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Labile Cd complexes increase Cd availability to plants.
Fien Degryse1, Erik Smolders, Roel Merckx
1Laboratory for Soil and Water Management, K.U. Leuven, Kasteelpark Arenberg 20, 3001 Heverlee, Belgium. fien.degryse@biw.kuleuven.be
Environmental Science & Technology
|March 3, 2006
Summary
Metal bioavailability models often overlook dissolved metal complexes. This study shows labile cadmium complexes significantly increase plant uptake, challenging the free ion concept in trace metal bioavailability.
Area of Science:
- Environmental Chemistry
- Plant Physiology
- Ecotoxicology
Background:
- Dissolved trace metals exist as free ions and complexes in the environment.
- Current bioavailability models primarily focus on the free metal ion.
- Observed increases in metal uptake suggest limitations in the free ion activity model.
Purpose of the Study:
- To investigate the influence of dissolved cadmium (Cd) complexes on plant uptake.
- To evaluate the role of complex lability in Cd bioavailability.
- To assess the validity of the free ion concept under varying complexation conditions.
Main Methods:
- Measured Cd uptake by spinach (Spinacia oleracea) from solutions with and without synthetic ligands.
- Analyzed Cd uptake at constant free ion concentrations across different complex treatments.
- Utilized the Diffusive Gradient in Thin Films (DGT) technique to measure diffusional fluxes.
Main Results:
- Cd uptake varied by nearly three orders of magnitude at the same free ion concentration.
- Plant uptake was highest in the presence of fast-dissociating (labile) Cd complexes.
- Diffusional fluxes measured by DGT correlated with plant uptake, supporting diffusion limitation.
Conclusions:
- Cd uptake by spinach is rate-limited by the diffusion of free Cd ions to root surfaces.
- Dissolved Cd complexes enhance Cd uptake, creating apparent exceptions to the free ion model.
- The concentration and lability of Cd complexes significantly influence Cd bioavailability.