Arsenic bioaccessibility in CCA-contaminated soils: influence of soil properties, arsenic fractionation, and particle-size fraction.

Arsenic bioaccessibility in soils near chromated copper arsenate (CCA)-treated structures has recently been reported, and results have shown that soil properties and arsenic fractionation can influence bioaccessibility. Because of the limited data set of published results, additional soil samples and a wider range of soil properties are tested in the present work. The objectives are: (1) to confirm previous results regarding the influence of soil properties on arsenic bioaccessibility in CCA-contaminated soils, (2) to investigate additional soil properties influencing arsenic bioaccessibility, and to identify chemical extractants which can estimate in vitro gastrointestinal (IVG) bioaccessibility, (3) to determine arsenic speciation in the intestinal phase of the IVG method and, (4) to assess the influence of two particle-size fractions on arsenic bioaccessibility. Bioaccessible arsenic in eight soils collected near CCA-treated utility poles was assessed using the IVG method. Five out of the eight soils were selected for a detailed characterization. Moreover, these five soils and two certified reference materials were tested by three different metal oxide extraction methods (citrate dithionite (CD), ammonium oxalate (OX), and hydroxylamine hydrochloride (HH)). Additionally, VMINTEQ was used to determine arsenic speciation in the intestinal phase. Finally, two particle-size fractions (<250 microm, <90 microm) were tested to determine their influence on arsenic bioaccessibility. First, arsenic bioaccessibility in the eight study-soils ranged between 17.0+/-0.4% and 46.9+/-1.1% (mean value 30.5+/-3.6%). Using data from 20 CCA-contaminated soil samples, total organic carbon (r=0.50, p<0.05), clay content (r=-0.57, p<0.01), sand content (r=0.48, p<0.05), and water-soluble arsenic (r=0.66, p<0.01) were correlated with arsenic bioaccessibility. The mean percentage of total arsenic extracted from five selected soils was: HH (71.9+/-4.1%)>OX (58.0+/-3.1%)>water-soluble arsenic (2.2+/-0.5%), while the mean value for arsenic bioaccessibility was 27.3+/-2.8% (n=5). Arsenic extracted by HH (r=0.85, p<0.01, n=8) and OX (r=0.93, p<0.05, n=5), showed a strong correlation with arsenic bioaccessibility. Moreover, dissolved arsenic in the intestinal phase was exclusively under the form of arsenate As(V). Finally, arsenic bioaccessibility (in mg/kg) increased when soil particles <90 mum were used.