Rhamnolipid-enhanced solubilization and biodegradation of PAHs in soils after conventional bioremediation

The application of a rhamnolipid biosurfactant for enhanced solubilization and biodegradation of slowly desorbing polycyclic aromatic hydrocarbons (PAHs) in contaminated soils was determined in this study. The soil samples exhibited different levels of pollution and different bioremediation stages: the first soil originated from a creosote-polluted site, contained 4370 mg kg -1 of PAHs and had not been bioremediated; the second soil was the same as the first but had received bioremediation treatment with nutrient amendment in biopiles for a period of 5 months and contained 580 mg kg -1 of PAHs after this treatment; the third soil was treated by bioremediation for several years to reduce the concentration of PAHs to 275 mg kg -1. The kinetics of PAH desorption were determined to assess the magnitude of the slowly desorbing fractions present in the polluted soil and to optimize the biosurfactant effectiveness in terms of biodegradation. The soils that had been treated by bioremediation were enriched in slowly desorbing PAHs. The rhamnolipid at a concentration above its critical micelle concentration enhanced biodegradation in the soils that had been bioremediated previously. The measurement of residual concentrations of native PAHs showed the promoting effect of the biosurfactant on the biodegradation of the slowly desorbing fractions. Interestingly, benzo(a)pyrene was biodegraded in the soil that had been bioremediated for a long time. Rhamnolipid can constitute a valid alternative to chemical surfactants in promoting the biodegradation of slow-desorption PAHs, which is one of the most important problems in bioremediation, but the efficiency depends strongly on the bioremediation stage in which the biosurfactant is applied

Rhizosphere-enhanced biosurfactant action on slowly desorbing PAHs incontaminated soil

We studied how sunflower plants affect rhamnolipid biosurfactant mobilization of slowly desorbing fractions of polycyclic aromatic hydrocarbons (PAHs) in soil froma creosote-contaminated site. Desorption kinetics of 13 individual PAHs revealed that the soil contained initially up to 50% slowly desorbing fractions. A rhamnolipid biosurfactantwas applied to the soil at the completion of the sunflower cycle (75 days in greenhouse conditions). After this period, the PAHs that remained in the soil were mainly present in a slowly desorbing form as a result of the efficient biodegradation of fast-desorbing PAHs by native microbial populations. The rhamnolipid enhanced the bioavailable fraction of the remaining PAHs by up to 30%, as evidenced by a standardized desorption extraction with Tenax, but the enhancement occurredwith only planted soils. The enhanced bioavailability did not decrease residual PAH concentrations under greenhouse conditions, possibly due to ecophysiological limitations in the biodegradation process thatwere independent of the bioavailability. However, biodegradationwas enhanced during slurry treatment of greenhouse planted soils that received the biosurfactant. The addition of rhamnolipids caused a dramatic shift in the soil bacterial community structure, which was magnified in the presence of sunflower plants. The stimulated groups were identified as fast-growing and catabolically versatile bacteria. This new rhizosphere microbial biomass possibly interacted with the biosurfactant to facilitate intra-aggregate diffusion of PAHs, thus enhancing the kinetics of slow desorption. Our results show that the usually limited biosurfactant efficiency with contaminated field soils can be significantly enhanced by integrating the sunflower ontogenetic cycle into the bioremediation design

Bioaccesibilidad en suelos de hidrocarburos aromáticos policíclicos depositados desde la atmósfera

