Adsorption and native microbiota of an agricultural soil are involved in the removal of fluoranthene

Several factors can influence the removal of polycyclic aromatic hydrocarbons from agricultural soils, such as the native microbiota, the physicochemical properties of the soil, soil management and addition of exogenous microorganisms. Nevertheless, the involvement of these factors has not been studied during fluoranthene removal at the microcosm level. In the present study, the effects of these factors were evaluated in microcosms composed of an organic agricultural soil (OAS-microcosm) and conventional agricultural soil (CAS-microcosm) contaminated with fluoranthene. According to their physicochemical properties, both soils were classified as silt loam. They had similar cation exchange capacities, water holding capacities and P-PO4^3-, but different pHs, electrical conductivities, and percentages of N, C, silt, clay and sand. Fluoranthene did not alter the native microbiota of the OAS- and CAS-microcosm because similar banding profiles were obtained in PCR-DGGE analysis of the 16S rRNA gene, and the total heterotrophic bacteria count as well as fluoranthene-degrading bacteria count were similar between microcosms with fluoranthene and their controls without fluoranthene. However, OAS- and CAS-microcosms showed higher respiratory activity than their controls (p<0.05). At the beginning of the degradation kinetics, OAS- and CAS-microcosms reached a higher percentage of fluoranthene removal than their abiotic counterparts (adsorption controls; p<0.05); towards the end of the degradation kinetics, no significant difference was observed between the OAS- and CAS-microcosms and their corresponding adsorption controls. The bioaugmentation assay using a fluoranthene-degrading bacterial consortium increased fluoranthene removal. This work showed that fluoranthene adsorption to soil and native microbiota of agricultural soils were involved in fluoranthene removal.