Cyclodextrins for Desorption and Solubilization of 2,4,6-Trinitrotoluene and Its Metabolites from Soil TAMARA W. SHEREMATA AND JALAL HAWARI* Biotechnology Research Institute, National Research Council of Canada, Montreal, Quebec, Canada H4P 2R2 Heptakis-2,6-di-O-methyl- -cyclodextrin (DM CD) and hydroxypropyl- -cyclodextrin (HPCD) (1% w/w solutions) were investigated for their ability to desorb 2,4,6- trinitrotoluene (TNT), 4-amino-2,6-dinitrotoluene (4-ADNT), and 2,4-diamino-4-nitrotoluene (2,4-DANT) from two artificially contaminated soils (an organic rich topsoil and an illite shale). The DM CD (which is highly surface active) was more effective than HPCD (negligible surface activity) for desorption of the three nitroaromatic compounds (NACs) from the two soils. The efficiency of both CDs for NAC removal from topsoil decreased with increasing amino substitution (i.e. TNT > 4-ADNT > 2,4- DANT), whereas for illite the efficiency generally decreased with increasing nitro substitution (i.e. TNT < 4-ADNT. 2,4-DANT). In general, the NAC removal efficiency increased with decreases in the sorption capacity constant (K d s ). The two CDs were also assessed for their ability to remove TNT from a highly contaminated topsoil (5265 mg/kg) obtained from a former manufacturing facility that had been aged for 10-40 yr. The estimated association constants (K s ) were comparable to those obtained for solubilization of pure TNT into aqueous solution. This study demonstrates the effectiveness of CDs in decontaminating a variety of soils containing both high and low levels of TNT and some of its associated metabolites. Introduction Soils contaminated with 2,4,6-trinitrotoluene (TNT) from activities in the munitions and defense industries is a worldwide environmental problem. In natural and engi- neered systems, it has been demonstrated that the nitro groups of TNT undergo reduction reactions to form amino derivatives that include 4-amino-2,6-dinitrotoluene (4- ADNT),2-amino-4,6-dinitrotoluene (2-ADNT),2,4-diamino- 6-nitrotoluene (2,4-DANT),and 2,6-diamino-4-nitrotoluene (2,6-DANT) (1, 2). It has been demonstrated that TNT and its amino derivatives can be irreversibly sorbed by soil (1, 3-11).Irreversible sorption has been postulated as a possible explanation for poor mineralization of TNT in soil (1). Surfactants have been shown to be capable of desorbing TNT from soil (12) and to subsequently enhance the mineralization of TNT by Phanerochaete chrysporium (13). However, there are potential drawbacks to the use of surfactantsfor in and exsitu remediation.Potentialoperating problems include sorption of the surfactant by soil, pre- cipitation of the surfactant, phase separation, and foaming (14). In addition, if surfactants are to enhance the bioavail- ability of contaminants, then they must be compatible with the accompanyingbiologicalprocess.Forexample,nonionic surfactants have been shown to inhibit mineralization of phenanthrene in soil water systems (15). Cyclodextrins (CDs) are cyclic oligosaccharides formed from the enzymatic degradation of starch (16). CDs are considered nontoxic and used in pharmaceuticals and as food additives (17). One class of CDs is able to enhance the solubilityofmanyorganic compounds byforminginclusion complexes with “guest”molecules.It has been demonstrated in the laboratoryand field that CDsare capable ofenhancing thesolubilityofanumberofcommon organiccontaminants (18-20). Hydroxypropyl- -cyclodextrin (HPCD) was also shown to significantly enhance the transport ofanthracene, pyrene, and trichlorobiphenyl through soil columns (21). In a further study, HPCD increased the solubility of phenan- threne by 124 times and its removal rate by 6 times by a phenanthrene degrading isolate (22). In a pilot-scale field test, HPCD increased the aqueous solubility of 12 target compoundsby100to20 000timesfrom anonaqueoussource in an aquifer (20). As discussed by McCray and Brusseau (20), CDs experience little or no sorption by soil and are not subject to precipitation,hence theyare easilyremoved from the subsurface (which may be of regulatory and economic concern). CDs have also been shown to enhance the solubilization ofthe explosive hexahydro-1,3,5-trinitro-1,3,5- triazine (RDX) from soil (23). Based on published data, it would appear that CDs are becoming comparable in cost with surfactants (24, 25). Particularly, it has been reported that the cost of -CD is as low as $4/kg (25). In comparison, the cost of food grade surfactants,that were evaluated for subsurface remediation, was estimated to be $2.2/kg (assuming 1% inflation in convertingto 1999$)(24).Adetailed comparison ofthe costs of surfactants and CDs for subsurface remediation was not found in the literature. However, since the cost of CDs has continuously decreased in recent years (24), investigations regarding their technical merit for subsurface remediation are justified. We recently demonstrated that significant sorption - desorption hysteresis exists for TNT,4-ADNT,and 2,4-DANT sorbed by natural and model soils (3). The purpose of the present studywas to examine the abilityoftwo CDs (heptakis- 2,6-di-O-methyl- -cyclodextrin (DMCD) and HPCD) to desorb TNT, 4-ADNT, and 2,4-DANT from two artificially contaminated soilsexamined in our earlier study(an organic rich topsoil and an illite shale) (3). The DMCD was selected because it is highly surface active, and the HPCD was selected because it is commonly used and less expensive. We also studied the ability of the two CDs to solubilize TNT from a highly contaminated soil obtained from a former manufacturingfacility,where contamination has existed for 10-40 yr. Desorption and solubilization data for soil were compared with the association constants that were estimated from CD-enhanced solubility of the three NACs. Experimental Section Chemicals . TNT (>99% purity) was provided by Defense Research Establishment Valcartier (Valcartier, PQ), 4-ADNT (>99% purity) was purchased from Omega Inc. (Le ´vis, PQ), and 2,4-DANT (>99% purity) was purchased from Accu- Standard Inc. (New Haven, CT). The HPCD and DMCD (no reported purity) were purchased from Aldrich (Oakville, ON). The CD solutions were prepared daily. Soils . The agricultural topsoil and illite green shale used are described in detail elsewhere in terms of soil properties *Correspondingauthor phone: (514)496-6267;fax: (514)496-6265; e-mail: Jalal.Hawari@nrc.ca. Environ. Sci. Technol. 2000, 34, 3462-3468 3462 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 16, 2000 10.1021/es9910659 CCC: $19.00 Published 2000 by the Am. Chem. Soc. Published on Web 07/08/2000