Soil bioremediation by cyclodextrins. A review

Remediation of soils contaminated by organic pollutants has become an urgent necessity worldwide. A wide variety of techniques have been developed but many of them are associated with drawbacks (complexity, high costs, environmental risks, etc.). Bioremediation, the use of living organisms to remediate polluted sites, is an alternative approach considered a cost-effective and more environmentally friendly technique, but the low bioavailability of the organic pollutants in soils is its main limitation. Cyclodextrins have been proposed as a greener alternative to organic solvents or synthetic surfactants for increasing organics bioavailability in soils. Cyclodextrins can form inclusion complexes with hydrophobic pollutants increasing their aqueous solubility and enhancing their bioremediation in soils. This review gives an overview on the use of cyclodextrins for this purpose, highlighting the advantages and disadvantages and perspectives of this technology for future research. The effect of those cyclodextrins more commonly used is analyzed, particularly hydroxypropyl-beta-cyclodextrin (HPBCD) and randomly methylated-beta-cyclodextrin (RAMEB), as well as some of the more common contaminants treated (almost 80% are industrial chemicals and the rest are pesticides) and the bioremediation strategies used (by microorganisms and/or phytoremediation). The review also provides a critical view on knowledge gaps and limitations of this technology which must be overcome to bring it for field-scale application.