Approved Abstracts

Bioremediation of a trifluralin contaminated soil using bioaugmentation and cyclodextrin



Author(s): Lara-Moreno A; Lara-Moreno A; Morillo E; Merchán F; Madrid F; Villaverde J;
Presenter: Esmeralda Morillo

Trifluralin (TFL) is an herbicide highly persistent with a strong adsorption capacity on soil particles. This compound is considered highly toxic to the environment and is included in the list of priority contaminants drawn up by European Commission (Directive 2008/105/EC), being its use as herbicide forbidden in the European zone. Although it is a photosensitive molecule, when it reaches the soil becomes a very persistent compound, being biodegradation its principal dissipation path. The aim of this study was to isolate microbial consortia and bacterial strains from a soil with historical application of herbicides to evaluate their potential to degrade TFL in contaminated soils. In this work different bioremediation techniques are considered for application on an agricultural soil artificially contaminated with TFL. These techniques consist in: i) biostimulation, using a nutrients solution (NS), ii) bioaugmentation, using a microbial degrading consortium (CMN) isolated from TFL enrichment cultures of this soil with historical herbicide application, seven individual bacterial strains isolated from this consortium using TFL as the sole C source (Bacillus aryabhattai CTFL1 ((MT293617), Pseudomonas guariconensis CTFL2 (MT293652), Pseudomonas brassicacearum CTFL3 (MT293866), Bacillus circulans CTFL4 (MT294022), Bacillus safensis CTFL5 (MT299749), Bacillus maritimus CTFL6 (MT294101) and Arthrobacter aurescens CTFL7 (MT294140), or an artificial bacterial consortium formed by these seven TFL-degrading bacterial strains (CBA) and/or iii) cyclodextrin (randomly methylated cyclodextrin, RAMEB), a biodegradable compound acting as an organic pollutant hydrosolubility enhancer and even as biostimulant for the soil endogenous microbiota due to its high C content.
TFL biodegradation experiments were conducted in the investigated soil during 100 days in presence of a NS, reaching 34.2% of biodegradation after 100 days and a calculated value of 50% of dissipation of the TFL initially presents in the soil (DT50) in a period of 644 days. Biodegradation assays were also performed after inoculating the two studied consortia and all the isolated bacterial strains. 61.8 % of TFL was removed by CMN and 74.2% when CBA consortia were inoculated, showing a drastic decrease of DT50 value till 5.9 and 11 days, respectively. In the case of isolated bacterial strains inoculation, the extent of TFL biodegradation was in a wide range (2.3% to 54.7%), and DT50 in the interval of 79.2 to 1933 days. The most efficient bacterial strain inoculated, both in percentage of TFL degraded and in DT50 value, was A. aurescens CTFL7. For this reason, bioaugmentation with CTFL7 bacterium was tested in presence of RAMEB, what provoked a drastic increase in herbicide biodegradation rate in soil up to 87.8%, achieving a DT50 value lower than 19 days.
Also an ecotoxicity assay was performed in order to confirm that the proposed bioremediation techniques were efficient in decreasing toxicity. The ecotoxicity test showed that after inoculating A. aurescens CTF7 and A. aurescens CTF7 + RAMEB the artificially contaminated soil, which presented an acute toxicity, became no toxic at the end of the biodegradation experiments.


Keywords: Trifluralin; Soil bioaugmentation; Cyclodextrin

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