therefore the aggregation with soil particles amplified.
However, the particle size becomes a major parameter as
surface atoms increase with a decrease in particle size (Alan
et al. 2020). Ag NPs of diameters around 10 nm showed
higher penetration capacity into the cell than of particle size
of 20–100 nm (Ivask et al. 2014; Goswami et al. 2017). The
surface charge of ENPs often governs their binding pattern
with clay or minerals in soil solution likewise the electrostatic interaction of negatively charge cerium oxide
nanoparticles was increased with clay edges. Similarly, the
low affinity of cerium oxide nanoparticles with the surface of
kaolinite suggested strong electrostatic interactions between
them. The charge-dependent aggregation was due to the
variation in hydrodynamic size and surface charge (Guo
et al. 2019). Further, the coarse surface of some clay minerals also provides binding sites for positively charged ENPs
(Ghorbanpour et al. 2020).
The retention of functionally stabilized Ag NPs was
increased with the interaction of iron and clay minerals
(Hoppe et al. 2014). Furthermore, the retention in the soil
largely depends on the ionic strength, mass concentration, and
particle numbers which contributes to the filling of retention
site and concentration-dependent mass transfer in soil solution (Alan et al. 2020). However, the increase in the magnitude of electrical double layer forces between the charged
colloids and minerals leads to the release of ENPs. Likewise,
Zn nanoparticles and carbon nanotubes have shown low
mobility in different ionic strength of clay minerals soil and
natural soil, respectively (Zhao et al. 2012). It might be related
to their shape, aspect ratio, surface charge, size distribution,
and interconnected soil pores. In addition to this, the surface
coating also responsible for their fate in the soil like a coating
of polyvinylpyrrolidone and citrate has boosted the transport
and reduced the retention of Ag NPs in soil, which related to
obstruction in the solid phase retention sites in soil (Kanel
et al. 2015). Consequently, ENPs surface modification generates electrostatic, steric, or repulsive forces which more
likely to reduce the aggregation and thus enhance their
transport and bioavailability (Goswami et al. 2017). Similarly, the uncoated Ag NPs were more bioavailable than
citrate-coated nanoparticles due to a rise in their stabilization
after coating (Cornelis et al. 2014). The transport of sodium
dodecylbenzene sulfonate surfactant on the transport of Ag
NPs and CNTs in saturated porous media has shown high
mobility in soil column and they exhibited similar transport
patterns as of natural clay soil (Tian et al. 2010).
Soil is the complex mixture with heterogeneous features
thus extrapolation of the effect of any one characteristic of
the ENPs cannot be described perspicuously. Nevertheless,
the complex mechanism simultaneously occurring in the soil
system helps to solve the question related to their abundance,
mobility, bioavailability, transformation, and toxicity.
6 Effect of Engineered Nanoparticles
on the Soil Properties
Being the natural sink of ENPs, the soil environment has
been critically affected by their presence. Most of the studies
have suggested the complex reactions occurring in soil
media have been actively mediated by both soil components
and ENPs (Pradhan and Mailapalli 2017; Abbas 2020). In
this view, the discussion about the effect of the ENPs on the
soil properties and edaphic biota has been elaborated here.
6.1 Effect on Physico-Chemical Properties
Soil pH is a major governing parameter that directly influences soil health, indicates its nutrient status, and also about
ionic strength of soil solution. Somehow, it plays a major
role in the ionization of various organic/inorganic compounds and changes their solubility and responsible for the
sorption of many compounds. It is pragmatic that variation
in the pH of the soil is sometimes mediated through the
accumulation of the different ENPs mentioned above
(Schultz et al. 2015). These variations in pH further lead to
toxicity in soil fauna and led to metal ion solubility, nutrient
availability, plant growth, and clay dispersion (Zhang et al.
2018; Tarafdar and Adhikari 2015). In another study, the
change in soil pH from 5.9 to 6.8 has shown no changes in
solubility of copper nanoparticles, however, it was positively
correlated with the change in the organic matter content of
soil (Gao et al. 2019). In contrast, the solubility of Zn was
related to negatively correlate with soil pH, due to its
retention and adsorption on the clay particles (García-Gómez
et al. 2018). In addition to this the agglomeration, discharge,
oxidation, and release of nanoparticles are highly dependent
on soil pH (Nowack et al. 2012). Likewise, the impact of pH
on ZnO ENPs breakdown has caused danger on the population of Folsomia candida and Eisenia fetida in soil (Kool
et al. 2011). The gravity-driven transport of ENPs like TiO 2 ,
CeO 2 , and Cu(OH) 2 owing to their effect on soil pH and
nutrient release in unsaturated soils has determined and
small changes in the soil pH were detected due to the release
of natural ions (Mg
2+ , H
+ ) through substitution suggesting
the high retention of ENPs in soil (Conway and Keller,
2016). Furthermore, the interaction of ENPs with dissolved
organic matter would greatly alter the magnitude of fate,
transport, binding, and bioavailability of ENPs in soil.