182 páginas.-- 38 figuras.-- 30 tablas.-- 104 referenciasEn esta tesis doctoral se ha investigado la bioaccesibilidad en suelos de hidrocarburos aromáticos policíclicos depositados desde la atmósfera. Este trabajo ha sido llevado a cabo gracias a nuestra participación dentro del proyecto "Diagnóstico de la Situación Ambiental del Campo de Gibraltar", por ello la mayor parte de las muestras utilizadas e n este estudio pertenecen a esta zona. Así el primer paso importante de este trabajo fue seleccionar y muestrear los puntos de esta zona que fuesen de interés para el desarrollo de esta tesis doctoral, teniendo en cuenta que las actividades industriales y urbanas del Campo de Gibraltar suponen una fuente potencial de contaminación por hidrocarburos aromáticos policíclicos (HAPs) a la atmósfera, que pueden al menos en parte, ser transferidos a los suelos de la zona. Inicialmente fue necesario poner a punto los métodos analíticos necesarios para poder llegar a determinar en los suelos las concentraciones de hidrocarburos aromáticos policíclicos que correspondían a niveles de fondo. Para ello se utilizaron muestras ambientales de referencia certificadas. Una vez que estaba a punto la metodología analítica, se cuantificó el contenido en HAPs de todas las muestras de suelo. La metodología empleada para ello fue la recomendada por la EPA (US-EPA SW-846, 1995). Los valores correspondientes a las muestras del Campo de Gibraltar dieron una media, que puede considerarse como una contaminación de fondo, probablemente debido a deposición atmosférica en la mayoría de los casos. Este valor está muy próximo al contenido medio observado en suelos rurales ingleses, y se encuentra por debajo del valor de fondo considerado en otros países europeos. Tras conocer el contenido en HAPs de las muestras de suelo, se procedió a determinar la bioaccesibilidad de estos compuestos mediante el estudio de las cinéticas de biodegradación. Estas experiencias revelaron que los HAPs eran bastante persistentes en estos suelos. Posteriormente se procedió al estudio de las posibles factores que podían estar causando este efecto. Dentro de estos factores se estudiaron la influencia sobre la bioaccesibilidad de la cantidad de microorganismos degradadores, la cantidad de HAPs inicial y el efecto de la adsorción de los HAPs en el suelo. Además para poder explicar mejor el fenómeno de adsorción en nuestros suelos, se estudió la influencia de la materia orgánica, la presencia de carbono negro y el envejecimiento de los HAPs en los suelos estudiados. Los datos obtenidos sobre la bioaccesibilidad de los HAPs sugirieron que la exposición crónica de los suelos a flujos, aunque bajos, de deposición de HAPs de la atmósfera daría lugar a la formación de fracciones muy resistentes a la biodegradación, lo que puede ser la causa de un aumento progresivo en la concentración de estos contaminantes. Este aumento ya se ha detectado en otros países con más larga tradición industrial, como por ejemplo el Reino Unido. Ver menosPeer reviewe

Biodegradación de suelos contaminados con hidrocarburos policíclicos aromáticos

39 páginas.-- 11 figuras.-- 6 tablas.-- 19 referencias.-- Memoria del XL Curso Internacional de Edafología y Biología Vegetal, 2003Debido a la actividad industrial desarrollada que existe en muchos paises europeos, una gran cantidad de contaminantes han sido vertidos al medio ambiente y éste es ciertamente un hecho que nos lleva a afrontar un serio problema de degradación del suelo y de sus aguas subterrimeas. Los contaminantes, y más concretamente los compuestos orgánicos, pueden encontrarse en el suelo debido por ejemplo a derrames desde los tanques de coches o camiones, a la descarga de residuos industriales o a los escapes desde el almacén o el depósito de los productos industriales. Aunque las concentraciones de estos productos sean bajas pueden alcanzar niveles que tienen efectos perjudiciales sobre los humanos, animales y plantas. En los últimos años ésta ha sido la situación que nos ha llevado a pensar sobre qué medidas podrian tomarse para evitar el deterioro de los suelos; una de estas medidas que se están investigando es la denominada biorrecuperación, de la cual vamos a hablar en el siguiente punto.Peer reviewe

Recalcitrance of polycyclic aromatic hydrocarbons in soil contributes to background pollution

