Abstraction: Nanotechnology is an emerging scientific discipline that has shown promise in humanising assorted life aspects runing from medical specialty to industrial stuffs. One such application of nanotechnology is for the redress of contaminated groundwater. Groundwater pollution is going a major job non merely for the underdeveloped states like India but besides for most of the developed states of the universe. In this regard the application of nanotechnology may turn out a blessing to the world by supplying an beforehand manner for groundwater intervention. The position of groundwater quality, basic thought of nanotechnology for redress and its practical pertinence, ongoing undertakings and future range in India has been reviewed through this article.
Keywords: Nanotechnology, groundwater, organochlorine, organophosphorus.
With the promotion of industrialisation, agricultural and urban activities the degrees of groundwater pollution have increased many creases in the last few decennaries. In India, this has led to the addition in the concentration of many organic and inorganic pollutants much more above the allowable bounds of imbibing H2O criterions [ 1 ] . A huge bulk of groundwater quality jobs are caused by taint, overuse, or combination of the two. Dirt and groundwater quality is easy but certainly worsening everyplace. Direct dumping of untreated wastewaters into the Wellss is going one of the major causes of groundwater pollution. Furthermore extended usage of pesticides in India has besides led to the addition in the pollutants concentrations in groundwaters [ 2 ] . The most harmful compounds that are happening their ways in groundwaters through assorted illegal industrial and agricultural activities includes assorted organochlorine & A ; organophosphorous pesticides, heavy metals and other carcinogenic compounds.
The application of nanotechnology for the redress of contaminations may give assuring consequences in future. The hunt for new and advanced stuffs is an of import undertaking of modern-day research in the environmental protection. In recent old ages, a great trade of attendings has been focused onto the application of nanostructured stuffs as adsorbents or accelerators to take toxic and harmful substances from effluent and air [ 3, 4 ] . Reactive nanoparticles appear to be utile in rectifying groundwater and therefore may turn out utile in taking pesticides and weedkillers in the environment [ 5 ] . Nanoparticles besides may supply a more efficient and controlled delivery/release method for the application of pesticides and fertilisers. Increasingly broad practical application of Fe nanoparticles has been achieved in assorted risky waste site redresss. Since 1996, after it was proposed for the first clip, the Fe nanoparticle engineering is at a important phase of its developmental procedure. Important research inventions have been accomplished in footings of man-made methods, surface belongings amendments, and augmentation for field bringing and reactions. It has been demonstrated by assorted research lab surveies that iron nanoparticles are valuable for the intervention of a broad array of common groundwater contaminations such as chlorinated organic compounds like pesticides and polychlorinated biphenyls ( PCBs ) , organic dyes and assorted other inorganic compounds.
Status of groundwater taint in India
Man ‘s activity at land surface, accidentally by agribusiness, domestic and industrial wastewaters, out of the blue by sub-surface or surface disposal of sewerage and industrial wastes has led to inauspicious effects on dirt and groundwater quality. Since 1954 the dominant group of pesticides called organochlorine insect powders have been extensively used in India for agribusiness every bit good as in public wellness sector [ 6 ] . Almost every organochlorine which includes ill-famed pesticides like DDT, endosulfan, dioxin, HCH ( hexachlorocyclohexane ) and aldrin has been found to do some environmental or human wellness jeopardy. The usage of organochlorines which are banned or restricted in most developed states are still being used in this state. As a consequence of the effects of intense agricultural activities, the surveies conducted on the taint of dirt and groundwater quality of Roorkee country, territory Haridwar, India indicated the presence of 17 organochlorine and 9 organophosphorous pesticides which were found to be much above the allowable bounds of Indian imbibing H2O criterions [ 2 ] . Their accretion in low concentration in the organic structure fat of mammals may present wellness jobs in long tally [ 7 ] and it has been reported that most Indians accumulate about 26 milligrams DDT in their organic structure through nutrient points. The continuity of toxic pesticides in dirt and H2O adversely affected dirt wellness [ 8 ] , aquatic life and quality of imbibing H2O [ 9 ] . Cypermethrin residues in groundwater samples from Guatemala used for human ingestion exceeded safe degrees of 0.5 I?gla?’1 in most of the instances. Contamination of dirt and groundwater has been reported globally [ 10 – 14 ] . The concentration of assorted organochlorine pesticides like endosulphan, DDT and lindane in the groundwater samples of Hyderabad metropolis, India has been found to be of the order of 0.5 to 1.3 AµgL-1 [ 15 ] . In the bosom of India ‘s green revolution belt, local husbandmans extensively use several banned and restricted pesticides. When 50 samples of dirt, groundwater and veggies were collected from assorted locations of the territory Meerut, India and analyzed for pesticides taint ; the presence of extended sums of pesticides was reflected both in the dirt surface every bit good as in groundwater organic structures [ 16 ] .
