Surprise: Chromium's in the home but where's it from?
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Stern, AH, CH Yu, K Black, L Lin, PJ Lioy, M Gochfeld and ZH Fan. 2010. Hexavalent chromium in house dust: A comparison between an area with historic contamination from chromate production and background locations. Science of the Total Environment http://dx.doi.org/10.1016/j.scitotenv.2010.07.035. |
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The results suggest why allergic dermatitis caused by chromium exposure persists even after known sources are removed. The authors can only guess at where the chromium VI is coming from and say more research is needed to discern sources as well as health impacts from these home exposures.
Context
The element chromium occurs naturally in rocks and soils in a form called chromium III. Humans need small amounts of this type because it is a vital micronutrient.
A more dangerous form, called hexavalent chromium – or chromium VI – is produced during chromium ore processing. Exposure to this variety occurs mainly from breathing dust in a work place that uses chromium, but may also occur by touching polluted soil or drinking contaminated water.
Work places with air exposures include facilities that refine chromium ore, those that use chromium during a production process and those that create industrial waste from the production process. Hexavalent chromium is used in many applications, including metal plating, stainless steel and pigments.
Hexavalent chromium is a carcinogen. It is known to cause lung cancer in workers who inhale the contaminated dust for long periods of time. In the United States, federal work safety limits are set at 5 micrograms per cubic meter (μg/m3) of air during an 8-hour period.
Lesser known health effects are skin ulcers, allergic sensitization and allergic dermatitis, a severe skin reaction that can occur after contacting chromium VI in dust. Similar to other metals that cause allergic conditions – for example beryllium – large exposures to the metal can make an individual sensitive. Once a person has become 'sensitized,' skin reactions can occur from contact with much smaller amounts of chromium than would not normally cause an allergic reaction.
Most of what we know about hexavalent chromium's impact on human health is from people who have been exposed at work. Few indoor air quality assessments have been done outside of the workplace, so very little is known about exposures at home, businesses and schools. Usually, these investigations result from suspected contamination.
What did they do?
Community concern over suspected chromium contamination led researchers in New Jersey to examine homes located near an old chromate production facility. Based on site evalutations, they selected 100 homes on or near land where chromate production plants operated. Twenty homes that were at least 1 mile away from any known source of hexavalent chromium pollution were chosen as ‘background’ sites for comparison.
Dust samples were collected from window wells, living areas and basements. Two dust samples were taken for each location and analyzed for hexavalent chromium levels.
The researchers compared the levels of hexavalent chromium in dust found in homes close to the facilities – a potential source of contamination – to homes farther away and without a direct source of chromium pollution.
What did they find?
Surprisingly, the researchers found that homes far away from the chromate production facilities had just as much indoor chromium in dust as those nearby. More specifically, they found no statistically significant differences in dust concentrations of chromium VI between homes located near the pollution source and those farther away that were considered to be unexposed.
Hexavalent chromium was found in the dust of all homes sampled. In homes near the chromate plants, the mean (± standard deviation) of hexavalent chromium concentration for all samples was 3.9 (± 7.0) micrograms per gram (μg/g) compared to the mean concentration for all background home samples of 4.6 (± 7.8) μg/g.
Several of the higher values measured in the study were from dust samples taken from wood surfaces. As well, there was a relationship between the level of chromium measured and the age of the house in areas considered to represent background levels. Some associations were also found between landscaping characteristics and chromium levels. Homes with no grass (dirt) and homes with a garden were associated with moderately higher chromium levels.
What does it mean?
Homes located farther away from a direct source of chromium pollution were contaminated with similar levels of hexavalent chromium as homes near a known industrial source.
The results suggest hexavalent chromium may be an important indoor air pollutant that has been previously unrecognized in the average home. The widespread background levels measured in house dust were unexpected and may challenge assumptions about how and where people are exposed to the carcinogen. As a yet unknown source, the contaminated house dust may also help solve the puzzle of why chromium-related allergies do not always go away after people are removed from a known source of exposure.
The findings, then, beg the question: how is chromium VI getting into homes that are far from industrial sources? The measured background levels were likely not from a local pollution source – such as the chromium processing facilities – but from other potential sources of chromium in the home, suggest the authors.
For instance, higher chromium levels were associated with both an aging home and dust collected from wood surfaces. Chromium used in wood stains from 1910 to 1970 may contribute to the levels that were found on wood surfaces. Higher chromium levels in homes without grass lawns may be due to increased dust being carried into the house with people and pets. Some building materials – such as cement – also contain hexavalent chromium, which could contribute to a home's overall dust contamination.
The houses examined in this study were limited to specific regions in New Jersey. It is not known how the results found here compare to other areas of the United States. In a recent indoor air quality evaluation in California, less than 25 percent of homes tested positive for hexavalent chromium. Regional factors such as development age and industrial history may influence exposures. Therefore, the overall range of chromium levels in U.S. homes is unknown.
The authors did not evaluate whether the chromium at the levels found could impact human health. The findings suggest further studies of indoor air quality for the pollutant are warranted. As hexavalent chromium is a known lung carcinogen, it would be important to understand how much of the chromium found in this dust makes it into the air where it can be inhaled and if the exposure could increase the risk for cancer.
The findings may have a more direct impact, however, on understanding allergic skin reactions induced by hexavalent chromium. Typically, symptoms associated with an allergy-induced skin disease improve or completely vanish when the exposure is removed. In some cases, symptoms of hexavalent chromium-induced allergic dermatitis do not go away even after leaving a known exposure source. These cases may not get better because the exposure has not been fully removed, as it is still in the dust in their homes, the researchers suggest.
ResourcesChromium (VI). Integrated Risk Information Systems. U.S. Environmental Protection Agency. Chromium toxicological profile. Agency for Toxic Substances and Disease Registry. Hexavalent chromium. Occupational Safety and Health Administration, U.S. Department of Labor. OSHA issues final standard on hexavalent chromium. 2006. Atlantic Environmental Inc. |
Chromium