The microbial accessibility of native phenanthrene and pyrene was determined in soils representing background scenarios for pollution by polycyclic aromatic hydrocarbons (PAHs). The soils were selected to cover a wide range of concentrations of organic matter (1.7-10.0%) and total PAHs (85-952 μg/kg). The experiments included radiorespirometry determinations of biodegradation with 14C-labeled phenanthrene and pyrene and chemical analyses to determine the residual concentrations of the native compounds. Part of the tests relied on the spontaneous biodegradation of the chemicals by native microorganisms; another part also involved inoculation with PAH-degrading bacteria. The results showed the recalcitrance of PAHs already present in the soils. Even after extensive mineralization of the added 14C-PAHs, the concentrations of native phenanthrene and pyrene did not significantly decrease. We suggest that aging processes operating at background concentrations may contribute to recalcitrance and, therefore, to ubiquitous pollution by PAHs in soils.Support for this research was provided by the Spanish Junta de Andalucía (projects “Diagnóstico de la Situación Ambiental del Campo de Gibraltar” and PAI RNM 312), and the Spanish Ministry of Science and Innovation (CGL2007-64199 and CGL2010-22068-C02-01).Peer Reviewe

Enhancing with biosurfactants the bioavailability of slow-desorption PAHs in contaminated soils

Poster presentado en el International Meeting on New Strategies in Bioremediation Processes BioRemid-2017, March 9th-10th, (2017)N

Use of a standardized desorption extraction method to study the effect of enhanced phase exchange in bioremediation

Poster (4.04P.10) presentado en SETAC SciCon SETAC Europe 30th Annual Meeting, Open Science for Enhanced Global Environmental Protection 3–7 May 2020 Dublin, IrelandThis work investigated the effect of bioremediation on bioavailability of native PAHs present in contaminated soils. Bioavailability has been measured with a single-time point Tenax extraction at 20 h because this method has been recently proposed by the International Organization for Standarization as one of the chemical methods to measure environmental bioavailability of nonionic pollutants (ISO/TS 16751). In addition, as a quality assurance, we also characterized the desorption kinetics of the full profile of PAHs in some of the studied samples to highlight the importance of ensuring the 20 h time window to capture the fast desorption when using this standarized method. This work is one of the first ones that use this ISO method systematically in the field of bioremediation, and shows its advantages when used in combination with total concentrations determined with conventional, exhaustive solvent extraction. The method was applied to different PAHs contaminated soils which had different level of total PAHs (66- 4370 mg Kg-1), and dissimilar origin and bioremediation approaches. Some samples were from traditional remediation approaches such as biostimulation and phytoremediation, and others were from bioavailiability oriented treatments such as involving either biosurfactants or bioaugmentation with specialized microbial inocula. In the samples which were from biosurfactants treatments, the effect of a rhamnolipid biosurfactant in solubilization and biodegradation of PAHs was studied previously. To do it, the desorption extraction with Tenax was also used succesfully and the results showed that rhamnolipid can constitute a valid alternative to chemical surfactants in promoting the biodegradation of slowdesorption PAHs, which is one of the most important problems in bioremediation. Furthermore, the results from the complete set of the studied samples in this work showed that the pollutant fractions extracted with Tenax during 20 h (D20) decreased after traditional bioremediation (biostimulation and phytoremediation), but they often increased in bioavailability-oriented treatments. Therefore, the application of D20 assessment provided us information on the bioremediation performance, not directly evident through the measurement of total PAH concentration

Microbial Transformation of Organic Chemicals in Soil Through Cometabolism and Bioavailability Assessment of the Parent Chemical and Transformation Products

