According to recent study conducted by (Liu et al., 2018), there 5 million sites globally contaminated by soil pollution having excessive amount of heavy metals as comparable to regulatory levels. In the study of (Takahashi, 2016) Cd ranks first in soil that exceed 7%, according to acceptable levels. CPCB identified highly polluted industrial areas based on Comprehensive Environmental Pollution Index (CEPI) rating. In sixteen states, forty three polluted zones were reported whose CEPI rating was more than 70 (Table 2) (Saha et al., 2017). Globally 80 million of ha in china exceeds heavy contamination in soil (Hu et al., 2015). In Europe necessary reductions on the annual emissions of Cd, Pb and Hg to avoid harmful effects have been introduced in the United Nations–Economic Commission Europe Protocol on heavy metals in 1998 (Changfeng et al., 2019).

Table 2: Highly polluted industrial areas in India

State	Highly polluted industrial areas	CEPI rating
Andhra Pradesh	Vishakhapatnam	70.82
Andhra Pradesh	Patancheru – Bollaram	70.07
Chhattisgarh	Kobra	83.00
Delhi	Nazafgarh drain basin	79.54
Gujarat	Ankleshwar	88.50
	Vapi	88.09
	Ahmedabad	75.28
	Vatva	74.77
	Bhavnagar	70.99
	Junagarh	70.82
Haryana	Faridabad	77.07
Haryana	Panipat	71.91
Jharkhand	Dhanbad	78.63
Karnataka	Mangalore	73.68
Karnataka	Bhadravati	72.33
Kerala	Greater Cochin	75.08
Madhya Pradesh	Indore	71.26
Maharashtra	Chandrapur	83.38
	Aurangabad	77.44
	Dombivalli	78.41
	Navi Mumbai	73.77
	Tarapur	72.01
Orissa	Angul Talcer	82.09
Orissa	Ib Valley	74.00
Punjab	Ludhiana	81.66
Rajasthan	Bhiwadi	82.91
	Jodhpur	75.91
	Pali	73.73
Tamil Nadu	Vellore (North Arcot)	81.79
	Cuddalore	77.45
	Manali	76.32
	Coimbatore	72.38
Uttar Pradesh	Ghaziabad	87.37
	Singrauli	81.73
	Noida	78.90
	Kanpur	78.09
	Agra	76.48
	Varansi-Mirzapur	73.79

Table 3: Different sources of heavy metals contaminating soil

Sources	As	Cd	Cr	Cu	Hg	Ni	Pb	Zn
Agriculture and Food waste	0~0.6	0~0.3	4.5 ~ 90	3 ~ 8	0 ~1.5	6 ~45	1.5 ~ 27	12 ~150
Farmyard Manure	1.2 ~ 4.4	0.2~1.2	10 ~60	14 ~80	0 ~0.2	3 ~36	3.2 ~20	150 ~ 320
Lodging and timber industrial wastes	0 ~ 3.3	0 ~2.2	2.2 ~ 18	3.3 ~52	0 ~2.2	2.2 ~23	6.6 ~8.2	13 ~65
Municipal Wastes	0.09 ~ 0.7	0.88 ~ 7.5	6.6 ~33	13 ~40	0 ~0.26	2.2 ~ 10	18 ~ 62	22 ~ 97
Municipal Sludge	0.01 ~ 0.24	0.02 ~0.34	1.4 ~ 11	4.9 ~ 21	0.01 ~ 0.8	5.0 ~ 22	2.8 ~ 9.7	18 ~ 57
Organic Wastes	0 ~0.25	0 ~ 0.01	0.1 ~ 0.48	0.04 ~0.61	-	0.17 ~ 3.2	0.02 ~ 1.6	0.13 ~ 1.2
Metal processing solid wastes	0.01 ~ 0.21	0 ~0.08	0.65 ~ 2.4	0.95 ~ 7.6	0 ~0.08	0.84 ~ 2.5	4.1 ~ 11	2.7 ~ 19
Coal ash	6.7 ~ 37	1.5 ~ 13	149 ~ 446	93 ~ 335	0.37 ~ 4.8	56 ~ 279	45 ~ 242	112 ~ 484
Fertilizers	0 ~0.02	0.03 ~0.25	0.03 ~ 0.38	0.05 ~ 0.58	-	0.20 ~ 3.5	0.42 ~ 2.3	0.25 ~ 1.1
Marl	0.04 ~ 0.5	0 ~ 0.11	0.04 ~ 0.19	0.15 ~ 2.0	0 ~ 0.02	0.22 ~ 3.5	0.45 ~2.6	0.15 ~ 3.5
Commodities impurities	36 ~ 41	0.78 ~ 1.6	305 ~ 610	395 ~ 790	0.55 ~ 0.82	6.5 ~ 32	195 ~ 390	310 ~ 620
Atmospheric deposition	8.4 ~ `8	2.2 ~ 8.4	5.1 ~ 38	14 ~ 36	0.63 ~ 4.3	11 ~ 37	202 ~ 263	49 ~ 135
Total	52 ~ 112	5.6 ~ 38	484 ~ 1309	541 ~ 1367	1.6 ~ 15	106 ~ 544	479 ~ 1113	689 ~2054

