Cadmium uptake by plants.

Food chain contamination by cadmium (Cd) is the most important pathway of Cd exposure to the general population, excluding smokers. Factors affecting transfer of Cd from soil and air to plants are reviewed. The direct deposition of airborne Cd in the plants has only a marginal influence on the crop Cd concentrations in rural areas with low atmospheric Cd deposition, i.e. < 2 g Cd ha(-1) y(-1). However, the indirect evidence is presented, predicting that airborne Cd may be the major source of crop Cd and dietary Cd in conditions where atmospheric Cd deposition is well above 10 g Cd ha(-1) y(-1). This situation may occur around pyrometallurgic smelters with high Cd emissions. The absorption of Cd by plant roots is more influenced by soil factors, controlling Cd bioavailability than by total soil Cd. Elevated soil-plant Cd transfer is observed in soils with chloride salinity, in zinc deficient soils and acid soils.