Fast method to quantify PAHs in contaminated soils by direct thermodesorption using analytical pyrolysis

International audienceA method for polycyclic aromatic hydrocarbon (PAH) quantification, based on pyrolysis at 450 °C combined with gas chromatography coupled with mass spectrometry and flame ionization detection (Py-GC-MS/FID), was developed and compared to a conventional PAH quantification method using accelerated solvent extraction and GC–MS analyses. The PAH contents of three coking plant soils, one gas plant soil, two wood-treating facility soils and one certified reference material (CRM-BCR 524) were determined using both methods. The results obtained with both methods showed a good match, especially in the case of the CRM. The other soil samples presented higher variability which was greatly reduced by crushing the samples to lower particle size (from < 500 to < 100 μm). Higher contents of low molecular weight (LMW) PAHs were quantified with the Py-GC-MS/ FID than with the conventional method, probably because of a slight cracking phenomenon occurring during the pyrolysis and/or a loss of the LMW compounds during the sample concentration required for the conventional method. Because of the limited sample preparation and the fact that no solvent was used, the pyrolysis-based method was proven to be a faster, less expensive and more environmentally friendly than the classical methods for PAH quantification in contaminated soils

Effect of thermal pre-treatment on the availability of PAHs for successive chemical oxidation in contaminated soils

International audienceThis is the premier study designed to evaluate the impact of thermal pre-treatment on the availability of polycyclic aromatic hydrocarbons (PAHs) for successive removal by chemical oxidation. Experiments were conducted in two soils having different PAH distribution originating from former coking plant sites (Homécourt, H, and Neuves Maisons, NM) located in northeast of France. Soil samples were pre-heated at 60, 100, and 150 °C for 1 week under inert atmosphere (N2). Pre-heating resulted in slight removal of PAHs (\textless10 %) and loss of extractable organic matter (EOM). Then, these pre-heated soil samples were subjected to Fenton-like oxidation (H2O2 and magnetite) at room temperature. Chemical oxidation in soil without any pre-treatment showed almost no PAH degradation underscoring the unavailability of PAHs. However, chemical oxidation in pre-heated soils showed significant PAH degradation (19, 29, and 43 % in NM soil and 31, 36, and 47 % in H soil pre-treated at 60, 100, and 150 °C, respectively). No preferential removal of PAHs was observed after chemical oxidation in both soils. These results indicated the significant impact of pre-heating temperature on the availability of PAHs in contaminated soils and therefore may have strong implications in the remediation of contaminated soils especially where pollutant availability is a limiting facto

A fast and new method to quantify PAHs in contaminated soils based on flash-pyrolysis coupled with molecular analysis

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Multistep thermodesorption coupled with molecular analyses as a quick, easy and environmentally friendly way to measure PAH availability in contaminated soils

International audienceWhether it is for risk assessment or for remediation purpose, contaminant availability in polluted soils is a key parameter to determine. Two methods were recently standardized for the estimation of the environmental available fraction of non-polar organics but, in some cases, their application on real historically contaminated soils does not provide satisfactory results. The present study aimed at proposing an alternative method for the estimation of PAH availability in soils, based on analytical thermal desorption and molecular analyses with the hypothesis that the binding strength between PAH and the solid matrix is linked to the desorption temperature. This hypothesis was validated by comparing the thermodesorption molecular distribution of different contaminated soils and of their respective extractable organic matter. Then, comparing the thermodesorption profiles of each studied PAH to the efficiency of biological and chemical remediation treatments through principal component analysis allowed obtaining the desorption temperature corresponding to PAH fractions available towards both treatments. This method was proven to effectively estimate the PAH fraction available towards biological (microbial incubation) and chemical (KMnO4 oxidation) treatments and present multiple advantages such as being fast, easy to execute and solvent fre

Effect of PAC (PAH & Polar-PAC) availability on terrestrial organisms’ ecotoxicity