Land is non merely contaminated by organic pesticides but besides the presence of immense concentrations of inorganic toxic metals and non metals have been reported. Among them the job of arsenous anhydride is most prevailing. Arsenic taint in groundwater and attendant human agony in West Bengal, India has been a major job which was foremost reported in December 1983 when 63 arsenic patients from 3 small towns were identified. At present 3000 small towns are arsenic affected. Harmonizing to the WHO recommended value of arsenous anhydride in imbibing H2O is about 10 mg/L which is much high so the allowable bounds off imbibing H2O criterions. In a survey, 95,000 people were clinically examined from arsenic affected territories of West Bengal and 10,100 people ( 9.4 % including 2 % kids ) were registered with arsenical tegument lesions. Studies reveal the presence of elevated degree of inorganic arsenous anhydride in nutrient concatenation and in those consumer merchandises where groundwater is used in affected small towns [ 17 ] . In position of increasing groundwater pollution in the modern universe there is an huge demand to modify the bing engineering for their redress which non merely works on little graduated table but can be employed on a big graduated table in nature to acquire the consequences in majority. Application of rearward osmosis and other H2O purification systems works on a confined graduated table and their applications are limited to the user merely. In order to look in a broader manner, nanotechnology provides a really recent and better manner to rectify dirt and groundwater in nature.
Nanotechnology an emerging technique
The solutions to most of the groundwater quality jobs are hard to observe and hard to decide moreover they are rather expensive, boring and non ever efficient. In the field of environmental protection one of the of import undertaking of modern research is to happen some new and advanced stuffs thereof. In recent old ages, a great trade of attending has been focused onto the pertinence of nanostructured stuffs as adsorbents or accelerators in order to take toxic and harmful substances from air and effluent [ 3, 18 ] . ‘Nanotechnologies are the word picture, design, production and application of constructions, devices and systems by commanding form and size at nanometer graduated table ‘ . Reactive Fe nanoparticles were found to be utile in rectifying groundwater and therefore besides may turn out utile in taking pesticides and weedkillers from the environment [ 5 ] .
In the field of nanotechnology the production of nanomaterials and merchandises incorporating them are quickly developing Fieldss which provides many chances for new invention. For the suspension of pollution production the application of nanotechnology is merely get downing to be explored which could dramatically catalyse the most extremist alterations in the field of environment [ 19, 20 ] . The major factor which defines the capableness of nanoparticles as an highly various redress tool includes their really little atom sizes ( 1-100 nanometer ) in comparing to a typical bacterial cell which has a diameter on the order of 1 Aµm ( 1000 nanometer ) . Hence nanoparticles can be transported efficaciously by the groundwater flow. Despite their small letter position, nanoscale atoms may keep the possible to cost-effectively reference some of the challenges of site redress [ 19, 21, 22 ] . Furthermore the nanoparticles can besides stay in suspension for ample periods of clip in order to establish an in situ intervention zone. As a consequence, nanoparticles can be anchored onto a solid matrix such as activated C and/or zeolite for improved H2O, effluent, or gaseous procedure watercourse intervention.
Fig 1. Practical application of permeable reactive barrier for land H2O redress.
Over the past few old ages, the field of redress has evolved continuously while developing and following new engineerings so as to better the redress procedure. Among those new engineerings the “ pump and dainty ” [ 23 ] is considered to be one of the most constituted systems. The basic rule involved in the pump and dainty systems is the expulsion of contaminated groundwater from land downstream of the taint site and so handling it before returning it to the land. However there are few drawbacks associated with this engineering ; for illustration the engineering is boring and expensive to run and keep while necessitating continual energy input [ 23 ] . In the early 1990s with the scrutiny for the cut downing capablenesss of metallic substances such as zero valent Fe ( ZVI ) to handle a broad scope of contaminations in risky effluent, the most common employment of ZVI has been established in the signifier of permeable reactive barriers ( PRBs ) ( Fig 1 ) designed to disrupt plumes in the subsurface and accordingly rectifying them.
