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

Abstract

Dichlorodiphenyltrichloroethane (DDT) is one of the persistent organic pollutants (POPs) that are highly toxic to the environment. Effective evalu- ation on the bioavailability of DDTs in soils is essen- tial 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 biodeg- radation 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 μ gg −1 for each compound) for 20 and 100 days, respectively. For each of the DDTs, a sig- nificant 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 degra- dation 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 biodegra- dation 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 bac- teria for degradation. This study provides the possi- bility of using the HPCD extraction method to predict the bioavailability of p,p'-DDTand o,p'-DDTin soils. But when HPCD was used as an additive in the bioremediation of DDT-contaminated soils, it might have a negative effect on biodegradation.