Section 2. Food and Agricultural Nanotechnology

Edible Crop Production by Nanotechnology: Is It a Sustainable Technology for Healthy Soil?

INTRODUCTION

Currently, thousands of engineered nanomaterials (ENMs) or engineered nanodevices (ENDs) with specific properties never seen before are being spread worldwide to increase the production of healthy, affordable, and innocuous food to shape sustainable development (Fernandez-Luqueno et al. 2018). However, daily new evidence regarding the toxicity of ENMs is being published in the most reputable journals, i.e., it looks like the cutting-edge knowledge regarding nanoscience and nanotechnology jeopardizes human and environmental health or hampers the pursuit of sustainable development goals.

It has to be remembered that nanoscience and nanotechnology have significantly increased the performance of hitherto unknown materials, which have allowed synthesis of ENMs with applications in the health, energy, environment, and agriculture sectors, among others, i.e., nanoscience and nanotechnology have changed lives with enormous benefits for a better and more comfortable existence (Medina-Perez et al. 2019).

However, no one can deny that the nanotechnological advances in the environmental and agricultural sectors are linked to concerns based on toxicological studies with soil microorganisms, animals, or crops in different experimental conditions at laboratory, greenhouse, or field scale. Fortunately, several advantages regarding the characteristics of the crops, pest or disease resistance, or better yield, among others, have also been reported in studies where ENMs or ENDs have been used (Leon-Silva et al. 2016; 2018).

The objective of this chapter is to discuss updated evidence published by worldwide scientists and by our research team to balance the advantages and disadvantages regarding the use of ENMs or ENDs in the agricultural sector to increase the quality, innocuity, and affordability of crops without jeopardizing soil quality, or human or environmental health.

NATURAL AND ENGINEERED NANOMATERIALS IN THE SOIL

According to the European Commission (2014), nanomaterials (NMs) are defined as natural, incidental, or manufactured materials that contain particles in a non-bound state or as an aggregate whereby 50% or more of the particles have a size distribution in the range of 1-100 nm. The origin, size, and shape of NMs define their properties; hence, NMs are different from existing microscale materials. Nanoparticles (NPs) can be formed naturally through processes that occur in the atmosphere, hydrosphere, lithosphere, and even the biosphere (Sharma et al. 2015). There are numerous examples of NPs that emanate from natural sources such as volcanoes, minerals, springs, and living organisms (Griffin et al. 2017). Natural nanomaterials (NNMs) can be found anywhere in nature, and researchers have been able to locate, isolate, characterize, and classify a wide range of NNMs (Figure 2.1).

However, the aggregation of NNMs with natural organic matter (NOM) is a complex material to investigate (Loosli et al. 2019; von der Heyden et al. 2019). Some examples are silver (Ag), gold (Au), iron (Fe), metal oxides that include Fe203, Mn02, and Si02 and metal sulfides such as Fe2S2, Zn3S3, and Cu3S3, which are among the most abundant in nature (Findlay et al. 2019; Mansor et al. 2019). NOM, under certain conditions, such as high temperatures, exposure to high solar radiation, and changes in soil pH, will promote the formation of inorganic NPs (Chakre and Sharon 2019; Yin et al. 2012; Pedrot et al. 2011).

Natural sources of nanoparticles

FIGURE 2.1 Natural sources of nanoparticles.

Inorganic NPs can be produced through biogeochemical processes, such as the NNMs that are present in the clouds of volcanic ash, which contain a wide variety of scattered NPs and microparticles that are primarily of silicate and iron origin (Griffin et al. 2017). The formation of NNMs occurs through the combination of several mechanical processes, such as weathering. It is noteworthy that NNMs are formed predominantly at phase boundaries, for example, solid-gas wind erosion, liquid-gas evaporation of seawater, or solid-liquid rock wear, among others (Sharma et al. 2015).

There is an additional type of NNMs that are synthesized by microorganisms. These microbes are composed of molecules of nanometric size, such as DNA, RNA, or proteins. There are reports in the literature that describe the various biological processes that are associated with the production of NPs, which include the redox conditions that some microorganisms use to store and transport electrons through the transitory production of inorganic NNMs, or the output of nanominerals based on Fe and silicon (Si), calcium carbonate, and calcium phosphate (Wu et al. 2019; Shrama et al. 2015; Faramarzi and Sadighi 2013). Therefore, various bacteria, fungi, and plants have been used to reduce metals like silver, gold, palladium, selenium, etc. (Ali et al. 2019; Rajeshkumar et al. 2018). It is noteworthy that in the soil the NNMs form colloids that consist of silicate clay minerals, Aluminum (Al) or Fe oxides/hydroxides, and organic colloids, which are made up of humic organic matter and biopolymers such as carbohydrates (Shrivastava et al. 2019).

