ACCUMULATION OF NATIVE ARSENIC IN ACID SULPHATE SOILS IN ALBERTA

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Abstract
Acid sulphate soils belonging to the Boundary and Josephine soil series were analyzed for As to determine mineral partitioning, form, and redistribution of the element. Samples of soil, natrojarosite, and zones enriched in iron oxides were collected from upper and lower slope positions. Levels in bulk samples were 10 times higher and levels in some Fe oxides were 100 times higher than normal background abundances. Arsenic was partitioned into silt and clay fractions and appeared related to the distribution of iron oxides in the size separates. Most of the translocated As accumulated in the vein-like network of segregated iron oxide in fractures extending downward from B horizons. These vein samples contained as much as 450 mg As kg−1, primarily as adsorbed As associated with both crystalline and amorphous forms of iron. Microbiologically mediated losses of As had depleted surface horizons of the element. The weathering of pyrite is believed to account for the accumulations of As in acid sulphate soils. Key words: Arsenic, acid sulphate soil, iron oxyhydroxides, trace elements
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