Efficient simultaneous removal of heavy metals and polychlorobiphenyls from a polluted industrial site by washing the soil with natural humic surfactants

Alessandro Piccolo,Antonio De Martino,Francesco Scognamiglio,Riccardo Spaccini,Roberto Ricci

doi:10.1007/s11356-021-12484-x

Alessandro Piccolo, Antonio De Martino + Show 3 more

Open Access

https://doi.org/10.1007/s11356-021-12484-x

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Abstract

We evaluated the effectiveness of natural organic surfactants such as humic acids (HA) from lignite to simultaneously wash heavy metals (HM) and polychlorobiphenyls (PCB) from a heavily contaminated industrial soil of northern Italy. Supramolecular HA promote in solution a micelle-like structure, where recalcitrant apolar organic xenobiotics are repartitioned from surfaces of soil particles during soil washing process. Concomitantly, the HA acidic functional groups enable a simultaneous complexation of HM. A single soil washing with HA removed 68 and 75% of PCB congeners for 1:1 and 10:1 solution/soil ratios, respectively. The same HA washing simultaneously and efficiently removed a cumulative average of 47% of total HM, with a maximum of 57 and 67% for Hg and Cu, respectively. We showed that washing a highly polluted soil with HA solution not only is an effective and rapid soil remediation technique but also simultaneously removes both HM and persistent organic pollutants (POP). Soil washing by humic biosurfactants is also a sustainable and eco-friendly technology, since, contrary to synthetic surfactants and solvents used in conventional washing techniques, it preserves soil biodiversity, promotes natural attenuation of unextracted POP, and accelerates further soil reclamation techniques such as bio- or phytoremediation.

Highlights

Malfunctioning of industrial activities often causes contamination of soils and waters by toxic and persistent organic pollutants (POP), such as polychlorobiphenyls (PCB) and/or heavy metals (HM)
Its capacity to remove organic contaminants from soils is due to its large content of methylenic chains and aromatic components, as evaluated by 13C-CPMAS-NMR spectroscopy, that confer to this humic acids (HA) a great degree of hydrophobicity (Spaccini et al 2002) and the capacity to form pseudo-micellar domains (Smejkalova and Piccolo 2008; Chilom et al 2009)
The HA surfactant property leads to formation of pseudo-micellar domains when the supramolecular structure of humic matter is arranged in aqueous solutions, and favors the repartition of highly hydrophobic pollutants like PCB from the soil surfaces into the humic pseudo-micelles

Summary

Introduction

Malfunctioning of industrial activities often causes contamination of soils and waters by toxic and persistent organic pollutants (POP), such as polychlorobiphenyls (PCB) and/or heavy metals (HM). The outcome of a remediation process depends on the physical–chemical and biological characteristics of soil (Jensen et al 2011; Tsang and Hartley 2014), and on the binding strength of pollutants on the organic and inorganic soil components. To increase their solubility and improve soil decontamination, strong complexing agents or acid and alkaline solutions are often employed in soil washing processes (Jean et al 2007; Zhang et al 2007). Nitrilotriacetic acid and citrate, though effective soil washing agents for As and Cu removal can be phytotoxic and degrade water quality when reaching ground and surface waters by leaching and runoff (Rasmussen et al 2015)

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