Cadmium toxicity and phytoremediation in trees - a review

Over time, the anthropic activity has contributed to alter biogeochemical cycle of heavy metals by releasing contaminants into water, soil and air. Due to contamination of environments with heavy metals, plants and animals consumed by population have presented some level of contamination, which has caused worries and also attempts to minimize these problem. Among heavy metals, cadmium is one of the most toxic to living creatures, occupying seventh position in toxic substances ranking, even with very low concentrations. One of measures adopted to reduce negative impact of soil contamination by heavy metals is phytoremediation. It consists of use of plants that tolerate presence of heavy metals in soil, absorbing, translocating and compartmentalizing them in aerial part, with little or no negative impact on plant growth. Among plants, trees are the most suitable for phytoremediation due to their considerable production of air biomass, which is associated with higher accumulation and consequently higher extraction of heavy metals. In this review, we address main nutritional, biochemical, physiological and molecular aspects of cadmium toxicity in plants, emphasizing role of trees in phytoremediation studies, especially recent studies on 'Khaya ivorensis' or African mahogany and its cadmium phytoremediation potential.