The non-toxic, biodegradable cyclodextrins (CDs) can solubilize poorly soluble organic contaminants such as PAHs, PCBs, chlorinated solvents, etc. via molecular encapsulation. CDs can be used for bioavailability enhancement either for aerobic, anaerobic or cometabolic biodegradation in soil or in other solid matrices .
BCD and HPBCD were used to improve the bioavailability of PAHs [2–4]. PCB biodegradation, especially of those with lower degree of chlorination can be enhanced by using RAMEB [5,6]. Similarly, the biodegradation of diesel oil, transformer oil and fuel oil was enhanced by RAMEB due to the enhanced bioavailability [7,8].
In the case of contaminants with extremely high affinity toward CD complexation, biodegradation can be hindered by the strong binding of the contaminant to the CD as it was observed for dichlorodiphenyltrichloroethane (DDT) and HPBCD . Most of the originally hydrophobic and biologically non-available organic compounds become more bioavailable by getting a hydrophilic outer surface after cyclodextrin complexation, but there are exemptions such as DDT, which bind so strongly to HPBCD that they together form a much larger and less bioavailable complex molecule at high HPBCD concentrations. In such cases it is important to find the optimal concentration of the complexing agent which still improves bioavailability.
- Hydrocarbon-polluted soil (beside a highway) was treated with BCD and nutrients to successfully remove the pollutants by biodegradation in 3 months .
- A combined cyclodextrin technology (CDT, ventilation, CD flushing, nitrogen and phosphorus amendment) was applied at a transformer station in Hungary. The soil was flushed with a RAMEB solution from time to time through the injection well, and, after a few days’ pause, the groundwater was continuously pumped out from the extractor wells on the other side of the transformer .
- A similar combined technology was used at a former fuel tank station on an agricultural site in Hungary contaminated with aged diesel and engine oil from leaking underground tanks . In this case, however, the injection and extraction were performed alternately in the same well. After addition of RAMEB, the hydrocarbon concentration in groundwater increased 10–40 fold and the specific oil-degrading bacteria 2–10-fold. The contaminant concentrations decreased significantly from 30,000 mg/kg to 3500 mg/kg and from >1000 mg/L to <200 mg/L in soil and water, respectively, at the end of the treatment.
Structure and symbol of beta-cyclodextrin (A), and its complexes with
phenanthrene (B) and DDT (C) .
 Gruiz, K., Meggyes, T. & Fenyvesi, E. (eds.) (2019) Engineering tools for environmental risk management. Volume 4. Risk Reduction Technologies and Case Studies. Boca Raton, Fl., CRC Press
 Bardi, L., Mattei, A., Steffan, S. & Marzona, M. (2000) Hydrocarbon degradation by a soil microbial population with beta-cyclodextrin as surfactant to enhance bioavailability. Enzyme and Microbial Technology, 27, 709–713.
 Wang, J.M., Marlowe, E.M., Miller–Maier, R.M. & Brusseau, M.L. (1998) Cyclodextrin-enhanced biodegradation of phenanthrene. Environmental Science & Technology, 32, 1907–1912.
 Stroud, J.L., Tzima, M., Paton, G.I., Semple, K.T. (2009) Influence of hydroxypropyl-beta-cyclodextrin on the biodegradation of C-14-phenanthrene and C-14-hexadecane in soil. Environmental Pollution, 157, 2678–2683.
 Fava, F., Di Gioia, D., Marchetti, L., Fenyvesi, E. & Szejtli, J. (2002) Randomly methylated β-cyclodextrins (RAMEB) enhance the aerobic biodegradation of polychlorinated biphenyl in aged-contaminated soils. Journal of Inclusion Phenomena and Macrocyclic Chemistry, 44, 417–421.
 Hu, J., Wang, Y., Su, X., Yu, C., Qin, Z., Wang, H., Hashmic, M.Z., Shi, J. & Shen, C. (2016) Effects of RAMEB and/or mechanical mixing on the bioavailability and biodegradation of PCBs in soil/slurry. Chemosphere, 155, 479–487.
 Gruiz, K., Molnár, M., Fenyvesi, É., Hajdu, Cs., Atkári, Á. & Barkács, K. (2011) Cyclodextrins in Innovative Engineering Tools for Risk-based Environmental Management. Journal of Inclusion Phenomena and Macrocyclic Chemistry, 70(3–4), 299–306
 Molnar, M., Leitgib, L., Fenyvesi, E. & Gruiz, K. (2009) Development of cyclodextrin-enhanced soil remediation: from the laboratory to the field. Land Contamination & Reclamation, 17(3–4), 599–610.
 Gao, H., Gao, X., Cao, Y., Xu, L. & Jia, L. (2015) Influence of Hydroxypropyl-β-cyclodextrin on the extraction and biodegradation of p,p′-DDT, o,p′-DDT, p,p′-DDD, and p,p′-DDE in soils. Water, Air, & Soil Pollution, 226(7), 208–220.
 Bardi, L., Ricci, R. & Marzona, M. (2003) In situ bioremediation of a hydrocarbon polluted site with cyclodextrin as a coadjuvant to increase bioavailability. Water, Air, & Soil Pollution: Focus, 3, 15–23.
 Leitgib, L., Gruiz, K., Fenyvesi, E., Balogh, G. & Murányi, A. (2008) Development of an innovative soil remediation: ‘cyclodextrin-enhanced combined technology’. Science of the Total Environment, 392, 12–21.