BIOAVAILABILITY OF CADMIUM 
    Cation Exchange Capacity (CEC)
    pH
    Soil Amendments
    Competitive Cations
    Fertilizer
    Mycorrhizae
    Chelation
       Phytochelatins (PCs)
       Phytochelatin Effectiveness
       Role of Sulfur in PCs
       Oxidative Stress
       Translocation
       Metallothioneins
       Organic Acids
       EDTA / EGTA

CADMIUM TOLERANCE AND
ACCUMULATION IN PLANTS
    Cell Wall Binding
    Reduced Transport
    Compartmentalization
    Chelation
    Phytoextraction factors
       Table 1.  Plant Accumulation
       Hyperaccumulators

CONCLUSIONS

LINKS

BIBLIOGRAPHY
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

INTRODUCTION

     Cadmium (Cd) is a heavy metal naturally present in soil at concentrations of slightly more than 1 mg Kg-1 (Peterson and Alloway, 1979). Not only is it non-essential for life, it is highly toxic to most organisms, having a toxicity 2-20 times higher than many other heavy metals (Vassilev, 1998).  It is therefore considered a very serious pollutant. Cd content in soil has been dramatically increased from anthropogenic sources including smelters and agricultural applications of fertilizer and sewage sludge. Since Cd in soil is available for plant uptake and subsequent human uptake, Cd in the environment poses a significant health risk.

     Cd is the fifth most toxic metal to vertabrates, and the fourth most toxic metal to vascular plants (Jones, 1939; Oberlunder and Roth, 1978). Toxic levels in soil are difficult to estimate because very little of Cd present in the soil is actually available for incorporation into biological systems, however, by best accounts, total Cd levels exceeding 8mg Kg-1, or soluble (bioavailable) levels exceeding .001 mg Kg-1, are considered toxic to plants (Kabata Pendius and Pendius, 1992; Bohn et al. 1985). Exposure to Cd results in so many physiological breakdowns that it is nearly impossible to determine which effects are primary and which are secondary (Prasad, 1995). Root et al. (1975) reported that Cd toxicity resulted in stunted growth and chlorosis.

     Since Cd poses a serious health risk to living organisms, and since it can be easily incorporated into the human food chain through uptake by agronomic crops or through grazing of contaminated plants by herbivores, much research has centered on how to either clean up Cd in soil to eliminate the threat, or to reduce the availability of Cd in soil so that the risk of it being incorporated into the food chain is reduced. Traditional methods of cleaning, or remediating, areas contaminated with heavy metals such as Cd most often include some kind of excavation and relocation of the contaminated soil to a hazardous waste landfill. Another traditional approach is to cap the polluted area with an impermeable soil and/or concrete layer to prevent leaching of the contaminant into groundwater by rainfall migrating through the soil, and to prevent any living thing from coming into contact with the pollutant. A more recent approach to remediating contaminated sites is called phytoremediation, a term which describes the use of plants to clean up contaminants from a substrate, whether it be soil, air or water. The efficacy of phytoremediation as a viable remediation technology is still being explored, yet so far the results are positive.
 
 

Next