Effect of toxic heavy metals on ecosystem

R. A. Bobdey 						R. U. Khope
Dept of Chemistry					 Dept of Chemistry
APJ Abdul Kalam University, 				Indore Shivaji Science College,
Indore, MP, India						 Nagpur, MH, India
radheshrab@gmail.com					khopeyru@gmail.com 

I. ABSTRACT:

Surface water has been exploited for numerous functions by way of human beings. It serves as a source of potable water after treatment and as a source of domestic water without treatment especially in rural areas in growing countries. It's been used for irrigation functions by farmers, and fishermen get their career from harvesting fish in so many freshwater assets. It is used for swimming and also serves as centres for visitor enchantment. Surface water, therefore, needs to be protected from pollution. Many human beings in growing countries of the sector still depend upon untreated surface water as their fundamental supply of home water. This is so due to the fact that there's an incessant supply of potable water or insufficient water delivery systems. This hassle is exacerbated in rural regions. Surface water is increasingly beneath undue stress because of population increase and multiplied industrialization. Trace metals in aquatic and soil frameworks exist in various different dissolvable and particulate structures that influence the impact of the metals on these biological systems. Proper techniques for inspecting and investigation are expected to precisely decide the low absorptions present. Despite the fact that appraisal of metals in numerous administrative projects depends on information for absolute metal fixations, such qualities seldom relate with impacts. Thusly, different means are required for the expectation of chance.

Keywords: heavy metals, toxic metals, pollution, GAC, activated carbon, lead.

II. INTRODUCTION

Pesticides, fertilizers, papermaking, and metal mining are just a few of the fast-growing industries that have continuously discharged a variety of pollutants directly into the aquatic ecosystem through wastewater. Even at very low concentrations, these pollutants pose a significant threat to aquatic organisms because they contain a lot of organic and inorganic chemicals, as well as harmful heavy metals like Ni, Co, Al, Pb, Cr, Cd, Hg, and Zn. Metal electroplating, mining, battery manufacturing, petroleum refinery, and paint manufacturing are all sources of these metals, particularly in developing nations. Agricultural wastes, domestic and sewage wastes are likewise carelessly
released into the water bodies. Be that as it may, water pollution by heavy metals is more
articulated than other contamination particularly when they are presented to the natural
environment.

III. EFFECT OF TOXIC METALS ON ECOSYSTEM

Water is the fundamental justification for life on Earth which persistently courses through quite possibly of Earth's most remarkable framework: the water cycle. Water streams endlessly between the sea and land. Earth's water is limited, implying that how much water is in, on, or above our planet doesn't rise or reduce.  
Freshwater is vital for our planet. Fresh water is crucial for individuals and natural life i.e., flora and fauna. It needs cautious administration since there's no other way to get around with the fact of water being limited. Freshwater sources include wetlands, lakes, rivers, streams and underground water. They naturally store and clean the water that is significant for individuals and natural life. 
Sound freshwater sources supply water for cropland, drinking, industrial use, energy formation and transportation. They additionally help to forestall disintegration, discard waste and give normal security from flooding. Be that as it may, we've been reckless with this fundamental asset. Freshwater sources have been blundered, resulting to contamination, drying streams and harmed territories. Somewhat recently we've lost so many of the world's wetlands and their natural life. Contaminated water has had severe health issues and economical costs.
Eutrophication-causing substances are rigorous in the wetlands with low and sometimes even high concentrations, this is because of the great typical organic index of the particular water body. Heavy metals are dumped at the base close to the central point of the wetlands. The complete potential environmental ecological risk index is increasing day by day, though Cd and Hg are the primary elements of heavy metal contamination. As a result, it is important to prevent and treat contaminated residues to prevent secondary contamination also, the scattering of both organic compounds and heavy metals are for the most part compelled by regular circumstances.
Water pollution with hazardous metals is one of the fundamental worries for human health in addition to the concern for environmental wellbeing. the discharge of heavy metals into water resources is extreme. Pollution troubles can also affect the quality of water supply. Commercial wastewaters from many factories incorporate heavy metals including copper, zinc, cadmium, lead, nickel, and chromium and many others which damage environment to big proportions. Increasing concentrations of those metals inside the water constitute an excessive health chance mainly because of their non-degradability and toxicity. The addition of undesirable material into the environment due to direct or indirect human activities is called pollution. The factors which propose pollution is known as pollutant. Pollutants can be chemical, physical or organic substance launched into the environment that's extremely dangerous to human beings and different living organisms.
The huge development of industries consisting of metallic mining operations, fertilizers, paper industries and pesticides have continuously been discharging diversified form of pollutants through wastewater immediately into aquatic ecosystem possessing a terrific hazard to aquatic organisms even at very low concentration which includes lot of chemical substances, each natural and inorganic, coloured materials, dangerous heavy metals like Zn, Ni, Co, Cr, Al, Cd, Pb, Hg, etc. A lot of these metals originate from sports of metallic electroplating, mining, battery manufacturing, petroleum refining and paint production in particular in developing countries. Agricultural wastes, home and sewage wastes are also continuously discharged into the water bodies. But water contaminations happening by heavy metals are extra severe specially while they're uncovered to the environment.
Almost all heavy metal elements are highly toxic when their concentration exceeds the tolerable limit in the ecosystem. High concentration of heavy metals may accumulate in the parts human body through water and food chain causing severe health problems if the metals exceed the permitted concentration. These metals are not biodegradable and accumulate in food chain. These are highly toxic and many are carcinogenic. They affect our ecosystem due to their lethal effects.

