Modeling studies have suggested that soil receives a
higher amount of ENPs than air or water. They easily adapt
different electrical, magnetic, optical, properties than its bulk
material and influence soil physico-chemical properties
which manipulates soil texture, particle size, soil pH,
microbial population, and simultaneously causes potential
toxicity. The release of ENPs to the soil could be from a
point or diffuse sources including liberation directly through
primary particles, or transformation after reactions like
agglomeration, aggregation, association with soil matrix, or
dissociation. Direct exposure pathways of ENPs to soils
occur when ENPs are used for delivery of fertilizer, pesticides, for remediation purposes, or via an accidental release.
However, the deliberate entry of ENPs to the soil environment may lead to bioaccumulation, expanded toxicity, loss
of organic matter, alteration in soil biodiversity, and altered
soil physico-chemical structures. The application of ENPs to
soil has varied according to application and includes two
major categories, i.e., (1) In the organic forms (carbon
nanotubes, fullerenes) and (2) inorganic forms (metal
nanoparticles, silica-based, and quantum dots). However, the
absence of proper monitoring methods and complex
heterogeneous environment of soil turns it difficult to measure than in any other environment. The fate and travel of
ENPs are usually governed by soil properties, like pH, texture, organic matter, water regime, and ionic strength. It is
often argued that during travel into soil components the
transformation of ENPs occurs which makes it difficult to
extrapolate in a realistic scenario.
The detailed study about the effect of ENPs in soil
ecosystem has outlined a clear sketch about modification in
microbial enzymatic activities due to metals and metal oxides, alteration in soil pollutant mobility, toxicity in the plant
(De La Rosa et al. 2011), accumulation in plant tissues, soil
and sediments (Cornelis et al. 2014), control of plant insects
(Debnath et al. 2012). However, the behavior and fate of the
ENPs in the soil will be determined by a complex set of
factors of both ENPs and soil. The chapter will provide an
overview of the ENPs in the agro-ecosystem considering
their synthesis, mobility, transformation, interaction, accumulation, toxicity, assessment methods, and impact on soil
health briefly. This would further be designed as a framework and provide relevant information for futuristic studies
regarding ENPs in soil environment.
2 Synthesis and Types of Engineered
Nanoparticles
Generally, two different synthesis approaches have been
employed for the construction of ENPs namely top-down
and bottom-up methods. The top-down is a destructive
approach, which involves the division of larger particles into
smaller particles ENPs. The top-down methods are usually
destructive methods that are costly, time-consuming, and not
suitable for large-scale production. Various methods like
mechanical milling, nanolithography, laser ablation, sputtering, and thermal decomposition chemical methods,
photo-lithography are suggested for this purpose (Dhand
et al. 2015). While in bottom-up known as building up
approach, the ENPs are formed from relatively simpler
substances. The bottom-up or constructive method is made
of material from atom to clusters to ENPs through sol–gel,
spinning, chemical vapor deposition, and pyrolysis processes (Khan et al. 2019).
Between organic and inorganic types they are mainly
applied in the form of metal/metal oxides, carbon-based,
silica-based, quantum dots, and dendrimers. Their application in the form of metal oxides such as ZnO, TiO 2 , CeO 2 ,
CrO 2 , Fe 3 O 4 , and binary oxides was frequently noticed
(Bhatt and Tripathi 2011).
To create silica ENPs, the covalent grafting of polymers
was carried out through the use of various polymers such as
polystyrene and polyacrylamide (Adams 2018). Nano-SiO 2
was reported to promote seed germination and stimulated the
antioxidant system, promote plant, and root growth (Gul
et al. 2014). Mesoporous silica was also used for delivery of
nutrients, fertilizers, drugs, gene, and DNA to the plant cell
due to their high surface area, pore-volume, stability, and
tunable structure. Thus, various nanodevices with tremendous effects could offer novel insights for the safer use of
these nanoparticles.
Carbon nanotubes (CNT) are cylindrical layers of graphene with single or multiwalled designed as open and
closed ends. Various nanodevices for application in agricultural purpose and pollutant remediation were constructed
due to their unique conductive, optical, and thermal properties. CNT can also make soil nutrient-rich and enhance its
biota as well as chemical and physical properties. CNT
provides adsorption sites due to the cylindrical structure and
a wide range of toxic compounds can easily absorb on it.
While the use of CNT-based nanosponges was identified as a
great tool for remediation of xenobiotics from soil (Manjunatha et al. 2016). Unfortunately, CNTs have shown
potential toxicity in human cells due to their penetrability
and accumulation in the cytoplasm (Prasad et al. 2017).
Nanocrystal quantum dots are semiconducting
heterostructured materials such as cadmium selenide (CdSe),
indium phosphide (InP), or zinc selenide (ZnSe) with controlled optical and electrical properties (Xiaoli et al. 2020).