Source: Nriagu and Pacyna, 1988

The parent material is the heavy metal present in the soil through which they are generated. 95 pr cent of the earth crust is made of ingenious rocks and 5 per cent is made of sedimentary rocks (Sarwar et al., 2016). Basically, basaltic ingenious rocks are rich in heavy metals such as Cu, Cd, Ni, and cobalt (Co), whereas shales contain large amounts of Pb, Cu, Zn, manganese (Mn), and Cd. Rocks contains heavy metal can directly mixed in soil environment by the natural process such as, terrestrial, biogenic, meteoric and volcanic process erosion; leaching; and surface winds (Muradoglu et al., 2015). The nature’s disturbance slowly occurs heavy metals geochemical cycle by anthropogenic process as a result one or more heavy metals accumulation inside the soil (Dixit et al., 2015). Recent changes occur in agricultural sector, urbanization and industrialization have contributing essentially to cut down the metal contamination in the soil. Mining and smelting are the anthropogenic activities (Chen et al., 2015),combustion of fossil fuel refining (Muradoglu et al., 2015), disposal of municipal wastes (Khan et al., 2016), application of pesticides (Ogunlade and Agbeniyi, 2011), sewage irrigation (Sun et al., 2013), and fertilizer application (Atafar et al., 2010) are contributed to gain heavy metals concentrations in the agricultural soil environment. Last few decades, worldwide annual release of heavy metals crossed 22,000 t (metric ton) for Cd, 939,000 t for Cu, 783,000 t for Pb, and 1, 35,000 t for Zn (Thambavani and Prathipa, 2012).

3. REMEDIATION OF HEAVY METAL POLLUTED SOILS:

So many strategies and methods are used to solving of the contamination problem the soil. Generally, technologies remediation can be divided in two strategies, situ remediation and ex situ remediation (Gomes et al., 2013). The treatment of Situ remediation is the pollutants in the original place, contaminated soil itself without moving. Ex situ remediation are having excavation and polluted soil removal for the treatment. As compared with ex situ remediation, in situ remediation is giving so many potential technical, environmental and economic advantages (Song et al., 2017). As well as, soil remediation appropriate selection method is depend on the factors of site, containment concentration, types of pollutants to be removed and the last use of the contaminated medium (Mulligan et al., 2001). Remediation cab be bring by the chemical, physical and biological methods.