Engineered nanoparticles (ENPs) are nanoparticles that are human-made for industrial and medical purposes, and currently they are also used in agriculture. It is noteworthy that naturally generated NPs are not comparable to ENPs, because NNMs are generally coated on the surface with polymers and surfactants that are found in the environment where they were produced (Chakre and Sharon 2019). Eventually, ENPs will enter the environment through water, soil, and air as part of human-based activities. However, ENPs are also used in the treatment of polluted water and soil by deliberately injecting ENPs into the soil or aquatic systems (Yang et al. 2019; Dong et al. 2014). NNMs are of great importance in the biogeochemical cycles, weathering processes, bioavailability, transport, and ecotoxicity of metals. In addition, these factors have contributed to the evolution and adaptation of higher organisms (Steinberg et al. 2006), hence, there is some concern because ENPs are made of specific structures that microorganisms may not recognize, and as a consequence, may induce toxic effects that are not observed in the micron-sized counterparts (Khan et al. 2017). Among the ENPs commonly used are the metals and oxides of Ag, Fe,0„ A120„ ZnO, and Ti02. Interactions of the soil microbiota with ENPs play a crucial role in the transport and destination of the ENPs; even though living organisms require these metals as micronutrients, higher doses of some of these metals can be cytotoxic (Dhand et al. 2015). ENPs are most likely to undergo significant modifications when exposed to soils, because of aggregation caused by the NOM interaction. This interaction changes the reaction speed, adsorption capacity, redox state, shape, and modifies the reactivity of the NPs, which consequently will attenuate or augment their fate in the environment and their bioactivity with plants (Liu et al. 2019; Luo et al. 2018).

ENPs can affect soil characteristics such as pH and organic matter, influence the production of exudates from plant roots and affect the growth of microbial communities in the rhizosphere. The results of a study undertaken by Kibbey and Strevett (2019) showed that ENPs (depending on their nature) could decrease or increase the bacteria in the rhizosphere (Table 2.1). Consequently, ENPs can cause changes in the lengths of the root and stem of the plant. Kibbey and Strevett (2019) hypothesized that ENPs prevent bacteria from adhering so that they can carry out synergistic interactions between the bacteria and the root to assimilate nitrogen and carbon, and other essential nutrients for plants. Other studies have revealed that the concentration and exposure of ENPs may have different effects on the soil microbial community (Moll et al. 2017; Shcherbakova et al. 2017; Shah et al. 2014). Wang et al. (2017) investigated the effect of different concentrations of silver nanoparticles (AgNPs) and observed that although the content of Acidobacteria, Actinobacteria, Cyanobacteria, and Nitrospirae decreased when increasing the doses of AgNPs, concomitantly, several other phyla, which included Proteobacteria and Planctomycetes were increased in number. Exudates from soil microbiota can induce the dissolution of ENPs and promote the absorption of

TABLE 2.1

Some Effects of Engineering Nanoparticles on Soil Microorganisms

Engineering

nanoparticle

Concentration in soil

Effects

References

Ag

0.01.0.10 and 1.00 mg kg"1 dry weight

Exposure time had significant effects on the relative variation of the microbial community.

Grim et al. (2019)

CuO. ZnO

10 mg kg'1

ENPs did not show an effect on the growth of microorganisms and their activity.

Josko et al. (2019)

ZnO

0. 10. 20. 30.40.60,90. 120. 150. 180, 240 Zn mg L"1

Zn bioaccumulation was found for the earthworm Eisenia Next lime andrei

Heet al. (2019)

Zerovalent iron (ZVI), ferrous sulfide (FeS) ferriferous oxide (Fe,Oj)

3% (w/w)

FeS-NPs have significantly changed microbial community richness and diversity, followed by ZVI and Fes04.

Peng et al. (2019)

Zero-valent iron particles (ZVI)

0. 1,5, 10 and 20 mg g"1 DW soil

The toxic effects of ZVI on soil microbial communities are soil dependent. In sandy-loam soil, bacterial biomass and diversity were negatively affected.

Gomez-Sagasti et al. (2019)

ZnO. TiO,. CeO:. Fe,04

0.5. 1.0, and 2.0 mg g'1

ZnO-NP in saline-alkali soil showed a higher effect on variance in their bacterial community composition, eg.. Bacilli. Alphaproteobacteria, and Gammaproteobacteria class.

You et al. (2018)

CeO,

1 mg L"1

Decreased the denitrifying bacteria, such as Flexibacter and Acinetobacter.

Wanget al. (2018)

Single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs)

0.05%, 0.1%, or 0.5% (w/w)

CNT caused fluctuations in microbial community function, differential tolerance size, and dose-dependence among bacterial genera.

Wu et al. (2019)

MWCNTs, reduced graphene oxide (rGO) and ammonia-functionalized graphene oxide (aGO)

One ng, 1 pg or 1 mg kg"1 dry soil

The composition of bacterial communities was significantly influenced over time.

Forstner et al. (2019)

Fullerene (C<,0), reduced graphene oxide (rGO) and MWCNTs

50 and 500 mg kg'1

rGO had greater changes in the bacterial composition, especially at the taxonomic level of the genus, particularly at the higher concentration.

Haoet al. (2018)

metal ions by plants (Zhao et al. 2016). In addition to the transformation in the rhizosphere, it has been found that the change in ENPs occurs within or on the surface of plant tissues and has different levels of accumulation that depend on the plant. ENPs such as ZnO, CuO, NiO, CeO,, Yb20, and La20, are capable of transformation that results in changes in speciation and accumulation in the tissues of plants (Lv et al. 2015). Zinc oxide nanoparticles (ZnO-NPs) were able to transform zinc phosphate when they were supplementing nutrition in wheat that was grown in the substrate. This is due to the uptake of zinc in the rhizosphere in its ionic form, and its subsequent translocation to the tissues of the plant. It has also been demonstrated for zinc citrate in the same way and zinc nitrate in soybean and cowpea (for example, Hernandez-Viezcas et al. 2013, Lopez-Moreno et al. 2010).

In soils, ENPs interact with the rhizosphere processes that influence the plants, which affect those processes and concerns factors that include the complexity and properties of the soil, the biological species found, and the intrinsic properties of the ENPs, including their nature, dose, and exposure time.

 
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