IV. POLLUTION AND THEIR TYPES:

Nowadays water pollution raises a great concern all over the world since water constitutes a basic necessity in life and thus, is essential to all living things. The presence of undesirable substance in any segment of environment primarily due to human activity discharging by products, waste products or harmful secondary products which are harmful to man and other organisms is called pollution.

There are different types of pollution present in ecosystem which may be classified as follows:

A.	Air pollution
B.	Radiation pollution
C.	Soil pollution
D.	Marine pollution
E.	Noise pollution
F.	Thermal pollution
G.	Water pollution

A.	Air Pollution

Hazardous substances occurring in air in solid, liquid or gaseous state, along with noise and radioactive radiation within the ecosystem in such extent that it can be extremely injurious to human beings or other living organisms is known as air pollutants. It is brought on because of the increasing use of fossil fuels in power plant, industries, transportation, mining and production of homes. pollutants are of two types (l) solid suspended particles, and (2) gaseous pollution like carbon dioxide (CO2), NOx etc.
Consistent with World health organisation (WHO) air pollution is defined as contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere. These rise up due to the activities done by human such as in manufacturing goods, producing energy and discharging of wastes into surrounding that can have an effect on plant metabolism. 
Air pollutant are of two types –
a) Main pollutants which originate from the source and immediately pollute the ecosystem eg. SO2, NO2, different Pesticides, etc.  
b) Subordinate pollutants which stand up from main pollutants with the aid of chemical reaction. a few essential air pollutants are: SO2 and black smoke which are the conventional pollutants standing up through use of coal and oil for home use and electricity generation. Lead is emitted in the shape of fume or dust in air with the aid of burning petrol, steel works, coal combustion, etc. Carbon dioxide is formed by the unfinished combustion of carbon-based fuels.

B.	Radiation Pollution:

The radiation pollution can be described as the physical pollution to the living organisms and their environment due to release of radioactive substances into the environment during nuclear explosions and testing of nuclear weapon manufacturing and decommissioning, mining of radioactive ores, coping with and disposal of radioactive waste, and injuries at nuclear strength plants. Nuclear tests are carried out to decide the effectiveness, yield, and explosive functionality of nuclear weapons. the share of radioactive pollutants is 15% of the whole power of the explosion. Radioactive pollution of water, water resources, and air space is the end result of radioactive fallout from the cloud of a nuclear explosion. Radionuclides are the primary resources of pollutants; they emit beta debris and gamma rays, radioactive substances.

C.	Soil Pollution:

Addition of materials which adversely affect the soil quality or its fertility is called soil pollution. The polluted water can also be the reason to pollute the soil. Solid waste such as mixture of plastics, clothes, glass, metal, organic matter, sewage, sewage sludge, building debris, generated from houses, industrial and commercial institutions cause soil to be polluted. Fly ash, iron and steel slag, medical and commercial wastes disposed on land are essential sources of soil pollution. Further, fertilizers and insecticides from agricultural use, which attain the soil as run-off and land filling by municipal waste are developing reason of soil pollution. Acid rain and dry deposition of pollution on land additionally make contributions to soil pollutants.
Soil pollution in other words, is the degradation of high-quality of soil due to immoderate chemical substances; heavy concentration of unwanted foreign elements and due to depletion of soil minerals and nutrients through rapid fee of soil erosion. This arises due to the excessive cultivation of vegetation, cultivation of cropland, insecticides and use of chemical fertilizers. 

