Influence of a natural nonionic surfactant on biodegradation of slowly desorbing PAHs in contaminated soi

Poster and abstract presented in the Setac Europe 35th Annual Meeting 11–15may 2025 | Vienna, Austria

In many cases, the residual pollutant concentrations after bioremediation suppose unacceptable risks, especially for hydrophobic organic compounds such as PAHs. The half-lives of these compounds are very high if are present as slowly desorbing forms, and may remain in the contaminated soils after bioremediation, still causing potential toxicity. The design of strategies to enhance the biodegradation of the slowly desorbing compounds is therefore needed in the bioremediation field. The use of biosurfactant agents, such as rhamnolipid, have been suggested as the environmentally friendly technology for the remediation of soils contaminated with hydrophobic organic compound (Posada-Baquero, et al., 2020, Sci. Total Environ, 720:137608). Plant-produced surfactants, such as Quillaja saponin, constitute a realistic alternative to microbial surfactants, as related to costs. Our objectives were: to characterize the initial desorption kinetics of native PAHs present in this contaminated soil to determine the extent of slowly desorbing fractions, to use 14C-PAHs radiorespirometry determinations as a physiological indicator of biodegradation, to study the effect of the saponin on the biodegradation and bioavailability of these compounds and to propose mechanisms to improve the action of this biosurfactant on slowly desorbing PAHs in contaminated soils. The soil used was a heavily creosote polluted soil with a PAHs total concentration of 4075 mg/kg. Saponin, a non-ionic biosurfactant, was added at concentration of 7 mg/g (w/w). The desorption kinetics, which was determined by Tenax extraction, was a necessary tool in the optimization of saponin role in bioremediation of PAHs. Saponin was added at 56 days, when the remaining PAHs were present in a slowly desorbing form as a result of the biodegradation of fast desorbing PAHs by the native microbial population of the soil. The biodegradation percentages of total PAHs (sum of 16 EPA PAHs) achieved were 59 % and 90 % for the natural attenuation and bioestimulation-saponin treatments, respectively. Thus, the data obtained by adjusting the desorption kinetics successfully predicted the right time for biosurfactant application during bioremediation. The results obtained show that an appropriate integration of the natural surfactant into bioremediation of PAHs contaminated soils, promoting biodegradation of the slow desorption fractions, improve the bioremediation performance and have lower costs and environmental impacts.

This research was supported by the Spanish Ministry of Science and Innovation (PID2019-109700RB-C21)

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