Use of cyclodextrins for chlorotoluron remediation in contaminated soils

Póster presentado en la 6th European Conference on Cyclodextrins. Santiago de Compostela, Oclober 2-4, 2019Chlorotoluron (3-(3-chloro-p-tolyl)-I,I-dimethylurea) (CHL) is a phenylurea herbicide used to control broadleaf and annual grass weeds in cereal fields. CHL may persist in soil and its leaching to the underlying aquifer may occur for at least 3 years after field treatment, being increasingly common to find the parent compound and its metabolites in groundwater in concentrations exceeding the drinking water threshold limit (0.1 ¡Lg L·!). It is a biologically active pollutant in the environment and exhibits a high toxicity. The aim of this work was to develop an effective bioremediation tool for an enhanced biodegradation of CLH in polluted soils that could increase the chance for a successful decontamination. In this process hydroxypropyl-~-cyclodextrin (HPBCD) was tested as extraction agent to improve CLH bioavailability, and was combined with the inoculation of a CLH microbial degrader consortium (bioaugmentation), in order to remove CLH from media getting a successful soil decontamination. Firstly, the effect of HPBCD on CLH desorption from soils was stodied to determine if the herbicide forms inclusion complexes with HPBCD, increasing its solubility and, therefore, its potential bioavailability to be degraded by soil microorganisms. Adsorption-desorption tests were performed in three soils with different organic matter (OM) content (Soill, 0.63%; Soil2, 1.91 %; Soil 3, 3.04%). The percentages of CLH extraeted with only water were related to the amount adsorbed by each soil, that is, the higher the sorption, the lower the pereentage of CLH removed from the soil with water. The pereentages of CLH extracted with HPBCD solutions were always higher than with water. CLH forms an inclusion complex with HPBCD, which acts as an extractant towards the CLH adsorbed on soil surfaee. The higher the OM of the soil and the amount ofCLH adsorbed, the higherthe extraction with HPBCD: Soil3»Soil2>Soil1. CLH biodegradation was always higher when the soils were inoenlated with the CLH degrader mierobial eonsortium than with the soils endogenous flora. However, when HPBCD was applied the behavior of the three soils was different. In Soils 1 and 3 the eonsortium inocnlated was highly effective for CLH degradation, and the addition of HPBCD did not improve it. On the contrary, in Soil 2, when the cyelodextrin is added together with the consortium, 95% CHL was degraded in 15 days, while for the consortium alone the degradation was 75%. In sorne soils (1 and 2) the eompetition between CLH and HPBCD as earbon sources for the soil flora, due to the biodegradability of HPBCD, was also observed. It ean be concluded that the use of HPBCD solution as a bioavailability enhaneer will depend not only on the physieoehemieal properties of the soil to be treated, but also on the behaviour of the endogenous flora present. It is therefore neeessary to earry out preliminary studies before a remediation proeess using eyelodextrins ean be applied to the soil.This work was supported by the Spanish Ministry of Science, Innovation and Universities (cofunded by FEDER), under the researeh projeet CTM2017-824 72-C2-1-R