Keywords

8.1 Introduction

Material with particle size of nanometer ranging between 1 and 100 are considered as nanoparticles and any technology that deals on nanoscale means nanotechnology. The growth of nanotechnology has considerably inflated its application of nanomaterial in different area (Khot et al. 2012). Different engineered carbon based nanomaterial (single and multi-walled carbon nanotubes), metal (quantum dots, nanogold, nanosilver) and metal oxide (titanium oxide, zinc oxide and cesium oxide) based nanomaterial, nano sized polymer material called dendrimers and nano composites material are built for different functional properties. The major advantages of nanomaterial over bulk material include decrease in melting point and surface area, increase in dielectric constant and mechanical strength (Nagi et al. 2012; Maddineni et al. 2015; Dasgupta et al. 2016a, b; Ranjan et al. 2016). In addition, size of nanoparticles enables them to absorb exceptionally on to other material (Nagi et al. 2012; Dasgupta et al. 2015; Ranjan et al. 2014, 2015, 2016). Because of all these unique behaviour and properties, nanoparticles have wider application in textiles, clothing, and cosmetics, pharmaceutical, electronic and paint industry. Also they are widely used for development of health care products and remediation of contaminated environment. In addition to its wider application in major industries, nanomaterials are also applied for the prospects of agriculture in several ways (Jain et al. 2016; Baruah and Dutta 2009; Handford et al. 2014; Sastry et al. 2010; Taghiyari et al. 2015; Dasgupta et al. 2016c). Figure 8.1 represents some of the applications of nanomaterials in different fields.

Fig. 8.1
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Applications of nanomaterials in various fields

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Escalation of human population has led to decrease in productive land to less than 11 % of total earth area (Mermut and Eswaran 2012). With limited availability of resources, development in agriculture has to be attained by increasing the fertility of a soil. Although conventional soil management methods are available, nanotechnology is reported by many researchers currently as an alternate technology for sustainable soil management. Fertility and quality of the agricultural soils primarily depends on quality and quantity of water available, micro and macro nutrients present in the soil. The depletion of nutrient quality in soil is predominantly caused due to man-made or natural soil erosion and accumulation of toxic pollutant in the soil. This paper reviews on application of different nanomaterials for improvement and remediation of soil.

8.2 Soil Amendments

Soil amendments are materials used to improve the physical properties of soil such as water retention capacity, nutrient availability, structure, drainage in order to produce better crop yields. Several soil amendments have been in use historically as fertilizers and soil conditioners. The purpose of fertilizers is to provide adequate nutrients for plant growth. Whereas, soil conditioners have minimum nutrient concentration but are added to enhance the biological, physical or chemical nature of soils. The indiscriminate and ineffective use of soil amendments can lead wastage of nutrients, hence nanotechnology was proposed to enhance the effective use of nutrients. The application of nanotechnology for agriculture includes (i) nanomaterials as enablers for delivery of agrochemicals (ii) sensors to monitor plant stress and soil conditions and (iii) improvement of plant traits against environmental stress and plant diseases. In this review, we will discuss about nanoparticles which are specifically used as nanofertilizer or as carriers for fertilizers. A summary of various types of nanomaterials used as soil amendments is given in Table 8.1.

Table 8.1 Nanomaterials used as soil amendments
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8.2.1 Nanoclays

Clays are an integral part of soil mainly consisting of phyllo-silicate minerals with varying water retention capacities. Clays offer high surface area and have a net negative charge which helps clays in retaining plant nutrients and act as a pH buffer in soil. Clays lose their plasticity and become brittle when the water content is reduced. Nanoclays are generally prepared from the smectite group of clays which includes montmorillinate. Nanoclays have been extensively used in preparing polymer nanocomposites which have been applied in paints, cosmetics, drug delivery and water treatment. Nano-clay polymer composites have also been used as nutrient carriers for enhancing plant growth and for enhancing the water retention capacity of soils.