Poster presentado en the SETAC Europe 31st Annual Meeting from 2–6 May 2021 in Seville, Spain.The main objective in this study was to integrate the bioavailability assessment in an approach that followed the OECD 307 mineralization and biodegradation guideline, where polar metabolites of a model non-ionic compound (pyrene) were produced by cometabolism. The integration of bioavailability assessments in contaminated soils is necessary for risks assessments and remediation approaches. In these measurements, the persistence of organic compounds in the soils plays a very important role. The incomplete biodegradation of these compounds through cometabolism, leading to transformation products, could even increase the risks, that is also important. Therefore, integrating cometabolic transformations in bioavailability determinations will lead to more realistic risk assessment of the bioremediation processes. A standardized method (ISO 16751:2020), based on Tenax extraction at 20 hours was used to measure bioavailability. This is a chemical method, preferably used with hydrophobic chemicals (Kow > 3), in which the potential bioavailable fraction is the amount of contaminant present in the matrix that can be released from the solid phase to the aqueous phase in a well-mixed water soil mixture and in presence of a receiving phase (Tenax). For this reason, the physico-chemical properties of the compounds in the system, is a very important factor that can affect the results of bioavailability and it is the objective of this study. The first step was an experiment in which the microbial transformation of 14C-pyrene by cometabolism assured the presence of transformation products in the system. In this way, the soil bacterium Pseudomonas putida G7 was used, and a passive dosing device (silicone O-rings) in a soil slurry experiment to control the release of the parent compound to the aqueous phase. The results of this experiment indicated that water soluble metabolites were produced and some possible metabolites were analyzed too (Fernández-López, et al., 2020). Then, we performed a bioavailability assessment to evaluate the effectiveness of this Tenax-based ISO method, and possible ways of optimization, in presence of the metabolites of pyrene, which are more hydrophilic compounds and therefore tended to remain in the aqueous phase and to sorb back to the soil. The results could be applied in future experiments with other compounds, such as pharmaceuticals, which are usually transformed partially as a result of their biological processing in soil.N

Effect of hydroxypropyl-β-cyclodextrin on diuron desorption and mineralisation in soils

2 figures, 4 tables, 52 references.Purpose The herbicide diuron has the unfortunate property of being strongly adsorbed onto soil organic matter particles, and hence, is slowly degraded in the environment because of its reduced bioavailability. The aim of this work was to gain insight into the fate and behaviour of diuron in the soil–water system, and develop and test an environmentally friendly soil decontamination technique that could give rise to an enhancement of diuron mineralisation by sensitive soil endogenous microorganisms, by means of increasing the bioavailability of the pollutant employing cyclodextrin (CD) solutions what would represent an improvement from both economic and environmental standpoints. Materials and methods Selected soil colloidal components: montmorillonite, a synthetic humic acid and a synthetic acicular goethite, and two different soils were employed in this study to perform batch adsorption–desorption experiments. Desorption experiments were performed using a 0.01 M Ca(NO3 ) 2 solution with and without hydroxypropyl-β- cyclodextrin (HPBCD) 50 mM. Assays to study the mineralisation of 14C-labelled diuron were performed in respirometers, into which 10 g of soil and 50 mL of mineral salts medium (MMK) were placed, obtaining a final concentration of 50 mg kg−1 and a radioactivity of approximately 900 Bq per flask. Results and discussion Humic acid could be clearly discerned as the major colloidal component responsible for adsorption. HPBCD was used in diuron desorption experiments from soil, showing a strong extracting power on its removal. The mineralisation of diuron in the presence and absence of HPBCD was tested in a soil managed with diuron for several years, involving therefore the presence of microorganisms that have some specificity for diuron. Natural soil attenuation for diuron was improved when a HPBCD solution was used in the presence of micronutrients as a bioavailability enhancer, obtaining 66 % of mineralisation in comparison to that obtained with only micronutrients addition (44 %). Conclusions The use of HPBCD solution at a very low concentration of only 10 times the diuron equimolar concentration in soil, acts as a bioavailability enhancer, accelerating the passage of the diuron-desorbing fraction from the soil particle surface to the soil solution, and hence, improving the accessibility of the microorganisms to the herbicide. Diuron mineralisation rate and the extent of its mineralisation were improved when the HPBCD solution was employed in the presence of micronutrients.Marina Rubio thanks the Spanish Research Council (CSIC) for her Predoctoral Research grant (JAE-Pre). We are indebted to Presmar S.L. for providing the technical diuron. This work was supported by Spanish Ministry of Science Innovation (co-funded by Fondo Europeo de Desarrollo Regional, FEDER), CTM2006-04626 and CTM2009-07335.Peer reviewe

Integrating bioavailability intro biodegradation assessment of hydrophobic organic chemicals

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