Direct Link between Fluoranthene Biodegradation and the Mobility and Sequestration of its Residues during Aging

Abstract

The aim of this study was to assess the influence of the polycyclic aromatic hydrocarbons (PAH)-degrading activity in the fate of fluoranthene in soils. Three soil samples with different degrading activities (an industrial soil, the same industrial soil after biostimulation, and an agricultural soil) were spiked with 14C-fluoranthene and incubated for 6 mo with monitoring of biodegradation and mineralization. To follow the distribution of the 14C-fluoranthene residues (i.e., 14C-fluoranthene and its degradation products) among the soil compartments, we performed successively leaching, centrifugation (to collect intra-aggregate pore water), solvent extraction, and combustion of the soil columns. In the industrial soil, no mineralization of 14C-fluoranthene was observed, and only 3% of the initial 14C-activity was non-extractable (with acetone:dichloromethane) after 165 d of incubation. The biostimulation (addition of unlabeled polycyclic aromatic hydrocarbons) increased the degrading activity in this soil (59% of 14C-fluoranthene was mineralized) and increased the residues sequestration (13% of 14C-activity was non-extractable). The microflora of the agricultural soil mineralized 14C-fluoranthene more slowly and to a lesser extent (25%) than the biostimulated soil, but a higher amount of 14C-activity was sequestered (41%). Thus, the rate and extent of 14C-fluoranthene mineralization seemed to be related to the 14C-activity sequestration by controlling the accumulation of degradation products in the soil. 14C-Fluoranthene biodegradation enhanced the concentration of 14C-polar compounds in the intra-aggregate pore water. Our results point out the close link between fluoranthene biodegradation and two key aging processes, diffusion and sequestration, in soils. Biodegradation controls the mobility and sequestration of residues by transforming fluoranthene into more polar molecules that can diffuse into the intra-aggregate pore water and then might become bound to the matrix or entrapped in the microporosity.