Measurement of Soluble and Total Hexavalent Chromium in the Ambient Airborne Particles in New Jersey

Abstract

Hexavalent chromium (Cr(VI)) in ambient airborne particulate matter (PM) is a known pulmonary carcinogen and may have both soluble and insoluble forms. The sum of the two forms is defined as total Cr(VI). Currently, there were no methods suitable for large-scale monitoring of total Cr(VI) in ambient PM. This study developed a method to measure total Cr(VI) in ambient PM. This method includes PM collection using a Teflon filter, microwave extraction with 3% Na2CO3-2% NaOH at 95°C for 60 minutes, and Cr(VI) analysis by 1,5-diphenylcarbazide colorimetry at 540 nm. The recoveries of total Cr(VI) were 119.5 ± 10.4% and 106.3 ± 16.7% for the Cr(VI)-certified reference materials, SQC 012 and SRM 2700, respectively. Total Cr(VI) in the reference urban PM (NIST 1648a) was 26.0 ± 3.1 mg/kg (%CV = 11.9%) determined by this method. The method detection limit was 0.33 ng/m3. This method and the one previously developed to measure ambient Cr(VI), which is soluble in pH ~9.0 aqueous solution, were applied to measure Cr(VI) in ambient PM10 collected from three urban areas and one suburban area in New Jersey. The total Cr(VI) concentrations were 1.05–1.41 ng/m3 in the winter and 0.99–1.56 ng/m3 in the summer. The soluble Cr(VI) concentrations were 0.03–0.19 ng/m3 in the winter and 0.12–0.37 ng/m3 in the summer. The summer mean ratios of soluble to total Cr(VI) were 14.3–43.7%, significantly higher than 4.2–14.4% in the winter. The winter concentrations of soluble and total Cr(VI) in the suburban area were significantly lower than in the three urban areas. The results suggested that formation of Cr(VI) via atmospheric chemistry may contribute to the higher soluble Cr(VI) concentrations in the summer.

Trivalent chromium solubility and its influence on quantification of hexavalent chromium in ambient particulate matter using EPA method 6800

“…The former include Na 2 CrO 4 , K 2 CrO 4 , and (NH 4 ) 2 CrO 4 ; the latter include PbCrO 4 , BaCrO 4 , and CaCrO 4 . Our recent work suggested that both groups were simultaneously present in the fresh ambient PM 10 collected in New Jersey and an aged reference urban PM (NIST 1648a) (Huang et al, 2014). The enriched 53 Cr(VI) spike used by EPA method 6800 (in the form of K 2 CrO 4 ) is only able to mimic the Cr(VI) with high solubility products (soluble Cr(VI)) in ambient PM.…”

“…The enriched 53 Cr(VI) spike used by EPA method 6800 (in the form of K 2 CrO 4 ) is only able to mimic the Cr(VI) with high solubility products (soluble Cr(VI)) in ambient PM. Therefore, we recommended separate measurement of soluble and total Cr (VI) in ambient PM (the difference between the two refers to insoluble Cr(VI)) (Huang et al, 2014), and EPA method 6800 can be used to correct soluble Cr(VI) conversion. In summary, the appropriate use of EPA method 6800 is important when measuring Cr(VI) in ambient PM.…”

“…To overcome Figure 3. The Eh-pH diagram of chromium (Huang et al, 2014). the problem, EPA method 6800 has been recently developed to enable in situ monitoring and subsequent correction of the Cr alteration via the isotopically enriched spikes.…”

“…The four locations were New Jersey Meadowlands District, Elizabeth Trailer (NJ Turnpike Exit 13), Rahway, and Piscataway. Site information can be found in Huang et al (2014). Briefly, the sampling site in the Meadowlands area (adjacent to the city of Lyndhurst) was surrounded by a large landfill site, historic chromite ore processing residue (COPR) waste sites, two major traffic routes (I-95 and NJ-21), and a PSEG Fossil LLC Hudson Generation Station.…”

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Fan (2014) Trivalent chromium solubility and its influence on quantification of hexavalent chromium in ambient particulate matter using EPA method 6800, Journal of the Air & Waste Management Association, 64:12, 1439-1445, DOI: 10.1080/10962247.2014 Measurement of carcinogenic Cr(VI) in ambient PM is challenging due to potential errors associated with conversion between Cr (VI) (a carcinogen) and Cr(III) (an essential nutrient). Cr(III) conversion is a particular concern due to its >80% atomic abundance in total Cr.

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