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Collaboration: Why collaborate to certify a new ambient-level hexavalent chromium standard reference material? Northern Ontario Ring of Fire • “The Ring of Fire” is a planned large-scale mineral mining site in the James Bay Lowland of Northern Ontario, Canada. • The area is one of Canada’s largest potential mineral mining sites and covers 5,000 square kilometers. • During the first 10 years of development, the site is estimated to have a potential of generating up to $9.4 billion in Gross Domestic Product, $6.2 billion for Ontario’s mining industry, and $2 billion in government revenue. R2 • The Ring of Fire is located in the Far North, which contains 40 percent of Ontario’s Aboriginal population and 106 of Ontario’s 133 First Nations. • Careful environmental monitoring of the chromium ore processing will minimize environmental contamination and reduce the risk of chromium exposure. • Assessment of the site’s natural state and background chromium levels is needed for continuous environmental monitoring. • Current chromium reference materials contain levels of chromium that are not suitable for background environmental monitoring. • The proposed Sigma-Aldrich ambient-level hexavalent chromium certified reference material a soil matrix (pictured below) will allow for improved analytical measurements. Current Status of Collaboration • The proposed hexavalent chromium certified reference material has been produced, homogenized, bottled, and distributed to all collaborating facilities. • Independent analysis is underway at all collaborating laboratories. • Planned collaborative literature publication outlining the details of the material, certification, results, and homogeneity. • Certified reference material will be available from Sigma-Aldrich for purchase later this year. Abstract: Several hexavalent chromium standards in soil, certified in the past decade, either have high concentrations of chromium or active matrices that render them unsuitable for validation studies that use natural soil untouched by industrial activity. NIST 2701, for example, is made of chromium processing ore residue (COPR) industrial waste material from New Jersey. It contains approximately four percent total chromium, with an unnaturally high Cr(VI) fraction (552.1 mg/kg). SRM-2701 also includes an active matrix that dominates the chemistry of the standard and causes significant Cr(III)/Cr(VI) species shift and biases during extraction. Presently, no ambient-background level standard containing an inert matrix is available for the appropriate validation of ambient level Cr(VI) in native or uncontaminated soil. An international collaboration is under way to produce a more appropriate series of low level soil certified standard reference materials for Cr(VI) analysis. Multiple laboratories in different locations are involved in certifying two new reference materials at ng/g levels. These were prepared by Sigma-Aldrich in larger batches and were distributed among the participating laboratories for collaborative certification. The methods used for certification are two EPA RCRA methods: alkaline extraction of hexavalent chromium by EPA method 3060A and speciated isotope dilution mass spectrometry analysis by EPA method 6800 (Update V, 2015). Chromium Toxicity: Chromium is found in the environment mainly as the trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) valence states: Trivalent Chromium • The majority of naturally occurring chromium is trivalent chromium. • Trivalent chromium is an essential dietary mineral and is thought to be required for proper lipid and sugar metabolism. • Biologically active trivalent chromium may be found in the glucose tolerance factor (GTF) complex, which facilitates the interaction of insulin with cellular receptor sites. • Fresh foods and drinking water contain trivalent chromium, and dietary deficiency of Cr(III) is associated with diabetes, infertility, and cardiovascular disease. R1 Hexavalent Chromium • Hexavalent chromium is produced mainly from human activities and is highly toxic since it is absorbed more readily than trivalent chromium by the lungs, gut, and skin. • Evidence suggests that Cr(VI) is carcinogenic, causes respiratory and dermal reactions, and damages the liver and kidneys. R1 • The risks associated with hexavalent chromium on human health is recognized by national and international organizations, including the United States Environmental Protection Agency (EPA), Occupational Safety and Health Administration (OSHA), and International Agency for Research on Cancer (IARC). The EPA is investigating the need to revise chromium drinking water regulations and California’s Proposition 65 (Safe Drinking Water and Toxic Enforcement Act of 1986) includes Cr(VI) on a list of chemicals that cause cancer, birth defects, or reproductive