INTRODUCTION:

The mining and metallurgical advancements cum industrial revolutions during last 7-8 decades have brought a massive redistribution of metals on the surface of the earth. The contamination of ecosystem by toxic metals has proved hazardous to both plant and man¹. Presence of toxic metals in air, soil and aquatic system has caused a serious threat to the biosphere and humanity in various ways².

Toxic metals are percolated to water bodies and farm soils mainly due to weathering of rocks and soil and direct use of domestic waste and sewage, agricultural and street runoff and due to a variety of human activities involving small as well as big industrial processes¹. Irrigation water may transport dissolved heavy metals to agri-fields, which may be incorporated to plant tissues². Once heavy metal contaminates the soil, it persists in the soil for many years due to its non-biodegradable nature, this makes metals to move freely long distances through air and water³. Heavy metals cannot be degraded in soil but can retain in soil one oxidation state to another state⁴. Further, the inputs from mining waste, washings of blast furnaces, smelting, manufacturing, finishing of metal and metal products, electroplating, battery manufacturing, coal- fields, power plants, automobile emission, burning of coal and fossil fuel, foundries- refectories, steel - cement - tile industries, manufacture and use of fertilizers, insecticides and pesticides, etc have contaminated largely our water bodies and ecosystems, which finally enters to the entire food chain system². The contamination of the environment by toxic metals, not only poses a threat for man and biosphere, but also reduces agricultural productivity and damage the health of ecosystem¹.

Several plants are capable of extracting toxic metals from contaminated soil or waste water and deposit them in its above-ground parts, these plant parts can be harvested to remove the contaminants^4,5. On bio-accumulation metals from farm-soil move to the food chain and thereby stored in human internal organs such as liver and kidney⁶. This unique characteristic of plant root system to selectively absorb metals from farm soil and to translocate the absorbed metals to its stem and leaves was called Phyto-remediation⁷. Heterogeneous accumulation of metals is usually observed among the different weeds, moreover metal accumulation varied within the plant tissues i.e. roots and shoots⁸. Phyto-remediation is an emerging technology for cleaning contaminated soils and water that employs the use of higher plants⁷. Thus, phyto-remediation is the capability of plants to bio-accumulate metals and pollutants from the contaminated soils and water bodies, into the roots and above-ground parts of the plant⁹. The process is efficient, cost-effective, environmentally friendly and low-tech process which uses plants for in situ treatment of land areas polluted by toxic metals and hazardous substances⁸. In phyto-remediation, the plant extracts, accumulates, and transfers contaminants and heavy metals from agri-soil and waste water⁹. Phyto-extraction is one of the types of phyto-remediation in which contaminants are concentrated in the roots, stems and foliage of the concerned plant⁷. The purification capacity of heavy metals by plants are affected by several factors, such as the concentration of the heavy metals, species of elements, plant species, duration of exposure, pH and temperature⁹.

The use of cost-free abundantly growing metal tolerant wild plants is added advantage of phyto-remediation of the polluted soils². Several wildly growing weeds offer good metal accumulating potential because of their survival under harsh conditions, fast growth and propagation and thus producing a considerable biomass¹⁰. The selected plant species possess the genetic potential to remove, degrade, metabolize, or immobilize a wide range of contaminants including heavy metals⁷. There has been a continuing interest in the evaluation of the metal bioaccumulation potential of native plant species, as these can withstand the local conditions of adaptation with the harmony of the ecosystem. Some of the important and notable research work published recently on this vibrant field is due to Shah et al., 2020, Kumar et al., 2022 and Tariq et al.,2020^3,8,11.

This study was aimed to assess the phyto-extraction potential of a wildly growing weed, Carrot grass, Parthenium hysterophorus L., Asteraceae growing on the barren land along with the National highways-58 for Cd, Cr, Cu, Ni and Pb by determining levels of bio-accumulated Cd, Cr, Cu, Ni and Pb in the soil, roots and shoot of the plant. The movement of studied heavy metals from soil to plant roots and their upward movement to shoot (stem and leaves) of Parthenium were computed in terms of bio-concentration factors, BCF_Root i.e. the movement of metals from soil to plant roots for each studied metals, translocation factors TF_Shooti.e.the movement of these metals from plant roots toplant shoot and biological accumulation coefficients, BAC_Shoot i.e. the movement of metals from soil to the shoot of Parthenium hysterophorus L. and these values were used to assess the phyto-extraction potential of the plant for studied metals.