D.	Marine Pollution:

The Marine pollution due to the domestic sewage in coastal part is the main pollutant. Every year about 4.4 Km3 of such wastes are discharged into the Indian Ocean. Similarly, Industrial waste of approximately 0.44 Km3 including paper material, chemical, pharmaceutical, plastic, leather, meals, jute, pesticide, oil and heavy metals like lead, zinc, cadmium and mercury are annually discharged into the seas round India. While some of these factors discharged into the rivers could cause essential problems to the marine water. Parallelly, pesticides believed that up to 25 percent of the (DDT) used thus far might also had been transferred to the sea. DDT and pesticides compounds have a super effect on marine biota and reasons screw ups in reproductivity in fish and inhibition of photosynthetic process.

E.	Noise Pollution:

Noise with the aid of definition is "Unnecessary sound with no value" or "any sound that is unwanted via the recipient". Noise in industries such as stone slicing and crushing, metallic forgings, loudspeakers, shouting by using hawkers, motion of heavy shipping vehicles, railways and airports results in irritation, an elevated blood pressure, lack of temper, decrease in work efficiency, lack of listening to which may be first brief but can become permanent if the noise pressure continues. It is therefore of utmost significance that excessive noise is managed. Noise level is measured in terms of decibels (dB). W.H.O. (world health organization) has prescribed optimum noise degree at 45 dB by means of day and 35 dB through night. anything above 80 dB is hazardous.

Thermal Pollution:

Power plant life- thermal and nuclear, chemical and other industries use lots of water for cooling functions and the used hot water is discharged into rivers, streams or oceans. The waste heat from the boilers and heating methods will increase the temperature of the cooling water. Discharge of hot water may also boom the temperature of the receiving water through 10 to 15° C above the ambient water temperature. That is referred to as thermal pollution. Increase in water temperature decreases dissolved oxygen within the water, which adversely affects aquatic life. In contrast to terrestrial ecosystems, the temperature of water bodies remains steady and does not alternate very often. Thus, aquatic organisms are adapted to a uniform regular temperature of the surroundings and any fluctuation in water temperature critically affects aquatic plants and animals. As a result, discharge of hot water from power plants adversely impacts aquatic life. Aquatic flora and fauna inside the heat tropical water survive dangerously close to their higher restrict of temperature, especially at some point of the warm summer time.

F.	Water Pollution:

The need for safe and clean water supply is an important element for living organisms especially for drinking purposes. Surface water has been exploited for numerous functions by way of human beings. It serves as a source of potable water after treatment and as a source of domestic water without treatment especially in rural areas in growing countries. It's been used for irrigation functions by farmers, and fishermen get their career from harvesting fish in so many freshwater assets. It is used for swimming and also serves as centres for visitor enchantment. Surface water, therefore, needs to be protected from pollution. main factor sources of freshwater pollution are raw and partially treated wastewater. the discharge of domestic and commercial wastewater has brought about the growth in freshwater pollutants and depletion of clean water resources. Maximum portions of wastewater generated in growing developing countries do not undergo any shape of treatment. In few city centres, diverse kinds of wastewater treatment facilities (WWTFs) exist however most of them are producing ill‐treated effluents, which might be disposed of onto freshwater courses.
In a few developed countries of the world, adequate supply of potable water and stepped forward sanitation centres have been accomplished. Strict environmental laws and tracking for compliance prevents undue pollutants to freshwater resources. Suitable waste control technologies and accelerated environmental safety cognizance have contributed immensely to the achievement story. This has led to fewer instances of waterborne diseases stated in comparison to developing countries.
Many human beings in growing countries of the sector still depend upon untreated surface water as their fundamental supply of home water. This is so due to the fact that there's an incessant supply of potable water or insufficient water delivery systems. This hassle is exacerbated in rural regions. Surface water is increasingly beneath undue stress because of population increase and multiplied industrialization. The ease of the accessibility of surface water makes them the quality preference for wastewater discharge. Wastewater which contains of numerous microorganisms, heavy metals, radionuclides, pharmaceutical, and personal care merchandise all discover their way to surface water assets inflicting irreversible harm to the aquatic atmosphere and to humans as the aesthetic price of such water is compromised. those pollutants lower the supply of useable water, increase the value of purifying it, contaminate aquatic resources, and affect food supplies. Pollution mixed with the human call for water affects biodiversity, ecosystem functioning, and the natural services of aquatic systems upon which society relies on.
Urban areas in most developing countries do have several wastewater controls structures a number of which are very powerful and meet global standards, but many others are plagued with terrible designs, upkeep troubles, and expansion which includes terrible funding in wastewater control systems. Most rural and negative groups often do not have any form of wastewater management structures. Effluents from large‐ and small‐scale industries are usually channelled to surface water courses, which often bring about pollution, loss of biodiversity within the aquatic ecosystem, and possibly fitness danger to people.
The event of harmful toxins in water bodies (ponds, lakes, river etc.) would affect the soundness of populace who rely upon these water sources to meet their day-to-day prerequisites (water, fish, food, and so forth.). Utilization of water and wetland merchandise replenished with metals would prompt the collection in the kidneys, liver and bones of people, bringing about constant disturbance of metabolic exercises, and lead to cardiovascular, neurological and renal sicknesses. [1,2]

