Labile Cd Complexes Increase Cd Availability to Plants

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• 作者：Fien Degryse ; Erik Smolders ; and Roel Merckx
• 刊名：Environmental Science & Technology
• 出版年：2006
• 出版时间：February 1, 2006
• 年：2006
• 卷：40
• 期：3
• 页码：830 - 836
• 全文大小：151K
• 年卷期：v.40,no.3(February 1, 2006)
• ISSN：1520-5851

文摘

Dissolved trace metals are present in the environment asfree ions and as complexes. Commonly used models topredict metal bioavailability consider the free ion as themajor bioavailable species. However, increases in metalavailability in the presence of metal complexes haverepeatedly been found. We measured the uptake of cadmium(Cd) by spinach (Spinacia oleracea) from solution inabsence or presence of synthetic ligands. At the samefree ion concentration, the uptake of Cd ranged over almost3 orders of magnitude and was largest in treatmentswith fast dissociating (i.e. labile) complexes. Similar resultswere found for the diffusional fluxes in these solutions,as measured with the DGT technique. The observed effectof Cd complexes on the plant uptake was in agreementwith model calculations in which plant uptake was assumedto be governed by the diffusional flux. These resultsstrongly suggest that Cd uptake is rate-limited by diffusionof the free ion to the root surface, even in stirred solutions.As a result, dissolved Cd complexes can increase Cduptake, resulting in apparent exceptions from the free ionactivity model. The magnitude of this increase dependsboth on the concentration and on the lability of the complexes.The free ion concept should therefore be reconsideredwhen transport limitations of the metal ion to the uptakesite prevail.