structures with nanospheres or nanocapsules shape (Ishtiaq
et al. 2020). The unique structures with a solid center and
surrounded spherical surface of dendrimers have shown
tremendous capability in the field of sensors development
and also as a sorbent for contaminants (Zhang et al. 2017). In
the future, more focused research toward the development of
application-specific nanoparticles through controlling reaction parameters, shape, size, and morphology should be
done.
3 Exposure of Engineered Nanoparticles
in Soil
The rapidly evolving synthesis of ENPs has provided maximum chances of ENPs to enter in soil compartment during
traveling. As far as the concern of their entry to the soil
ecosystem, they can enter through point or nonpoint sources.
The direct exposure route consists mainly of the application
of nanofertilizers, nanopesticides, seed treatment preparation, agrofilms, or for remediation of contaminated land or
groundwater. However, the accidental liberation was primarily from diffuse emission, ENPs containing products,
solid waste disposal, landfilling, and incineration or mishandling of those during transportation (Walden and Zhang
2016). The product matrix has severely affected the ENPs
physical and chemical characteristics and thus long-term
application of ENPs resulted in bioaccumulation in soil.
Nonetheless, after liberation, they get interacted with the
heterogeneous structure of the soil. Soil provides a suitable
habitat for the retention of ENPs, as they can adsorb on the
soil pores, forms aggregates with organic matter, or establish
electrostatic interaction, ligand exchanges networking with
the soil-solid matrix. The surface chemistry of ENPs plays
an important role in deciding its mobility, stability with
inorganic and organic soil colloidal suspension (Alimi et al.
2018). The release of silver nanoparticles was found more in
presence of natural organic matter as without that in the soil
the reduction in negative surface potential of ENPs would
cause more aggregation in soil (Li et al. 2013).
Application of wastewater sludge enriched with Zn and
Ag nanoparticles in soil final concentration of 1400 and
140 mg/kg for Zn and Ag, respectively, has shown a
reduction in the fungal community in soil (Durenkamp et al.
2016). The calculated risk assessment of ENPs released
through personal care products has suggested that about 43%
of it ends up in landfills, 0.8% directly goes to the soil, and
32% in water bodies. The uprising concentration of ENPs
was mainly due to the usage of sunscreen, facial moisturizer,
hair coloring agents, body wash, toothpaste, and shampoo
(Keller et al. 2014). After entering the ecosystem, it is very
easy to enter the soil either via wastewater sludge, landfilling, or atmospheric deposition. However, the fate of ENPs
after liberation has been described in detail in the later
section. The impetus of the application of ENPs in the soil
through key drivers is being summarized in Table 1. This
would provide insight into their application in various forms
and possible impacts on the soil ecosystem.
4 The Fate of Engineered Nanoparticles
in the Soil
The modification in the physico-chemical characteristics
took place due to major transformation reactions occurring
between soil matrix and ENPs. The soil reaction occurring
inside soil pore or soil solution resulted in either their
retention or mobilization. The surface area, size, charge,
density, and shape of ENPs play a major role in determining
their fate in the soil matrix. The complex and heterogeneous
environment of soil leads to aggregation, sedimentation,
dissolution, the transformation of ENPs. Furthermore, their
bioavailability in the soil is mainly influenced by soil
chemistry and soil microorganism (Dwivedi et al. 2015). It is
well predicted that the residence time of ENPs is more in soil
and sediments than in aquatic system. Based on their
biodegradation potential, they eventually build up in the soil
and thus become bioavailable for plants and terrestrial
organisms. Although many theories have been suggested to
the fate of ENPs in soil, however, clear mechanisms of fate
remain unclear due to the heterogeneous surface of the soil.
The interaction between these processes and the ENPs
transfer determines the fate and finally the ecotoxicological
potential of ENPs in the soil matrix. The upcoming section
will summarize the different fate behavior of ENPs according to the consensus of various scientific theories.
4.1 Engineered Nanoparticles and Colloids
Many processes inside the soil matrix are generally governing their fate in soil. Regarding this, colloids of the soil
(diameter <1 lm) play a magnificent role in the interaction
chemistry of ENPs. These fractions of soil are very mobile
and active components with high surface area and often turn
as carriers for different contaminants and nutrients in the
soil. These colloid particles govern the transport of various
engineered nanoparticles and then impart to environmental
pollution (Pan and Xing 2012). The Derjaguin–Landau–
Verwey–Overbeek (DLVO) theory and the colloid filtration
theory both have explained their transport in the soil porous
media due to the structural similarities between natural
Engineered Nanoparticles in Agro-ecosystems: Implications …
105
et al. 2020). The unique structures with a solid center and
surrounded spherical surface of dendrimers have shown
tremendous capability in the field of sensors development
and also as a sorbent for contaminants (Zhang et al. 2017). In
the future, more focused research toward the development of
application-specific nanoparticles through controlling reaction parameters, shape, size, and morphology should be
done.