Table-1 Major Sources and Toxic Effect of Various Heavy Metals on Ecosystem.

Metal pollutant	Major Source	Toxic effect to ecosystem	
Copper	Electronics plating, paint manufacturing, wire drawing, copper polishing, and printing operations	Dizziness, diarrhoea, normocytic, hypochromic anaemia, leukopenia, and osteoporosis Reproductive and developmental toxicity, neurotoxicity, and acute toxicity.	
Nickel	Electroplating, non-ferrous metal, mineral processing, copper sulphate manufacturing.	Reduced lung function, lung cancer, chronic bronchitis, dermatitis, chronic asthma.	
Zinc	Mining	and manufacturing processes	metal-fume fever for short term, gastrointestinal distress, nausea and diarrhoea.	
Lead	Manufacturing of batteries, pigments, electroplating, ammunition	Spontaneous abortion, brain damage, anorexia, malaise, anaemia, loss of appetite, nervous system damage.	
Mercury	Volcanic eruptions, forest fires,
battery	Corrosive to skin, eyes, muscles, neurological and renal disturbances,	
Arsenic	Smelting, mining, energy production from fossil fuels, rock sediment’s, Metal processing plants, burning of fossil fuels, mining of arsenic containing ores
and use of arsenical pesticides	Bone marrow depression, hemolysis, liver tumors, gastrointestinal symptoms, cardiovascular and nervous system functions disturbances, Internal cancer, skin
lesions and death	
Cadmium	Electroplating, smelting, alloy manufacturing, pigments, plastic and mining	Itai–Itai disease, carcinogenic, renal disturbances, lung insufficiency, bone lesions, cancers, hypertension, weight
loss, liver and kidney damage	
Chromium	Electroplating, paints and pigments, metal processing, steel fabrication and canning industry	Epigastric pain, nausea, vomiting, severe diarrhea, lung tumors, Carcinogenic, mutagenic, teratogenic, Normocytic, hypochromic   anemia, leukopenia, and osteoporosis; copper deficiency	