A series of nanoclay-polymer composite nutrient carriers were prepared by the reaction of different types of clays such as kaolinite, mica and montmorillonite with partially neutralized acrylic acid and acryl amide with N,N-methylene bisacrylamide as a crosslinker and ammonium persulfate as an initiator. Six different types of nanoclays were used with different types of clays with and without amorphous aluminosilicate. Among the different nano-polymer composites, the percentage release of nutrients at 48 h ranged from around 70 % in the polymer/clay (montmorillonite) composite to 90 % in the polymer/clay (kaolinite) composite proving that these nanoclays can be utilised for slow release of nutrients. Further the nanopolymer composites were loaded separately with di-ammonium phosphate and urea solution. Release of phosphorous and total mineral nitrogen from the polymer composites loaded with diammonium phosphate and urea, respectively, were compared with corresponding conventional fertilizer. Release of Phosphorous and Nitrogen were studied independently with a factorial experiment under four types of fertilizer in combination with three types of soils alfisol, inceptisol and vertisol. Cumulative Phosphorus and total mineral Nitrogen recovery significantly increased over conventional fertilizer. The increase in recovery was +88.3 % and +27.3 % for phosphorous and nitrogen respectively with nanomontmoillonite. Higher Recoveries were a result of slow release property of nanopolymers which reduced nutrient losses (Sarkar et al. 2014, 2015).

Nano-sized AlZnFe2O4/poly (Acrylamide-co-acrylic acid) superabsorbent nano- composite was synthesized and the effects of different levels of nanocomposite were studied to evaluate the moisture retention properties of sandy loam soil. The soil amendment with 0.1, 0.2, 0.3 and 0.4 w/w% of nanocomposite enhanced the moisture retention significantly at field capacity compared to the untreated soil. Seed germination and seedling growth of wheat was found to be notably improved with the application of the nanocomposite. A delay in wilting of seedlings by 5–8 days was observed for nanocomposite-amended soil, thereby improving wheat plant growth and establishment (Shahid et al. 2012).

8.2.2 Nanominerals

Natural zeolites are hydrated aluminosilicates based on an infinite three-dimensional structure of tetrahedrons such as SiO4, AlO4, FeO4 joined by oxygen atoms. Zeolites consist of interconnected channels and cavities of molecular dimensions where cations allowing the ion exchange exist. Zeolite materials allow an introduction of new functional groups through several processes of modification, improving substantially its activity and selectivity on the removal several substances (Inglezakis et al. 2002). Sulphate loaded nano zeolites were prepared and its activity was analysed in a percolation reactor (Thirunavakkarasu and Subramanian 2014). Sulphate release from fertilizer-loaded nanozeolite was available even after 912 h of continuous percolation, whereas sulphate from Ammonium sulphate was exhausted within 384 h. The effectiveness of micro and nanoporous zeolite as a carrier for urea for slow release of nitrate was investigated by Manikandan and Subramanian (2014). Results revealed that the nitrogen release from the urea blended with nanozeolite (1:1) was up to 48 days while the conventional Zeolite – urea (1:1) mix was up to 34 day and the Nitrogen release ceased to exist in urea within 4 days without the presence of Zeolites.

Growth of Maize on sandy loam soil with and without the presence of porous silica nanoparticles was studied by Suriyaprabha et al. (2012).The increased surface area of silica nanoparticles led to accumulation of nanosilica in the plants and also increased the leaf size thereby leading to larger surface area for photosynthesis. Similarly, the effect of nano Si on growth characteristics of tomato was studied under salinity levels and has delivered promising results in salt tolerance (Haghighi et al. 2012). Using mesoporous silica as carrier for urea for slow release of nitrogen resulted in a fivefold increase in the availability period (Wanyika et al. 2012).

The supplement of the nanoscale hydroxyapatite was found to increase the level of chlorophyll and vitamin C and decrease the level of malondialdehyde in pakchoi plant shoots grown on Cd contaminated soil. The level of antioxidant enzymatic activity in the plant also increased as result of the addition of hydroxyapatite. The results confirmed that nanohydroxyapatite can be applied to reduce the plant uptake of Cd and resist the Cd stress (Li and Wu 2013). Nanohydroxyapatite was evaluated as a potential fertilizer to improve phosphorous availability in comparison with bulk hydroxyapatite and triplesuperphosphate for the growth of wheat (Montalvo et al. 2015). Although nanohydroxyapatite performed better than bulk hydroxyapatite, most likely because of faster dissolution, triplesuperphosphate was still a more efficient phosphorous fertilizer.

8.2.3 Metal and Metal Oxide Nanoparticles

Metal and Metal oxide nanoparticles such as Zinc, Iron, Titanium and their oxides have shown potential in promoting plant growth. Biosynthesized protein encapsulated, crystalline natured nano Zn (15–25 nm) was evaluated as a nanofertilizer for enhancing the growth of pearl millet. Beneficial effects were observed on shoot and root lengths, chlorophyll content leading to a grain yield of 37.7 % over the control without nano Zn (Tarafdar et al. 2014). Release of Zn to the soil using a nano-sized manganese hollow core shell was evaluated in a percolation reactor system. The results showed that the Zn-fortified core shell released Zn for more than 696 h while Zn release ceased after 408 h in ZnSO4-fertilized soil (Yuvaraj and Subramanian 2014).

