Bioavailability modification and fungal biodegradation of PAHs in aged industrial soils

Bioavailability of pollutants in contaminated soils represents an important factor influencing the bioremediation process. We investigated the impact of the bioavailability of polycyclic aromatic hydrocarbons (PAHs) on the efficacy of mycoremediation of aged matrices. Two historically contaminated soils, differing in both overall PAH concentrations (2320 vs. 612mgPAHskg-1) and in the relative amount of the non-bioavailable fraction (4.0 vs. 32%, respectively), were incubated with two white rot fungi – Irpex lacteus and Pleurotus ostreatus. When relating biodegradation results with the amount of PAH bioavailable fractions estimated by sequential supercritical fluid extractions, the correlation coefficients ranged from 0.60 to 0.83. In order to assess a possible increase of the mycoremediation efficiency, four different mobilizing agents (MAs), i.e. soybean oil, Tween 20, Tween 80 and olive-mill wastewater, were added to soil prior to fungal incubations. The addition of MAs to the soil with a negligible amount of the non-bioavailable fraction had either a limited or even a negative impact on PAH degradation. The same was true also in the case of the other soil, characterized by a larger non-bioavailable fraction. Both white rot fungi under study markedly degraded PAHs in historically contaminated soils differing significantly in PAH content and the bioavailability. However, both the fungi performed better in the soil with higher pollutant bioavailability. Consequently, a preliminary determination of non-bioavailable fraction might provide a useful indication of the performance of bioremediation treatment.