Physical and chemical methods used for remediation.
Pollution is one of the biggest challenges of current times. For control of environmental pollutants, degradation of these contaminants is need of times. Degradation of pollutants can be achieved by various physical and chemical or by physicochemical approaches. Since these methods are in efficient, hence development of biological methods began. Bioremediation is the approach of using bacteria, fungi, plants, algae, etc. to degrade wide range of environmental pollutants. Nano-bioremediation is one of such method which has received lot of attention in past few years. Nano-sized particles have large surface area relative to their volumes and thus have enhanced chemical and biological reactivity. Nano-bioremediation aims at reducing the contaminant concentrations to low risk-based levels and alleviating environmental impacts simultaneously. It brings the benefits to both nanotechnology and bioremediation together to achieve remediation which is more efficient, less time taking and eco-friendly.
- Environmental Pollution
Problem of Environmental pollution is not limited only to developed countries but the challenges of waste management are also being faced by developing countries which is gradually growing day by day. The situation of effective management of environmental contaminants is grim in developing countries. Automation of most of the industries, establishment of new industries, ineffective disposal mechanisms adopted by these and similar establishments have led the world to face serious problems of municipal solid waste management, air, water and land pollution, various types of dangerous organic and inorganic pollutants that have entered into water, soil, and air by these industrial and urban waste. The developments and technical progress have led to increased harmful effects by accumulated pollutants into the surroundings. The major kinds of pollution, usually classified on the basis of environment, are air pollution, water pollution, and land pollution (Figure 1). Modern society is also concerned about specific types of pollutants, such as noise pollution, light pollution, and plastic pollution. Pollution of all kinds has negative effects on the environment, wildlife and impacts human health and well-being. Pollution is causing a lot of harm to human and animal health, plants and trees as well as the wider environment and has been harshly affecting the entire ecosystem and disrupting the marine life in lakes and streams causing depletion of the natural flora and fauna [1, 2].
Air pollution is increasing day by day due to release of smoke and toxic gases from various industries, transportation mediums, and various other human activities such as burning of wood, coal for fuels, etc., natural events such as forest fires. Air pollution is very common in large cities. Air pollutants cause significant damage to human health, vegetation, and cultural heritage .
Soil pollution is mainly caused by the disposal of municipal and industrial wastes as well as contaminated slurries from treatment plants at the waste disposal sites. Disposal and dumping of excessive use of single-use plastics, accumulation of chemicals such as pesticides, DDT, fertilizers, industrial use chemicals, raw materials for various manufacturing and production units, human activities such as deforestation, etc. have led to increased land pollution .
The problem of water pollution has grown with the increased amount of industries being set up and release of untreated industrial effluent in the water bodies such as ponds, lakes, riverine systems situated in the nearby vicinity of these industries. These industrial discharges include many toxic substances such as chemicals, heavy metals, metals and non-metals, floods runoffs, pesticides, fertilizers and acid rains, etc. . In addition, greenhouse gas emissions such as methane and carbon dioxide continue to drive global warming and pose a great threat to biodiversity and public health .
The deposition of increased amount of toxicants and contaminants in our environment, have led to development and evolution of various technologies to reduce these pollutants and make our environment a better place to live. The developed technologies include use of various chemical, physical, physiochemical technologies to degrade environmental pollutants. In the last half decade bioremediation approaches has gained a lot of attention as the other technologies are either not much effective, are cost intensive and also leaves other accumulants into the environment .
Remediation of pollutants using nanotechnology based approaches is the recent advancements for the development of more effective, cost effective technologies for mitigating different type’s pollutants form all kinds of environments . Nanotechnology products, processes, and applications are expected to contribute significantly to the environment and eliminate protection by saving raw materials, energy and water as well as by reducing greenhouse gases and hazardous wastes (Figure 2). By the use of nanomaterials, therefore, promises certain environmental benefits and sustainability effects .
The word “nano” meaning “dwarf” in the Greek language refers to dimensions of the orders of magnitude 10−9. Nanotechnology is the field of applied science, focuses on the design, synthesis, characterizations, and application of materials and devices on the nanoscale. It is also known as the study of phenomena and the manipulation of materials in the nanoscale. Nanotechnology can detect the presence of pathogens or toxic agents in air, water and soil are of great importance for human health and protection of the environment by offering equipment that has extremely sensitive and fast measurement with sensor equipment. Nanomaterials are less bulky, easy to operate, and having low cost [5, 8].
In addition to this, nanomaterials help to improve the quality and performance of many consumer products. Therefore, nanotechnology is very useful in solving environmental pollution .
Accumulation of harmful air pollutants such as NOx, SOx, CO, etc., is increasing day by day. Nanotechnology is one of the current methods used in the world for controlling air pollutants using nanosensors, nanocatalysts, nanocomposites, nano filters, and nano-biomaterials .
Toxic gases in the air can be cleaned with help of nanotechnology but the most important thing is its continued control. Molecular level detection of toxic gases is done with the help of nanosensors such as nanocontact sensors and cantilever sensors. Nano contact sensors have been developed which can detect heavy metal ions and radioactive elements and cantilever sensors have been developed to sense VOCs, heavy metals, and pesticides. Nanocatalyst materials can be used as an environmental catalyst in the purification of automobile exhaust gases and air filtration. It is widely used in purification of water. Carbon nanotubes (CNT) have hollow ring structures composed of carbon atoms. CNT is divided into two parts, the first one is single-wall nanotubes and the second is multi-wall nanotubes which can be used to trace pollution and collect information on environmental pollutants .
