The occurrence and dispersion of potentially toxic elements in areas covered with black shales and slates in Korea

Abstract

Potentially toxic heavy metals together with other elements are present in some natural geological materials and the Okchon black shale in Korea provides an important example of this. The dispersion of these elements in the rocks and soils derived from this shale are examined. Geochemical surveys were undertaken in 11 study areas in the Okchon Zone underlain by black shales, slates, phyllites and limestones. After appropriate preparation of rocks and soils, samples were analysed for multi-elements by INAA, ICP-AES and ICP-MS. Some potentially toxic elements are highly enriched in the Okchon black shales and soils developed from these shales in the Dukpyungri and Majeonri areas. In particular, mean concentrations in soils in the Dukpyungri area are 34 μg/g As, 43 μg/g Mo and 3.4 μg/g Se which are significantly higher than the worldwide average for soils. The degree of enrichment decreases in the order: forest > upland farm = paddy > playground soils, and discriminant analysis by geochemical characteristics separates soils in the black shale area from those in other rock areas in terms of Se, Zn, Mo and Cd.