International audienceHistorically contaminated sites have gained attention in recent decades. Some of them, e.g., former coking plants are contaminated by polycyclic aromatic compounds (PACs), including PAHs and polar-PACs (O/N/S-PACs). PACs are known to be toxic to soil organisms [1]. The exposure of terrestrial organisms to freshly contaminated soil with PAHs and polar-PACs demonstrated significant toxicity towards several organisms.However, for some soils sampled from historically contaminated sites exhibiting a higher PAC content, tests performed on earthworms have shown a limited impact on mortality rates [2]. As reported by several studies, in historically contaminated sites, PAC (bio)availability is generally limited. This phenomenon known as "aging" [3,4], is a main factor to consider in the evaluation of toxicity risk in soil contaminated by PAC [5]. In fact, for a refined estimation of the environmental risk and understanding of the impact of the PAC (bio)availability on toxicity, it is neccesery to combine a complete chemical characterization (total content and available fraction of PACs) and biological expositions [6].This work aims to evaluate the toxicity of two aged coking plant soils by running bioassays on invertebrates and plants. The toxicity of these soils (low PAC availability) will be compared with the same soils previously treated (heating) to increase their PAC availibility.A pre-heating treatment was carried out in order to increase PAC availability [5], then the soil was extracted with dichloromethane (DCM) and the PACs (i.e., PAHs and O/N/S PACs) were quantified by GC-MS. As a second step, ecotoxicity tests were performed through limit assays using acute bioassays. The purpose of this step is to evaluate the earthworm viability rate and seed development of plants (seedling emergence and growth) and to highlight the importance of taking into account the availability factor.Results of this study showed that soils with identical physico-chemical properties but exhibiting contrasted levels of PAC availability induced different ecotoxic responses of terrestrial organisms, an increased availability leading to a much higher toxicity. These results pointed out the importance of considering the contamination availability parameter in risk assessment and not only the total contaminant concentration.References: [1] Wang et al. (2022) Environmental Challenges, 9, 100613.[2] Eom et al. (2007), Ecotoxicology and Environmental Safety, 67(2),190-205[3] Fernández et al. (2005), Ecotoxicology and Environmental Safety, 62(2), 174-184[4] Boulangé et al. (2019) Chemosphere 224: 437‑44. [5] Biache, C. et al. (2021) Talanta 228: 122235.[6] Juvonen et al. (2000), Ecotoxicology and Environmental Safety,47(2), 156-16

Effect of PAC (PAH & Polar-PAC) availability on aquatic organisms’ ecotoxicity

International audienceHistorically contaminated sites have gained attention in recent decades. Some of them, e.g., former coking plants, are contaminated by polycyclic aromatic compounds (PACs), including 16 US-EPA PAHs and polar-PACs (O/N/S-PACs) which can induce potential risk for aquatic organisms[1]. Several studies reported that PAC (bio)availability can be limited in such sites, due to aging phenomenon [2,3], explaining the low impact on soil biota of some heavily contaminated soils . Consequently, bioavailability is a major factor to consider in the risk evaluation associated to PAC-contaminated soil and PAC transfer to the aqueous phase [2, 3] but is scarcely taken into accountThe objective of this work is to evaluate the influence of the PAC availability on PAC transfer from soil to the aqueous phase and its consequences on toxicity towards model aquatic organisms. Two soils (HOM and THI) were sampled on former coking plants. Aliquote of both soils were heated at 100 °C under inert atmosphere for one week in order to increase PAC availability by 10-30% for HOM and THI respectively [4]. Batch leaching tests were carried out according to the ISO 18772 (2008) procedure, PACs were quantified in the leachates by GC-MS after solid phase extraction. Simultaneously, ecotoxicity tests were performed through limit assays using standard acute bioassays. Rotifers and daphnie mobility and reproduction rate, respectively, as well as the growth inhibition of algae were evaluated.Results showed that leachates from raw soils have identical physico-chemical properties , except ionic strength that was ten times higher in THI than in HOM leachate. The PAC content was higher in HOM than in THI leachate, with polar PAC concentrations of 37300 and 6150 ng/L and PAH concentrations of 95 510 and16 030 ng/L for HOM and THI, respectively.Both leachates exhibited a similar PAH distribution. The results show a preferencial release of low-molecular-weight PAHs and polar PACs, especially O-PAC, mainly by dissolution, while higher-molecular-weight PAHs are released in association with colloids. An Important toxic effect of growth inhibition (85%) was observed on algae for both leachates. No toxic effects were observed in daphnie mobility and only THI leachate induced a slight decrease on rotifer reproduction (25%).The pre-heating treatment increased PAC content in leachates by 35% and 74% for HOM and THI, turning them into 105678 and 48094 ng/L for 16 PAHs and into 98100 and 39300 ng/L for polar PAC, respectively. As a result ,the leachates from preheated soils were more toxic than those from raw soils. Algae growth inhibition was observed to be 8% higher for both soils' pre-heated leachates. As for raw soil leachate, THI presented no toxic effects on daphnia mobility, and it exhibited a similar degree of toxicity on rotifer reproduction. On daphnia, however, HOM demonstrated 95% mobility inhibition and presented a toxic effect on rotifer reproduction (37%).This study showed that soils with similar chemical composition but contrasting levels of PAC availability release higher amounts of PACs into the aqueous phase, contributing to important ecotoxic responses in aquatic organisms.These results pointed out the importance of considering the contamination availability parameter in risk assessment and not only the total contaminant concentration.References: [1] Eom et al. (2007), Ecotoxicology and Environmental Safety, 67(2),190-205[2] Fernández et al. (2005), Ecotoxicology and Environmental Safety, 62(2), 174-184[3] Boulangé et al. (2019) Chemosphere 224: 437‑44. [4] Biache, C. et al. (2021) Talanta 228: 122235

