ARSENIC AND ANTIMONY IN THE SOIL-VEGETATION-STREAM WATER SYSTEM OF EASTERN ALASKA

The mobility of As and Sb through the soil-vegetation-stream water system was investigated near gold-bearing quartz vein deposits. The study area, located in eastern Alaska, is typified by a continental climate and boreal forest vegetation. Known mineralization in the area include the Pogo and Grizzly Bear deposits and the Grey Lead and Blue Lead mines. To characterize the mobility of As and Sb through the soil-vegetation-stream water system in this area we measured As and Sb concentrations in grayleaf willow (Salix glauca L.), soil, soil pore water, and stream water. Water and selective extraction of the soil was used to determine the phase association of the As and Sb in the soil. Arsenic concentrations range from <1 to 400 µg/L in stream water; < 0.01 to 0.14 mg/Kg in willow leaves; <1 to 4.8 µg/L in soil pore water; and, for the A, B, and C soil horizons, 0.6 to 1000 mg/Kg, 2.7 to 800 mg/Kg, and 2.6 to 770 mg/Kg, respectively. Antimony concentrations range from <0.1 to 18.2 µg/L in stream water; <0.003 to 0.23 mg/Kg in willow leaves; < 0.3 µg/L in soil pore water; and, for the A, B, and C soil horizons, 0.3 to 24 mg/Kg, 0.6 to 74.2 mg/Kg, 0.2 to 37 mg/Kg, respectively. The percentage of the total soil As extracted by water was ten times greater than that of Sb. A significantly (p-value = 0.00) greater percentage of the As and Sb in the A and B soil horizons was water extractable compared to the C horizon soils. Arsenic in the soils is associated with the organic, Fe-oxide, and sulfide fractions of the selective extraction. In contrast Sb is primarily associated with the sulfide and residual fractions. The difference in soil pore water concentration and water extractability between As and Sb is consistent with the difference in the phase association.