In 1994, PRBs were foremost installed at the field graduated table to offer a placeholder for the more constituted pump and dainty systems. This engineering was restricted merely to the shoal plumes up to a deepness of 50 foots due to their little deepness installing capablenesss. Furthermore to forestall contaminations from besieging the PRB, plumes had to be carefully differentiated and demarcated [ 24 ] . Problems occur from a lessening in Fe responsiveness caused by the precipitation of metal hydrated oxides and metal carbonates onto the surface of the Fe [ 25 ] . The low responsiveness of ZVI toward lightly chlorinated compounds resulted in the formation and finding of risky by-products. Merely as PRBs were designed to supply a better option to the pump and dainty engineering, new engineerings are now available to vie with PRBs. Iron nanoparticles and their derived functions provide a possible for more effective and cheap replacement to many remedial engineerings [ 26 ] . The atom little size of the Fe nanoparticles ( 1-100 nanometer ) facilitates a really high degree of remedial flexibleness.
The usage of nano ZVI, bimetallistic nanoparticles, and emulsified zerovalent nanoparticle forms the whole sole for both dirt and groundwater redress. Besides these the most latest research besides indicated that C nanotubes may besides turn out to be a most effectual tool in rectifying contaminated Waterss [ 27 ] . The most basic signifier of the nano Fe engineering encompasses nano ZVI and reactive nanoscale Fe merchandise ( RNIP ) [ 26, 28 ] . The practical pertinence of these nano zero valent Fe ( Fe0 ) particles lies in the fact to acquire oxidized into +2 and +3 oxidization provinces thereby cut downing other organic every bit good as inorganic drosss. Metallic Fe ( Fe0 ) serves efficaciously as an negatron giver:
Fe0 a†’ Fe2+ + 2e- — — — — — — — – [ 1 ]
Chlorinated hydrocarbons on the other manus accept the negatrons and undergo reductive dechlorination [ 29, 30 ] :
RCl + H+ + 2ea?’ a†’ RH + Cla?’ — — — — — — — — — [ 2 ]
Fig 2. Core shell theoretical account of nano zerovalent Fe demoing assorted chemical mechanisms.
From a thermodynamic position, the yoke of the reactions [ 1 ] and [ 2 ] is frequently energetically extremely favourable:
RCl + Fe0 + H+ a†’ RH + Fe2+ + Cla?’ — — — — — [ 3 ]
The standard decrease potency ( Ea-¦ ) of ZVI ( Fe2+/Fe ) is a?’0.44 V, which is lower than many organic compounds like chlorinated hydrocarbons and metals such as Pb, Cd, Ni, and Cr hence these organic compounds and metals are therefore prone to decrease by ZVI nanoparticles. Over the last few old ages, nano ZVI has been extensively used in the debasement of toxic and risky organic pollutants like lindane and astrazine [ 31 ] , pentachlorophenol [ 32 ] , 4,4′-dinitrostilbene-2,2′-disulfonic acid [ 33 ] etc. The survey for the reductive capacity of zero valent metals have focused non merely on halogenated ( chlorinated ) hydrocarbons e.g. DDT, DDD, DDE ) [ 34 ] , but besides on taint of H2O due to nitrate [ 35 ] , arsenic [ 36, 37 ] , Cr ( VI ) and Pb ( II ) [ 38, 39 ] , s-triazines [ 40 ] , RDX [ 41, 42 ] and perchlorate [ 43 ] .
Several recent surveies provided cherished attack into cardinal nano ZVI belongingss associated with the possible to transform metal ions such as Cd, Ni, Zn, As, Cr, Ag, and Pb, every bit good as ill-famed inorganic anions like perchlorate and nitrate [ 44 – 48 ] . ZVI nanoparticles have been found to posses comparatively higher capacity than conventional sorptive media and farinaceous Fe atoms for the remotion and/or decrease of these inorganic ions. Furthermore several surveies have predicted that bimetallistic Fe nanoparticles ( Pd-Fe, Pt-Fe, Ni-Fe, Ag-Fe ) can accomplish comparatively higher debasement rates and prevent or cut down the formation of toxic by-products [ 26, 49 ] . Bimetallic Fe nanoparticles involve a 2nd and frequently less reactive metal such as Pd, Ni, Pt, or Ag along with Fe nanoparticles. As with the add-on of metal accelerators to nano ZVI atoms, the formation of emulsified zero valent Fe ( EZVI ) besides represents an sweetening to the bing nano ZVI engineering. Emulsion droplets can be created utilizing a nutrient class wetting agent, biodegradable vegetable oil, H2O, and nano ZVI, where a surfactant-stabilized oil-liquid membrane signifiers around the Fe atoms in H2O [ 50 ] .
