Removal of polycyclic aromatic hydrocarbons from soil: a comparison between bioremoval and supercritical fluids extraction.

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic substances which are resistant to environmental degradation due to their highly hydrophobic nature. Soils contaminated with PAHs pose potential risks to human and ecological health, therefore concern over their adverse effects have resulted in extensive studies on their removal from contaminated soils. The main purpose of this study was to compare experimental results of PAHs removal, from a natural certified soil polluted with PAHs, by biological methods (using bioaugmentation and biostimulation in a solid-state culture) with those from supercritical fluid extraction (SFE), using supercritical ethane as solvent. The comparison of results between the two methods showed that maximal removal of naphthalene, acenaphthene, fluorene, and chrysene was performed using bioremediation; however, for the rest of the PAHs considered (fluoranthene, pyrene, and benz(a)anthracene) SFE resulted more efficient. Although bioremediation achieved higher removal ratios for certain hydrocarbons and takes advantage of the increased rate of natural biological processes, it takes longer time (i.e. 36 d vs. half an hour) than SFE and it is best for 2-3 PAHs rings.

Nickel and vanadium concentrations and its relation with sediment acute toxicity.

Sediments from Pánuco River historically have contained elevated levels of numerous contaminants that may pose risks to ecological receptors and humans. Sediments were sampled and characterized to determine the acute sediment toxicity and its relationship with contaminants. Results demonstrated that toxicity was significantly correlated with fitness index (r = 0.82, p < 0.001), TOC (r = 0.55, p < 0.5), Ni (r = 0.95, p < 0.001), and V (r = 0.93, p < 0.001), but not with PAHs (r = 0.20, p < 0.5) during rainy and dry seasons. Although a great heterogeneity exists, the river outlet presents the biggest problems, due to dredging allow the metal desorption from solid to water phase, increasing the metal bioavailability.

Polyaromatic hydrocarbons (PAHs) and metal evaluation after a diesel spill in Oaxaca, Mexico.

Pollution in the marine environment due to a diesel spill takes days to months to complete natural remediation owing to its low volatility. Metal and PAH contamination caused by an accidental diesel spill were studied. V, Ni and Hg levels increased immediately after the spill, while PAH levels decreased after 1 month (79.4-7.6 microg kg(-1)). At the diesel spill point, fluoranthene exceeded acute and chronic levels, although most of the PAHs were within the range of low effects. In fish body burden, the highest bioaccumulation factor (2.63 for naphthalene) was related to the lower molecular weight PAHs.

Phenanthrene removal by Penicillium frequentans grown on a solid-state culture: effect of oxygen concentration.

Phenanthrene removal by Penicillium frequentans was compared under aerobic and microaerophilic conditions in a solid culture amended with low quantities of an agricultural residue. An inoculum of P. frequentans grown on sugarcane bagasse pith was mixed with soil spiked with 200 mg l(-1) of phenanthrene, to obtain a final bagasse/soil ratio of 1:16. The C/N ratio was adjusted to 60 and the moisture content to 40%. The oxygen concentrations were adjusted to 20%, 10%, 5%, 2% and close to 0%, in the soil-gas phase for each treatment. There were statistically significant (p<0.05) differences in the metabolic activity at different oxygen concentrations, measured as CO2 production. Phenanthrene removal rates increased with oxygen concentration, reaching 52% removal after 17 days of incubation for the treatment with 20% O2. Nevertheless, oxygen-limited (microaerophilic) conditions did not preclude phenanthrene degradation.

Bioavailable cadmium during the bioremediation of phenanthrene-contaminated soils using the diffusive gradients in thin-film technique.

AIMS: To study the impact of fungal bioremediation of phenanthrene on trace cadmium solid-solution fluxes and solution phase concentration. METHODS AND RESULTS: The bioremediation of phenanthrene in soils was performed using the fungus Penicillium frequentans. Metal behaviour was evaluated by the techniques of diffusive gradient in thin-films (DGT) and filtration. Fluxes of cadmium (Cd) show a significant (P < 0.002) increase after the start of bioremediation, indicating that the bioremediation process itself releases significant amount of Cd into solution from the soil solid-phase. Unlike DGT devices, the solution concentration from filtration shows a clear bimodal distribution. We postulate that the initial action of the fungi is most likely to breakdown the surface of the solid phase to smaller, 'solution-phase' material (<0.45 microm) leading to a peak in Cd concentration in solution. CONCLUSIONS: Phenanthrene removal from soils by bioremediation ironically results in the mobilization of another toxic pollutant (Cd). SIGNIFICANCE AND IMPACT OF THE STUDY: Bioremediation of organic pollutants in contaminated soil will likely lead to large increases in the mobilization of toxic metals, increasing metal bio-uptake and incorporation into the wider food chain. Bioremediation strategies need to account for this behaviour and further research is required both to understand the generality of this behaviour and the operative mechanisms.