Publication details

The kinetics of solid-phase microextraction measured for freshly added and aged hydrophobic compounds in two different soils



Year of publication 2015
Type Article in Periodical
Magazine / Source International Journal of environmental analytical Chemistry
MU Faculty or unit

Faculty of Science

Field Soil contamination adn decontamination incl. pesticides
Keywords solid-phase microextraction (SPME); extraction kinetics; equilibrium; ageing; organic carbon (OC) content
Description The proper choice of exposure times is critical if the freely dissolved concentration of chemicals in soil porewater is to be measured via the equilibrium solid-phase microextraction (SPME) as the times to equilibrium may vary depending on compound and soil properties. To reveal the effects of compound hydrophobicity, ageing and soil organic matter content on times to equilibrium, the SPME uptake was measured for five freshly added and aged hydrophobic organic compounds (phenanthrene, pyrene, lindane, p,p-DDT and polychlorinated biphenyl (PCB) 153) in two contrasted soils (arable and forest soil). The tested compound-soil systems behaved kinetically different. Longer equilibrium times were observed with increasing hydrophobicity of compounds for aged compared to freshly added chemicals and for the forest soil in comparison to the arable soil. The calculated soil-porewater partition coefficients (i.e. sorption coefficients, K-d) of chemicals differed between soil types mainly due to various organic carbon (OC) contents as evidenced by the comparable K-oc values (i.e. K-d values normalised to soil OC content). Similar K-oc values were also found with the various extent of ageing, indicating that both the freshly added and aged compounds linearly partitioned between the soil organic matter and porewater. Our results suggest that, for a respective compound, variations in equilibrium times may be expected depending upon the residence time and the organic matter content in soil where the longest equilibrium times seems to appear for a combination of aged compounds and high organic soils. With regard to this outcome, the effect of the level of sample depletion due to the SPME extraction (LDSPME) on equilibrium times was assessed. At LDs(SPME) of up to 10%, equilibrium times increases linearly with LDs(SPME) for p,p-DDT and PCB 153. For phenanthrene (LDSPME<10%), and for lindane and pyrene (1.2% 40%), no clear relationships were observed.
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