21Polycyclic aromatic hydrocarbons (PAH) are persistent organic compounds of major concern 22 that tend to accumulate in the environment, threatening ecosystems and health. Brownfields 23 represent an important tank for PAHs and require remediation. 24Researches to develop bioremediation and phytoremediation techniques are being conducted as 25 alternatives to environmentally aggressive, expensive and often disruptive soil remediation 26 strategies. 27The objectives of the present study were to investigate the potential of saponins (natural 28 surfactants) as extracting agents and as bioremediation enhancers on an aged-contaminated soil. 29Two experiments were conducted on a brownfield soil containing 15 PAHs. In a first 30 experiment, soil samples were extracted with saponins solutions (0; 1; 2; 4 and 8 g.L -1 ). In a 31 second experiment conducted in microcosms (28°C), soil samples were incubated for 14 or 28 32 days in presence of saponins (0; 2.5 and 5 mg.g -1 ). CO 2 emissions were monitored throughout 33 the experiment. After the incubation, dehydrogenase activity was measured as an indicator of 34 microbiological activity and residual PAHs were determined. In both experiments PAHs were 35 determined using High-Performance Liquid Chromatography and Fluorimetric Detection. 36The 4 g.L -1 saponins solution extracted significantly more acenaphtene, fluorene, phenanthrene, 37 anthracene, and pyrene than water. PAHs remediation was not enhanced in presence of saponins 38 compared to control samples after 28 days. However CO 2 emissions and dehydrogenase 39 activities were significantly more important in presence of saponins, suggesting no toxic effect 40 of these surfactants towards soil microbiota. 41

Polycyclic aromatic hydrocarbons (PAH) are persistent organic compounds of major concern that accumulate in the environment, especially soils, and require remediation. Researches to develop bioremediation and phytoremediation (alternative eco-friendly technologies) are being conducted. First, a bioaccessibility measurement protocol was adapted to a brownfield soil using Tenax® beads in order to compare PAHs bioaccessibility in soil samples. PAHs desorption kinetics were established, described by a site distribution model, and a common extraction time was calculated (48 h). Second, the role of two Fabaceae (Medicago sativa L. or Trifolium pratense L.) root exudates in enhancing PAHs bioaccessibility and biodegradation in the studied soil was evaluated during microcosms experiments (28 °C). The CO 2 emissions were significantly higher in presence of T. pratense exudates; the dehydrogenase activities showed improvements of the soil microbial activity in presence of two types of root exudates compared to untreated soil samples; the PAHs residual contents decreased more in untreated samples than in the presence of T. pratense exudates; and M. sativa exudates lowered PAHs bioaccessibility but not residual contents.

Polycyclic aromatic hydrocarbons (PAHs) are health-concerning organic compounds that accumulate in the environment. Bioremediation and phytoremediation are studied to develop eco-friendly remediation techniques. In this study, the effects of two plants (Medicago sativa L. and Trifolium pratense L.) on the PAHs’ bioaccessibility in an aged-contaminated soil throughout a long-term rhizoremediation trial was investigated. A bioaccessibility measurement protocol, using Tenax® beads, was adapted to the studied soil. The aged-contaminated soil was cultured with each plant type and compared to unplanted soil. The bioaccessible and residual PAH contents were quantified after 3, 6 and 12 months. The PAHs’ desorption kinetics were established for 15 PAHs and described by a site distribution model. A common Tenax® extraction time (24 h) was established as a comparison basis for PAHs bioaccessibility. The rhizoremediation results show that M. sativa developed better than T. pratense on the contaminated soil. When plants were absent (control) or small (T. pratense), the global PAHs’ residual contents dissipated from the rhizosphere to 8% and 10% of the total initial content, respectively. However, in the presence of M. sativa, dissipation after 12 months was only 50% of the total initial content. Finally, the PAHs’ bioaccessible content increased more significantly in the absence of plants. This one-year trial brought no evidence that the presence of M. sativa or T. pratense on this tested aged-contaminated soil was beneficial in the PAH remediation process, compared to unplanted soil.