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Cyclodextrin enhanced extraction of PAHs from spiked and aged soils. Effect of co-contaminants

AuthorsMorillo González, Esmeralda ; Sánchez Trujillo, Mª Antonia ; Lacorte Bruguera, Silvia ; Villaverde Capellán, J.
Issue Date2013
CitationBook of abstracts of 14th EuCheMS International Conference on Chemistry and the Environment. ICCE 2013, Barcelona, June 25 - 28, 2013
AbstractPolycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants. Excessive inputs from anthropogenic activities have caused serious environmental contamination and threaten to adversely affect human health. To address the associated environmental concerns, innovative remediation technologies are urgently needed. It has been observed that as soil-pollutant contact time increases, pollutant bioavailability and extractability decreases. This phenomenon has been termed “aging”. Cyclodextrins (CDs) appeared as promising complexing agents to mobilize hydrophobic aromatic pollutants in soils while minimizing environmental impact, due to their non-toxic character. The aim of this study was to investigate the feasibility of a cleanup strategy using hydroxypropyl-β-cyclodextrin (HPBCD) solution to enhance soil washing for extracting PAHs. We examined the potential of HPBCD for assessing the extractable fractions of PAHs in single and co-contaminant spiked and aged soils. Three soils with different properties were selected in order to assess the effect of aging according to the characteristics of the sorbent. The extractions were done using two different solutions, an aqueous electrolyte solution and a HPBCD solution, and were carried out at 1, 35, 70 and 100 days after spiking. The soils were spiked individually with fluorene, fluoranthene, pyrene or anthracene, and with a mix of the PAHs considered as priority pollutants by US-EPA. The highest extraction percentages were obtained for 3- and 4-ring PAHs, because of the appropriate size and shape of these compounds relative to those of the hydrophobic cavitiy of HPBCD, especially 3-ring PAHs. The better the guest molecule fills the CD cavity, the stronger the hydrophobic and van der Waals interactions are. In contrast, in the case of the less voluminous PAHs such as naphthalene, acenaphthene and acenaphthylene, the complexes with HPBCD are formed, but the interaction with the CD is very low, and their extraction from the soil was less efficient, presenting no advantage relative to the use of the electrolyte solution. In the case of 5- and 6-ring PAHs the tendency to form complexes with HPBCD is extremely weak due to steric hindrance. The results indicate that the extractable fraction of PAH was inversely correlated to the number of benzene rings and their octanol–water partition coefficient. With increasing hydrophobicity, the affinity of PAHs to HPBCD did not increase to the same degree as to soil organic matter. Therefore, PAHs that were not extracted by HPBCD almost certainly are not bioavailable and, consequently, they are not potentially toxic to the environment. When the mix of PAHs was extracted, differences in the effectiveness of HPBCD depending on the aging were only appreciable for 2- and 3-ring PAHs. Differences depending on the soil used were appreciable only when individual PAHs were extracted. The effect of the presence of individual PAHs or a mix of PAHs in relation to their percentages of extraction is discussed
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(IDAEA) Comunicaciones congresos
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