWL. Products that have been certified under these standards must have a Performance Data Sheet (PDS), which provides details concerning testing. Most products will report the actual test results on the PDS including average influent, average effluent and maximum effluent concentrations.
The risks of consuming chromium in water are much less than the risks of inhaling hexavalent chromium—Cr(VI). High levels of chromium that achieve a dose of over 600 times the MDWL can cause death, but it should also be understood that low levels of some forms of chromium are required as nutrients. There's currently inadequate evidence to mark any form of chromium as a carcinogen when consumed in water. If an individual wishes to minimize their exposure to chromium in water, there are several technologies—most notably RO and distillation systems—that have been tested and shown to work very efficiently at removing chromium. With the added awareness of chromium, perhaps the questions regarding long-term health effects will be answered soon.
About the authors
FYI—More on Chromium
• California Department of Health Services, "Chromium-6 (Hexavalent Chromium) in Drinking Water":