Technical guidance on normal levels of contaminants in Welsh soil : Cadmium (Cd) : January 2013

Abstract

Cadmium (Cd) is a metallic element naturally occurring in trace amounts at the Earth’s surface. It is toxic to humans, animals and plants, and known to be a human carcinogen. The metal associates with sulphide ores, mainly the mineral sphalerite (ZnS), and its cycling can be highly influenced by accumulation in plants and organic debris. Its abundance in igneous and sedimentary rocks is generally low, not exceeding 0.3 mg/kg, although Cd can concentrate in metalliferous ore deposits, in argillaceous (fine grained) rocks and in coal. A contributing factor in determining the Cd content of soil is the chemical composition of the parent material. Areas in which soils are enriched in Cd are those with high naturally occurring Cd concentrations, usually associated with sulphide mineralisation, in the underlying rocks. Cadmium is an element associated with many of the mineralised areas and the accompanying mining and processing activities such as ore smelting. Zinc smelters may cause large emissions of fumes enriched in CdO. Phosphate fertilisers and sewage sludges are also sources of Cd in soil. The presence of Cd in car tyres and motor oil often accounts for the relative accumulation of Cd in roadside soils. Other important anthropogenic sources are Ni-Cd batteries and coal burning