As we know many toxic and non-biodegradable materials such as xenobiotics, heavy metals, leads, inorganic compounds cannot be eliminated by the biological and physicochemical method at environmental standards from wastes . Nano-filters, nano-photocatalyst, and nanoporous catalysts are used for waste management. Nano filters can remove 60–70% of Chemical Oxygen Demand (COD) and 50% of ammonium in the leachate, anions, cations, arsenic, uranium, chromium, and pathogens from the wastewater. Nano-filter technology can be widely used in the separation and purification of gases and pollutant vapors in various industries and preventing their release into the environments. It is used in water treatments in homes, offices, and industries. Nano-photocatalyst is a nanotechnology that can absorb heavy metals from wastewater. Nanoporous catalysts can be used to convert the wastes into ethanol . Another nonporous material, manganese oxide has great adsorption of toxic due to its large surface area and molybdenum disulphide (MoS2) is used for energy-efficient desalination of water which filters five time more than conventional ones. To clean oil spills in the water bodies, a nanofabric paper towel has been developed which are woven from tiny wires of potassium manganese oxide that can absorb oil 20 times its weight [2, 8, 11].
Another use of nanotechnology is in human health and safety. It is used in many cosmetics, dyes, textiles, foods, medicines, medical equipments, and many other materials. Therefore with the help of nanotechnology, we can protect the sustainability of human health and environment. It also helps in waste management and monitoring pollutants. It also helps in reducing the emission of greenhouse gases and the discharge of hazardous chemicals in water bodies .
Nanoparticles can also harm human health and the environment. Due to the quick absorbance of nanoparticles through the skin, mucous and respiratory tract, causing new and unknown toxins that can threaten human health. Due to the lack of knowledge of the effect of nanomaterials in the environment and human society, we do not have a sufficient defense mechanism against them. Therefore, possible risks and its impact on organisms and environment should be considered .
2. Nano-remediation of soil pollution
2.1 Soil pollution
After air and water, soil is the third main components of an environment. Soil plays very important role in many activities like in plant growth (the prime activity of soil), gives anchorage to plants, supports many forms of life, provides proper environment to microbes for decaying the dead materials into simpler component which further goes in biological cycle perform by the living organism .
Soil pollution can be defined as the reduction in the productivity of soil due to presence of soil pollutants. Soil pollutants reduce the productivity of soil because it shows an adverse effect on the physical, chemical and biological properties of soil. Soil pollution occur due to pesticides, carcasses, tins-cans, fertilizers, organic manual, chemicals, bottles, plastics, paper, leather goods, discarded food, clothes and radioactive wastes (Figure 3) .
Sometimes soil pollution can be the reason of water pollution as well as air pollution, these chemicals leaches into groundwater and reaches to the water stream like lake, pond, sea and also the some volatile compound release harmful gases in the atmosphere respectively .
2.2 Causes of soil pollution
There are many causes of soil pollution and some are as follows:
2.2.1 Types of contaminants
Organic and inorganic are the two major groups of chemicals which cause soil pollution. Soil is polluted by many chemicals like simple inorganics ions to complex organic molecules.
2.2.2 Inorganic pollutants
In the environment due to industry, mining, transportation and urban activities inorganic pollutants are released. Inorganic pollutants can interact both extracellular and intracellular levels respectively and this make it high risk component for environment .
Some elements known as Micronutrients are essentials for in small amount and become toxic when increase the concentration for example B, Cl, Cu, Fe, Mn, Mo and Zn. Metals like Cd, Cr, Cu, Hg, Ni, Pb, V and Zn, metalloids like As, Bo, and Sb, non- metals like Se, actinoids like U and halogens like I and F are the inorganic contaminants which causes soil pollution when exceed the certain threshold .
Some elements are toxic at all concentration for examples Hg, As and Tl and some form organomettalic compound which are highly toxic and lipophilic for example methylmercury and tributyl tin oxides .
2.2.3 Organic pollutants
Organic compounds in which carbon is the main elements in the structure with or without functional groups. Organic pollutants include several groups like pesticides, hydrocarbons, polycyclic aromatic hydrocarbon (PAHs), polychlorinated biphenyl (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) polychlorinated dibenzofurans (PCDF), polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), surfactants, or pharmaceuticals. This group separately or together pollutes the soil for examples the groups of PCBs include 209 congeners [17, 18].
The compounds are used due to its wide range of physical properties like polarity, solubility, volatility etc. These compounds shows different behaviors in environment and toxicity in organism due to its physical properties even come in same group.
Some of the organic compounds can be degraded or bio transformed but many of them shows resistant to both chemical as well as biochemical transformation and have long half-lives for example polyhalogenated compounds. Due to its molecular stability it remains in soil for very long time and effect environment and can travel to long distance [19, 20].
2.3 Origin and sources of soil pollution
Soil contaminants can be naturally or anthropogenic. Natural activities like weathering of rocks and volcanic activities or forest fires can produces organic, inorganic or both types of pollutants respectively. Human can also cause soil pollution accidentally or deliberately. Mining, smelting, disposal of wastes, fossil fuel combustion, gaseous works, industries, sports shooting, and application of agrochemicals or sewage are the human activities which cause soil pollution. Nuclear accidents, flooding by rivers or seas, leaks from landfills, or accidental spills are the accidental pollution (Figure 4) . Above all examples mining is one of the important sources of toxic elements.
2.4 Effects of soil pollution
Due to direct or indirect contact with contaminated soil, the health risks increases and causes many diseases. Ecological balance also disturb due to increase in pollution of soil as well as health of many living organisms is also under risk. Soil pollution affects the quality of soil which causes deaths of many organisms which are essential for the growth of plant (e.g., earthworm). Indirectly the soil pollution also affects the life of predators like birds which move to other places in search of food.
People who were living near polluted land are prone to health risk as polluted soil can cause poisoning directly and indirectly i.e. children playing near waste land come in direct contact and food which grow on polluted land cause disease indirectly like migraines, nausea, fatigue, skin disorders and even miscarriages are common symptoms seen in a people which are live near polluted land and drink polluted water .
2.5 Nano remediation of soil pollution
There is several ways to remediate soil pollution but here we are discussing about remediation of soil pollution by nanoparticles.
