3 research outputs found
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><sub>rap</sub>) and slowly
(%<i>F</i><sub>slow</sub>) 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><sub>rap</sub> occurred when AC was increased from 0 to
5%, with a corresponding increase in %<i>F</i><sub>slow</sub>. Desorption rate constants followed the progression <i>k</i><sub>rap</sub> (% h<sup>–1</sup>) > <i>k</i><sub>slow</sub> (% h<sup>–1</sup>) and were in the order of 10<sup>–1</sup> to 10<sup>–2</sup> and 10<sup>–3</sup> to 10<sup>–4</sup>, respectively. Linear regressions between
%<i>F</i><sub>rap</sub> and the fractions degraded by a
phenanthrene-degrading inoculum (%<i>F</i><sub>min</sub>) indicated that slopes did not approximate 1 at concentrations greater
than 0% AC; %<i>F</i><sub>min</sub> often exceeded %<i>F</i><sub>rap</sub>, indicating a fraction of sorbed phenanthrene
(%<i>F</i><sub>slow</sub>) 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