Biomass Growth and Remediation Efficiency of Chrysopogon zizanioides (L.) Nash for artificially contaminated Alluvial soil

Abstract

Though Chrysopogonzizanioides(vetiver grass) has potential characteristics for remediation of contaminated soils, sediments, and water, but it has very limited application for the remediation of contaminated alluvial soil. The vetiver was planted to evaluate its biomass growth in artificially contaminated alluvial soil in Prayagraj, India for the purpose of its remediation. The vetiver was planted on alluvial soil mass artificially contaminated by two heavy metal salts, lead nitrate (Pb(II)) and potassium dichromate (Cr(VI)), for a period of 150 days. The vetiver grass, having 10cm root and 20cm shoot length, was planted in total 30 treatment boxes of dimensions 45cm x 45cm x 90cm, made of GI sheets. Four replicates (100, 300, 500, and 700mg/kg) of lead (Pb(NO3)2), four replicates (50, 100, 200, and 400mg/kg) of chromium (K2Cr2O7), one mixed replicate (Cr-100+Pb-300), and one control have been selected. With increasing Cr-concentration in soil, vetiver shows a higher toxic effect, resulting in reduced biomass production with increased Cr-accumulation in roots. Whereas increasing Pb-concentration in soil, biomass production increases with minimum toxic effects. 65-75% of Cr and Pb were found to accumulate in root tissues and only 10-15% were translocated to aerial parts from roots tissues. The findings reveal that vetiver has good potential for rhizostabilization of Pb and Cr from polluted soils, minimizing the risk to contaminate groundwater and entering into the food chain as well as enhanced biomass of vetiver would be utilized for slope stabilization of embankments constructed on erodible soils and as a potential renewable energy source.

Introduction

Background and Environmental Concern

Industrialization, urbanization, and lifestyle changes have led to the overexploitation of natural resources and increased environmental contamination—especially soil, air, and water pollution. Among pollutants, heavy metals are of serious concern due to their toxicity and persistence in the environment. Common sources include mining, industry, landfills, and agriculture. The most hazardous metals include lead (Pb), chromium (Cr), arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu), and mercury (Hg).

2. Impact of Heavy Metals

Heavy metals affect human/animal health (e.g., cancer, liver/kidney damage, neurological issues) and plants (e.g., stunted growth, leaf chlorosis, necrosis). For example:

• Cadmium: kidney dysfunction, leaf browning.

• Chromium: cancer, reduced seed emergence.

• Lead: CNS damage, dark green foliage.

• Mercury: mental deterioration, stunted growth.

• Copper: hypertension, yellow/purple leaves.

3. Soil Contamination in India

Heavy metals are present in surface soil in cities like Prayagraj, with lead, chromium, and zinc found in high concentrations. Regulatory limits and acceptable levels have been defined for safe exposure, with Cr(VI) and Pb(II) being highly toxic and carcinogenic.

4. Phytoremediation as a Solution

Due to the limitations (cost, environmental harm) of traditional remediation methods, phytoremediation—using plants to extract or stabilize contaminants—offers an eco-friendly and cost-effective alternative. Ideal phytoremediation plants should:

• Tolerate and accumulate heavy metals

• Have deep, fibrous roots

• Grow rapidly with high biomass

5. Role of Vetiver Grass

Vetiver (Chrysopogon zizanioides), a fast-growing perennial from the Poaceae family, is promising for phytoremediation. It has:

• A deep, fibrous root system

• High tolerance to contaminants

• Strong biomass production

Despite its potential, vetiver has been underutilized in India’s alluvial soils, which make up 43% of the land (mainly in northern plains). The Central Pollution Control Board (CPCB) identifies 280 contaminated sites in India, 43 of which are in Uttar Pradesh.

6. Study Objective and Location

The study aimed to evaluate vetiver’s growth and metal extraction ability in contaminated alluvial soil (without fertilizers), carried out at Motilal Nehru National Institute of Technology, Prayagraj, Uttar Pradesh.

7. Materials and Methods

• Soil: Virgin alluvial soil was collected and characterized (pH: 7.65, field capacity: 43%). It was low-compressibility silt (ML) with quartz, kaolinite, illite, and other minerals.

• Contaminants: Soils were artificially contaminated with lead nitrate (Pb(NO?)?) and potassium dichromate (K?Cr?O?).

• Plant Material: Vetiver was sourced from Chennai and grown in the lab garden.

• Setup: 30 galvanized iron boxes (45×45×90 cm) were used, each with soil sampling holes, allowing depth-specific analysis over 150 days.

• Climate: The monsoon season aided growth, with rainfall around 250–300 mm.

