Low molecular weight organic acid- and surfactant-enhanced phytoremediation of co-contaminated soils

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

Delft

Otro; Summer School on Contaminated Sediments: characterization and remediation; 2013

UNESCO-IHE Institute for Water Education

Introduction: The contamination of soils with heavy metals (HMs) and total petroleumhydrocarbons (TPHs) is a diffuse environmental issue of significant relevance. Phytoremediationcan be defined as the use of plants to remove pollutants from the environment or to make themharmless, and such strategy can be used to deal with HM and TPH contaminated soils (Salt et al.,1998). For the remediation of HMs, plants have a central role through the immobilization, extractionand/or volatilization of HMs (Salt et al., 1995). In contrast, despite the ability of plants to detoxifysome xenobiotics, compared to microorganisms they only play a secondary role in the directdegradation of organic chemicals (Gerhardt et al., 2009). Plant promoted biodegradation is themain contribution of remediation enhancement of soil TPHs in the presence of vegetation. For thisreason, the role of the rhizosphere is critical as root exudates may enhance the biodegradation oforganic compounds by stimulating microbial growth and activity at the root level (Kuiper et al.,2004). A key factor limiting the phytoremediation efficiency of both HMs and TPHs is the lowbioavailability of these contaminants (Semple et al., 2004). To increase the ability of pollutants to betransferred from a soil compartment to plants and microorganisms, different amendments can beused and as a consequence, it is possible to improve the effectiveness of the phytoremediationprocess (Evangelou et al., 2007; Gao et al., 2007). This research plan proposes the use of lowmolecular weight organic acids (LMWOAs) and surfactants as amendments to increase thebioavailability of HMs and TPHs, in order to enhance the phytoremediation efficiency ofcontaminated soils.Main Objective: To study the effect of LMWOAs and surfactants on the phytoremediationof soils contaminated with HMs and TPHs.Methods: Five pot experiments were performed varying experimental conditions (Table 1:Experimental design). Plants were harvested, dried and used for biomass determination of shootsand roots. Subsequently, plant heavy metal content was analyzed by ICP-OES after plant wetdigestion. Soil samples (from plant rhizosphere in case of vegetated pots) were collected for thequantification of hydrocarbons by GC-FID after acetone extraction, as well as soil lipase activity(colorimetric assay) and most probable number of hydrocarbon degraders (microplate assay). Soilsolution samples were taken with Rhizon® samplers and used for the determination of heavy metalcontent.Results: Our first results indicate that alfalfa plants tolerate the LMWOA citric acid and thesurfactant Tween® 80 at different concentrations, sometimes higher than those applied in otherstudies. M. sativa is able to germinate and grow in co-contaminated polluted soil and showspotential for LMWOA-assisted phytoextraction of HMs, as well. In addition, the presence of M.sativa enhanced soil lipase activity and number of soil hydrocarbon degraders, improvement whichwas higher with the simultaneous application of combined amendments (citric acid and Tween® 80).Conclusions and future work: The implemented process showed promising results for theassisted phytoremediation of urban soils contaminated both by HMs and TPHs. Future work will include the use of biologically produced compounds (organic acids and biosurfactants) to convertthis chemically-assisted remediation process into a biologically-assisted process. In addition, thescale of phytoremediation experiments will be changed from growth chamber to greenhouse.