3 Exposure of Engineered Nanoparticles
in Soil
The rapidly evolving synthesis of ENPs has provided maximum chances of ENPs to enter in soil compartment during
traveling. As far as the concern of their entry to the soil
ecosystem, they can enter through point or nonpoint sources.
The direct exposure route consists mainly of the application
of nanofertilizers, nanopesticides, seed treatment preparation, agrofilms, or for remediation of contaminated land or
groundwater. However, the accidental liberation was primarily from diffuse emission, ENPs containing products,
solid waste disposal, landfilling, and incineration or mishandling of those during transportation (Walden and Zhang
2016). The product matrix has severely affected the ENPs
physical and chemical characteristics and thus long-term
application of ENPs resulted in bioaccumulation in soil.
Nonetheless, after liberation, they get interacted with the
heterogeneous structure of the soil. Soil provides a suitable
habitat for the retention of ENPs, as they can adsorb on the
soil pores, forms aggregates with organic matter, or establish
electrostatic interaction, ligand exchanges networking with
the soil-solid matrix. The surface chemistry of ENPs plays
an important role in deciding its mobility, stability with
inorganic and organic soil colloidal suspension (Alimi et al.
2018). The release of silver nanoparticles was found more in
presence of natural organic matter as without that in the soil
the reduction in negative surface potential of ENPs would
cause more aggregation in soil (Li et al. 2013).
Application of wastewater sludge enriched with Zn and
Ag nanoparticles in soil final concentration of 1400 and
140 mg/kg for Zn and Ag, respectively, has shown a
reduction in the fungal community in soil (Durenkamp et al.
2016). The calculated risk assessment of ENPs released
through personal care products has suggested that about 43%
of it ends up in landfills, 0.8% directly goes to the soil, and
32% in water bodies. The uprising concentration of ENPs
was mainly due to the usage of sunscreen, facial moisturizer,
hair coloring agents, body wash, toothpaste, and shampoo
(Keller et al. 2014). After entering the ecosystem, it is very
easy to enter the soil either via wastewater sludge, landfilling, or atmospheric deposition. However, the fate of ENPs
after liberation has been described in detail in the later
section. The impetus of the application of ENPs in the soil
through key drivers is being summarized in Table 1. This
would provide insight into their application in various forms
and possible impacts on the soil ecosystem.
4 The Fate of Engineered Nanoparticles
in the Soil
The modification in the physico-chemical characteristics
took place due to major transformation reactions occurring
between soil matrix and ENPs. The soil reaction occurring
inside soil pore or soil solution resulted in either their
retention or mobilization. The surface area, size, charge,
density, and shape of ENPs play a major role in determining
their fate in the soil matrix. The complex and heterogeneous
environment of soil leads to aggregation, sedimentation,
dissolution, the transformation of ENPs. Furthermore, their
bioavailability in the soil is mainly influenced by soil
chemistry and soil microorganism (Dwivedi et al. 2015). It is
well predicted that the residence time of ENPs is more in soil
and sediments than in aquatic system. Based on their
biodegradation potential, they eventually build up in the soil
and thus become bioavailable for plants and terrestrial
organisms. Although many theories have been suggested to
the fate of ENPs in soil, however, clear mechanisms of fate
remain unclear due to the heterogeneous surface of the soil.
The interaction between these processes and the ENPs
transfer determines the fate and finally the ecotoxicological
potential of ENPs in the soil matrix. The upcoming section
will summarize the different fate behavior of ENPs according to the consensus of various scientific theories.
4.1 Engineered Nanoparticles and Colloids
Many processes inside the soil matrix are generally governing their fate in soil. Regarding this, colloids of the soil
(diameter <1 lm) play a magnificent role in the interaction
chemistry of ENPs. These fractions of soil are very mobile
and active components with high surface area and often turn
as carriers for different contaminants and nutrients in the
soil. These colloid particles govern the transport of various
engineered nanoparticles and then impart to environmental
pollution (Pan and Xing 2012). The Derjaguin–Landau–
Verwey–Overbeek (DLVO) theory and the colloid filtration
theory both have explained their transport in the soil porous
media due to the structural similarities between natural
Engineered Nanoparticles in Agro-ecosystems: Implications …
105