Aqueous chemistry of airborne hexavalent chromium during sampling

Abstract

Cr(III) is an essential micronutrient for the proper function of human being, while Cr(VI) is a carcinogenic chemical, which has been one of the hazardous air pollutants defined by US Environmental Protection Agency (US EPA) in 2004. Accurate measurements of atmospheric hexavalent chromium concentration are required to evaluate its toxicity. In the present study, a simulation tool using MATLAB program was developed to evaluate soluble and insoluble chromium species formed during the Cr(VI) field sampling (500 ml, 0.12 M HCO3− buffer, pH = 9, 24 h, cellulose filter) which will assist us to better quantify the hexavalent chromium concentration. In this study, Cr(VI) was found to be dominant in soluble form as CrO42− and in precipitated form as (NH4)2CrO4, CaCrO3, BaCrO4, and PbCrO4 at pH = 9 cellulose filter. Secondly, reduction of Cr(VI) to Cr(III) was higher than the oxidation of Cr(III) to Cr(VI). Basic pH solutions retard the conversion of Cr(VI) in the presence of Fe(II) and As(III) and facilitate the precipitation of Cr(III). The presence of the NaHCO3 as buffer on the cellulose filters and also in the filter extraction solution may add to the precipitation of Cr(VI) as NaCrO4. This study provides new insights to improve cellulose sampling filters, and the filter extraction solutions to either prevent Cr(VI) precipitation during the wet analysis of Cr(VI) or improve the Cr(VI) analysis methods to quantify total Cr(VI) (soluble and insoluble Cr(VI)).