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Type: Journal article
Title: Is rhamnolipid biosurfactant useful in cadmium phytoextraction?
Author: Wen, J.
McLaughlin, M.
Stacey, S.
Kirby, J.
Citation: Journal of Soils and Sediments, 2010; 10(7):1289-1299
Publisher: Springer
Issue Date: 2010
ISSN: 1439-0108
Statement of
Jia Wen, Mike J. McLaughlin, Samuel P. Stacey and Jason K. Kirby
Abstract: Purpose: Successful chelant-assisted phytoextraction requires application of an eco-friendly metal-complexing agent which enhances metal uptake but does not pose a significant risk of off-site movement of metals. Rhamnolipid biosurfactant has been used to enhance cadmium (Cd) removal from contaminated soil by washing. It has a strong affinity for Cd compared to some other hazardous metals, suggesting that rhamnolipid could be useful in Cd phytoextraction. This study investigated the potential use of rhamnolipid to enhance Cd phytoextraction. Materials and methods: Adsorption patterns of rhamnolipid in soils were investigated by batch adsorption experiments. Hydrophobicity of rhamnolipid–metal complexes were determined by assessing partitioning in an octanol/water system. Phytotoxicity of rhamnolipid to maize (Zea mays) and chelant-assisted phytoextraction efficiency of maize and sunflower (Helianthus annuus) were determined in pot experiments. Results and discussion: The results showed that rhamnolipid was prone to adsorb strongly to soil at low application rates (0.1–1.7 mM) possibly due to its hydrophobic interactions with soil organic matter, hence reducing its capacity to complex and transport metals to plant roots. Rhamnolipid mobility increased (i.e. decreased soil phase partitioning) at elevated concentrations (∼4.4 mM), which increased soil solution Cd concentrations possibly due to its reduced hydrophobic nature. The use of rhamnolipid at concentrations >4.4 mM severely reduced maize biomass yield, reducing the potential for chelantassisted phytoextraction. At lower concentrations of rhamnolipid (0.02–1.4 mmol/kg), there was insignificant enhancement of Cd accumulation by plant (Z. mays and H. annuus) shoots, likely through strong retention of the chelant (or Cd-associated rhamnolipid) on soil surfaces. Conclusions: High rates of rhamnolipid addition to soils in this study caused severe phytotoxicity to maize and sunflower. Lower rates of rhamnolpid addition to soils in this study did not improve Cd accumulation by plants. Therefore, the sorption of rhamnolipid (or Cd-associated rhamnolipid) to soils, along with the phytotoxicity and phytoextraction results, suggests that neither low nor high concentrations of rhamnolipid are likely to consistently assist Cd phytoextraction using maize or sunflower.
Keywords: Adsorption; Partition coefficient; Phytoextraction; Phytotoxicity; Rhamnolipid
Rights: Copyright Springer-Verlag 2010
RMID: 0020096859
DOI: 10.1007/s11368-010-0229-z
Appears in Collections:Agriculture, Food and Wine publications
Environment Institute publications

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