In advancement of research, engineered nanoparticles plays a very important role in removal of environmental pollution as they are cheaper and more reactive.
For the treatment of environmental pollution engineered nanoparticles also enhance in situ method. Examples of some engineered nanoparticles used in soil remediation are given below:
Nanoscale calcium peroxide – used for degrading organic compounds like gasoline
Nanoscale zero valent iron – utilized for destroying organic compounds that are halogenated
Nanoscale metal oxides – used for metal adsorption
The above methods are considered as novel work but the effect of these engineered nanoparticles is yet to be studied .
From the above examples calcium peroxide is the best option because it releases peroxide very slowly which increases the attenuation time of the remediating reagent but due to its slow effective speed reaction, it shows some drawbacks. The speed of reaction of calcium peroxide nanoparticles can be increase by increase in surface to volume ratio .
2.6 Advantages of using nanoparticles
Large surface area – which helps in faster interaction.
Presence of active sites – helps in increasing decontamination efficiency.
Small size – helps in easy delivery at the contamination sites.
Non-toxic at certain concentration.
Easily modified according to requirement.
Pollutants can easily detected by use of nanomaterials.
Low cost – the cost of remediation of soil pollutant is low.
Effective and environmental friendly 
2.7 Disadvantages of using nanoparticles
Difference in function of natural and synthesized nanoparticles.
Specific surface properties and chemistry for specific soil contaminants.
Shows toxicity at certain size i.e. if size is less than 100 nm it shows pulmonary toxicity.
Inhalation of nanoparticles can also cause damage inside body for examples FeO nanoparticles if inhaled, it release Fe(III) ion, also cause oxidative damage due to release of Fe (IV) ion.
Nanoparticles used in soil pollution degradation like Fe and magnetite responsible for oxidative stress response.
3. Nanotechnology: an approach to improve water quality through nanoparticles
We need fresh water; it is a big task to have abundant fresh water for agriculture and industrial applications [30, 31]. More than one billion people in the world are facing challenges to have fresh water and in near future situation can be worst. It is estimated that the average supply of water to per person will drop by a factor of 1/3rd, which will result in premature death of millions of people. Non-contaminated water is also not in reach to meet proper agricultural practices . The need of great amount of fresh water is leading towards the contamination of ground water through the use of pesticides, fertilizers and other chemicals.
Novel, sustainable and cost-effective approach is needed to tackle these problems. Nanotechnological researches have enabled us to find the solution for remediation and purification of waste water. Water resources within reach are usually contaminated with pathogens, salts, metals(Cu, Pb, As, etc.), pesticides, herbicides, pharmaceuticals and personal care products (PPCPs) and radioactive elements due to natural occurrences or anthropological activities [33, 34, 35].
Although the conventional methods are effective in many ways, still this method are quite outdated and not much cost effective and requires more man power and specificity and also, conventional methods are not applied to lower concentrations of pollutants (Table 1).
|Precipitation||Suitable ion is applied to precipitate the metal salts.||Efficiency is affected by low pH and sludge disposal process makes it expensive.|
|Ion-exchange||Solid-phase matrix material is used which has ability to exchange cations or anions.||This method cannot handle high metal concentration and is relatively expensive.|
|Electrowinning||Electric current is passed from an inert anode through a leach solution for the recovery and removal of heavy metals.||The migration of ions to the cathode surface creates a ‘zone of depletion’, which hinders the process.|
|Electrocoagulation||Electro-chemical based approach when electric current is used to remove metals from solution.||It is an intensive process and places a lot of strains on electrodes, resulting in wear and tear.|
|Cementation||A type of precipitation involving an electrochemical approach in which metals with greater oxidation capacity flows into the solution.||Efficiency is influenced by various factors, such as pH, surface area of absorbent and its surface energy, etc.|
|Membrane filtration||Separation of metals from water takes place by semi-permeable membrane with pressure gradient.||Water pretreatment and monitoring makes the process expensive.|
|Electrodialysis||Analogous to RO except for Driving force in which electric field is applied across semi-permeable membrane.||Efficiency is affected by porosity, pH, flow rate, conductivity, etc.|
|Reduction||Reductants (H2S, diothionites) are injected deeply to polluted regions.||Toxic intermediate formation takes place.|
|Chemical washing||Heavy metals are directly removed by means of strong extrants like acids.||Deterioration of soil quality, which is hazardous to surrounding.|
|Chelate flushing||Chelating agents are used for extracting huge quantity of heavy metals.||Chelates are expensive and carcinogenic.|
The conventional methods which are used in removing pollutants and particulate matters are broadly categorized into three categories:
Physical treatment methods
Chemical treatment methods
Biological treatment methods
The most promising methods can be said to be the biological treatment methods which includes bioremediation through different organisms, biofiltration, biosorption, etc. These are basically useful for in-situ treatment but these are slow processes and take much time but cheap and cost-effective. Biological treatment methods are quite effective but in current scenario these cannot fulfill the human requirements as pollution is many folds so a quick and highly efficient method is needed which can be fulfilled by use of nanoparticles which are quite fascinating in present days.
Nanoremediation has played an efficient and effective solution for challenges of site remediation and for the process of environmental cleanup in a cost effective manner. As their sizes are too small and have unique surface coating, these can pass through the smallest spaces and can remain suspended in ground water and then can go farther at larger distribution.
3.2 Nano bioremediation of heavy metals
The major global concern is contamination of heavy metals because of their toxicity and threat to flora and fauna . Anthropogenic activities are the main cause for pollution of heavy metals. There are 65 groups of heavy metals which can be distinguished on a number of criteria, like cationic- hydroxide formation, specific gravity >5 g/ml, complex formation, hard- soft acids and bases, eutrophication and environmental toxicity. Higher doses can cause birth defects, cancer, skin lesions, retardation, major organ damage such as liver and kidneys . Industries of electroplating, cement, paint, etc. discharges heavy metals such as Cd, Cu, Pb, Hg, Ni, Zn and As which are highly toxic to living organisms. The waste water is directly discharged to water bodies without any prior treatment. These can cause serious mutations and Physiological damages to organisms of habitat .