3.1 Physical remediation:

In the physical remediation process of stopping or reversal of soil damage includes soil replacement, isolation, containment method and thermal treatment by physical treatment (Yao et al., 2012). Replacement of soil by including techniques such as landfilling, capping encapsulation. Removal of soil can dilute effectively the concentration of pollutant and soil environmental capacity increases and also contaminated soil who are serious in nature is suitable for the small place because of high cost and heavy workload. Isolation can be cause in pollutants and it is containing installing barrier walls, to stop further dispersion from the site. Impermeable material is made by physical barriers, such as, steel, cement, bentonite, and for capping grout are used, horizontal and vertical containment. The soil isolation method or containment is not a direct remediation process, but a measurement was used to reduce obviously heavy metals migration into the ground water (Jankaite and Vasarevicius, 2005). The treatment of thermal is organised on the basis of containments volatility to heating the subsurface to remediate the soil. The methods of heating including conductive heating mainly, steam-based heating and electrical resistive heating and radio frequency heating (Song et al., 2017). So the technology shown that the removing contaminants effectively with high vapour pressure such as Hg; as well as, it is affecting greatly properties of soil (Chang and Yen, 2006). Soil has shown that exhibit drastic changes physiochemical composition and mineralogical composition factors fewer than 600°C treatments, which was removed intentionally Hg from the soil (Roh et al., 2000).Huang et al. (2011) suggest that the heavy metals removal by chemical extraction and heavy washing can be done before thermal treatment for removal of Hg, because of thermal decontamination can leads metals repartitioning. For example, heavy metals in iron or Mn oxides transformed into acid-extractable, organic-matter-bound, and residual forms after thermal treatment at 550°C, whereas Cr, Cu, and Ni became less mobilized and difficult to extract, which may greatly affect the effectiveness of subsequent decontamination approaches (Huang et al., 2011).

3.2 Chemical remediation:

Remediation of chemical is a method in which reactions and reagents of chemical, principles are used for the removal of contaminants (Song et al., 2017). Including the main remediation stabilization/solidification, vetrification, soil washing, soil flushing and electro kinetics (EK; Jankaite and Vasarevicius, 2005). Solidification/stabilization technology is always applying for the mixing of contaminated soils with materials or reagents to decrease the heavy metal contaminants mobility. Physical encapsulation is solidification of the contaminants in a solid matrix formed by cement, bitumen, asphalt, and thermoplastic binders, at the time of stabilization including chemical reactions to decrease contaminant mobility. Additions of Bonemeal (finely ground, poorly crystalline apatite, Ca10(PO4)6OH2) has a capability to stop pollutant metals in soil and also decrease metal bioavailability by the generation of matal phosphates (Hodson et al., 2000). A cost effective variety and eco friendly resources of waste have been found not only for stopping metals in contaminated soils, also to improve quality of soil, such as lime-based agents (Lim et al., 2013), calcined oyster shells (Yong et al., 2010), eggshells (Soares et al., 2015), waste mussel shells (Otero et al., 2015), and calcined cockle shell (Islam et al., 2017).

Washing and flushing of soil are essential methods of remediation by water or proper water solution for the removal of contaminants from the soil (U.S EPA, 2006). For getting the removal of optimal heavy metal, by washing agents such as water (Dermont et al., 2008), saponin (Maity et al., 2013), organic acid (Kim et al., 2013), chelating agents (Jiang et al., 2011), surfactants (Sun et al., 2011), and low-molecular-weight organic acids (Almaroai et al., 2012) are shown to be effective on stimulating desorption of soil contaminants. EDTA has been found are the most efficient chelating agent for the heavy metals removal from contaminated soils (Lestan et al., 2008). The EDTA advantages includes low biodegradability, high efficiency of metal removal, proper recycling techniques availability and decreasing effect on soil microorganism and activity of enzyme (Qiao et al., 2017).