With regard to redress of environmental contaminations, the scope of nanotechnology applications mirrors the spectrum of ‘nonnano ‘ schemes for contaminant redress. Two of the major differentiations that define types of conventional redress engineerings besides apply to nanotechnologies for redress: in situ versus ex situ. In situ engineerings involve intervention of contaminations in topographic point, whereas ex situ refers to intervention after taking the contaminated stuff to a more convenient location ( e.g. pumping contaminated groundwater to the surface and intervention in aboveground reactors ) . Assorted types of nanostructured adsorbants are most likely to be applied antique situ, where they can be recovered with the concentrated risky stuff that they adsorb. Atoms of Fe can be used in antique situ slurry reactors to handle dirt, sediment [ 51 ] , and solid waste. In instances of H2O and/or effluent intervention, grounding nanoparticles onto a solid matrix, such as activated C, can turn out highly effectual. On the other manus the injection of nano Fe into the land represents the most common deployment of this engineering therefore far. Overall the procedure provides a figure of remedial benefits. In comparing with PRBs, nanoparticle injection allows redress at greater deepnesss and in countries unapproachable by PRBs ( i.e. land covered by a edifice ) . Most significantly, this technique facilitates beginning zone redress, a clear benefit for site killing. Nanoparticles can be assorted with H2O to organize slurry that can be injected utilizing force per unit area or gravitation into a contaminated plume. Once injected, the atoms remain in suspension, organizing a intervention zone. Nano scale Fe merchandise ( NIP ) injections merely work for aqueous stage beginning zone intervention and while they can heighten heavy not aqueous stage liquids ( DNAPL ) disintegration, NIP injections can non straight treat DNAPL. Emulsified zero valent Fe offers a solution to this job in the signifier of an external oil membrane [ 52 ] .
Since 2000, several in situ field presentations using the usage of the nano ZVI engineering have been conducted in contaminated groundwater site, including the first field pilot trial [ 53 ] in Trenton, New Jersey, from May 8 to July 18, 2000. Numerous pilot trials undertaken by Golder Associates ( between 2003 and 2005 ) in North America ( United States and Canada ) , Europe, and Australia have been used to roll up a big sum of field informations that was interpreted together to set up the first cross comparing between assorted field applications. The engagement of Fe nanoparticles for many academic and commercial field graduated table trials are in advancement or have reached completion along with many more sites yet to be scheduled for assorted other field surveies. Some of them are as follows: Naval air technology station, Lakehurst, New Jersey ; Naval air station, Jacksonville, Florida [ 53 ] ; Public service electric and gas company ( PSE & A ; G ) , Klockner route site, New Jersey etc. sites for the redress of groundwater in shallow aquifer against assorted chlorinated hydrocarbons have already been completed by the injection of bimetallistic Fe nano atoms in 2005. In add-on to this many other nanotechnology applications for effluent intervention and site redress are presently in the research and development phases.
There is no uncertainty in stating that the quality of groundwater is diminishing twenty-four hours by twenty-four hours and there is an huge demand for following a new and advanced technique for the redress of groundwater as a whole. Indian scientists are besides actively working on the synthesis of assorted types of nano atoms. It has been reported that halocarbons undergo catalytic devastation and mineralization with Ag and gold nanoparticles in solution forming metal halides and formless C [ 54 ] . Jain et al. , [ 55 ] suggested that Ag nanoparticles coated polyurethane froth works as an antibacterial H2O filter which can be extensively used for practical intents. Besides Gold and Ag nanoparticles have been used in the sensing and extraction of endosulfan, an of import pesticide in the underdeveloped universe, from H2O solutions in sub ppm concentrations proposing possible applications [ 54 ] . Even a porous thin movie of TiO2 has been found to be extremely efficient for the debasement of naphthalene and anthracene. The rate invariables are high and the reactions largely follow the first order dynamicss [ 56 ] . A squad of research workers from IIT Chennai has developed nanoparticles that can get rid of organochlorine pesticides. The quantitative remotion of chlorpyrifos and Malathion have been efficaciously achieved by gold and Ag nanoparticles in solution province every bit good as in supported signifier over activated aluminum oxide. It has been observed that complete remotion of these pesticides occurs when contaminated H2O is passed over nanoparticles supported on aluminum oxide [ 57 ] . Thus nanotechnology has been able to demo promising consequences in this manner. In India, there is a great demand for following such a technique to rectify groundwater and a batch of farther range in research and development is still there to be worked on.