Quantum dots (QDs) can be employed for live imaging in
plant tissue for retrieving information about physiological
processes. Sometimes, ENPs were made by dendrimers, and
these are normally organic-based ENPs which are complex,
multifunctional polymers with their size range between 1
and 10 nm diameters. They are having branched asymmetric
104
D. Mishra et al.
higher amount of ENPs than air or water. They easily adapt
different electrical, magnetic, optical, properties than its bulk
material and influence soil physico-chemical properties
which manipulates soil texture, particle size, soil pH,
microbial population, and simultaneously causes potential
toxicity. The release of ENPs to the soil could be from a
point or diffuse sources including liberation directly through
primary particles, or transformation after reactions like
agglomeration, aggregation, association with soil matrix, or
dissociation. Direct exposure pathways of ENPs to soils
occur when ENPs are used for delivery of fertilizer, pesticides, for remediation purposes, or via an accidental release.
However, the deliberate entry of ENPs to the soil environment may lead to bioaccumulation, expanded toxicity, loss
of organic matter, alteration in soil biodiversity, and altered
soil physico-chemical structures. The application of ENPs to
soil has varied according to application and includes two
major categories, i.e., (1) In the organic forms (carbon
nanotubes, fullerenes) and (2) inorganic forms (metal
nanoparticles, silica-based, and quantum dots). However, the
absence of proper monitoring methods and complex
heterogeneous environment of soil turns it difficult to measure than in any other environment. The fate and travel of
ENPs are usually governed by soil properties, like pH, texture, organic matter, water regime, and ionic strength. It is
often argued that during travel into soil components the
transformation of ENPs occurs which makes it difficult to
extrapolate in a realistic scenario.
The detailed study about the effect of ENPs in soil
ecosystem has outlined a clear sketch about modification in
microbial enzymatic activities due to metals and metal oxides, alteration in soil pollutant mobility, toxicity in the plant
(De La Rosa et al. 2011), accumulation in plant tissues, soil
and sediments (Cornelis et al. 2014), control of plant insects
(Debnath et al. 2012). However, the behavior and fate of the
ENPs in the soil will be determined by a complex set of
factors of both ENPs and soil. The chapter will provide an
overview of the ENPs in the agro-ecosystem considering
their synthesis, mobility, transformation, interaction, accumulation, toxicity, assessment methods, and impact on soil
health briefly. This would further be designed as a framework and provide relevant information for futuristic studies
regarding ENPs in soil environment.
2 Synthesis and Types of Engineered
Nanoparticles
Generally, two different synthesis approaches have been
employed for the construction of ENPs namely top-down
and bottom-up methods. The top-down is a destructive
approach, which involves the division of larger particles into
smaller particles ENPs. The top-down methods are usually
destructive methods that are costly, time-consuming, and not
suitable for large-scale production. Various methods like
mechanical milling, nanolithography, laser ablation, sputtering, and thermal decomposition chemical methods,
photo-lithography are suggested for this purpose (Dhand
et al. 2015). While in bottom-up known as building up
approach, the ENPs are formed from relatively simpler
substances. The bottom-up or constructive method is made
of material from atom to clusters to ENPs through sol–gel,
spinning, chemical vapor deposition, and pyrolysis processes (Khan et al. 2019).
Between organic and inorganic types they are mainly
applied in the form of metal/metal oxides, carbon-based,
silica-based, quantum dots, and dendrimers. Their application in the form of metal oxides such as ZnO, TiO 2 , CeO 2 ,
CrO 2 , Fe 3 O 4 , and binary oxides was frequently noticed
(Bhatt and Tripathi 2011).
To create silica ENPs, the covalent grafting of polymers
was carried out through the use of various polymers such as
polystyrene and polyacrylamide (Adams 2018). Nano-SiO 2
was reported to promote seed germination and stimulated the
antioxidant system, promote plant, and root growth (Gul
et al. 2014). Mesoporous silica was also used for delivery of
nutrients, fertilizers, drugs, gene, and DNA to the plant cell
due to their high surface area, pore-volume, stability, and
tunable structure. Thus, various nanodevices with tremendous effects could offer novel insights for the safer use of
these nanoparticles.
Carbon nanotubes (CNT) are cylindrical layers of graphene with single or multiwalled designed as open and
closed ends. Various nanodevices for application in agricultural purpose and pollutant remediation were constructed
due to their unique conductive, optical, and thermal properties. CNT can also make soil nutrient-rich and enhance its
biota as well as chemical and physical properties. CNT
provides adsorption sites due to the cylindrical structure and
a wide range of toxic compounds can easily absorb on it.
While the use of CNT-based nanosponges was identified as a
great tool for remediation of xenobiotics from soil (Manjunatha et al. 2016). Unfortunately, CNTs have shown
potential toxicity in human cells due to their penetrability
and accumulation in the cytoplasm (Prasad et al. 2017).
Nanocrystal quantum dots are semiconducting
heterostructured materials such as cadmium selenide (CdSe),
indium phosphide (InP), or zinc selenide (ZnSe) with controlled optical and electrical properties (Xiaoli et al. 2020).
Quantum dots (QDs) can be employed for live imaging in
plant tissue for retrieving information about physiological
processes. Sometimes, ENPs were made by dendrimers, and
these are normally organic-based ENPs which are complex,
multifunctional polymers with their size range between 1
and 10 nm diameters. They are having branched asymmetric
104
D. Mishra et al.