MATERIALS AND METHODS:

Chemicals and equipment:

For determination of Cd, Cr, Cu, Ni and Pb on Atomic Absorption Spectrometer all the required standard stock solutions of metal ions used were procured from Sigma-Aldrich. For preparing working standards the Sigma-Aldrich standards are diluted to required concentrations. All the reagents, chemicals and solvents used were of Analytical grade⁶. Double distilled water was used for all purposes.

Selection of Plant:

Plants suitable for bio-accumulation and phytoextraction studies should ideally have the highly branched deep root system to yield high above-ground biomass, good ability to extract heavy metals from soil particles, high efficiency to accumulate heavy metals, efficient translocation of the accumulated heavy metals from roots to shoots, ability to tolerate toxic effects of heavy metals and excellent adaptability to harsh climatic conditions, e.g. draught and high temperature^{2, 10}. For heavy metals bio-accumulation studies wide spread and abundantly growing wild plant, commonly known as carrot grass, Parthenium hysterophorus L., Asteraceae, was selected because of its fast growing ability and high biomass yield^{2, 10}. Parthenium is an aggressive annual herbaceous weed with vigorous growth and excellent adaptive potential for survival in diverse environmental, now found almost everywhere globally through import of grain seeds and livestock feed^{10, 12}. Native to subtropics of North and South America, Australia and Africa, arrived India as contaminants in PL 480 wheat imported from US in 1950s¹³. Now it grows in both agricultural and non-agricultural habitats across the globe and has became world’s most devastating and hazardous weed found on abandoned lands, developing residential colonies, railway tracks, roads, gardens, agricultural fields, etc. Plant is allelopathic and can harm agro-ecosystems, it produces thousands of small white capitula each yielding five seeds on maturity, a single plant can produce 10,000 -15000 seeds¹³. It is not only found in disturbed sites but is also very common in cultivated fields, forming huge, pure patches with no other plant in its vicinity¹³. Parthenium has some levels of metal tolerance; with adequate accumulation, translocation and uptake potential of the metals^14,15.

Photograph of Parthenium hysterophorus L., Asteraceae during flowering stage

Sampling and pre-treatment of soil samples:

The area selected for this study was a barren land along with the boundary wall of Kali Kamali agriculture farm between Geetanagar and Ugrsen nagar, Rishikesh, Dehradun, Uttarakhand, India that falls on the Haridwar- Badrinath National Highway (NH58). Five representative soil samples were collected randomly from the selected site at a depth of 20-25 cm. The collected soil samples were air dried for 8-10 days, followed by oven drying at 100⁰C for 24 hours. Stones and other non-soil particles were removed by hand picking from all the samples. The dried samples were finely grinded separately to obtain homogenized fine particles and then sieved through 2 mm nylon sieve and stored in clean, dry and labeled bottles, for determination of studied metals.

Sampling and pre-treatment of plant samples:

For determination of the bio-accumulated levels of Cd, Cr, Cu, Ni and Pb in Parthenium hysterophorus L, the samples were collected from five locations of the study area during August 2018. The collection of samples and determination of metals were performed in accordance to Standard Methods¹⁶. Young but fully developed Parthenium plants were uprooted from the soil carefully to get the plant with roots. To collect the entire root system of the plant samples, the sampling area of the site was irrigated for one hour for sufficient wetting the deep soil, to uproot easily the plant samples with entire root system. After discarding damaged and decayed leaves and other parts, the plant samples were kept in fresh poly bags and brought to the laboratory, the samples were washed carefully with tap water 2-3 times to remove dust and soil particles. Then, the plant samples were washed 2-3 times using distilled water. To make the cleaned plant samples moisture free, these were placed for few hours over clean filter paper sheets on a table top kept in a dust free area. The semi-dried plant samples were cut to separate roots from shoots and placed on separate fresh filter paper sheets. The separated samples of roots and shoots were first air-dried for 8-10 days separately in dust free area of the laboratory and then oven dried for few hours at 80⁰C to a constant weight. Dried samples of roots and shoots were finely grinded to fine powder and were kept separately in sample bottles and labeled.

