A new standard for chemical testing has been developed for a carcinogenic chromium salt. The hexavalent chromium ion was at the heart of the pollution controversy on which the movie Erin Brokovich was based.
US scientists at the National Institute of Standards and Technology (NIST) have issued a new reference material that will help environmental scientists detect the cancer-causing pollutant more accurately in soil samples. The new reference material will provide a crucial benchmark for the high-quality chemical measurements needed to guide and assess cleanup efforts, the organisation says.
Hexavalent chromium
Most of us think of chromium as a component of chrome, the silvery material used to protect ferrous metals from the elements and a rusty demise. Chromium ions exist in several forms including, chromium(III), which is a micronutrient, and chromium(VI), the carcinogenic hexavalent form. Both of these forms, or oxidation states, of the metal are released during chromium ore extraction. The products of extraction are used in anti-corrosion agents, in paints and dyes, and in tanning leather.
Unfortunately, reprocessed chromium waste contains compounds of both the trivalent and hexavalent forms of chromium. During the 1940s and 1950s, this waste was dumped across sites in the USA. In New Jersey alone, authorities have identified more than 160 sites now requiring cleanup because of the presence of chromium(VI).
Unfortunately, cleanup efforts are confused by the ambiguous chemistry of chromium. Its ions can interact with organic carbon and iron in the soil and be affected by soil pH. The result is that, depending on the chemical conditions, the higher (VI) or the lower (III) oxidation state may be present at different levels. The presence of the former may pose a significant risk to health through leaching into ground water or through environmental exposure. So, it is important to know soil conditions and testing parameters.
The ambiguity of chromium’s oxidation states currently hampers regulatory agencies hoping to enforce health and safety rules. A site labelled as hazardous may not present adequate evidence at the site or given a change in soil conditions. If a site is identified as contaminated when it is not, then expensive remediation efforts will be wasted, but a site marked uncontaminated represents a health risk to local residents.
To aid in reducing the uncertainty surrounding these important measurements, NIST scientists have prepared and assigned certified values for Standard Reference Material (SRM) 2701, Hexavalent Chromium in Contaminated Soil, High Level. This standard was collected from a known contaminated site and processing was applied to compensate for the chameleon-like chemical properties of chromium. The Standard Reference Material will allow investigators to calibrate their analytical equipment and so identify safe or contaminated sites much more precisely.
Further reading
Standard Reference Materials homepage
http://ts.nist.gov/measurementservices/referencematerials
Hexavalent Chromium page
https://www-s.nist.gov/srmors/view_detail.cfm?srm=2701
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