Environmental Engineering Reference
In-Depth Information
Several studies in literature have demonstrated the applicability of
integrated systems to degrade dif erent chlorinated compounds.
He
et
al.
[69] successfully transformed 2,2,´4,5,5´-pentachlorobiphenyl to
2,2´,4-trichlorobiphenyl using nFe
0
/Pd and then treated the end prod-
uct with aerobic bacteria to further degrade the compound. Similarly,
Triclosan (2,4,4´-trichloro-2´-hydroxydiphenyl ether, TCS) was also
reported to get completely transformed into nontoxic products in a
sequential treatment system comprised of nFe
0
/Pd and laccase in the
presence of syringaldehyde [123]. Polybrominated diphephenyl ether
was also reported to undergo degradation in a sequential treatment sys-
tem involving nFe
0
and
Sphingomonas sp.
PH-07 [124].
Sphingomonas sp.
PH-07
was also reported to degrade dechlorinated product of Triclosan
in a nano-bio hybrid system [125]. h e combined use of nFe
0
and auto-
trophic hydrogen-bacteria was found to have a 3.2-fold higher dechlori-
nation rate for trichloroethylene (TCE) in comparison to their individual
ef ect showing synergistic ef ect, of combined method on overall dechlo-
rination reaction [126]. A similar synergistic ef ect was also observed by
Singh
et al.
[127] while studying γ-HCH dechlorination with stabilized
nFe
0
/Pd and
Sphingomonas sp.
strain NM05
in soil system.
14.7 ChallengesAhead
14.7.1 Toxicity
Along with nanoremediation, nanoecotoxicology has also emerged as a
discipline concerned with the potential risks associated with the release of
nanoparticles in the environment. In recent years several articles have been
devoted to the toxic ef ect of nFe
0
on bacterial cells, mammalian nerve
cells, bronchial epithelial cells, i sh embryo, etc. [128-132]. In general,
nanoparticles exert toxic ef ect on microbes by disrupting cell membranes,
increasing membrane permeability, interrupting energy transduction, pro-
ducing reactive oxygen species, lipid peroxidation, DNA damage, etc. [128,
129]. h e toxicity of iron is based on its ability to catalyze the formation
of hydroxyl radicals (OH
-
) from superoxide (O
2
-
) and hydrogen peroxide
(H
2
O
2
). h ese reactive species show strong biochemical activity, af ecting
antioxidant enzymatic activities, peroxidation of membrane lipids, modi-
i cation of nucleic acids, dysfunction of cellular components, hypoxia and
eventually cause cell death and tissue injury [129, 132]. Some research-
ers reported that partial oxidation/aging and surface modii cation of nFe
0
,
could decrease its toxic properties [130, 133, 134].
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