Digestion of the soil and plant samples:

To estimate the accumulated Cd, Cr, Cu, Ni and Pb in soil, 1.0 g of the finely grinded soil samples were digested separately with HNO₃–HCl–HClO₄mixture(5:1:1) for several hours to get transparent extracts, which was filtered and diluted to a volume of 100 mL with double distilled water¹⁷.

However, to evaluate the bio-accumulated metals in Parthenium hysterophorus L, 1.0 g of the grinded samples of roots and shoots were subjected to nitric acid -perchloric acid (5:1, v/v) digestion following the standard methods¹⁶, for several hours to get a transparent light colored liquid, which was then filtered in a 100 mL volumetric flasks and make up to the mark with double distilled water.

Estimation of Metals in extracts of soil and plant parts:

The concentration (mg/kg, dw) of cadmium, chromium, copper, nickel and lead in the transparent extracts of soil samples and in the root and shoot extracts of Parthenium hysterophorus L. were determined on Atomic Absorption Spectrophotometer, PerkinElmer Analyst-200 Model by following the standard procedure, using an air-acetylene flame¹⁶. Various standard stock solutions of metal ions used in the analysis of metals were from Sigma-Aldrich, which were diluted to required concentrations for preparing various working standards. All the estimations were run in triplicate. All chemicals, reagents and solvents used were of analytical grade. Double distilled water was used for all purposes.

RESULTS AND DISCUSSION:

The observed levels of Cd, Cr, Cu, Ni and Pb in the samples of soil collected from the study area and in the roots and shoots of the Parthenium hysterophorus L are presented in Table-1.

Levels of Metals in Soil Samples:

Soil is an important part of the terrestrial ecosystem and it is the sink for heavy metals and becomes a medium to spread heavy metals into water bodies, organisms, and atmosphere¹⁸. In developing countries, frequent use of waste water for crop irrigation is in practice that increases levels of toxic metals in soil which may enter to farm products and food chain, affecting human life³. Root system of the plant bio-accumulates certain useful nutrients along with other metals from farm soil which depends upon their availability in soil system near the plant roots, characteristics of farm soil and plant age¹. The metal bioaccumulation potential of plants differs widely due to their diverse morphology and may be significantly selective for one or more metals⁵. In present investigation the levels of studied metals (Table-1, Fig.-1) in soil samples collected from the study area were found in the order: Pb (8.12±0.48) > Cr (7.18± 0.39) > Cu (5.64± 0.26) > Ni (3.91± 0.21) > Cd (1.31± 0.08). On comparing these results with few of the earlier published works, it was noted that the levels of studied metals in soil samples reported from industrial area of Islamabad, Pakistan by Malik, et al., 2010 varied as: Pb (2.0-29.0), Cu (8.9 to 357.4), Ni (41.4-59.3) and Cr (40.2-927.2 mg/kg)¹⁹. The levels of metals reported from a Coal mines area soil on Varanasi-Singrauli Highway by Singh et al., 2010 varied as, Cu (30.14)> Pb (26.48) > Ni (8.96)> Cr(6.41) > Cd (2.98µg /g, dw); reported from a heavy traffic area soil from Khour Company area, Attock, Pakistan by Bashir et al., 2014 varied as: Pb (79.46 ± 45.7) > Ni (24.85± 2.17)> Cu (14.79 ± 8.64)> Cd (1.1 ± 0.1) and reported from Hussain Sagar Lake, Hyderabad by Subha and Srinivas, 2017 were varied as Pb (128.75)>Cu (97.05) >Cr (90.87)> Cd (46.87) > Ni (39.35, mg/Kg)^5,20,21. The levels of Cd reported by Singh et al., 2010 and Bashir et al., 2014 were comparable with the present results, while the results of Cu, Pb, Ni and Cr reported by Malik,et al., 2010 and Bashir et al.,2014 were comparatively higher^5,19,20. However, the levels of studied metals reported by Subha and Srinivas, 2017 were much higher than the present results²¹.

