Citric acid- and Tween® 80-assisted phytoremediation of multi-contaminated soils vegetated with alfalfa

AGNELLO, A. C.; HUGUENOT, D.; VAN HULLEBUSCH, E.D.; ESPOSITO, G.

Heraklion

Conferencia; 11th International Phytotechnologies Conference; 2014

International Phytotechnology Society

The combination of phytoextraction and rhizodegradation phytotechnologies can be employed together with the aim to remediate soils multi-contaminated by inorganic and organic pollutants [1]. However, low bioavailability of contaminants represents a significant limitation in phytoremediation [2]. To overcome this constraint, biodegradable amendments such as low molecular weight organic acids with metal chelating ability and surfactants, which enhance the solubility of organics, can be added to soils [3].The present study assessed the phytoremediation potential of alfalfa (Medicago sativa L.) in a multi-contaminated soil as well as the effects of citric acid and Tween® 80 (polyethylene glycol sorbitan monooleate), applied individually and in combination, on the phytoremediation process.The experimental design included a pot experiment in the growth chamber. One month old alfalfa seedlings were transplanted to a soil contaminated by heavy metals (Cu, Pb, Ni and Zn) and petroleum hydrocarbons. Pots were fortnightly treated with citric acid (15 mmol kg-1 dry soil), Tween® 80 (0.036 mmol kg-1 dry soil), or the combination of both compounds. Vegetated and non-vegetated controls received distilled water instead of amendments. Each condition was repeated in triplicates. Plants were harvested after 30, 60 and 90 days, every time three days after amendment application. Soil samples (from the rhizosphere in the case of vegetated pots) were taken at the same times. Plant parts were dried, weighed, mineralized and analyzed for their content in Cu, Ni, Pb and Zn by ICP-OES. The number of aliphatic hydrocarbon degraders and the activity of lipase enzyme were determined in soil samples by the most-probable-number method and a colorimetric assay, respectively [4, 5].The results showed that alfalfa plants could tolerate and grow in the multi-contaminated soils. Over the 90-day experimental time, shoot and root biomass increased and negligible plant mortality arose. Heavy metals were uptaken by alfalfa to a limited extent, and mostly by plant roots. Heavy metal concentration in plant tissues were in the following order: Zn > Cu > Pb > Ni. Alfalfa rhizosphere effect was manifest, enhancing both microbial population (alkane degraders) and activity (lipase enzyme), with rhizosphere effects of 28.11 and 2.04, respectively, after 90 days. Soil amendments did not significantly enhance plant metal concentration or total uptake. By contrast, the combination of citric acid and Tween® 80 significantly improved alkane degraders (5.3-fold increase) and lipase activity (1.0-fold increase) in the rhizosphere of amended plants, after 30 days of experiment.This evidence supports the phytoremediation potential of alfalfa species to facilitate the remediation of multi-contaminated soils and the possibility to enhance the phytoremediation process through the joint application of citric acid and Tween® 80.References: [1] Salt, D.E., Smith, R.D., Raskin, I., 1998. Phytoremediation. Annual Review of Plant Physiology and Plant Molecular Biology 49, 643-668. [2] National Research Council, 2003. Bioavailability of Contaminants in Soils and Sediments: Processes, Tools, and Applications. The National Academies Press, Washington, DC. [3] Agnello, A.C., Huguenot, D., van Hullebusch, E.D., Esposito, G., 2013. Enhanced phytoremediation: a review of low molecular weight organic acids and surfactants used as amendments. Critical Reviews in Environmental Science and Technology. DOI:10.1080/10643389.2013.829764 [4] Wrenn, B.A., Venosa, A.D., 1996. Selective enumeration of aromatic and aliphatic hydrocarbon degrading bacteria by a most-probable-number procedure. Canadian Journal of Microbiology 42, 252-258. [5] Margesin, R., Feller, G., Hämmerle, M., Stegner, U., Schinner, F., 2002. A colorimetric method for the determination of lipase activity in soil. Biotechnology Letters 24, 27-33.Acknowledgements: The financial support by the Erasmus Mundus Joint Doctorate Programme ETeCoS3 (Environmental Technologies for Contaminated Solids, Soils and Sediments) under the grant agreement FPA n°2010-0009 as well as the MOY labelled programme n°2010/038 are greatly appreciated.