Beneficial effect of individual nano Fe, P and K on saffron flowering was analysed by Amirnia et al. (2014). Results indicated that nanofertilizers were effective in enhancing the flowering traits of saffron plant. Magnetite (Fe3O4) nanoparticles were synthesized and applied as foliar spray and soil additive to basil plant. Nanoparticles applied were effective in increasing all the measured traits such as chlorophyll content, carbohydrate content, oil content shoot/root length etc. for both foliar spray and soil additive methods (Elfeky et al. 2013).

8.3 Soil Remediants

Anthropogenic activities have led to soil contamination is various parts of the world. Mining, agriculture, Industries, waste disposal are some of the factors which lead to soil pollution. An estimated 3,000,000 potentially contaminated sites are present globally which not only pose risk to human health, ecosystem but also pose a huge economic loss (Singh and Naidu 2012). Common contaminants include petroleum hydrocarbons, chlorinated solvents, persistent organic pollutants, pesticides, inorganics, heavy metals and radioactive constituents (Naidu 2013). Soil remediation methods are well established and have been in use for decades. Remediation technologies could be exsitu or insitu. Table 8.2 gives a summary of the remediation technologies available and the contaminant classes treated.

Table 8.2 Methods used for soil remediation and the contaminant classes
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Nanomaterials with their enhanced reactivity towards contaminants and better mobility could be a potential choice for remediating soils. The application of nanomaterials for mitigating soil pollution includes degradation of pollutants, detection and sensing of pollutants, enhancers for remediation processes. Table 8.3 gives a summary of the research work carried out for evaluating the role of nanoparticles for soil remediation.

Table 8.3 Nanoparticles used for soil remediation
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8.3.1 Nanomaterials for Contaminant Stabilization

Stabilization techniques effectively reduce the hazard potential of a contaminant by converting it into less soluble, mobile or toxic forms. Stabilization could be done either by physical methods or chemical reactions. The mobility of organic and inorganic compounds can be reduced through various precipitation, complexation, and adsorption reactions. The potential of Fe nano oxide (maghemite and magnetite) and amorphous Mn oxides for stabilizing Cd, Cu and Pb in contaminated soils was investigated by Michálková et al. (2014). Results from batch and column experiments coupled with adsorption tests proved that the amorphous MnO was the most effective treatment for the stabilization of metals in the studied soil samples at the given w/w ratios (1 and 2 %, w/w). Metal stabilization was a result of combined specific adsorption onto the oxide surface together with an increase in soil pH promoting the adsorption of metallic cations. Nano TiO2 and CeO2 were utilized to adsorb Cu(II) and mitigate its bioavailability and toxicity to Tobacco plants (Wang et al. 2015a, b). The addition of the nanoparticles along with humic acid resulted in increased the root length by 90 % and 100 % for nano TiO2 and nano CeO2 respectively. The results indicated that nanoparticles were successful in reducing the Cu(II) phytoxicity by reducing the bioavailable soluble Cu(II). The study also reported no phytotooxicity by individual TiO2 and CeO2 nanoparticle which makes their usage more amenable.

The effect of nano zero valent iron (nZVI) coated with carboxy methyl cellulose on the degradation of DDT in soil columns was investigated by El-Temsah et al. (2013). Addition of nZVI and subsequent leaching with water led to a reduction in DDT concentrations in soil of almost 50 % compared to controls without nZVI. However the use of nZVI resulted in negative effects on plant growth. It was also observed that the oxidation of nZVI with aging reduces the negative effects of the presence of nanoparticles. Le et al. (2015) developed an integrated remediation system for dechlorination of aroclor 1248 using chemical catalysis and biodegradation. Dechlorination was achieved by treatment with bimetallic nanoparticles Pd/nFe under anoxic conditions. Dechlorination efficiency was 99 %, 92 %, 84 %, and 28 % of tri-, tetra-, penta-, and hexachlorinated biphenyls, respectively. The resulting biphenyl was found to be biodegraded rapidly by Burkholderia xenovorans LB400.

