Bioaccessibility of Chromium and Copper in Soils near CCA-Treated Wood Poles

Because of the potentially high metal 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 Cr, Cu, and As for children. Therefore, a strong need exists to provide data on oral bioavailability of these elements in field-collected CCA-contaminated soils. Recently, As bioaccessibility in CCA-contaminated soils was assessed but data for Cr and Cu are lacking. Therefore, the objectives of this study were (1) to assess the bioaccessibility of Cr and Cu in contaminated soils collected near in-service CCA-treated utility poles; and (2) to determine the influence of selected soil properties on their bioaccessibility. Cr and Cu bioaccessibilities (in vitro gastrointestinal method) were determined on surface soil samples collected immediately adjacent to 12 CCA-treated utility poles after 18 months of service. Bioaccessible Cr and Cu were also determined in three certified reference materials. Total soil Cu concentrations in soils varied from $95.6\pm 4.5$ to $\mathrm{3,580}\pm 0680\mathrm{mg}∕\mathrm{kg}$ , whereas total soil Cr concentrations were lower and ranged between $26.4\pm 2.1$ to $394\pm 53\mathrm{mg}∕\mathrm{kg}$ . Copper gastrointestinal bioaccessibility ranged between $19.4\pm 3.6\%$ and $89.4\pm 4.9\%$ (mean value: $54.1\pm 23.4\%$ ), whereas Cr bioaccessibility varied from below detection $(<0.3\%)$ to $32.9\pm 17.6\%$ (mean value: $8.5\pm 10.1\%$ ). Bioaccessible Cr and Cu were both negatively correlated with silt content ( $r^2=0.39$ , $p<0.05$ , and $r^2=0.65$ , $p<0.005$ , respectively). Copper bioaccessibility was also negatively correlated with total organic carbon content ( $r^2=0.64$ , $p<0.01$ ). Using conservative exposure parameters, the mean potential Cr intake from incidental ingestion of soil near CCA-treated utility poles was very low $(0.03\pm 0.03\mathrm{\mu }\mathrm{g}\mathrm{Cr}∕\mathrm{kg}\mathrm{body}\mathrm{weight}∕d)$ . The estimated mean Cu intake was also low $(2.5\pm 1.2\mathrm{\mu }\mathrm{g}\mathrm{Cu}∕\mathrm{kg}\mathrm{body}\mathrm{weight}∕d)$ in spite of its higher bioaccessibility. These values are much lower than the dietary reference intakes and oral minimal risk levels for Cu and Cr.