3.3 Biological remediation:

Bioremediation is having technique of sate of the art which is used for the in a certain degree heavy metal contaminated soil ecosystem restoration. This technique is used for biological mechanism inherent in plants and microorganism to destroy or to remove or stopping hazardous contaminants from the polluted environment (Ayangbenro and Babalola, 2017). It’s a cost effective and eco-friendly technique for removal of heavy metal with physical methods and conventional chemical, which are very expensive often and ineffective for down concentrations of metal, for forming the essential amount of toxic sludge (Ojuederie and Babalola, 2017). Blaylock et al. (1997) observed that 50 to 60 per cent saving was done when the treatment by bioremediation of one acre of pb-contaminated soil is compared for the use of conventional methods such as landfill and excavation. Heavy metals bioremediation can be done by the use of plants, microorganism or the both. The commonly used microorganism for heavy contaminated soil removal are fungi and bacteria, however, algae and yeast are also applied frequently (Coelho et al., 2015).Microorganism studies example are used treatment of bioremediation for heavy metals including, Sporosarcina ginsengisoli (Achal et al., 2012), Pseudomonas putida (Balamurugan et al., 2014), and Bacillus subtilis (Imam et al., 2016). Microorganism bioremediation will be succeed if it is consortium of bacterial strains is used in place of single strain culture. Kang et al. (2016) studied that the essential effect of mixture of bacteria mixtures (Viridibacillus arenosi B-21, Sporosarcina soli B-22, Enterobacter cloacae KJ-46, and E. cloacae KJ-47) on the bioremediation of a mixture of Cd, Cu, and Pb from contaminated soils. They studied that demonstration of bacterial mixture higher resistance and heavy metals remediation efficiency are by comparing with single strain cultures. In remediation of heavy metals mechanism is used from contaminates soils which including microorganism by the precipitation process, bio absorption by sequestration by intracellular metal binding proteins, and conversion of metals to get the innocuous forms by the enzymes (Ojuederie and Babalola, 2017).

4. CONCLUSION:

Frequent growth in urbanization and industrialization accompanied, heavy metals soil pollution is a major concern, by its heavy impact on animal and human health. For example, industrial waste water used for irrigation develop large area of land is polluted and it also leads to the contamination of grain in million tons per year. However, there is necessity of effective remediation methods. The chemical and physical traditional techniques for clean-up and restoration of soils contamination by heavy metals have serious effects on cost, and transformation of soil properties and a related micro flora, or capable creation of problems of secondary pollutions. By the comparison, phytoremediation is major option for problem solving. It is a cost effective and eco-friendly, with no requirements of expensive equipment’s and contaminated sites special care. As well as, phytoremediation is also having some weak points. For example, long time has been taken for the contaminants removal from the compared sites with chemical and physical methods, and application scope related to confine is required background site knowledge and characteristics of contamination remediation objectives, remediation efficiency, cost-effectiveness, remediation time, and public acceptability. Research is in progress to visible native plant species to polluted soil remediate with toxic metals and to assessing the various parameters availability on phytoremediation. As well as, biotechnical approaches application are making progress in plants for getting heavy metals phytoremediation, however, needs of some more effects to expose for the application success of this technique on commercial scale for the cleave of soil which is contaminated.

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Received on 29.04.2020 Modified on 19.05.2020

Asian J. Research Chem. 2020; 13(4):299-304.

DOI: 10.5958/0974-4150.2020.00058.9

Heavy metals	Harmful effects
Cd	Bone disease, coughing, emphysema, headache, hypertension, itai–itai, kidney diseases, lung and prostate cancer, lymphocytosis, microcytic hypochromic anemia, testicular atrophy, vomiting
As	Brain damage, cardiovascular and respiratory disorder, conjunctivitis, dermatitis, skin cancer
Pb	Anorexia, chronic nephropathy, damage to neurons, high blood pressure, hyperactivity, insomnia, learning deficits, reduced fertility, renal system damage, risk factor for Alzheimer’s disease, shortened attention span
Cr	Bronchopneumonia, chronic bronchitis, diarrhea, emphysema, headache, irritation of the skin, itching of respiratory tract, liver diseases, lung cancer, nausea, renal failure, reproductive toxicity, vomiting
Hg	Ataxia, attention deficit, blindness, deafness, decrease rate of fertility, dementia, dizziness, dysphasia, gastrointestinal irritation, gingivitis, kidney problem, loss of memory, pulmonary edema, reduced immunity, sclerosis
Cu	Abdominal pain, anemia, diarrhea, headache, liver and kidney damage, metabolic disorders, nausea, vomiting
Ni	Cardiovascular diseases, chest pain, dermatitis, dizziness, dry cough and shortness of breath, headache, kidney diseases, lung and nasal cancer, nausea