So far there is relatively little information on the behaviour of thorium in the environment. It is generally believed that mobility of thorium in soil is rather low. Th⁴⁺ is readily soluble, but may be quickly adsorbed or precipitated as hydrolysate. On the other hand, tetravalent thorium may be strongly complexed with soil organic matter. This may result in the increasing mobility of Th in soil. The chemical toxicity of Th is similar to that of heavy metals, but radio-toxic effects caused by ionising activity is an added feature of the actinide. An increase of Th content in plants may cause a decrease of concentration of such essential macro-nutrient as calcium and variations in concentrations of many trace elements. Growth of wheat in soil and water artificially contaminated with thorium may lead to significant bioaccumulation of this metal and its removal from the growth media.