Remediation of a diesel contaminated soil by means of anionic and non-ionic surfactants: Effect on soil phosphorus availability and Vicia Faba L. growth.

In the present study, the effectiveness of two surfactants (Polysorbate 80 - Tween 80 and Sodium Dodecyl Benzensulphonate - SDBS) was investigated for the remediation of a hydrocarbon-contaminated soil. Moreover, it was elucidated the impact of surfactants on soil phosphorus (P) availability and phytotoxic effect on the growth of Vicia Faba L. An experimental laboratory-scale apparatus (bench and pilot scale) was set up for the simulation of a soil flushing intervention. Different surfactant concentrations and flushing flow rates were investigated. Hydrocarbon extraction efficiency was evaluated after treatment and phytotoxicity tests were performed by means of germination index (GI). The treated soil with the pilot scale apparatus was then used for Vicia Faba (faba beans) cultivation in pots. The growth of Vicia Faba plants was monitored and, at the end of the growth period, the plants were uprooted and subjected to biometric and chemical analyses. Results highlighted that the use of surfactants significantly increased the efficiency of hydrocarbons extraction compared to flushing test with water (19.6 %, 53.9 %, and 65.6 % for water, 0.1 % by weight of Tween 80 and SDBS, respectively, at pilot scale). Referring to Vicia Faba L., the plants grown in the blank control and in the soil treated with Tween 80 reached the same average height thus suggesting that this surfactant does not inhibit plant growth. In contrast, the lowest plant growth occurred in the soils treated with SDBS; this suggests a negative impact on plant growth. Due to the reduced plant growth, total P uptake was the lowest in plants grown in SDBS-treated soils, although such soils experienced a 20 % increase of soil available P. This increase could be ascribed to P supplied by the surfactant or high P availability as a consequence of soil pH decrease.