Rôle de la disponibilité des composés aromatiques polycycliques de sols historiquement contaminés dans la réponse écotoxique d’organismes terrestres

International audiencePlus de 300 000 sites potentiellement impactés par des Hydrocarbures Aromatiques Polycycliques (HAP) ont été recensés en Europe, dont plus de 1 500 en France (BASOL). Le diagnostic et le suivi de ces sites se fait généralement par la quantification des composés réglementés (16 HAP US-EPA) sans toutefois tenir compte de leur disponibilité et de la présence de contaminants apparentés tels que les composés aromatiques polycycliques (CAP) polaires. L’exposition d’organismes terrestres à des sols fraîchement contaminés par les HAP ou les CAP polaires, est connue pour provoquer des effets toxiques importants. Cependant, les sols historiquement contaminés, comme les sols d’anciennes cokeries, induisent généralement un impact toxique limité, en raison du phénomène de « vieillissement » (ou « aging »), entraînant une réduction de la disponibilité des CAP dans le temps. La disponibilité est donc un paramètre crucial à prendre en compte lors de l’évaluation des risques associés à une contamination au CAP. L’objectif de cette étude est de mieux comprendre le rôle de la disponibilité des CAP d’un sol historiquement contaminé dans la réponse toxique d’organismes terrestres. Ainsi, deux sols historiquement contaminés ayant subis un « vieillissement » naturel (disponibilité en CAP limitée), ont été étudiés. Ces sols ont été modifiés pour (i) augmenter la disponibilité de la contamination (chauffage modéré) ou (ii) éliminer la pollution (extraction solvant). Les modalités « brutes » et « chauffées » permettent de comparer des niveaux de disponibilité différents tandis que les sols extraits constituent des références sans contaminant. Les paramètres physico-chimiques, les niveaux de contamination et la disponibilité ont été déterminés pour ces trois modalités de sol. En parallèle, des tests d’écotoxicité standardisés (plantes et vers de terre) ont été réalisés sur les sols bruts, chauffés et extraits. Les résultats ont démontré que les sols historiquement contaminés exposés à un chauffage modéré présentaient les réponses écotoxiques les plus élevées. En effet, le chauffage a permis d’augmenter la (bio)disponibilité des CAP, sans modifier les autres propriétés physico-chimiques du sol, ce qui permet d’imputer directement les effets toxiques observés à l’augmentation de la disponibilité. Ces résultats soulignent l’importance de prendre en compte ce paramètre dans l’évaluation des risques. Ils suggèrent, par ailleurs, que la méthode de chauffage modéré constitue un outil possible pour une évaluation des risques à long terme associés aux sols historiquement contaminés plus protectrice pour l’environnement et la santé humaine, qui peut s’avérer pertinente dans le contexte de changement climatique actuel