Metal levels in the roots and shoots of Parthenium:

Usually, plants have a characteristic ability to selectively bio-concentrate certain metals from contaminated soil and water in root cells²². For proper growth and to complete the life cycle, plants acquire, accumulate, translocate and store essential micronutrients as per their metallic and cellular needs, along with some other non-essential metals from agri-soils¹. Absorption by plant roots is one of the main routes of entrance of metal ions in the plants, however foliar absorption of metals through stomata on leaf surface, out of the road dust, soil and rainwater also notable⁹. Absorption and accumulation of metals in plant tissues depend upon temperature, moisture, organic matter, pH and nutrients availability in soil². Plants absorb water and nutrients from the soil solution by osmosis. Root hair cells of plants have a large surface area, thin walls and are close to the xylem cells, to absorb the water from soil by osmosis. Once the micronutrients and water reached inside the root cells, these are translocated to the above ground parts of the plant. Transpiration of water from leaves create suction on the water at the root surface that initiates the movement of soil solution toward the plant roots. The accumulation of a metal in plants depends on its bio-availability in soil solution around the plant root system and soil pH that influence the metal bio-availability²³. Plant uptake mechanism is selective and preferentially acquires some ions over others. Selectivity depends on structure and membrane transporters which recognizes, binds and transports specific ions⁷. Under normal growing conditions, plants can accumulate certain metal ions greater than the surrounding medium²². For phyto-extraction to occur, contaminants must be bio-available to be absorbed by roots, which depend on metal solubility in soil solution i.e. soil pH which affects metal bio-availability and metal uptake into roots²⁴.

Fig-1: Levels (mg/Kg) of studied metals in Soil, Roots and Shoot of Parthenium hysterophorus L.

The Table-1, Fig.-1 presents the levels of bio-accumulated Cd, Cr, Cu, Ni and Pb in the underground part (roots) and the above ground parts (shoots) of Parthenium hysterophorus L, was: Pb (6.67± 0.34) > Cu (6.11 ±0.27) >Cr (6.05± 0.23) >Ni (4.14± 0.18) > Cd (1.42± 0.11) and Pb (7.22±0.29) > Cr (5.97±0.23)>Cu (5.96±0.25)>Ni (5.13±0.21) > Cd (1.70±0.14 mg/Kg, dw), respectively. Thus, the overall metal uptake registered by Parthenium plant i.e. in its roots and shoots both, were: Pb (13.89) > Cu (12.07)>Cr (12.02)>Ni (9.27) > Cd (3.12mg /Kg, dw). As the limits of heavy metals in plants set by WHO,2007 was Cd (0.01), Cr (1.30), Cu (10.0), Ni (10.0) and Pb (2.0 mg/Kg), therefore it can be said that Parthenium hysterophorus L, plant samples collected from NH- 58 have accumulated Cd, Cr, Cu and Pb beyond the WHO permitted limits set for plants²⁵. The order of bio-accumulated metals in the root of Parthenium was Pb> Cu> Cr> Ni> Cd, which differ slightly than for shoots, Pb> Cr> Cu> Ni> Cd. Further, the accumulation of Cd, Ni and Pb in the above ground parts of the plant was higher than in the roots. However, the levels of accumulated Cr and Cu in the plant roots were higher than the shoots. On comparing these results with other results, it is noted that the levels of metals in the root and shoots of Parthineum, collected from a Coalmines area on Varanasi-Singrauli Highway, were comparable, except Pb and Cu, with the present results, the results of Pb and Cu in roots and shoot were higher⁵. Similarly, the levels of metals in root (Pb 13, Cu 59.3, Ni 7 and Cr 34.2 mg/Kg, dw) and in shoot (Pb 36, Cu 111.6, Ni 18.2 and Cr 76.9mg/Kg,dw) were reported from industrial area of Islamabad, Pakistan, which were much higher than present study¹⁹. The levels of heavy metals reported in Parthenium from heavy traffic soil of Khour Company area, Attock, Pakistan varied as: Pb (65.10 ± 12.16) > Ni (44.89 ± 2.79)> Cd (25.30 ± 0.87) > Cu (.22.63 ± 4.05)²⁰. The levels of metals in Parthenium, Ni (7.53 ± 0.53) > Pb (7.12 ± 0.75) > Cu (2.14 ± 0.14) > Cd (0.24 ± 0.001), reported by Ahmad and Al-Othman,2014 in fly-ash soil near Badarpur Power Plant, New Delhi were lower than the present findings¹⁸. Heavy metals levels in the shoot of Parthenium grown near Hussain Sagar Lake, Hyderabad reported by Subha and Srinivas,2017 as, Cd (221.53) > Ni (182.43) > Cu (178.01) >Cr (139.72) >Pb (93.31 mg/Kg, dw), which were much higher than reported in this investigation²¹. However, the levels of Cu, Pb and Cd in roots and shoot of Parethenium samples collected from University road soil and NHA soil, Islamabad by Tariq et al, 2020, Cu found in the roots were 18.91 ± 0.21 and 17.19 ± 0.32 and in shoots, 19.87 ± 0.12 and 17.72 ± 0.15mg/Kg, respectively, while Cd not detected in any samples¹¹. Similarly, Pb in University Road soil and NHA soil found in roots were 4.39 ± 0.19 and 4.32 ± 0.24 and in shoot 7.82 ± 0.12 and 6.45 ± 0.29mg/Kg,dw, respectively¹¹. These results were also higher than the present results. In a pot test reported by Samreen et al., 2017, that in Parthenium plant shoot Ni was found slightly greater than Cr, while Cr shows much greater accumulation in roots than shoot in comparison to the nickel²⁶. These findings reported on different soils, including the present one, revealed that the levels of accumulated Cd, Cr, Cu, Ni and Pb reported in roots and shoot of Parthenium varied widely. The wide variations in accumulated levels of heavy metals compiled here reflected the dependency of the metal uptake and their translocation to the above ground parts of the Parthenium hysterophorus L, on the soil characteristics of the sampling site, agronomy and climatic conditions⁵.

