Douglas fir trees grown on an artificially Cd-contaminated soil, can tolerate this trace element (up to 68 mg/kg in soil) during several months. Most of the absorbed Cd is retained in roots (25 mg/kg DM), but transfer to aerial part is also effective. Showing the highest content, up to 6 mg/kg DM, among all the aboveground parts, barks seem to be a preferred storage compartment. However, the transfer factor is quite low, about 0.3. Another objective of this study was to compare the cell wall components of trees exposed to increasing Cd amounts in soil. A decrease in lignin and an increase in pectin contents were observed in response to increasing soil cadmium concentration. A concurrent reduction in methyl-esterification of pectin suggests than the structure of this major binding site could therefore be modified as a reaction to cadmium contamination. Future prospects will focus on the modulation of pectin composition in response to Cd exposure.
This paper shows that natural materials such as barks can successfully replace synthetic resins for industrial purposes. Evaluated in batch conditions, biosorption of uranium on suitably prepared Douglas fir barks took place in less than 10 min and appeared to be optimum at pH>4. The biosorption process of uranium (uranyl form UO 2 2+ ) was characterized in the optimal physico-chemical conditions and could be mathematically modeled as a Langmuir isotherm. With a maximum uranium specific uptake q max value of 1.16 meq.g -1 (138 mgU.g -1 ) it was found that the sorption capability of Douglas fir barks was at least five times higher for uranium than for other heavy metals such as lead. Adsorption of uranium contained in water leached from a former uranium mine was then monitored over a one-month period in a laboratory-scale chromatography column. The fixation capacity remained fairly constant throughout the whole testing period. Water radioactivity decreased from 1500 mBq. L
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