Influence of Activated Charcoal on Desorption Kinetics and Biodegradation of Phenanthrene in Soil

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 mineralization of phenanthrene in four soils was investigated after 1, 25, 50, and 100 d 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 rapidly (%<i>F</i>_rap) and slowly (%<i>F</i>_slow) 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 %<i>F</i>_rap occurred when AC was increased from 0 to 5%, with a corresponding increase in %<i>F</i>_slow. Desorption rate constants followed the progression <i>k</i>_rap (% h^–1) > <i>k</i>_slow (% h^–1) and were in the order of 10^–1 to 10^–2 and 10^–3 to 10^–4, respectively. Linear regressions between %<i>F</i>_rap and the fractions degraded by a phenanthrene-degrading inoculum (%<i>F</i>_min) indicated that slopes did not approximate 1 at concentrations greater than 0% AC; %<i>F</i>_min often exceeded %<i>F</i>_rap, indicating a fraction of sorbed phenanthrene (%<i>F</i>_slow) remained microbially accessible. Therefore, HPCD-desorption kinetics alone may not be an adequate basis for the prediction of the bioaccessibility of PAHs to microorganisms or bioremediation potential in AC-amended soils

Mycelia Promote Active Transport and Spatial Dispersion of Polycyclic Aromatic Hydrocarbons

To cope with heterogeneous subsurface environments mycelial microorganisms have developed a unique ramified growth form. By extending hyphae, they can obtain nutrients from remote places and transport them even through air gaps and in small pore spaces, repectively. To date, studies have been focusing on the role that networks play in the distribution of nutrients. Here, we investigated the role of mycelia for the translocation of nonessential substances, using polycyclic aromatic hydrocarbons (PAHs) as model compounds. We show that the hyphae of the mycelial soil oomycete <i>Pythium ultimum</i> function as active translocation vectors for a wide range of PAHs. Visualization by two-photon excitation microscopy (TPEM) demonstrated the uptake and accumulation of phenanthrene (PHE) in lipid vesicles and its active transport by cytoplasmic streaming of the hyphae (‘hyphal pipelines’). In mycelial networks, contaminants were translocated over larger distances than by diffusion. Given their transport capacity and ubiquity, hyphae may substantially distribute remote hydrophobic contaminants in soil, thereby improving their bioavailability to bacterial degradation. Hyphal contaminant dispersal may provide an untapped potential for future bioremediation approaches

Pyrogenic carbon and its role in contaminant immobilization in soils

<p>Pyrogenic carbon (PyC), including soil native PyC and engineered PyC (biochars), is increasingly being recognized for its potential role as a low-cost immobilizer of contaminants in soils. Published reviews on the role of soil native PyC as a sorbent in soils have so far focused mainly on organic contaminants and paid little or no attention to inorganic contaminants. Further, a comprehensive review on the production of both natural PyC and engineered PyC (biochars), mechanisms involved, and factors influencing their role as soil contaminant immobilizer is so far not available. The objective of this review is thus to systematically summarize the sources, formation, and properties of PyC, including its quantification in soils, followed by their roles in the immobilization of both organic and inorganic contaminants in soils. Effectiveness of PyC on bioavailability, leaching, and degradation of soil contaminants was summarized. Notably, the mechanisms and factors (for the first time) influencing the immobilization processes for soil contaminants were also extensively elucidated. This review helps better understand and design PyC for soil contaminant immobilization.</p