8.3.2 Nanomaterials in Thermal Treatment

Thermal treatments for soil remediation include incineration, steam injection and extraction and vitrification. Vitrification is a high temperature process in which organic matter is incinerated and mineral matter is melted and a slag is quickly cooled to obtain the contaminant entrapped in a matrix. Nano Ca/Cao mixtures were used to immobilized radionuclides 133 Cesium from contaminated soil through vitrification. The removal efficiency achieved with the nanoparticles was 96 % at 1,200 °C. The investigation results have showed that a certain amount of 133Cs was the entrapped inside new aggregates, produced during the thermal treatment with nCa/CaO (Mallampati et al. 2015a, b).

Thermal desorption of polychlorinated biphenyls in the presence of nZVI was evaluated by Liu et al. (2014). The presence of nZVI gave improved efficiency of desorption at 300 °C. The desorption efficiency was dependent on nZVI concentration and temperature. Nano Zerovalent Iron was also used to enhance thermal degradation of polychlorinated dibenzo-. p-dioxins and dibenzofurans at low temperatures (Lundin et al. 2013).

8.3.3 Nanomaterials for Enhancing Phytoremediation

Phytoremediation is a low cost and effective insitu remediation method for contaminated soil reclamation. Phytoremediation involves uptake, containment, degradation of contaminants by plants. Several reports are available in literature evaluating the effect of nanomaterials for enhancing phytoremediation Gao and Zhu 2014; Wang et al. 2014, 2015) . The effect of nanosilicon on lead toxicity, uptake and accumulation in rice varieties Yangdao 6 and Yu 44 grown on lead contaminated soil was analysed by Liu et al. (2015). The biomass increased by 3.35–11.8 % higher and lead concentration in shoots and grains was reduced by 27–54 % and 21–41 % respectively by adding nanosilicone to lead contaminated soil. The results indicate that nanosilicone was effective in preventing the lead transfer from rice roots to aboveground parts by complexation with lead.

E-waste contaminated soil containing Pb and polychlorobiphenyls was remediated by phytoextraction using Impatiens balsamina in the presence of three different nanozerovalent iron particles – free, vermiculite supported and activated carbon supported zerovalent iron. Free and vermiculite supported nanozero valent iron were found to increase accumulation of Pb in plants and activated carbon supported nano zero valent iron reduced the bioavailability of Pb (Gao and Zhou 2013, 2014).

8.3.4 Nanomaterials for Electrokinetic Remediation

Electrokinetic remediation is an emerging technology which involves application of a low-intensity, direct current through the soil to separate and extract contaminants from soil. The current is applied across electrode pairs that have been implanted in the ground on each side of the contaminated soil. During the process positively charged chemical species, such as metals, ammonium ions, and some organic compounds, move toward the cathode, and negatively charged chemicals, such as chloride, cyanide, fluoride, nitrate, and negatively-charged organic species, migrate toward the anode. Various additives such as surfactants can be added to enhance the remediation process. The combined effect of nanozerovalent iron and electrodialysis of polychlorinated biphenyls (PCB) was evaluated by Gomes et al. (2014a, b). H+ generated near the anode in electrodialytic chamber solubilized the transition metal from soils which in turn aided in dechlorination of PCB to biphenyl compound (Gomes et al. 2014a, b). Yang and Chang (2011) evaluated the treatment efficiency of combining emulsified nano zerovalent iron and electrokinetic remediation for Trichloroethylene (TCE) on contaminated soil. Electro kinetic remediation enhanced transport of nanoparticles through the soil matrix from anode to cathode chamber. During the transport, hydrophobic TCE diffuses into nano zerovalent iron present in the inner aqueous region through emulsion and becomes dechlorinated.

8.4 Conclusion

Nanotechnology has the potential to provide solutions for better soil management through improving nutrient quality of soil and alleviating soil pollution. Although the efficacy of Nanomaterials as plant growth promoters and remediation agents has been proved, knowledge of the fate and effect of nanomaterials in soil has to be careful considered. Nanomaterials have been reportedly toxic to various organisms and also effect human health (Mukherjee et al. 2014; Zou et al. 2014; Smulders et al. 2015). In this context, any new development involving the application of nanoparticles directly into the environment has to take into consideration the fate, transport and effect on the soil ecosystem, plant toxicity. Several researchers have attempted to understand the fate and transport of nanoparticles (Anjum et al. 2015; Sun et al. 2015) but many more investigations have to be carried out on the stability of the various types of nanoparticles alone and in combination with various contaminants (Fig. 8.2).

Fig. 8.2
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Application of nanomaterials for soil management

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