The ubiquitous organic matter is generally composed of
heterogeneous and different molecular compounds and thus
multiple interaction mechanisms such as hydrogen bonding,
electrostatic interaction, hydrophobic binding, p-p interaction, cation bridging, and adsorption take place between
ENPs and organic matter surface. These interaction leads to
Engineered Nanoparticles in Agro-ecosystems: Implications …
109
However, the particle size becomes a major parameter as
surface atoms increase with a decrease in particle size (Alan
et al. 2020). Ag NPs of diameters around 10 nm showed
higher penetration capacity into the cell than of particle size
of 20–100 nm (Ivask et al. 2014; Goswami et al. 2017). The
surface charge of ENPs often governs their binding pattern
with clay or minerals in soil solution likewise the electrostatic interaction of negatively charge cerium oxide
nanoparticles was increased with clay edges. Similarly, the
low affinity of cerium oxide nanoparticles with the surface of
kaolinite suggested strong electrostatic interactions between
them. The charge-dependent aggregation was due to the
variation in hydrodynamic size and surface charge (Guo
et al. 2019). Further, the coarse surface of some clay minerals also provides binding sites for positively charged ENPs
(Ghorbanpour et al. 2020).
The retention of functionally stabilized Ag NPs was
increased with the interaction of iron and clay minerals
(Hoppe et al. 2014). Furthermore, the retention in the soil
largely depends on the ionic strength, mass concentration, and
particle numbers which contributes to the filling of retention
site and concentration-dependent mass transfer in soil solution (Alan et al. 2020). However, the increase in the magnitude of electrical double layer forces between the charged
colloids and minerals leads to the release of ENPs. Likewise,
Zn nanoparticles and carbon nanotubes have shown low
mobility in different ionic strength of clay minerals soil and
natural soil, respectively (Zhao et al. 2012). It might be related
to their shape, aspect ratio, surface charge, size distribution,
and interconnected soil pores. In addition to this, the surface
coating also responsible for their fate in the soil like a coating
of polyvinylpyrrolidone and citrate has boosted the transport
and reduced the retention of Ag NPs in soil, which related to
obstruction in the solid phase retention sites in soil (Kanel
et al. 2015). Consequently, ENPs surface modification generates electrostatic, steric, or repulsive forces which more
likely to reduce the aggregation and thus enhance their
transport and bioavailability (Goswami et al. 2017). Similarly, the uncoated Ag NPs were more bioavailable than
citrate-coated nanoparticles due to a rise in their stabilization
after coating (Cornelis et al. 2014). The transport of sodium
dodecylbenzene sulfonate surfactant on the transport of Ag
NPs and CNTs in saturated porous media has shown high
mobility in soil column and they exhibited similar transport
patterns as of natural clay soil (Tian et al. 2010).
Soil is the complex mixture with heterogeneous features
thus extrapolation of the effect of any one characteristic of
the ENPs cannot be described perspicuously. Nevertheless,
the complex mechanism simultaneously occurring in the soil
system helps to solve the question related to their abundance,
mobility, bioavailability, transformation, and toxicity.
6 Effect of Engineered Nanoparticles
on the Soil Properties
Being the natural sink of ENPs, the soil environment has
been critically affected by their presence. Most of the studies
have suggested the complex reactions occurring in soil
media have been actively mediated by both soil components
and ENPs (Pradhan and Mailapalli 2017; Abbas 2020). In
this view, the discussion about the effect of the ENPs on the
soil properties and edaphic biota has been elaborated here.
6.1 Effect on Physico-Chemical Properties
Soil pH is a major governing parameter that directly influences soil health, indicates its nutrient status, and also about
ionic strength of soil solution. Somehow, it plays a major
role in the ionization of various organic/inorganic compounds and changes their solubility and responsible for the
sorption of many compounds. It is pragmatic that variation
in the pH of the soil is sometimes mediated through the
accumulation of the different ENPs mentioned above
(Schultz et al. 2015). These variations in pH further lead to
toxicity in soil fauna and led to metal ion solubility, nutrient
availability, plant growth, and clay dispersion (Zhang et al.
2018; Tarafdar and Adhikari 2015). In another study, the
change in soil pH from 5.9 to 6.8 has shown no changes in
solubility of copper nanoparticles, however, it was positively
correlated with the change in the organic matter content of
soil (Gao et al. 2019). In contrast, the solubility of Zn was
related to negatively correlate with soil pH, due to its
retention and adsorption on the clay particles (García-Gómez
et al. 2018). In addition to this the agglomeration, discharge,
oxidation, and release of nanoparticles are highly dependent
on soil pH (Nowack et al. 2012). Likewise, the impact of pH
on ZnO ENPs breakdown has caused danger on the population of Folsomia candida and Eisenia fetida in soil (Kool
et al. 2011). The gravity-driven transport of ENPs like TiO 2 ,
CeO 2 , and Cu(OH) 2 owing to their effect on soil pH and
nutrient release in unsaturated soils has determined and
small changes in the soil pH were detected due to the release
of natural ions (Mg
2+ , H
+ ) through substitution suggesting
the high retention of ENPs in soil (Conway and Keller,
2016). Furthermore, the interaction of ENPs with dissolved
organic matter would greatly alter the magnitude of fate,
transport, binding, and bioavailability of ENPs in soil.
The ubiquitous organic matter is generally composed of
heterogeneous and different molecular compounds and thus
multiple interaction mechanisms such as hydrogen bonding,
electrostatic interaction, hydrophobic binding, p-p interaction, cation bridging, and adsorption take place between
ENPs and organic matter surface. These interaction leads to
Engineered Nanoparticles in Agro-ecosystems: Implications …
109