Development of an eco-friendly alternative to a standard cyclodextrin extraction method for understanding the...

Polycyclic aromatic hydrocarbons (PAHs) are particularly found in soils with current or former industrial activities. Although their total concentration is commonly given for risk assessments, some PAHs irreversibly bound to soil particles are not accessible for living organisms; so it is important to assess the bioaccessible fraction most likely to lead to organisms exposure. A new methodology was developed, using a polymer of carboxymethyl-β-cyclodextrin (pCMCD) to extract readily desorbed PAH fraction, followed by microextraction before GC-MS analysis. It allowed simplifying and minimizing the overall procedure, which better fitted with the green analytical chemistry principles compared to the standard procedure using hydroxypropyl-β-cyclodextrin. The new procedure was applied to several industrial and urban soils that have been contaminated for several decades. Their bioaccessible fraction appeared particularly low (2.4-9.6%). Soil's parameters were responsible of the PAH low mass-transfer ability, such as particle size or organic matter content. But more surprisingly, cationic exchange capacity (CEC) and total content of nitrogen (N content) had also influence on the remaining bioaccessible fraction, particularly in N-poor and sandy (of low CEC) soils. An industrial soil, combining low N content and high concentrations of metal co-contaminants, was tested for PAH biodegradation. Although stimulation of soil microorganisms could appear promising, only a portion of the bioaccessible fraction could be dissipated. So in co-contaminated aged and mineralized soils, even the PAH remaining bioaccesssible fraction could not be entirely dissipated which makes it difficult to envisage natural or biostimulated remediation of such industrial soils.