Inorganic arsenic speciation in soil and groundwater near in-service chromated copper arsenate-treated wood poles

The environmental impact of chromated copper arsenate (CCA)-treated utility poles is linked to the possible soil and groundwater contamination with arsenic. The objective of the present study was to determine the arsenic speciation in soil and groundwater near in-service CCA-treated poles. Arsenite (As[Ill]) and arsenate (As[V]) concentrations were determined in 29 surface and subsurface soil samples collected near eight CCA-treated wood poles. Temporal variability of total arsenic concentrations and inorganic arsenic speciation was also assessed in groundwater at two sites through four sampling events over a 19-month period. Arsenic speciation was carried out by a solvent extraction method using ammonium pyrrolidine dithiocarbamate-methyl isobutyl ketone, and total arsenic was quantified by inductively coupled plasma/atomic emission spectrometry/hydride generation. Average arsenic concentrations in surface soils immediately adjacent to utility poles ranged from 153 +/- 49 to 410 +/- 150 mg/kg but approached background levels (below 5 mg/kg) within 0.50 m from the poles. A positive correlation was found between surface soil As concentration and total Fe content. In subsurface samples (0.50 m), arsenic levels were generally high in sandy soils (up to 223 +/- 32 mg/kg), moderate in clayey soils (up to 126 +/- 26 mg/kg), and relatively lower in organic soils (up to 56 +/- 24 mg/kg). Arsenic(V) was the predominant arsenic species in surface (>78%) and subsurface soils (>66%). Total arsenic concentrations in groundwater below the clayey site were high and varied widely over time (79-390 mu g/L), with 30 to 68% as As(III). Below the utility pole located on the organic site with a high Fe content, lower total arsenic levels (12-33 mu g/L) were found, with As(III) ranging from 0 to 100%.