October 2012
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36 Reads
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62 Citations
Environmental Science and Technology
The observed strong sorption of polycyclic aromatic hydrocarbons (PAHs) to black carbon (BC) presents potential implications for PAH bioaccessibility in soils. The effects of BC on the desorption kinetics and mineralisation of phenanthrene in four soils was investigated after 1, 25, 50 and 100d soil-PAH contact time, using sequential hydroxypropyl-β-cyclodextrin (HPCD) extractions in soils amended with 0, 0.1, 1 and 5% (dry wt. soil) activated charcoal (AC, a form of BC). The Rrapidly (%Frap) and slowly (%Fslow) desorbing phenanthrene fractions and their rate constants were determined using a first-order two-compartment (biphasic) desorption model. A minimum 7.8-fold decrease in %Frap occurred when AC was increased from 0-5%, with a corresponding increase in %Fslow. Desorption rate constants followed the progression krap(% h-1) > kslow(% h-1) and were in the order of 10-1 to 10-2 and 10-3 to 10-4, respectively. Linear regressions between %Frap and the fractions degraded by a phenanthrene inoculum (% Fmin) indicated that slopes did not approximate 1 at concentrations greater than 0% AC; %Fmin often exceeded %Frap, indicating a fraction of sorbed phenanthrene (%Fslow) remained microbially accessible. Therefore, sorption-HPCD-desorption kinetics alone may not be an adequate basis for the prediction of the bioaccessibility of PAHs to microorganisms and/or bioremediation potential in AC amended soils.