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.

Cassino, Gaeta

Otro; Summer School on Biological Treatment of Solid Waste; 2014

Università degli Studi di Cassino e del Lazio

Introduction: The combination of phytoextraction and rhizodegradation phytotechnologiescan be employed together with the aim to remediate soils multi-contaminated by inorganic and organicpollutants [1]. However, low bioavailability of contaminants represents a significant limitation inphytoremediation [2]. To overcome this constraint, biodegradable amendments such as low molecularweight organic acids with metal chelating ability and surfactants, which enhance the solubility oforganics, can be added to soils [3].Objectives: To assess the phytoremediation potential of alfalfa (Medicago sativa L.) in amulti-contaminated soil as well as the effects of citric acid and Tween® 80 (polyethylene glycol sorbitanmonooleate), applied individually and in combination, on the phytoremediation process.Methodology: 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, Niand Zn) and petroleum hydrocarbons. Pots were fortnightly treated with citric acid (15 mmol kg-1 drysoil), Tween® 80 (0.036 mmol kg-1 dry soil), or the combination of both compounds. Vegetated andnon-vegetated controls received distilled water instead of amendments. Each condition was repeatedin triplicates. Plants were harvested after 30, 60 and 90 days, every time three days after amendmentapplication. Soil samples (from the rhizosphere in the case of vegetated pots) were taken at the sametimes. Plant parts were dried, weighed, mineralized and analyzed for their content in Cu, Ni, Pb and Znby ICP-OES. The number of aliphatic hydrocarbon degraders and the activity of lipase enzyme weredetermined in soil samples by the most-probable-number method and a colorimetric assay,respectively [4, 5].Results: The results showed that alfalfa plants could tolerate and grow in the multicontaminatedsoils. Over the 90-day experimental time, shoot and root biomass increased andnegligible plant mortality arose. Heavy metals were uptaken by alfalfa to a limited extent, and mostlyby 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-foldincrease) and lipase activity (1.0-fold increase) in the rhizosphere of amended plants, after 30 days ofexperiment.Conclusions: This evidence supports the phytoremediation potential of alfalfa species tofacilitate the remediation of multi-contaminated soils and the possibility to enhance thephytoremediation process through the joint application of citric acid and Tween® 80.