In Vitro Gastrointestinal Bioavailability of Arsenic in Soils Collected near CCA-Treated Utility Poles

Because of the potentially high arsenic concentrations found in soils immediately adjacent to chromated copper arsenate (CCA)-treated wood structures and utility poles, CCA-contaminated soil ingestion may be a significant exposure route to arsenic for children. Therefore, a strong need exists to provide accurate data on oral relative bioavailability (RBA) of arsenic (in vivo or in vitro) in field-collected CCA-contaminated soils. The objectives of this study were (1) to assess arsenic bioaccessibility in contaminated soils collected near in-service CCA-treated utility poles, (2) to determine the influence of soil properties and arsenic fractionation on arsenic bioaccessibility, and (3) to estimate an average daily arsenic intake from incidental soil ingestion. Arsenic bioaccessibility (in vitro gastrointestinal (IVG) method) was determined on surface soil samples collected immediately adjacent to 12 CCA-treated utility poles after 18 months of service. Bioaccessible arsenic was also determined in 3 certified reference materials. Total arsenic concentrations in soils (<300 μm) varied from 37 ± 2 to 251 ± 12 mg/kg, irrespective of soil organic matter content with the major soil-bound arsenic species being As(V). Arsenic bioaccessibility ranged between 25.0 ± 2.7 and 66.3 ± 2.3% (mean value 40.7 ± 14.9%). The mean value was in agreement with the in vivo arsenic RBA reported by Casteel et al. (2003) in soil near CCA-treated utility poles. Bioaccessible arsenic was positively correlated with total organic carbon content (r² = 0.36, p < 0.05) and with water-soluble arsenic (r² = 0.51, p < 0.01), and was negatively correlated with clay content (r² = 0.43, p < 0.05). Using conservative exposure parameters, the mean daily arsenic intake from incidental ingestion of contaminated soil near CCA-treated utility poles was 0.18 ± 0.09 μg As kg^-1 d^-1. This arsenic intake appeared negligible compared to the daily intake of inorganic arsenic from water and food ingestion for children.