Trace metals in aquatic and soil frameworks exist in various different dissolvable and particulate structures that influence the impact of the metals on these biological systems. Proper techniques for inspecting and investigation are expected to precisely decide the low absorptions present. Despite the fact that appraisal of metals in numerous    administrative projects depend on information for absolute metal fixations, such qualities seldom relate with impacts. Thusly, different means are required for the expectation of chance. Bioavailability of metals relies upon their speciation, whose significance was first settled for copper in aquatic systems where the noxiousness of metals is connected with the movement of the free metal ion. Little groupings of normal natural matter unequivocally complex metals enhancing toxicity. Table 1.1 shows major sources and toxic effect of various heavy metals on our ecosystem. [3,4]
Now drinking water is recognized as a major source of human intake of arsenic in organic and most toxic inorganic form. Arsenic is found in natural environment in food, soil, air and water and behaves as a metalloid. Food contains both organic and inorganic arsenic whereas drinking water contains primarily inorganic forms of As. As(III) species are more mobile in groundwater and 60-times toxic than As (V). About one-third of the arsenic in the atmosphere comes from high temperature natural processes such as coal-fired power plants, burning vegetation and volcanic activity. Rest comes from human activities. Due to natural geological contamination, high levels of inorganic arsenic can be found in drinking water that has come from deep drilled wells. Arsenic causes skin and internal cancers, cardiovascular disease, mental development of children and neurological effects The WHO recommended limit of arsenic in drinking water should not exceed 10 µg/L [5].
Cadmium and its compounds are widely used. It is dangerous, extremely toxic in relatively low dosages can cause kidney damage, renal disorder, high blood pressure, bone fraction, destruction of red blood cells, heart disease, cancer and diabetes. Cadmium concentrates in the kidney, liver and various other organs is considered more toxic than lead or mercury [6].
Chromium is available in two oxidation states Cr(III) and Cr(VI) in the climate which have differentiating toxicity levels, portability and bioavailability. Cr(III) is fundamental in human sustenance (particularly in glucose digestion), moderately harmless and stationary, while Cr(VI) compounds are poisonous can cause cellular breakdown in the lungs. Cr(VI) is a strong oxidizing agent which moves promptly through soils and aquatic environments being consumed through the skin. Chromium and its mixtures are generally utilized in leather tanning, concrete, dyeing, metallurgical processes, wood additives, paint, textile, steel creation and canning businesses which produce enormous amounts of poisonous wastewater effluents. 0.1 mg/L is greatest fixation limit for chromium to release into inland surface waters and 0.05 mg/L into consumable water [7]. Constant inward breath of Chromium (VI) intensifies expands the gamble of lung, nasal and sinus disease. Serious dermatitis skin ulcer cause from contact with Chromium (VI) compounds [8]. The radicals during the reduction of Cr(VI) to Cr(III) happens inside the cell [9]. 
Copper is most commonly present in the effluents from brass manufacture, petroleum refining, boilers, pipes, cloth making, marine painting, electro-plating, mining and different agrochemical industries [10].
Antimony is a toxic compound and as a high priority pollutant for water supplies used for drinking purposes. US EPA, EU have established a very low maximum permissible contaminant level 6 and 5µg/L of Sb for safe drinking water. High concentrations of Sb produced from production of flame retardants, batteries, chemicals, ceramics as well as in certain mining fields. Sb can be found in two oxidation states as Sb(III) and Sb(V) in water. Sb(III) considered to be more toxic than Sb(V) , becomes significant only in less oxygenated systems [11].
Zinc is one of the toxic metals. High concentration of zinc is due to discharge of wastewater from various industries like galvanizing, metallurgical, electroplating, mining, paints and pigments, pharmaceuticals, fibre production, ground wood pulp, newsprint paper, batteries, petroleum and petrochemical into water bodies. Zinc is non degradable metal ions hence carried away to the food chain and ultimately get deposited in the living organisms, causing several diseases. It enters into water through natural as well as anthropogenic sources. Erosion of soil and rocks has been found to be highly responsible for zinc contamination in water. According to WHO, the permissible concentration of zinc in drinking water is 5 mg/L [12].
Nickel occurs naturally in soil, sea salts, and volcanic ash and as particles in smoke from forest fires in the form of sulphides, arsenides, antimonides and oxides. Ni (II) is more toxic and carcinogenic than Ni (IV). According to ISI: Bureau of Indian Standard (BIS) the industrial effluent permissible discharge level of Ni (II) into inland water is 3.0 mg/L. Nickel accumulates in the food chain and once it gets absorbed into the body it cannot be easily excreted. Nickel is released into the environment by industrial processes, such as leather tanning, electroplating, wood preservation and steel manufacturing. Higher concentration of nickel causes cancer of lungs, nose, bone, headache, dizziness, nausea and vomiting, chest pain, tightness of the chest, shortness of breath, rapid respiration, cyanosis and extreme weakness [13].
Cobalt is an essential trace element and plays an important role in animals, bacteria, yeasts and plants. It is discharged in industrial activities such as mining, electroplating, painting, metallurgy, pigmenting and lithium-ion batteries. Such discharges can result in serious health effects for animals and humans, including contact dermatitis, paralysis, lung irritation and bone defects. Exposure to ionizing radiation is associated with an increased risk of developing cancer. The permissible limits of cobalt in irrigation water and livestock wastewater are 0.05 and 1 mg/L respectively [14].

Table-2 USEPA set Maximum Contaminated Level (MCL) standards, for toxic metals [15].

