Enriched Levels of Arsenic in Post‐Active Acid Sulfate Soils in Alberta

Three post‐active acid sulfate soils derived from weathered pyritic shale were analyzed for total As. Levels found in B and C horizons were nearly 10 times higher than normal background abundances. Secondary iron oxides formed from the weathering of pyrite acted as scavengers of As. Samples of segregated iron oxyhydroxide collected from B horizons contained up to several hundred mg As kg −1 . Natrojarosite and clay separates from the same horizons contained from 30 to 50 mg As kg −1 . Pyrite is believed to be the source of the elevated levels of As.