If possible, we will be pleased to have uses of microbes in bioremediation of toxic heavy metals with interest of nanofabrication of environmentally useful submicron scale particles. In that condition, microbes can be utilized in an eco-friendly and effective remediation of heavy metals .
There are mainly three attributes of nanotechnology which are being used in nanobioremediation-
Use of clean and green nanoparticles
To remove hazardous materials from composite sites
Nanobioremediation prefers in-situ treatment of contaminants because it’s economical, highly efficient and can be applied on larger scale .
3.3 Nanoiron and its derivatives
The nano zero-valent iron (nZVI) is most widely used nanomaterial. These are helpful in removing aqueous contaminants by reductive dechlorination or by reducing to an insoluble form, in case of chlorinated solvents and in case of aqueous metal ions respectively. Iron will also go for ‘redox’ reaction with dissolved oxygen and water. Heavy metals such as As and Cr, pesticides, chlorinated solvents and nitrates can be removed from ground water and water bodies using nZVI. The zero valent iron can be used to remove highly toxic, mobile and predominant arsenic species [As(III) and As(V)] in anoxic ground water (Figure 7) .
3.4 Single-enzyme nanoparticles
Enzymes are biocatalysts, can enhance the process of bioremediation. Their usefulness in economical way is limited as compared to synthetic catalysts, as the enzymes lack stability and longer catalytic life. To increase the stability in an effective way, magnetic iron nanoparticles can be made and on applying magnetic field these can be separated out from reactants or products .
The word “
3.6 Titanium dioxide (TiO2) based nanoparticles (NPs)
Semiconducting, photolytic, energy-converting, electrical and gas sensing capabilities are found in TiO2. Rutile, anatase and brookite are three polymorphs of TiO2 crystals found in nature. These NPs are commonly available, affordable and non-toxic that’s why these can be used to remove organic contaminants. The light energy is greater than band gap of semiconductor TiO2 is necessary for the removal of different organic pollutants .
3.7 Bimetallic NPs
Halogenated Organic Compounds (HOCs) can be easily transformed to low or no toxic material by metals such as Zinc and Tin, which are more effective as compared to Iron. The complete dechlorination of many chlorinated aliphatic compounds to hydrocarbons can be achieved by superior catalytic ability of Palladized iron [52, 53, 54].
3.8 Photocatalytic NMs
Photocatalysis is used in the deterioration of organic contaminants in an effective manner, it is an advanced oxidation process (AOP). Even, trace amounts of pathogens and pollutants can be removed by oxidation process through photocatalysis. Catalyzation and other methods to modify NMs can improve the efficiency and remediation speed [55, 56].
3.9 Air pollution
Air pollution can be defined in many ways, one of the most used definitions of air pollution is the occurrence of chemical compounds in the atmospheric air that are toxic and present at concentration that may be injurious to animals, vegetation and humans. Air pollution decrease the quality of air due to presence of chemicals which are not present originally but resulting of human activity and it also change the lives on earth because of global warming and depletion of ozone layer .
3.10 Types of air pollutants
Air pollutants can be different types depending on the source, form and condition under which pollutants are generated.
3.10.1 Primary pollutants
Primary pollutants are the pollutants which are discharged directly in air.
Particulate matter (PM10 and PM2.5); Carbon oxides (e.g. carbon monoxide); Oxides of sulfur; Ammonia; Light hydrocarbons; Volatile organic compounds; Metals (lead, mercury, cadmium) .
3.10.2 Secondary pollutants
Secondary pollutants are the pollutants which are formed when the chemical reaction occur between two gases present in the atmosphere.
Sulfur dioxide, oxides of nitrogen, ammonia and non-methane volatile organic compound .
3.11 Causes of air pollution
Air pollution can be cause by naturally as well as man-made activities.
The examples of natural sources are emissions from plants, from the biomass of the ocean, volcanic gas and the re-suspension of dust in arid areas such as deserts.
The examples of man- made source are combustion engines (both diesel and petrol), household and industry solidfuel combustion for energy production (coal, lignite, heavy oil and biomass), other industrial activities (building, mining, manufacture of cement, smelting), agriculture, with the use of entrants, and the erosion of roads by vehicles and abrasion of brakes and tyres .
3.12 Other causes are
3.12.1 Urbanization and industrialization
Urbanization and Industrialization are one of the major cause of air pollution due to urbanization there is increase in use of automobiles and due to industrialization there is an increase in cutting of trees which increase the air pollution rapidly .
3.12.2 Burning of fossil fuels
Burning of fossil fuels is also the main cause of air pollution. Burning of fossil fuel can release a variety of primary and secondary pollutants as well as airborne oxide and also SO2, CO2, CO, hydrocarbons, organic compounds, chemicals, and nitrogen oxides (NOx). Due to burning of fossil fuel climates change and global warming is also increase due to release of major greenhouse gases (carbon dioxide, methane (CH4), nitrous oxide, and fluorinated gases) .
3.13 Effect of air pollution
The air pollution shows adverse effect on human health and causes many diseases like acute respiratory infection, pulmonary disease, cardiovascular disease etc.
3.13.1 Acute respiratory infection (ARI)
Acute respiratory infection is one of the common disease causes by air pollution. In this the pollutants can effects the lungs and show some symptoms like cough, sinusitis and ditis media .
3.13.2 Pulmonary disease
Pulmonary disease can cause due to inhalation of air pollutants which cause allergic disease and pulmonary disease such as asthma, atopic dermatitis and allergic rhinitis and lung cancer .
3.13.3 Cardiovascular disease (CVDs)
The pollutants like PM, PAHs, CO, heavy metal, and other organic pollutants are the main cause of cardiovascular disease .