Water
Pollutant	Toxic effect	MCL
(mg/L)	
Arsenic	Skin manifestations, visceral cancers, vascular disease	0.05	
Cadmium	Kidney damage, renal disorder, human carcinogen	0.01	
Chromium	Headache, diarrhea, nausea, vomiting, carcinogenic	0.05	
Copper	Liver damage, Wilson disease, insomnia	0.25	
Nickel	Dermatitis, nausea, chronic asthma, coughing, human carcinogen	0.20	
Mercury	Rheumatoid arthritis, and diseases of the kidneys, circulatory
system, and nervous system	0.00003	
Zinc	Depression, lethargy, neurological signs and increased thirst	0.80	
Lead	Damage the fetal brain, diseases of the kidneys, circulatory
system, and nervous system	0.006	

Lead is a metal belongs to the group IV elements and period 6 of the periodic table. It is a naturally occurring bluish-grey metal usually found as a mineral along with sulphur or oxygen. It is broadly used in industries such as storage-battery manufacture, printing, pigment manufacturing, petrochemicals, fuel   combustion   and   photographic materials. Lead is a highly toxic metal and has the ability to accumulate in living organisms. Lead poisoning can cause cognitive impairment, behavioural disturbances, kidney damage, anaemia, and toxicity to the reproductive system and nervous system. As per IS: 10500, the permissible limit of lead in drinking water is upto 0.01mg/L [16]. 
In the process of haemoglobin synthesis and porphyrin metabolism, It forms metal complexes with oxo-groups in enzymes to affect enzyme activity [17]. Lead ions are taken into body via inhalation, ingestion or skin adsorption. As a result, when the body is exposed to lead, it can act as a cumulative poison. Lead accumulates mainly in bones, kidney, brain and muscles and may cause many serious disorders like kidney disease, anaemia, nervous disorder and sickness even death. Lead can replace calcium which is an essential mineral for strong bones and teeth while play important role in sympathetic actions of nerve and blood vessel for normal functioning of nervous system. The concentration of lead damages cognitive development especially in children. It also acts as an enzyme inhibitor in body e.g., replaces essential element zinc from heme enzymes [18].
Exposure to Pb can occur through inhalation of contaminated dust particles and aerosols or by ingesting contaminated food and water. Lead poisoning in humans damages the kidneys, liver, heart, brain, skeleton and the nervous system. Initial symptoms of poisoning associated with exposure to Lead may include headache, dullness, memory loss and being irritable18. Lead poisoning may cause disturbance of haemoglobin synthesis and anaemia. In children, chronic exposure to low levels of Lead may decrease their intelligence capacity. According to the International Agency for Research on Cancer (IARC), Lead is a possible carcinogenic substance in humans. The regulatory limit of Pb in drinking water according to US EPA is 15 ppb8. The WHO recommended safe limits of Pb in wastewater and soils used for agriculture are 0.01 and 0.1 ppm respectively.
Lead is one of the commonly detected heavy metals in wastewater which have been launched into the water bodies without right effluent treatment previous to its discharge. The presence of lead is in the shape of stable metal in the earth’s crust with a density of eleven.34 g/cm3, melting point of 327 °C, and boiling factor of 1755 °C. Lead is soluble in nitric acid and hot concentrated sulfuric acid, but not soluble in water at 25 °C and in organic solvents [19].
It is generally used inside the plumbing system due to its unique properties along with low melting factor and corrosion resistance. Lead is persistent in water, air, and soil and especially derived from numerous synthetic products including solders, paints, ceramics, water pipes, leaded gasoline, and shielding for X-ray machines. The call for lead is increasing yearly because of the increase of the commercial sector. The batteries enterprise is responsible for 80% of the global lead intake where over thirds of lead is used as car batteries. China is one of the most important lead-producing countries for lead-based batteries which is predicted to grow the lead manufacturing demand [20].
Natural materials that are available in large quantities or certain waste from agricultural operations may have potential to be used as low-cost adsorbents, as they present unused resources, widely available and are environmentally friendly [21].
The effective and economical technology is biosorption. In this case, different biological materials like cellulose, hemicelluloses and lignin have different metal binding capacities which used as effective adsorbents for removal of pollutants due to the existence of functional groups such as carboxyl, hydroxyl, methoxyl and phenols [22].

