Influence of hydroxypropyl-β-cyclodextrin on the extraction and biodegradation of phenanthrene in soil

A study was conducted to investigate the effect of hydroxypropyl-beta-cyclodextrin (HPCD) on the aging and biodegradation of phenanthrene (PHE) in soil. Soil was spiked with PHE at 25 mg(PHE)/kg(SOIL) and HPCD at a range of concentrations from 0 to 3.5 g(HPCD)/kg(SOIL) and aged for 1, 84, and 322 d. At each time point, a variety of analyses were performed to assess the loss and aging of the PHE in the soil. Methods included determination of total PHE remaining, dichloromethane (DCM) and butan-l-ol (BuOH) extractions, and determination of PHE extractable by an aqueous HPCD shake extraction. Mineralization assays were also carried out to assess the availability of the PHE to a PHE-degrading bacterial inoculum. It was found that the presence of HPCD in the soils increased PHE loss from the aged soil systems, particularly at the higher application rates. Dichloromethane and BuOH extractabilities were reduced with aging and increasing HPCD concentration, as was the amount of PHE that was extractable using an aqueous HPCD shake extraction or that was available for mineralization. The DCM and BuOH extraction yielded similar results, and both greatly overestimated the availability of the PHE to the degraders, whereas the HPCD extraction results were very similar to that of PHE biodegradation. This study indicates that cyclodextrins have potential for use as alternatives to surfactants in enhancing the desorption/solubilization and degradation of recalcitrant organic contaminants in soil.