Cardiovascular disease is severe when particulate matter increases and shows symptoms like ischemic stroke, myocardial infarction, cardiac arrhythmia, heart failure, and atrial fibrillation .
Particulate matter is one of the major factors which cause CVDs and induce the oxidative stress, systemic inflammation and increases the blood coagulability, and autonomic and vascular imbalance .
3.14 Nano-remediation of air pollution
Air pollution can be remediated in many ways and one of the best ways is use of nanoparticles like nanocatalyst, nano-membranes and photocatalyst semiconductor.
Nanocatalyst helps in gaseous exchange by increasing the surface area for the reaction of gases which increases the chemical reaction and help in conversion of harmful gases which are release from cars and industries into harmless gases. Nanofibre catalysts are one of the examples which are used in industries for the removal of organic compounds from the smoke stacks.
Nanostructured membrane is another way to separate methane or carbon dioxide from smoke due to having small pores. The best example is the Carbon nanotubes (CNTs) which are more efficient than other membrane for trapping greenhouse gases which is released by the mining and power generation. CNTs have major advantages as it can trap gases hundred times faster than other membranes .
The other approach for the remediation of air pollution is using of nanosize semiconductor photocatalyst. Photocatalyst are the catalyst that oxidized organic pollutants into nontoxic materials for examples titanium dioxide (TiO2), zinc oxide (ZnO), iron (III) oxide (Fe2O3) and tungsten oxide (WO3) and used in many ways .
Photocatalyst and semiconductor can use together to remediate air pollution by using the principle of semiconductor i.e. oxidizing of organic molecules by light. The process includes, at a sufficient light exposure the charge is moved from valence band to conduction band and causes the oxidation of surrounding substance. The semiconductor photocatalyst can be modified according to reactivity and selectivity .
4. Challenges of using NPs
There are several problems related in in-situ transport processes of nano-particles which depict the reactivity loss of zero valent ion-particles with time [64, 65]. Apart from this, several researchers have found that the in-situ application of nano-particles leads to clustering effect enhanced the deposition of nano-particles which blocks the pore of soil due to which difficulty faced to reach the targeted contaminated areas [66, 67]. Due to clogging effect of soil, filtration process becomes major issue in use of nZVI remediation. Besides this, NPs are denser than water molecules which lead to settle down of NPs in fluid medium, causing clogging effect .
Many studies have shown the effectiveness of nZVI application, but its effects to local microbes are still in early stages [69, 70, 71, 72]. Lonf term effects and ethical issues related to use of NPs are hindrance to environmental agencies to implement NPs on field scale. Hence, application of NPs primarily depends on regulatory affairs and policies of each country, that’s why use of NPs is limited to European countries and nZVI extensively used in US [73, 74, 75].
There is a great concern related to use of NPs due to their negative effect on microbes. Number of studies has been done to address the toxicity of NPs with microbes. However, these studies have been performed on controlled laboratory conditions [76, 77, 78, 79, 80, 81]. However, contrary results have also been reported with some studies showing inhibitory effects on microbes where as some of the studies have showing stimulatory effects of NPs .
Thus, till date the existing results are controversial and lacks proper studies on field level as these studies are based on type of NPs and tested microbes, pollutants and also, several studies have used specific culture media in controlled lab environment .
5. Future prospects
The field of nanotechnology has gained attention among the researchers due to its number of beneficial effects like large surface area, multiple uses, tolerance to harsh conditions, easy and efficient manipulations, greater efficiency and many more.
We are marching towards a greener approach in management of industrial effluents due to the integration of NPs with microbes and enzymes [14, 84]. The residues left are either biocompatible or they can be easily removed by using simple filtration or precipitation techniques.
Continuous studies and its merits provide a vision for new discoveries into products. It is possible to produce synthetic ‘living-like’ or ‘nano-bots’ type things which will remediate hazardous pollutants and heavy metals from environments. So, the application of these organisms/products on a large scale will be a stepping stone for industries and environment.
Ms. Urmil, Environmental Application of Nanotechnology, International Journal of Engineering Research and Technology RACEE, (2015) Vol 4, Issue 03
Madkour L. H., Environmental Impact of Nanotechnology and Novel Applications of Nano materials and Nano devices. Nanoelectronic Materials. (2019) 605-699. Springer
McCormick R. A. and Holzworth, G.C., Air Pollution Climatology. Air Pollution (2013) 1976, 643-700
Bünemann E. K., Bongiorno G., Bai Z., Creamer R. E., De Deyn G., de Goede R., Fleskens L., Geissen V., Kuyper T. W., Mäder P., Pulleman M., Sukkel W., van Groenigen J. W., Brussaard L., Soil quality – A critical review, Soil Biology and Biochemistry(2018), 120, 105-125
Mojtaba T., Mohsen S., Nasser K. and Ali A., Benefits and Application of Nanotechnology in Environmental Science: an Overview. Biointerface Research in Applied Chemistry (2021) 11, 7860 – 7870
Nathanson, J. A. , Pollution. Encyclopedia Britannica (2021),
Babatunde D. E., Iheanacho H. D., Babatunde O. M., Gbadamosi S. L., Babalola I. P. and Oluranti A., Environmental and Societal Impact of Nanotechnology, IEEE Access (2020) Vol 8, 4640-4667
Rani K. and Sridevi V., An Overview on Role of Nanotechnology in Green and Clean Technology. Austin Environ Sci. (2017) 2(3): 1026
Mansoori G. A., Bastami T. R., Ahmadpour A. and Eshaghi, Z., Environmental Application of Nanotechnology. Annual Review of Nano Research, (2008), 439-493
Chokshi N. P. and Bora L., An Overview of Nanotechnology in Waste Water Treatment. Resource recovery, water reuse and recycle for sustainable development, (2014), 1-5
Yunus I. S., Harwin, Kurniawan A., Adityawarman D. and Indarto A., Nanotechnologies in Water and Air Pollution Treatment. Environmental Technology Reviews (2012), 1:1, 136-148
Koul, B., and Taak, P., Soil Pollution: Causes and Consequences. Biotechnological Strategies for Effective Remediation of Polluted Soils. Springer, Singapore, (2018), 1-37
Mishra R. K., Mohammad N., and Roy C. N., Soil Pollution: Causes, Effects and Control. Tropical Forest Research Institute (2015). 3(1), 20-30
Saha J. K., Selladurai R., Coumar M. V., Dotaniya M. L., Kundu S. and Patra A. K., Major Inorganic Pollutants Affecting Soil and Crop Quality. Soil Pollution-An Emerging Threat to Agriculture Springer, Singapore (2017), 75-104
Yuvaraj, M., & Mahendran, P. P., Soil Pollution Causes and Mitigation Measures. Biotica Research Today, (2020), 2(7), 550-552
Megharaj M., Ramakrishnan B., Venkateswarlu K., Sethunathan N. & Naidu R., Bioremediation Approaches for Organic Pollutants: A Critical Perspective. Environment International, (2011), 37(8), 1362-1375
Chen D., Cheng Y., Zhou N., Chen P., Wang Y., Li K., Huo S., Cheng P., Peng P., Zhang R., Wang L., Liu H., Liu Y., Ruan R., Photocatalytic Degradation of Organic Pollutants using TiO2-based Photocatalysts: A Review. Journal of Cleaner Production, (2020), 268, 121725.
