Evaluation of the Potential Cadmium Phytoremediation in the Nickel Hyperaccumulating Plant Odontarrhena Inflata

Document Type : Research Paper

Authors

• Behrooz Salehi-Eskandari ¹
• Lila Nasr Nasrabadi ²

¹ Department of Biology, Payame Noor University, Tehran, Iran

² Payame Noor University, Tehran, Iran

Abstract

Keywords

• Growth
• Heavy metals
• Phytoremediation
• Translocation factor
• Serpentine soils

Main Subjects

• ..

Introduction

 Serpentine soils are derived primarily from ultramafic rocks composed of ferromagnesian silicates. These soils are often rich in heavy metals, predominantly Ni, and poor in essential macronutrients. Moreover, they are usually shallow, stony, highly porous, and low in organic matter, resulting in low water-holding capacity. Low Ca/Mg ratios further characterize them. Therefore, vegetations of natural serpentine are floristically very distinct from non-serpentine vegetations in neighboring areas. Serpentine areas are widespread in many parts of our country, but in the western parts (Kermanshah), they have high precipitation (700 mm) and rich vegetation. Phytomining can be considered a new technology that uses a hyperaccumulator for economic metal recovery. It provides an innovative approach that can exploit low-grade Ni resources in soils derived from ultramafic outcrops, which are not accessible using conventional mining technologies. Hyperaccumulator plants collected heavy metals in their shoots at the highest concentration specific to each heavy metal. Odontarrhena inflata is a nickel-hyperaccumulating Iranian serpentine endemic in Kermanshah province. It has high potential for Ni-agricultural mining. Cadmium (Cd) is one of the most toxic non-essential heavy metals. Some hyperaccumulator plants can accumulate more than one heavy metal. Given that there was no report on the resistance and accumulation of this hyperaccumulator plant against the heavy metal cadmium, we decided to evaluate its resistance and accumulation compared to nickel in the present study.

Material and methods

Soil samples were collected from around the roots of the Ni-hyperaccumulator O. inflata plant growing in a serpentine habitat. The acidity, water holding capacity, and organic compounds were determined, and after acid digestion, the concentration of heavy elements was measured by the use of acid digestion and different solvents.  Seeds of O. inflata were collected around the Kermanshah serpentine soils. The seedlings were grown in a greenhouse with a 16 h photoperiod (light intensity 200 μEm⁻² s ⁻¹), day/night temperature of 25/20 °C, and regularly watered with one-fourth-strength modified Hoagland’s solution for 25 days. Then they were exposed to 0, 50, 100, 200, 300, and 350 mg/L treatments of Ni and 0, 10, 20, and 40 mg/L treatments of Cd for 14 days. The nutrient solutions were aerated continuously and changed every three days. Shoot and root dry weights were measured after drying in an oven at 70 °C for 48 h, and Ni and Cd concentrations were determined in roots and shoots using a flame atomic absorption spectrophotometer (AAS, Shimadzu model 6200). The Ni and Cd translocation factor (TF) from root to shoot was calculated as their concentration in the shoot divided by their concentration in the root. 

Result

 The results show that the serpentine soils of this region are rich in Fe (iron) and Mg (magnesium), low in organic matter and water holding capacity, high average Ni (1468 mg/Kg), low calcium to magnesium ratio (47/0), and alkaline pH. With increasing concentrations of Ni and Cd, the shoot and root dry weight decreased, so that in the highest concentrations of Ni (350 µm) and cadmium (40 µm), the dry weight of shoots decreased by 47.7 and 65.5%, respectively, compared to the control group, and the dry weight of roots reduced in these highest treatments by 38.4% and 46.2%, respectively. It should be noted that the high concentration of Ni in the medium was more than 8.7-fold that of Cd. Ni and Cd accumulated in the roots at the highest concentration by 3140 and 3858 µg/g dry weight, respectively. But these metals accumulated in the shoot were 6516 (Ni) and 353 (Cd) µg/g dry weight, respectively, of O. inflata. The translocation factors (Tf) were recoded, 2.7 and 0.13 for Ni and Cd, respectively.

Conclusions

The characteristics of the studied soil indicate nutrient deficiency, rich in heavy elements, especially Fe, Mg, and Ni, which is in agreement with other reports of serpentine soils. The dry weight of the shoots and roots of the hyperaccumulator plant decreased as the concentrations of Ni and Cd in the medium increased. This decrease was greater at the highest level of Cd. Accumulation of Ni and Cd in shoots and roots increased with increasing concentrations of these heavy elements in the medium. The translocation factor of Ni and Cd was higher and lower than 1, respectively, so Ni and Cd accumulated in the shoots and roots of O. inflata. This demonstrates that O. inflata is a Ni-hyperaccumulator but an excluder for Cd. Therefore, the fact that this plant is a hyperaccumulator of Ni cannot be a basis for its hyperaccumulation of other heavy elements. Regarding the adaptation of this plant to Iranian serpentine soils, it can be used for nickel phytomining and phytoremediation in serpentine and nickel-contaminated soils.

Funding

The study was funded by the University of Payame Noor, Country, Islamic Republic of Iran, and Grant No. 48497.

Authorship contribution

Conceptualization, Behrooz Salehi-Eskandari; methodology, Behrooz Salehi-Eskandari; software, Behrooz Salehi-Eskandari; validation, Behrooz Salehi-Eskandari and Lila Nasr Nasrabadi; formal analysis, Behrooz Salehi-Eskandari; investigation, Lila Nasr Nasrabadi; resources, Behrooz Salehi-Eskandari; data curation, Lila Nasr Nasrabadi; writing—original draft preparation, Behrooz Salehi-Eskandari; writing—review and editing, Behrooz Salehi-Eskandari; supervision, Behrooz Salehi-Eskandari; project administration, Behrooz Salehi-Eskandari. All authors have read and agreed to the published version of the manuscript.

Declaration of Generative AI and AI-assisted technologies in the writing process

No artificial intelligence tools were used in the article writing process.

Data availability statement

Data would be available on request from the first author.

Acknowledgements

The authors are thankful to the Graduate School of Payame Noor University for providing the research facilities needed for this study. The authors would like to express their sincere gratitude to Dr Mohammad Ghafoori for her invaluable guidance throughout this study. His insightful feedback and expertise were instrumental in shaping this research. The authors would like to thank anonymous referees for their constructive comments.

Ethical considerations

The authors avoided data fabrication, falsification, and plagiarism, and any form of misconduct.

Conflict of interest

The authors declare no conflict of interest.