The aim of this paper was to study the effect of the addition of ß-cyclodextrin derivatives (CDs) on the mobility of Polycyclic Aromatic Hydrocarbons (PAHs) spiked on a soil in laboratory conditions. The soil selected was contaminated with potentially toxic elements (PTEs) due to the holding dam burst at the Los Frailes mine in Aznalcóllar in 1998, to simulate a co-contaminated soil. CDs are biodegradable agents capable to increase PAHs solubility, and, therefore, their biodegradability, in order to remediate the soil. Nevertheless, possible PTEs mobility and availability increases due to CDs addition has to be also controlled in co-contaminated soils in order to avoid soil toxicity and/or leaching and consecuently groundwater contamination. Leaching column tests (12 cm height) were conducted to check whether the addition of two cyclodextrins (Hydroxypropyl-ß-cyclodextrin, HP-ß-CD, and randomly methylated-ß-cyclodextrin, RAMEB) affected the mobility of PAHs and PTEs. Only some PAHs (2-, 3- and 4-rings) leached along the columns and were detected in leachates with both CDs, but with higher contents for HPBCD than RAMEB (0.12-14.1% and 0.05-3.18% of the total content reespectively). These PAHs have been solubilized and mobilized by the formation of an inclusion complexes with the CDs because of the appropriate size and shape of these compounds relative to those of the hydrophobic cavities of the CDs studied. The availability of the PAHs remaining in soil at the end of the assays decreased with the use of CDs, probably because the more labile content of these pollutants have been leached as soluble complex with the CDs. The highest values of PAHs availability were obtained for 2- and 3-rings PAHs. The higher molecular weight that were not mobilised by the CDs were not also bioavailable and, therefore, they are not potentially toxic to the environment. Study of the evolution of PTEs in the leachate did not showed significant mobility in the presence of CDs, both in the original soil and in the PAHs spiked soil, with the exception of Cu with RAMEB which leached although in low proportion. The complexing capacity of Cu with dissolved organic matter could be responsible of this result. Due to the mobility of Cu in the presence of RAMEB, special attention should be paid to this aspect in order to avoid a toxicity of the extract that could affect the microorganisms responsible of the biodegradation of PAHs. PTEs availability (EDTA extraction method) at the end of the assay it is not affected by the use of CDs. We conclude that the use of these CDs, but especially HPBCD, can be a useful tool for the recovery of soil co-contaminated with PAHs and PTEs as it increases the availability and mobility of PAHs, with minimal influence on PTEs, which could help make PAHs more accesible to microorganisms, and, through microbial biodegradation, remove these pollutants from soil.

This work was supported by the Spanish Ministry of Economy and Competitiveness (co-funded by the Fondo Europeo de Desarrollo Regional, FEDER), under the research project CTM2013- 2599-R.

Póster presentado en el 11º Congreso Ibérico y 8º Iberoamericano de Contaminación y Toxicología Ambiental, Madrid 11-13 de julio de 2018

Peer Reviewed