Rajput M. S., Dwivedi V. and Awasthi S. K., Biodegradation of Pyridine Raffinate by microbial laccase isolated from Pseudomonas monteilii& Gamma proteobacteriumpresent in Woody Soil. Biocatalysis and Agricultural Biotechnology, (2020), 26, 101650
Cachada A., Rocha-Santos T. and Duarte A. C., Soil and Pollution: An Introduction to the Main Issues, Soil Pollution, Academic Press (2017)
Rajput M. S., Dwivedi V. and Awasthi S. K., Enzymatic Degradation of Pyridine Raffinate using Response Surface and Artificial Neural Network Simulation. Indian Journal of Experimental Biology, (2020), 58, 584-592
Souza L. R. R., Pomarolli L. C. and da Veiga M. A. M. S., From Classic Methodologies to Application of Nanomaterials for Soil Remediation: An Integrated View of Methods for Decontamination of Toxic Metal(oid)s, Environmental Science and Pollution Research, (2020), 27(10), 10205-10227,
Swartjes F. A., Introduction to Contaminated Site Management. Dealing with Contaminated Sites- From Theory towards Practical Application, Springer, Dordrecht (2018), 3-89
Bakshi M. and Abhilash P. C., Nanotechnology for Soil Remediation: Revitalizing the Tarnished Resource, Nano-Materials as Photocatalysts for Degradation of Environmental Pollutants, Elsevier (2020), 345-370
Sarkar A., Sengupta S. and Sen S., Nanoparticles for Soil Remediation, Nanoscience and Biotechnology for Environmental Applications, Springer Cham., (2019) 22, 249-262
Mueller N. C., and Nowack B., Nanoparticles for Remediation: Solving Big Problems with Little Particles, Elements, (2010), 6(6), 395-400,
Khodaveisi J., Banejad H., Afkhami A., Olyaie E., Lashgari S. and Dashti R., Synthesis of Calcium Peroxide Nanoparticles as an Innovative Reagent for Insitu Chemical Oxidation. Journal of Hazardous Materials, (2011), 192(3), 1437-1440
Rabbani M. M., Ahmed I. and Park S. J., Application of Nanotechnology to Remediate Contaminated Soils. Environmental Remediation Technologies for Metal-Contaminated Soils, Springer, Tokyo (2016) 219-229
Srivastav A., Yadav K. K., Yadav S., Gupta N., Singh J. K., Katiyar R., and Kumar V., Nano-phytoremediation of Pollutants from Contaminated Soil Environment: Current Scenario and Future Prospects. In Phytoremediation, (2018), 383-401. Springer, Cham
Qian Y., Qin C., Chen M. and Lin S., Nanotechnology in Soil Remediation−Applications vs. Implications, Ecotoxicology and Environmental Safety, (2020), 201, 110815
Ditta A., How helpful is Nanotechnology in Agriculture? Adv. Nat. Sci. Nanosci. Nanotechnol. (2012), 3:33002
Cross KM, Lu Y, Zheng T, Zhan J, McPherson G, John V. Water Decontamination using Iron and Iron oxide Nanoparticles. Nanotechnology Applications for Clean Water. Norwich, NY, William Andrew Inc., 2014, 347-364
Dave S. and Sharma R., Use of Nanoparticles in Water Treatment: A Review. Int. Res. J. Environment Sci. (2015), 4(10), 103-106
Dasgupta N., Ranjan S. and Ramalingam C., Applications of Nanotechnology in Agriculture and Water Quality Management, Environ Chem Lett (2017), 15, 591-605
Xue X. Y., Cheng R., Shi L., Ma Z., and Zheng X., Nanomaterials for Water Pollution Monitoring and Remediation. Environmental Chemistry Letters, (2017), 15(1), 23-27
Rajput M.S., Mishra B. N., Biodegradation of Pyridine Raffinate using Bacterial Laccase Isolated from Garden Soil. Biocatalysis and Agricultural Biotechnology. (2019), 17, 32-35
Chibuike G. U. and Obiora S. C. (2014) Heavy Metal Polluted Soils: Effect on Plants and Bioremediation Methods. Applied and Environmental Soil Science, 2014, 752708, 1- 12
Kaur S., and Roy A. Bioremediation of Heavy Metals from Wastewater using Nanomaterials. Environment, Development and Sustainability, (2020), 1-24
Dixit R., Malaviya D., Pandiyan K., Singh U. B., Sahu A., Shukla R., Singh B. P., Rai J. P., Sharma P. K., Lade H and Paul, D. Bioremediation of heavy metals from soil and aquatic environment: an overview of principles and criteria of fundamental processes. Sustainability, (2015), 7(2), 2189-2212
Rajendran P. and Gunasekaran P., Nanotechnology for Bioremediation of Heavy Metals. Environmental Bioremediation Technologies, Springer, Berlin, (2007a) 211-221
Rizwan M., Singh M., Mitra C. K., and Morve R. K., Ecofriendly Application of Nanomaterials: Nanobioremediation. Journal of Nanoparticles, 2014, 431787
Jagdale S., Hable A., and Chabukswar A., Nanobiotechnology for Bioremediation: Recent Trends. Biostimulation Remediation Technologies for Groundwater Contaminants, (2018), 259-284
