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

Dichlorodiphenyltrichloroethane (DDT) is one of the persistent organic pollutants (POPs) that are highly toxic to the environment. Effective evaluation on the bioavailability of DDTs in soils is essential for risk assessment and soil remediation. The aims of this study were to verify the feasibility of the hydroxypropyl-β-cyclodextrin (HPCD) extraction method for predicting the bioavailability of DDT, dichlorodiphenyldichloroethane (DDD), and dichlorodiphenyldichloroethylene (DDE) in soils, and to examine the effect of HPCD on their biodegradation in different soils. Four soils were aged with a mixture of p,p′-DDT, o,p′-DDT, p,p′-DDD and p,p′-DDE (0.25 μg g⁻¹ for each compound) for 20 and 100 days, respectively. For each of the DDTs, a significant positive correlation between HPCD-extractable fraction and biodegradable fraction in each soil was observed. It was demonstrated that the amounts of HPCD-extractable p,p′-DDT and o,p′-DDT were not significantly different from the amounts that were degradable as assessed from their degradation by Enterobacter sp. LY402 (p > 0.05). Such 1:1 relationship between extraction and degradation was not obtained in the cases of p,p′-DDD and p,p′-DDE, as the amounts of degradable p,p′-DDD and p,p′-DDE were lower than the amounts that were extractable with HPCD. Additionally, the biodegradation of p,p′-DDT, o,p′-DDT, p,p′-DDD, and p,p′-DDE was inhibited in the presence of HPCD, which could be due to the binding of the compounds to HPCD, making them less available to access the bacteria for degradation. This study provides the possibility of using the HPCD extraction method to predict the bioavailability of p,p′-DDT and o,p′-DDT in soils. But when HPCD was used as an additive in the bioremediation of DDT-contaminated soils, it might have a negative effect on biodegradation.