V. GRANULAR ACTIVATED CARBONS

Activated Carbon is extensively used for the removal and recovery of hazardous metals due to its availability and high affinity towards the scavenging of metal ions. The Granular Activated Carbon has following advantages on adsorption. 
1.	GAC has a large capacity to adsorb pollutants and organic molecules.
2.	GAC can adsorb and retain a wide variety of chemicals at the same time.
3.	GAC has an extremely large capacity to catalytically destroy ozone, a major component of smog.
4.	GAC works well under a wide range of temperature and humidity conditions.
5.	GAC adsorbs odours and chemicals preferentially to moisture.
6.	GAC is inert and safe to handle and use.
Activated carbon is a microcrystalline, porous and non-graphitic form of carbon that has been processed to improve its internal porosity. This material can be characterized by a large specific surface area of 500-2500 m2/g. Surface area is the most significant physical property of activated carbon due to it increases the physical adsorption of gases and dissolved substances from medium. Activated carbons are an effective adsorbent for many contaminants present in wastewater [23].

There are two basic processes of producing activated carbon; physical activation and chemical activation. In physical activation process, carbonization and activation of carbon carried out in two separate steps. This is a high temperature process as compared to that of chemical activation. In chemical activation, both carbonization and activation carried out simultaneously. The raw material is soaked with certain inorganic salts and this soaked mass is then carbonized at low temperatures to yield an active char after washing with acid and water. The products obtained by the chemical activation process are mostly used in systems of liquid phase purification. On the basis of physical characteristics, activated carbons can broadly classified as Powdered activated carbon (PAC), Granulated activated carbon (GAC), Extracted activated carbon (EAC), Impregnated carbon, Polymer coated carbon, etc. Coconut shells can be used for fuel and is source of charcoal. Activated carbon manufactured from coconut shell is considered superior to those obtained from other sources. This is mainly because of small macrospores structure which renders it more effective for the adsorption of gas and vapor and for the removal of colour, oxidants, impurities and odour of compounds [24].
	
VI. REFERENCES
	
1. L. Jarup., “Hazards of heavy metal contamination”, Br. Med. Bull, Vol. 36, Issue 1, Page 167–182, 2003.
2. N. Johri, G. Jacquillet ,R. Unwin, “Heavy metal poisoning the effects of cadmium on the kidney”, Biometals, Vol. 23, Issue 1, Page 783–792, 2010.
3. Y. A. Yahaya and M. M. Don “Pycnoporus sanguineus as potential biosorbent for heavy metal removal from aqueous solution: A review”, journal of physical science”, Vol. 25, Issue 1, Page 1-32, 2014.
4. S. Jenish, R. Manikandan, “A review of recent research works on the design of batch adsorption systems for heavy metal removal using agricultural biosorbents”, International Journal of Engineering Research, Vol. 2, Issue 6, Page 117-124, 2014.
5. A. Zunaira, C. Zhi, Removal of arsenic from drinking water using rice husk, Appl. Water Sci., Vol. 7, Issue 1, 1449-1458, 2017.
6. M. J. Amiri, E. Fadaei, A. Baghv and Z. Ezadkhasty, “Removal of heavy metals Cr(VI), Cd(II) and Ni(II) from aqueous solution by bioabsorbtion of Elaeagnus angustifolia”, Int. J. Environ. Res., Vol. 8 Issue 2, Page 411-420, 2014.
7. D. Seshi Kala, “Sorption of hexavalent chromium by various biosorbents”, Int. Res. J. Pharm. App. Sci., Vol. 4, Issue 3, Page 1-3, 2014.
8. B. D. Veena, A. A. Jahagirdar, M. N. Zulfiqar Ahmed, “Adsorption of chromium on activated carbon prepared from coconut shell”, International Journal of Engineering Research and Applications, Vol. 2, Issue 1, Page 364-370, 2012.
9. D. D. Darapure, I. Krishna and R. Padma Sree, “Artificial Neural Network (ANN) approach for modeling Chromium (VI) adsorption from aqueous solution using a borasus flabellifer coir powder”, International Journal of Applied Science and Engineering, Vol. 12, Issue 3, Page 177-192, 2014.
10. M. Dutta, J. K. Basu, “Removal of Cu2+ from electroplating industrial wastewater by using microwave assisted activated carbon”, International Journal of Recent Development in Engineering and Technology, 28-31, 2014.
11. K. Simeonidis, V. Papadopoulou, S. Tresintsi, E. Kokkinos, A. I. Katsoyiannis, I. Anastasios, and M. Mitrakas, “Efficiency of iron-based oxy-hydroxides in removing antimony from ground water to levels below the drinking water regulation limits”, Sustainability, Vol. 9, Issue 238, Page 1-11, 2017.