Kumar S. R. and Gopinath P., Nano-Bioremediation Applications of Nanotechnology for Bioremediation. Remediation of Heavy Metals in the Environment, (2016) 27-48
Xu P., Zeng G. M., Huang D. L., Feng C. L., Hu S., Zhao M. H., Lai C., Wei Z., Huang C., Xie G. X. and Liu Z. F. Use of Iron oxide Nanomaterials in Wastewater Treatment: A Review. Sci Total Environ. (2012), 1(424), 1-10
Stevenson L. M., Adeleye A. S., Su Y., Zhang Y., Keller A. A., and Nisbet, R. M., Remediation of Cadmium Toxicity by Sulfidized Nano-iron: The Importance of Organic Material. ACS Nano, (2017), 11(10), 10558-10567
Şahutoğlu A. S. and Akgül C. One-phase Synthesis of Single Enzyme Nanoparticles (SENs) of Trametes versicolorLaccase by In situ Acrylamide Polymerisation. Biocatalysis and Biotransformation, (2020), 38:1, 64-74
Svenson S., and Tomalia, D. A., Dendrimers in Biomedical Applications—Reflections on the Field. Advanced Drug Delivery Reviews, (2012), 64, 102-115
Khin M. M., Nair A. S., Babu V. J., Murugan R., and Ramakrishna S., A Review on Nanomaterials for Environmental Remediation. Energy & Environmental Science, (2012), 5(8), 8075-8109
Undre S. B., Singh M. and Kale R. K., Interaction Behaviour of Trimesoyl Chloride Derived 1st Tier Dendrimers Determined with Structural and Physicochemical Properties Required for Drug Designing. J Mol Liq. (2013a), 182, 106-120
Undre S. B., Singh M., Kale R. K. and Rizwan M., Silibinin Binding and Release Activities Moderated by Interstices of Trimesoyl, Tridimethyl, and Tridiethyl Malonate first-tier Dendrimers. J Appl Polymer Sci (2013b), (130), 3537-3554
Das S., Chakraborty J., Chatterjee S., and Kumar, H., Prospects of Biosynthesized Nanomaterials for the Remediation of Organic and Inorganic Environmental Contaminants. Environmental Science: Nano, (2018), 5(12), 2784-2808
Irshad M. A., Nawaz R., Zia ur Rehman M., Adrees M., Rizwan M., Ali S., Ahmad S., Tasleem S., Synthesis, Characterization and Advanced Sustainable Applications of Titanium Dioxide Nanoparticles: A Review. Ecotoxicology and Environmental Safety, (2021), (212), 111978
Liu W. J., Qian T. T., and Jiang, H., Bimetallic Fe Nanoparticles: Recent Advances in Synthesis and Application in Catalytic Elimination of Environmental Pollutants. Chemical Engineering Journal, 236, 448-463
Bhandari G., Environmental Nanotechnology: Applications of Nanoparticles for Bioremediation. Approaches in Bioremediation, Nanotechnology in the Life Sciences, Springer, Cham. (2018), 301-315
Ukaogo P. O., Ewuzie U. and Onwuka C. V., Environmental Pollution: Causes, Effects and the Remedies. Microorganisms for Sustainable Environment and Health, Elsevier (2020)
Wahab R., Khan F., Kaushik N., Musarrat J. and Al-Khedhairy A. A., Photocatalytic TMO-NMs Adsorbent: Temperature-Time dependent Safranine Degradation, Sorption Study Validated under Optimized Effective Equilibrium Models Parameter with Standardized Statistical Analysis. Sci Rep (2017) 7, 42509
Balbi T., Caratto V., Fabbri R., Camisassi G., Villa S., Ferretti M. and Canesia L., Photocatalytic Fe-doped n-TiO2: From synthesis to Utilization of in vitro Cell Models for Screening Human and Environmental Nanosafety. Resource-Efficient Technologies (2017), 3(2), 158-165
Li M. and Mallat L., Health Impacts of Air Pollution, SCOR (2018), 1-42
Schraufnagel D. E., Balmes J. R., Cowl C. T., De Matteis S., Jung S. H., Mortimer K. and Wuebbles D. J., Air Pollution and Non-communicable Diseases: A Review by the Forum of International Respiratory Societies’ Environmental Committee, Part 2: Air Pollution and Organ Systems. Chest, (2019), 155(2) 417-426
Tran V. V., Park D. and Lee Y. C., Indoor Air Pollution, related Human Diseases, and Recent Trends in the Control and Improvement of Indoor Air Quality, International Journal of Environmental Research and Public Health, (2020), 17(8), 2927
Raaschou-Nielsen O., Beelen R., Wang M., Hoek G., Andersen Z. J., Hoffmann B. and Vineis P., Particulate Matter Air Pollution Components and Risk for Lung Cancer. Environment International, (2016), 87, 66-73
Bhawana P. and Fulekar M., Nanotechnology: Remediation Technologies to Clean up the Environmental Pollutants. Res J Chem Sci ISSN, 2231, (2012), 606X,
Uzoigwe J. C., Prum T., Bresnahan E. and Garelnabi M., The Emerging Role of Outdoor and Indoor Air Pollution in Cardiovascular Disease. North American Journal of Medical Sciences, (2013), 5(8), 445
Folli A. (2011). Photocatalytic Cementitious Materials Containing Highly Active Nanosized TiO2: Mechanisms of Air Pollution Remediation and the Effect of the Alkaline Environment. NORDIC Concr Res, (2011), 44, 11-24