problems. Under Proposition 65, the maximum allowable dose level (MADL) for hexavalent chromium is 8.2 μg/day. • Sources of hexavalent chromium found in the environment include airborne emissions from chemical plants and incineration facilities, cement dust, contaminated landfill, effluents from chemical plants, road dust from catalytic converter erosion and asbestos brakes, tobacco smoke, topsoil and rocks, and chromium ore processing. • Workplace exposure to hexavalent chromium is often from industrial processes that include drilling muds, chrome plating, textile manufacturing, paint pigments, wood treatment, and welding of alloys or steel. The OSHA exposure limit is 5 μg Cr(VI) per cubic meter of air. • Due to the prevalence and toxicity of the Cr(VI) species, environmental and workplace monitoring is essential for reducing human exposure to hexavalent chromium. Chromium Species Interconversion: • Measurement of chromium species in environmental, biological, dietary, and industrial samples is difficult when using traditional analytical methods. • Chromium species interconversion occurs during sample processing and instrumental analysis, which may introduce oxidizing and reducing agents, UV light, and changes in the sample pH/oxidation/ reduction potential (Eh). • The Cr(III)/Cr(VI) species distribution is predicted by the sample pH-Eh values: o Cr(VI) is relatively stable at high pH and Eh. o Cr(III) is relatively stable at low pH and Eh. Objective: Due to the potential for species interconversion, accurate determination of the concentrations and stabilities of the Cr(III) and Cr(VI) oxidation species requires a method that is capable of correcting for interconversion, bias, and instrumental error. EPA method 6800 with molecular speciated isotope dilution mass spectrometry (SIDMS) and EPA alkaline extraction method 3060A are being used to produce data that qualifies, quantitates, and certifies the new Sigma-Aldrich ambient-level hexavalent chromium certified reference material (CRM) with a soil matrix. The new CRM is needed to facilitate routine quantitation of hexavalent chromium during ambient-level environmental sample analysis. The methods use known amounts of enriched, isotopically-labelled 50-Cr(III) and 53-Cr(VI) spikes in the sample preparations to correct for the Cr(III) and Cr(VI) interconversion during sample extraction and instrumental analysis. Ion chromatography (IC) is used to separate the Cr(III) and Cr(VI) oxidative species before analysis by inductively coupled plasma mass spectroscopy (ICP-MS). The final 50/52-Cr(III), 53/52-Cr(III), 50/52-Cr(VI), and 53/52- Cr(VI) isotopic ratios are used to calculate the concentrations of Cr(III) and Cr(VI) in the original unaltered sample by correcting for species interconversion during the processing. e Instrumentation: Acknowledgements: • Applied Isotopes Technologies , Inc. • Duquesne University • Bayer School of Natural and Environmental Sciences • The Kingston Research Group • Metrohm USA Inc Collaborative Certification of a New Ambient-Level Hexavalent Chromium Standard Reference Material in a Soil Matrix James Henderson 1 , Patrick Benecewicz 1 , Anil Vishnuvajjhala 1 , Weier Hao 1 , Logan Miller 1 , Matt Pamuku 2 , Jennifer Crawford 2 , Teresa Switzer 3 , Vasile Furdui 3 , Pam Wee 4 , Francine Walker 5 , Bob O’Brien 6 , Stuart Procter 7 , and H. M. Skip Kingston 1 (1) Duquesne University, Pittsburgh, PA (2) Applied Isotope Technologies Company, Pittsburgh, PA (3) Ministry of Environment, Toronto, Canada (4) Agilent Technologies Company, Santa Clara, CA (5) Chemical Solutions Company, Harrisburg, PA (6) Sigma-Aldrich Company, St. Louis, MO (7) Metrohm USA Inc., Riverview, FL Cr(III) Cr(VI)) = Total Chromium Metrohm 850 Professional IC with 858 Professional Sample Processor Agilent 7700 Series ICP-MS References: R1: Rahman, G. M. M.; Kingston, H. M. S.; Towns, T. G.; Vitale, R. J.; Clay, K. R. Determination Of Hexavalent Chromium by Using Speciated Isotope-Dilution Mass Spectrometry after Microwave Speciated Extraction of Environmental and Other Solid Materials. Analytical and Bioanalytical Chemistry. 2005, 1111–1120. R2: Ontario Chamber of Commerce. Beneath the Surface: Uncovering the Economic Potential of Ontario’s Ring of Fire. Online: http://www.occ.ca/Publications/Beneath_the_Surface_web.pdf. 2014. United States Environmental Protection Agency (EPA). Method 3060A, Alkaline Digestion for Hexavalent Chromium. SW-846, Revision 1, Test Methods for Evaluating Solid Waste, Physical/Chemical Methods; US Government Printing Office (GPO), Washington, DC. 2014. Kingston, H. M. S.; United States Environmental Protection Agency (EPA). Method 6800, Elemental and Molecular Speciated Isotope Dilution Mass Spectrometry. SW-846, Update V, Test Methods for Evaluating Solid Waste, Physical/Chemical Methods; US Government Printing Office (GPO), Washington, DC. 2014.
