Cadmium phytoextraction: present state, biological interactions and research needs

Abstract

Cadmium is a toxic metal for living organisms and an environmental contaminant. Agricultural soils in many parts of the world are slightly to moderately contaminated by Cd due to long term use of phosphatic fertilisers, sewage sludge application as well as smelter dust spreading. Cd phytoextraction is a promising and environmentally friendly approach for soil decontamination. Plant potential for Cd extraction generally depends on shoot Cd concentration and shoot biomass yield. Some ecotypes of the metal hyperaccumulator species Thlaspi caerulescens J. & C. Presl possess an extraordinary Cd accumulation and tolerance, but have low biomass yield. Some fast growing trees (Salix, Populus) and high biomass producing crops (Brassica, Helianthus, Nicotiana) are also considered as suitable species for phytoextraction as they might compensate lower Cd accumulation with much higher biomass yields. Moreover, they deliver “production” which eventually can be utilised, making the phytoextraction process more feasible from economical point of view. At present, plant potential for Cd phytoextraction is limited by: (1) low biomass yield and some undesirable characteristics of Thlaspi caerulescens, (2) low shoot Cd concentration and ability to withstand Cd of biomass plans, (3) economical factor. There are two general approaches for further development of Cd phytoextraction: genetic transformations to improve plant factor and agronomy-related optimisations in many different aspects. To overcome the main biological bottlenecks limiting successful phytoextracton, a good knowledge about Cd uptake, plant defence network against Cd as well as some possibilities to reduce chronic Cd toxicity is fundamental. This paper provides information about the plant potential for Cd phytoextraction, the biological backgrounds of this approach as well as some recent achievements and prospects.