Uptake of metals and their bio-concentration and Translocation:

Uptake of metals from agri-soil into root cells is a step of major importance for the process of phytoextraction⁷. After entering to plants from bulk soil through their root system metals further move to the above ground parts of the plant. Plant uptake of metals from soil may occur either passively with the mass flow of water into the roots, or through active transport crosses the plasma membrane of root epidermal cells⁷. However, for phytoextraction to occur metals must also be transported from the root to the shoot. The ascent of saps containing dissolved nutrients, minerals and some toxic metals, from the root to the shoot through phloem column is partly controlled by leaf transpiration⁷. To understand the extent of bio-concentration of studied metals and the magnitude of their translocation to the aerial parts of the plants, the bio-concentration factor (BCF), translocation factor (TF) and biological accumulation Coefficient (BAC) were computed as described earlier^24,27,28. The various BCF, Tf and BAC due to Cd, Cr, Cu, Ni and Pb for Parthenium hysterophorus L were computed and used to evaluate the bio- accumulation of studied metals from soils in roots and then their translocation to the shoots. These values also provide the information about the ability and magnitude of the plant to bio-concentrate studied metals in plant parts relative to their levels in agri-soil and thereby the assessment of phyto-extraction potential of the plant for these metals⁹.

Bio-concentration of metals in Parthenium plant:

Bio-concentration factor is unique ability of a plant to take up and accumulate heavy metals and other contaminants in its tissues from agri-soils. A value of bio-concentration factor (BCF) gives an idea about the bio-absorption of that metal from soil and its bio-magniﬁcation in various plant parts, roots, stem and leaves²⁹. BCF values are used to determine the amount of heavy metals consumed by the plant with reference to its concentration in the soil⁹. The bio-concentration factor (BCF) was calculated as metal concentration ratio of plant roots to soil²⁴. BCF values may also be computed as the ratio of concentration of a metal in plant tissue of root or shoot to the concentrations in soil using the relation:

Concentration of a metal in plant roots or shoots

BCF = -----------------------------------------------------

Concentration of that metal in concerned soil

In this study, the soil to root bio-concentration factors (BCF_Root) for Cd, Cr, Cu, Ni and Pb in Parthenium hysterophorus L were computed (Table-2, Fig-2) in the order of: Cd (1.08) ~ Cu (1.08) >Ni (1.06) >Cr (0.84) >Pb (0.82). Thus the values of BCF_Rootfor Cd, Cu and Ni were >1, while for Cr and Pb the BCF_Root were <1.

