Temporal Evolution of PAHs Bioaccessibility in an Aged-Contaminated Soil during the Growth of Two Fabaceae

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.