12. S. Rajoriya, K. Balpreet. “Adsorptive removal of zinc from waste water by natural biosorbents”, International Journal of Engineering Science Invention, Vol. 3, Issue 6, Page 60-80, 2014.
13. C. N. Deepa and S. Suresha, “Biosorption of Ni(II) in aqueous solution and industrial wastewater by leaves of araucaria cookie”, Int. J. Res. Chem. Environ., Vol. 4, Issue 4, Page 101-108, 2014.
14. R. Gao, W. Yiming, Z. Yefei, T. Jin and D. Wei, “Cobalt(II) bioaccumulation and distribution in rhodopseudomonas palustris”, Biotechnology and Biotechnological Equipment, Vol. 31, Issue 3, Page 527-534, 2017.
15. S. K. Gunatilake, “Methods of removing heavy metals from industrial wastewater”, Journal of Multidisciplinary Engineering Science Studies, Vol. 1, Issue 1, Page 12-18, 2015.
16. S. J. Khurshid and I. H. Qureshi, “The role of inorganic elements in human body”, The Nucleus, Vol. 21, Issue 3, 1984.
17. M. S. Rajput, A. K. Sharma, S. Sharma S. and Verma, “Removal of lead(II) from aqueous solution using low cost abundantly available adsorbents: A review”, International Journal of Chemical Studies, Vol. 3, Issue 1, Page 09-14, 2015.
18. N. H. Yarkandi., “Removal of lead(II) from waste water by adsorption”, Int. J. Curr. Microbiol. App. Sci., Vol. 3, Issue 4, Page 207-228, 2014.
19. W. Hassler, “Preparation and evaluation of powdered activated carbon from lignocellulosic materials”, Chemical publishing Co, Inc., New York, Vol. 15, Issue 1, Page 165-168, 1974.
20. O. Kadlec, A. Varhanikova and A. Zukal, “Structure of pores of active carbons prepared by water vapour and zinc dichloride activation”, Carbon, Vol. 8, Issue 1, Page 321, 1970.
21. Lenntech., “Lead (Pb) - Chemical properties, health and environmental effects”, Retrieved on January 1, from https://www.lenntech.com/periodic/elements/pb.htm. (2019).
22. Statista, “World production of lead from 2005 to 2017 (in 1,000 metric tons)”, Retrieved, November 19, 2018, from https://www.statista.com/statistics /264872 /worldproduction-of-lead-metal/, 2018.
23. M. Asid, M. I. Jilani, R. Nadeem, M. A. Hanif, T. M. Ansari, “Adsorption of Pb(II) using novel pleurotus sajor-caju and sunflower hybrid biosorbent”, Environment Protection Engineering, Vol. 40, Issue 2, Page 5-15, 2014.
24. M. S. Rajput, A. K. Sharma, S. Sharma, S. Verma, “Removal of lead (II) from aqueous solution using low cost abundantly available adsorbents: A review”, International Journal of Chemical Studies, Vol. 3, Issue 1, Page 09-14, 2015.
25. Bobdey Radhesh Atul, Dr. Neeta Gupta, Prof. Dr. Ramdas U. Khope “Studies on the Efficacy of Coal-Based Adsorbent in Removal of Toxic Metal Lead from Waste Water”, published by Corrosion and Protection Journal, Vol-50, Issue 11, Page 182-187, 2022.
26. Bobdey Radhesh Atul, Dr. Neeta Gupta, Prof. Dr. Ramdas U. Khope “Adsorption studies of lead from waste water using porous coal-based adsorbent in conjunction with organic chelating agent, Guaiacol”, published by NeuroQuantology Journal, Vol-20, Issue 22, Page 1167-1172, 2022.
27. R. A. Bobdey and R. U. Khope, Analysing 4- Methyl Catechol for Surface Modification of Granular Activated Carbons in Order to Change Its Adsorptive Properties Towards Toxic Metal Lead from Aqueous Solution, Asian Journal of Organic & Medicinal Chemistry, Vol. 7, No. 2, 2022, Pages 256-260.