Influence of uraniferous black shales on cadmium, molybdenum and selenium in soils and crop plants in the Deog-Pyoun-g area of Korea

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Abstract
The influence of naturally occurring uraniferous black shales on cadmium, molybdenum and selenium concentrations in soils and plants is examined. The possible implications of element concentrations to animal and human health are considered for the Deog-Pyoung area. Geochemical surveys have been undertaken within 13 river tributary valleys in the area underlain by uraniferous black shales and black slates or grey chlorite schists. Sampling of rocks, soils and plants has been carried out along transect lines within each valley. Samples were analysed for trace elements by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and for uranium by Neutron Activation Analysis (NAA). Soil pH, cation exchange capacity, loss on ignition and particle size distribution have been measured for selected samples. Average trace element concentrations of the Okchon uraniferous black shales were 6.3 μg g−1 Cd, 136 μg g−1 Mo and 8.6 μg g−1 Se. Soils derived from these rocks tend to reflect their extreme geochemical composition. Trace element concentrations in alluvial soils derived in part from these black shales averaged 1.2 μg g−1 Cd, 20 μg g−1 Mo and 1.5 μg g−1 Se. Trace element concentrations in plants were found to be influenced by those of soils. Cadmium accumulated in tobacco leaves up to 46 μg g−1 (D.M.) and leafy plants such as lettuce contain up to 0.5 μg g−1 Se (D.M.). In addition to total concentrations in soils, soil pH is a major factor influencing uptake of Mo into crop plants and soil texture for Se. Concentrations of trace elements in plants also varied between plant species. The relative concentrations of Cd were found to vary in the order tobacco > lettuce > red pepper > rice grain. Elevated concentrations of Cd in crop plants and in tobacco may possibly have deleterious effects on human health in this area. The low Cu:Mo ratio in rice stalk of 2.65:1 may be associated with disturbed Cu metabolism in ruminant animals which regularly consume this material.