Tosco T., Papini M. P., Viggi C. C., and Sethi R., Nanoscale Zerovalent Iron Particles for Groundwater Remediation: A Review. J. Clean. Prod. (2014), 1, 10-21
Yan W., Lien H. L., Koel B. E. and Zhang W. X., Iron Nanoparticles for Environmental Clean-up: Recent Developments and Future Outlook. Environ. Sci. Process & Impacts (2013) 63-77
Reddy K. R., Nanotechnology for Site Remediation: Dehalogenation of Organic Pollutants in Soils and Groundwater by Nanoscale Iron Particles. Proceedings of the 6th International Congress on Environmental Geotecnics, New Delhi, India (2010), 1,163e180
Kharangate-Lad A., and D’Souza N. C. Remediation of Toxic Environmental Pollutants Using Nanoparticles and Integrated Nano-Bio Systems. Rhizobiont in Bioremediation of Hazardous Waste. Springer, Singapore, (2021), 443-482
Berge N. D. and Ramsburg C. A., Iron-mediated Trichloroethene Reduction within Non-aqueous Phase Liquid. J. Contam, Hydrol. (2010), 118 105e116
Liu Z. G. and Zhang F. S., Nano-zerovalent Iron Contained Porous Carbons Developed from Waste Biomass for the Adsorption and Dechlorination of PCBs. Bioresour. Technol. (2010), 101, 2562-2564
Reddy K. R., Khodadoust A. P. and Darko-Kagya K., Transport and Reactivity of Lactate-modified Nanoscale Iron Particles in PCP-contaminated Soils. J. Hazard, Toxic, Radioact. Waste, (2012), 16, 68-74
Klaine S. J., Koelmans A. A., Horne N., Carley S., Handy R. D., Kapustka L., Nowack B., von der Kammer F., Paradigms to Assess the Environmental Impact of Manufactured Nanomaterials. Environ Toxicol Chem. (2012), 31(1):3-14
Lee C., Kim J. Y., Lee W. I., Nelson K. L., Yoon J. and Sedlak D. L., Bactericidal Effect of Zero-valent Iron Nanoparticles on Escherichia coli. Environ. Sci. Technol., (2008) 42, 4927-4933
Mueller N.C. and Nowack B., Application of Nanoscale Zero Valent Iron (NZVI) for Groundwater Remediation in Europe. Environ. Sci. Pollut. Res. (2012), 19, 550-558
Wilkin R. T., Lee T. R., Sexton M. R., Acree S. D., Puls R. W., Blowes D. W., Kalinowski C., Tilton J. M. and Woods L. L. Geochemical and Isotope Study of Trichloroethene Degradation in a Zero-Valent Iron Permeable Reactive Barrier: A Twenty-Two-Year Performance Evaluation. Environmental Science & Technology, (2019, )53(1), 296-306
Mirzajani F., Ghassempour A., Aliahmadi A., and Esmaeili M. A., Antibacterial Effect of Silver Nanoparticles on Staphylococcus aureus. Research in Microbiology, (2011), 162(5), 542-549
Lara H. H., Garza-Treviño E. N., Ixtepan-Turrent L., and Singh D. K., Silver Nanoparticles are Broad-spectrum Bactericidal and Virucidal compounds. Journal of Nanobiotechnology, (2011) 9(1), 1-8
Swain P., Nayak S. K., Sasmal A., Behera T., Barik S. K., Swain S. K., Mishra S. S., Sen A. K., Das J. K. and Jayasankar P. Antimicrobial Activity of Metal Based Nanoparticles against Microbes Associated with Diseases in Aquaculture. World Journal of Microbiology and Biotechnology, (2014), 30(9), 2491-2502
Schacht V. J., Neumann L. V., Sandhi S. K., Chen L., Henning T., Klar P. J., Theophel K., Schnell S., and Bunge M., Effects of Silver Nanoparticles on Microbial Growth Dynamics. Journal of Applied Microbiology, (2013), 114(1), 25-35
Rudramurthy G. R., Swamy M. K., Sinniah U. R., and Ghasemzadeh A., Nanoparticles: Alternatives against Drug-resistant Pathogenic Microbes. Molecules, (2016), 21(7), 836
Griegar K. D., Fjordboge A., Hartmann N. B., Eriksson E., Bjerg P. L., Baun A., Environmental Benefits and Risks of Zerovalent Iron Nanoparticles, (nZVI) for in situ Remediation: Risk Mitigation or Trade-off? J. Contam. Hydrol (2010) 118, 165-183
Greulich C., Braun D., Peetsch A., Diendorf J., Siebers B., Epple M., and Köller M., The Toxic Effect of Silver Ions and Silver Nanoparticles towards Bacteria and Human Cells occurs in the Same Concentration Range. RSC advances, (2012), 2(17), 6981-6987
Lampron K. J., Cha D. K., and Chiu P., Microbial Reductive Dehalogenation of Chlorinated Ethenes Coupled with the Corrosion of Fe°. Hazardous and Industrial Waste Proceedings, 30th Mid-Atlantic Conference. CRC Press, 2014, 448
Zhang K., Yang W., Liu Y., Zhang K., Chen Y. and Yin X., Laccase Immobilized on Chitosan-coated Fe3O4 Nanoparticles as Reusable Biocatalyst for Degradation of Chlorophenol. J. Mol.Struct. (2020), 128769
Dixit M., Liu H., Luo J. and Shukla P., Effluents Detoxification from Pulp and Paper Industry using Microbial Engineering and Advanced Oxidation Techniques. J. Hazard. Mater (2020), 122998