2006). Despite this low mobility, the influence of ZVI can be expanded by the
release and transport of Fe
2+ , thus affecting a more important zone.
The introduction of ZVI particles in the environment is responsible for the local
change in biogeochemical conditions, thus affecting their fate, transport, and reactivity, but also the microbial community activity and growth (Lowry et al. 2012;
Jang et al. 2014; Wagner et al. 2014). As for pollutants, the growth and transformation of the oxide shell can trap microbes, resulting in their quantitative removal from
aqueous phase (Noubactep 2011). It is also suggested that the antimicrobial activity
is dependent on the size and the dose of the particles, but also on the species (Fajardo
et al. 2012; Velimirovic et al. 2015). As an example, a bactericidal effect on
Escherichia coli was observed only for nanoscale particles (Lee et al. 2008), but a
similar toxicity was observed for iron nanoparticles and iron filings to a
TCE-degrading microbial community (Zabetakis et al. 2015). The adverse effects
on microorganisms and plants can include physical damage, such as the disruption of
the cell membrane architecture, or biochemical destruction, such as interference in
energy transduction or oxidative stress due to the formation of ROS (Wiesner et al.
2006; Auffan et al. 2008; Keenan et al. 2009; Kim et al. 2010; Chen et al. 2011;
Fajardo et al. 2013; Fu et al. 2014b; Xie et al. 2017; Ghosh et al. 2017). As
previously mentioned, the formation of ROS, such as hydrogen peroxide (H 2 O 2 ),
superoxide radical (
•
O 2
À
), hydroxyl radical (
•
OH), and Fe(IV) species, is the consequence of the oxidation of active Fe species (Fe
0 and Fe
2+ ) (He et al. 2016).
The aging of ZVI particles in water, i.e., their aggregation and the growth/
transformation of iron oxides/hydroxides with time, and the use of stabilized ZVI
by surface modification are likely to mitigate the cytotoxicity of nZVI particles
(Phenrat et al. 2009b; Li et al. 2010; Dong et al. 2016a; Lefevre et al. 2016). The
aging of bimetallic particles results generally in the deactivation of the catalyst by
common groundwater solutes (Muftikian et al. 1996; Munakata and Reinhard 2007;
Han and Yan 2014; Han et al. 2016c) and the gradual encapsulation of the second
metal due to the growth of iron oxides/hydroxides shell (Zhu and Lim 2007; Yan
et al. 2010b; Dong et al. 2018), resulting in a progressive loss in reactivity and
toxicity. However, the release in solution of the second metal by dissolution can also
occur (Dong et al. 2018).
Some studies have highlighted the positive impact of the polymeric coating on
iron particles due to a high bioavailability and synergetic effect with environment
(He et al. 2010; Yan et al. 2013; Tosco et al. 2014). The selection of the polymer,
which can serve as a biostimulant, is therefore important in order to combine both
abiotic and biotic degradation. Indeed, hydrogen is generally considered as the direct
electron donor in anaerobic reductive dechlorination, and is typically produced from
the anaerobic oxidation of carbon substrates (fermentation), such as organic acids or
alcohols (Levin et al. 2004). In presence of iron-reducing bacteria (IRB), the
reduction of Fe(III) in Fe(II) species can depassivate iron particles (Roden and
Zachara 1996; Gerlach et al. 2000; Williams et al. 2005), which can result in the
reactivation of the particles for reductive dechlorination but also in the methylation
or in the possible remobilization of entrapped pollutants such as heavy metals (Xie
et al. 2017).
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
313
release and transport of Fe
2+ , thus affecting a more important zone.
The introduction of ZVI particles in the environment is responsible for the local
change in biogeochemical conditions, thus affecting their fate, transport, and reactivity, but also the microbial community activity and growth (Lowry et al. 2012;
Jang et al. 2014; Wagner et al. 2014). As for pollutants, the growth and transformation of the oxide shell can trap microbes, resulting in their quantitative removal from
aqueous phase (Noubactep 2011). It is also suggested that the antimicrobial activity
is dependent on the size and the dose of the particles, but also on the species (Fajardo
et al. 2012; Velimirovic et al. 2015). As an example, a bactericidal effect on
Escherichia coli was observed only for nanoscale particles (Lee et al. 2008), but a
similar toxicity was observed for iron nanoparticles and iron filings to a
TCE-degrading microbial community (Zabetakis et al. 2015). The adverse effects
on microorganisms and plants can include physical damage, such as the disruption of
the cell membrane architecture, or biochemical destruction, such as interference in
energy transduction or oxidative stress due to the formation of ROS (Wiesner et al.
2006; Auffan et al. 2008; Keenan et al. 2009; Kim et al. 2010; Chen et al. 2011;
Fajardo et al. 2013; Fu et al. 2014b; Xie et al. 2017; Ghosh et al. 2017). As
previously mentioned, the formation of ROS, such as hydrogen peroxide (H 2 O 2 ),
superoxide radical (
•
O 2
À
), hydroxyl radical (
•
OH), and Fe(IV) species, is the consequence of the oxidation of active Fe species (Fe
0 and Fe
2+ ) (He et al. 2016).
The aging of ZVI particles in water, i.e., their aggregation and the growth/
transformation of iron oxides/hydroxides with time, and the use of stabilized ZVI
by surface modification are likely to mitigate the cytotoxicity of nZVI particles
(Phenrat et al. 2009b; Li et al. 2010; Dong et al. 2016a; Lefevre et al. 2016). The
aging of bimetallic particles results generally in the deactivation of the catalyst by
common groundwater solutes (Muftikian et al. 1996; Munakata and Reinhard 2007;
Han and Yan 2014; Han et al. 2016c) and the gradual encapsulation of the second
metal due to the growth of iron oxides/hydroxides shell (Zhu and Lim 2007; Yan
et al. 2010b; Dong et al. 2018), resulting in a progressive loss in reactivity and
toxicity. However, the release in solution of the second metal by dissolution can also
occur (Dong et al. 2018).
Some studies have highlighted the positive impact of the polymeric coating on
iron particles due to a high bioavailability and synergetic effect with environment
(He et al. 2010; Yan et al. 2013; Tosco et al. 2014). The selection of the polymer,
which can serve as a biostimulant, is therefore important in order to combine both
abiotic and biotic degradation. Indeed, hydrogen is generally considered as the direct
electron donor in anaerobic reductive dechlorination, and is typically produced from
the anaerobic oxidation of carbon substrates (fermentation), such as organic acids or
alcohols (Levin et al. 2004). In presence of iron-reducing bacteria (IRB), the
reduction of Fe(III) in Fe(II) species can depassivate iron particles (Roden and
Zachara 1996; Gerlach et al. 2000; Williams et al. 2005), which can result in the
reactivation of the particles for reductive dechlorination but also in the methylation
or in the possible remobilization of entrapped pollutants such as heavy metals (Xie
et al. 2017).
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
313