Determination of Cr(III), Cr(VI) and total chromium in atmospheric aerosol samples

Abstract

This study addresses the optimization and validation of an analytical method based on the ultrasound-assisted extraction of soluble Cr from atmospheric particulate matter (PM) and subsequent determination of Cr(III) and Cr(VI) by catalytic adsorptive stripping voltammetry (CAdSV) by using diethylenetriammino pentaacetic acid (DTPA) as complexing agent in the presence of nitrate. We evaluated the influence of various filter materials and of extracting conditions and validated the method on both reference material and real PM10 samples. The accuracy of total extractable Cr determination was checked by parallel ICP-OES measurements. The determination of total chromium was performed by ED-XRF. Results of field campaigns carried out in two industrial areas (North Italy and Tunis) and at a peri-urban site near Rome are reported. At the peri-urban site, the total Cr concentration in PM10 ranged from 2 to 5 ng/m3, with a soluble fraction of 5-13%, and Cr(VI) concentration was always below the detection limits (50 pg/m3). In the industrial area of Northern Italy, total Cr concentration ranged between 6 and 11 ng/m3, the soluble fraction was about 11-28% and detectable amounts of Cr(VI) were found, with a Cr(VI)/Cr(III) ratio ranging from 0.5 to 2.5. A further increase of Cr(VI) concentration was evidenced at the industrial site of Tunis, where the total Cr concentration ranged from 6 to 26 ng/m3, with a soluble fraction accounting for about 8-44% and a Cr(VI)/Cr(III) ranging from 1.6 to 3.6. The results of size-segregated samples, collected in Northen Italy by a 10-stage cascade impactor, indicate a relevant fine fraction of Cr(VI), with Cr(VI)/Cr(III) ratios increasing with the decrease of particle size.

Keywords

• particulate matter
• cromium speciation
• catalytic stripping voltammetry
• size distribution