Efecto del surfactante no-ionico triton x-100 sobre la biodegradación de PAH y la comunidad microbiana de un suelo crónicamente contaminado

CECOTTI, MARTINA; MORA, VERONICA C.; VIERA, MARISA; MORELLI, IRMA S.

Mar del Plata

Congreso; X Congreso Argentino de Microbiología General, SAMIGE; 2014

SAMIGE- Sociedad Argentina de Microbiología General

Polycyclic aromatic hydrocarbons (PAH) are poorly soluble, hydrophobic compounds which have been released into the environment on large scale. These facts, along with its high bioconcentration factor, toxicity and mutagenicity, make PAH priority pollutants. Bioremediation can be limited by the bioavailability of soil-bound PAH and strong sorption to soil, which is exacerbated by the long aging of contaminants in soils. A possible way of enhancing the bioavailability of PAH is the application of surfactants, molecules which consist of hydrophilic and hydrophobic parts. Because of this property these molecules decrease levels of surface and interfacial tension. PAH-degradation processes involving surfactant utilization need to be optimized for each of the factors influencing biodegradation, including surfactants type and concentration and the microorganisms present in the process. The aim of this study was to examine the effect of adding the non-ionic surfactant Triton X-100 to a soil chronically contaminated with a petrochemical sludge, on PAH biodegradation and bioavailability and its impact on soil microbial community. A critical micelle concentration was determined for Triton X-100 in the aged soil (26 mg/gDRY SOIL). Microcosms consisting in 60 gr of soil (20% moisture content) were assembled in two different conditions, without surfactant (C) and with Triton X-100 at 26 mg/gDRY SOIL (T). The microcosms were incubated at 24 ºC, for 30 days. Analysis of the hydrocarbons soil concentration and quantification of its bioavailable fraction (Amberlite XAD-2) were carried out by GC-FID. The number of cultivable heterotrophic bacteria (R2A), aliphatic-degrading bacteria (NMP) and PAH-degrading bacteria (NMP), and the genetic diversity of the bacteria soil community (PCR-DGGE of 16S rDNA) were also determined. The initial soil hydrocarbons concentration was 573 ± 38 mg/g DRY SOIL. The extraction with Amberlite XAD-2 showed that only 5% of hydrocarbons were bioavailable. After 30 days of treatment, while the C microcosm showed 17% of hydrocarbons elimination, the T microcosm reached a 45%, along with a significant increase in the bioavailable hydrocarbons fraction (25%). The analysis of the chromatograms showed that the surfactant enhanced the removal of both alkanes and PAH. However, the T microcosm showed a stimulatory effect on the number of alkanes hydrocarbon degrading bacteria, but not in PAH-degrading bacteria counts. The DGGE profiles showed that the Triton X-100 produced drastic changes in the structure of soil microbial community, but important changes in the DGGE profiles were also observed when the surfactant was added to an uncontaminated soil. Our results show that the addition of surfactant could be an efficient strategy to enhance PAH biodegradation in aged contaminated soils. While the increase of hydrocarbons bioavailability was demonstrated, we cannot exclude a direct biostimulatory effect of surfactant on the soil microbial community.