Conclusion

The biomass growth of vetiver (Chrysopogon zizanioides(L.) Nash) inalluvial soilhas been investigated. Two heavy metal salt, K2Cr2O7 and Pb(NO3)2, were used to contaminate the soil artificially. Based on the experimental study and discussion, following are the main conclusions. 1) Exponential growth of vetiver was observed during 150 days of plantation in artificially contaminated alluvial soil by Cr and Pb. The vetiver growth was observed highest between 60 to 90 days of plantation. 2) Chromium (Cr(VI))shows the toxic effects on growth of vetiver with decreased survival rate, reduced mass production, lesser number of leaves, stems (tillers), stems with flower and the color of the leaves were varying from light green to light yellowish. In the treatment box number-4 (Cr-400 mg/kg), the vetiver was planted with 9 clumps out of which only six survived with reduced biomass growth. 3) Lead (Pb(II))shows the positive effect on mass growth of vetiver. In all the Pb-treated soil, the vetiver had 100% survival rates. With increase in Pb-concentration in soil, the biomass growth was also enhanced in terms of number of leaves, stems and more stem with flowers. The color of leaves varied from light green to dark green.In the treatment box number-8 (Pb-700 mg/kg),highest mass growth was observed in terms of increased number of leaves, stems, stems with flowers, and height of shoot and roots. The overall growth of vetiver (shoot & root length, stems, leaves, weight of biomass) was found in decreasing order with increasing the concentration level of Cr, while in case of Pb the growth of vetiver was found to be increasing with increasing the concentration levels of Pb in soil. 4) In the combined contamination of Cr and Pb, enhanced growth of biomass was observed as compared to Cr-contaminated soil and reduced as compare to Pb-contaminated soil and virgin soil. The reduction was observed in terms of height (length) and mass of shoots and roots, and the number of leaves and stems. The growth was higher in case of Pb-contaminated soil as comparison to Cr-contaminated soil. 5) The huge biomass growth of vetiver in Pb-contaminated soil, makes it a potential candidate for stabilization of embankment constructed with erodible soils or soils which are prone to high erosion. 6) The structure of the roots in contaminated and uncontaminated alluvial soil was found to be massive,fibrous and with enhanced roots hairs. The average growth of rootsin virgin soil was found to be approximately 1.3cm/day which was reduced in contaminated soil. The roots of the vetiver below the top soil surface (0-4cm), were found to be very fine and meshed with each other creating a fine and fibrous net/wall like structure and bound the top soil very well, enabling the plant to retain water and moisture.The massive and fibrous roots systems ensure high contact surfaces area for soil particles and contaminants resulting in efficient phytoremediation of contaminated soil. In the Cr-contaminated soil the growth of roots was considerably reduced in comparison to root growth in virgin soil whereas in Pb-contaminated soil, enhanced growth of roots was observed. 7) Cr and Pb both were found to accumulate more in the root of vetiver grass and a small amount,almost 15-20% of Cr and Pb in soil was translocated to shoot,above ground part of vetiver grass. 8) A comparison of vetiver biomass growth in Cr(VI) and Pb(II) contaminated soil indicates that the effects of Pb(NO3)2-contamination lead to better growth of vetiver however in K2Cr2O7-contaminated soil, the growth was appreciably reduced due to higher accumulation of chromium within its root tissues. A little amount of Cr and Pb were translocated from vetiver root to shoot. For higher biomass growth in lead nitrate contaminated soil, the nitrogen associated with the salts might be in support of biomass growth as a fertilizer which was not observed in case of potassium dichromate due to presence of potassium.The results indicate that the vetiver grass is a potential candidate for rhizostabilization (phytoremediation) of Cr and Pb from contaminated soil. By the rhizostabilization of contaminants, vetivergrass was found effective to reduce the risk of contaminants to move downward (groundwater contamination) andminimize the associated human health risk due to toxicity of Cr and Pb through food chain. The higher biomass growth of vetiver in contaminated soil makes it a suitable candidate for erodible soil stabilization, carbon sequestration, and for higher renewable biomass energy production through pyrolysis. Acknowledgement The author acknowledges the support of team members of Center for Interdisciplinary Research, Motilal Nehru National Institute of Technology Allahabad, Prayagraj for providing XRD facility and Material Science & Engineering, IIT Kanpur for providing the FESEM/XRF facility for their kind co-operation in the analysis of the results. Conflicts of interests/competing interests The authors declare no competing interests Supplementary Information Not applicable. Data availability The data used to support the findings of this study are available from the corresponding author upon request. Ethics approval Not applicable. Consent for publication All authors consent to submit this manuscript for publication.

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Copyright © 2025 Pawan Kumar, Amrendra Singh. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.