Table-2: Bio-concentration Factors (BCF) and Translocation Factors (TF) and Bio-accumulation coefficients (BAC) of studied Metals in Parthenium hysterophorus L

Parameters	Cd	Cr	Cu	Ni	Pb
BCF _Root	1.08	0.84	1.08	1.06	0.82
TF _Shoot	1.20	0.99	0.98	1.24	1.08
BAF	1.30	0.83	1.06	1.31	0.89

The bio- accumulation potential of plant root system for heavy metals differs widely due to their diverse morphology and may be significantly selective for one or more metals¹. On comparing these results with earlier findings of Sanghmitra et al., 2011, on Parthenium hysterophorus L. wildly growing around Visakhapatnam city, the BCF_R and BCF_S values being 8.33 and 1.67 for Cd, respectively, depicts the ability of the plant to accumulate a particular metal with respect to its concentration in the soil substrate, similarly, BCF values reported by Subha and Srinivas, 2017, from Hussain Sagar Lake area, Hyderabad, for Ni was higher in the range of 2.92 to 6.85 followed by BCF for Cd ranging from 2.41 to 4.72, the overall BCF order was: Cd (4.73)>Ni (4.64)>Cu (1.83)>Cr(1.54)>Pb (0.72). Both these findings have reported much higher BCF than the present findings^{21, 30}. Parthenium grown on the fly ash near Coal mines on Varanasi-Singrauli Highway reported by Singh et al., 2010 showed the enrichment factor (EF) values of studied metals in contaminated soil was as: Cd (2.33) > Ni (1.58) > Pb (1.42) > Cr (1.11) > Cu (1.10), which were higher than the present findings⁵. In a pot test Samreen and Khan, 2017 reported high BCF values for Ni (5.29) and for Cr (8.22) in Parthenium. Hysterophorus²⁶. The BCF values, Pb (8.24), Cu (48), Cd (44), Ni (37) for Parthenium reported by Ahmad and Al-Othman, 2014 were much higher than present findings¹⁸. As most of the BCF_R values are >1, except for Cr and Pb in Parthenium hysterophorus L., therefore, it can be used for phyto-extraction of Cu, Cr, and Ni from contaminated soil.

Translocation of metals to above ground parts of Parthenium plant:

The translocation factor (TF) is the ability of the plant to translocate heavy metals from lower parts (roots) of the plants to above ground parts (shoots i.e. stem and leaves)⁴. Translocation Factor (TF) was described by Cui et al, 2007 and Li et al, 2007 as the ratio of heavy metals in plant shoot to that in plant root^{27, 28}. The translocation factor (TF) signifies the mobility of metals from roots to the upper parts of the plant and thus it accounts the removal of metals from the agri-soils²⁹. TF is the measure of translocation of a metal from the roots to a upper part of the plant, which is calculated by the equation:

Concentration of metal in stem and /or leaf

TF = ------------------------------------------------------

Concentration of metal in roots of the plant

In present study the root to shoot translocation, TF_Shoot were Ni (1.24) >Cd (1.20) > Pb (1.08) > Cr (0.99~ 1.00)> Cu (0.98 ~ 1.00). For a metal accumulator plant species the TF should be >1 and for non-accumulators TF invariably <1³⁰. The TF values for Pb, Ni, Cd and Cu on Parthenium was reported by Ahmad and Al-Othman as, 8.5, 4.3, 3.3and 1.05, respectively. On the basis of the TF values Parthenium hysterophorus was found more efficient for translocation of Pb, Ni, Cd in comparison to Cu and the order of reported translocation factors (TF) was: Pb (8.5) > Ni (4.3) > Cd (3.3) > Cu (1.05)¹⁸. Parthenium grown on the fly ash contaminated site near Coal mines on Varanasi-Singrauli Highway reported by Singh et al., 2010 showed translocation factor (TF) of metals from root to shoot was found to be in the order of Pb (1.03) > Ni (0.94) > Zn (0.85) > Cd (0.82) > Cr (0.73)⁵. These TF values suggested that Pharthenium hysterophorus can efficiently be used for phyto-extraction of Pb, Ni and Cd from metal contaminated soil1⁸. The order of TF values reported by Malik et al, 2010 were Pb (2.8)> Ni (2.6) > Cr (2.2) > Cu (1.9), which also suggested efficient translocation and suitability of the Parathenium plant phytoextraction of these metals¹⁹. The TF value for Cd on Parthenium plant reported by Sanghmitra et al, 2011 was 2.5³⁰. The high values of TF>1 for Pb, Ni and Cd suggested that Pharthenium hysterophoirus can be used for phytoextraction of Pb, Ni and Cd^19,30. TF for Ni and Cr reported by Samreen and Khan, 2017 varied as Ni (1.04)> Cr (0.82)²⁶.

Concentration of heavy metal found in the upper part (stem and leaf) of the plant

TF = --------------------------------------------------------------------------

Concentration of heavy metal found in the lower part (roots) of the plant

In present study the root to shoot translocation, TF_Shoot were Ni (1.24) >Cd (1.20) > Pb (1.08) > Cr (0.99~ 1.00)> Cu (0.98 ~ 1.00). For a metal accumulator plant species the TF should be >1 and for non-accumulators TF invariably <1 ³⁰. The TF values for Pb, Ni, Cd and Cu on Parthenium was reported by Ahmad and Al-Othman, 2014 as, 8.5, 4.3, 3.3and 1.05, respectively¹⁸. On the basis of the TF values Parthenium hysterophorus was found more efficient for translocation of Pb, Ni, Cd in comparison to Cu and the order of reported translocation factors (TF) was : Pb (8.5) > Ni (4.3) > Cd (3.3) > Cu (1.05)¹⁸. Parthenium grown on the fly ash contaminated site near Coal mines on Varanasi-Singrauli Highway reported by Singh et al., 2010 showed translocation factor (TF) of metals from root to shoot was found to be in the order of Pb (1.03) > Ni (0.94) > Zn (0.85) > Cd (0.82) > Cr (0.73)⁵. These TF values suggested that Pharthenium hysterophorus can efficiently be used for phyto-extraction of Pb, Ni and Cd from metal contaminated soil¹⁸. The order of TF values reported by Malik et al, 2010 were Pb (2.8)> Ni (2.6) > Cr (2.2) > Cu (1.9), which also suggested efficient translocation and suitability of the Parathenium plant phytoextraction of these metals¹⁹. The TF value for Cd on Parthenium plant reported by Sanghmitra et al, 2011 was 2.5³⁰. The high values of TF>1 for Pb, Ni and Cd suggested that Pharthenium hysterophoirus can be used for phytoextraction of Pb, Ni and Cd^{19, 30}. TF for Ni and Cr reported by Samreen and Khan, 2017 varied as Ni (1.04)> Cr (0.82)²⁶.

Fig. 2 -BCF, TF and BAC for studied metals in Parthenium hysterophorus L.

Biological accumulation coefficient (BAC):

The bio-concentration coefficient or biological accumulation Coefficient, BAC_Shoot of studied heavy metals from soil to the plant’s shoot was calculated as ratio of heavy metal in shoots to that in soil, as suggested by Li et al., 2007 and Cui et al., 2007 as follow^27,28.

Concentration of metal in plant shoots

BAC = --------------------------------------------------------

Concentration of metal in concerned Soils

The order of various soil to shoot biological accumulation coefficients, BAC_Shoot for studied heavy metals in Parthenium hysterophoirus L. (Table-2) was, Ni (1.31) > Cd (1.30)> Cu (1.06) > Pb (0.89) >Cr (0.83), thus the values of BAF for Ni, Cd and Cu were >1 and others were < 1 and varied between 1.31 and 0.83. The biological accumulation coefficient (BAF) signifies the extent of accumulation of metals in plant’s upper parts, if the value of BAF < 1 or BAF = 1 then it means that plants do not accumulate the metals rather the plant only absorb the metals. When, the value of BAF > 1, the plant under study considerably accumulates the metals²⁰. The BAC values reported by Malik et al.,2010 were Pb (1.7) and Cu (1.4)¹⁹. BAC for Ni and Cr reported by Samreen and Khan, 2017 on Parthenium hysterophorus were, Ni (5.5) and Cr (6.77), which suggested that the plant can be used as phytoremediaton of Ni and Cr from contaminated soil²⁶. The order of BAF for Parthenium hysterophorus grown on K. Company soil, Pakistan was Pb < Ni < Cu < Cd²⁰. Plants with high BCF values, generally > 1 are suitable for phyto-extraction⁵. Thus, on the basis of observed high BCFs, TFs and BAC values suggested that Parthenium hysterophorus L. has potential for phytostabilization and phytoextraction for the concerned metals, therefore the plant can be used for phytoextraction of Cd, Cr, Cu, Ni and Pb from contaminated site¹⁹.

CONCLUSIONS:

Parthenium hysterophorus L growing on the barren land soil along with the National Highways, the order of bio-accumulated levels of heavy metals in the roots and shoots of the plant were: Pb (6.67± 0.34) > Cu (6.11 ±0.27) >Cr (6.05± 0.23) >Ni (4.14± 0.18) >Cd (1.42± 0.11) and Pb (7.22±0.29) >Cu (5.96±0.25)>Cr (5.97 ±0.23)>Ni (5.13±0.21)> Cd(1.70±0.14 mg/Kg.dw), respectively. The plant not only accumulated the Cd, Cr, Cu, Ni and Pb considerably, but grows rapidly with great biomass due to easy adaptation to different conditions. The order of soil to root bio-concentration factors, BCF_Root for studied metals registered by Parthenium hysterophorus L was, Cd (1.08)~ Cu (1.08) >Ni (1.06) >Cr (0.84) >Pb (0.82), values for Cd, Cu and Ni were >1, while for Cr and Pb the BCF_Root were <1. The root to shoot translocation, TF_Shoot were Ni (1.24) >Cd (1.20) > Pb (1.08) > Cr (0.99~ 1.00) > Cu (0.98 ~ 1.00). The values of BAC_Shoot, in Parthenium hysterophoirus L. for studied heavy metals were, Ni (1.31) > Cd (1.30)> Cu (1.06) > Pb (0.89) >Cr (0.83). When, the biological accumulation coefficient, BAF values being > 1, the plant under study considerably accumulates the metals in its upper parts. Comparatively higher BCF, TF and higher BAC values for studied metals suggested that the plant has potential to translocate studied metals to the above ground parts of the plants. As plant Parthenium hysterophorus L has shown the ability to translocate the studied metals to its above ground parts, the plant is suitable for phyto-extraction of studied heavy metals from the contaminated soil.

ACKNOWLEDGEMENT:

The author is thankful to Dr. S. K. Dabral, former Head and Dr. Dayadhar Dikshit, Department of Chemistry, Pt. L.M.S. Govt. Post Graduate College (Autonomous College) Rishikesh, Dehradun, Uttarakhand, for help in the analysis of metals and valuable discussion.

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Received on 12.06.2023 Modified on 01.07.2023

Asian J. Research Chem. 2023; 16(4):277-284.

DOI: 10.52711/0974-4150.2023.00046

Metals	Concentration in Soil (n = 5)	WHO Limits for Soil (Mg/Kg)	Concentration (mg/Kg, dw ± σ)		WHO Limits for Plants (mg/kg)
Metals	Concentration in Soil (n = 5)	WHO Limits for Soil (Mg/Kg)	Root	Shoot	WHO Limits for Plants (mg/kg)
Cadmium	1.31± 0.08	1.00	1.42±0.11	1.70±0.14	0.01
Chromium	7.18± 0.39	50.00	6.05±0.23	5.97±0.23	1.30
Copper	5.64± 0.26	20.00	6.11±0.27	5.96±0.25	10.0
Nickel	3.91± 0.21	20.00	4.14 ±0.18	5.13±0.21	10.0
Lead	8.12 ±0.48	10.00	6.67 ±0.34	7.22±0.29	2.0

INTRODUCTION:

To estimate the accumulated Cd, Cr, Cu, Ni and Pb in soil, 1.0 g of the finely grinded soil samples were digested separately with HNO3 –HCl–HClO4 mixture (5:1:1) for several hours to get transparent extracts, which was filtered and diluted to a volume of 100 mL with double distilled water17.

BCF = -----------------------------------------------------

Concentration of that metal in concerned soil

Translocation of metals to above ground parts of Parthenium plant: