Bioscience Evidence 2024, Vol.14, No.4, 154-160 http://bioscipublisher.com/index.php/be 155 2000). When applied to the skin: Zn is likely unsafe. Using zinc on broken skin may cause burning, stinging, itching, and tingling. Similarly, Pb consumption is associated with great risk to brain development, where irreversible damage can occur. Higher levels can damage the kidney and nervous system in both children and adults. Very high lead levels may cause seizures, unconsciousness and death (Madhu and Sadagopan, 2020). The development and production of plants depend on several nutrients such as Mg, Cu, Mn, Zn, Fe, Ca, Mo and Ni. Some of these are micronutrients that can improve a variety of cellular processes in plants, including pigment biosynthesis, ion homeostasis, gene regulation, respiration, enzyme activity, sugar metabolism, photosynthesis, nitrogen fixation, etc., at relatively low concentrations (Tiwari and Lata, 2018). However, they can negatively impact plant growth, development and reproduction when they are accumulated at concentrations above their optimal levels (Rashid et al., 2023; Angon et al., 2024). Arsenic, cadmium, zinc and lead are among the prominent heavy metals identified as common pollutants, exerting adverse effects on the intricate interplay between soil health, plant vitality, and the overall well-being of human and animal populations (Herawati et al., 2000). Studies have shown that these heavy metals can persist in nature for more than twenty years (Kapoor and Singh, 2021), and the only solution is to remove them from soil to a permissible level for plants. According to Madhu and Sadagopan (2020), a lot of studies have been conducted on remediation techniques for heavy metal polluted soil, including in-situ remediation techniques (surface capping, encapsulation, electrokinetic extraction, soil flushing, chemical immobilization, phytoremediation or bioremediation) and ex-situ remediation techniques (landfilling, soil washing, solidification or vitrification). Although these methods have high performance, most of them are expensive, harmful to the environment and time-consuming. Phytoremediation has been identified for cost-effectiveness and environmentally friendly approach to removal of heavy metals from soil. It emerges as a widely accepted solution, utilizing the inherent capabilities of plants to degrade or remove pollutants from the soil environment (Haq et al., 2020; Islam et al., 2024). There are advantages of using phytoremediation. It is economically feasible as it is an autotrophic system powered by solar energy; it is simple to manage; and the cost of installation and maintenance is low. Also, it is eco-friendly as it can reduce exposure of the pollutants to the people and environment particular underground water. Chromolaena odorata (L.), commonly known as Siam weed is a fast-growing perennial, diffuse and scrambling shrub. It is an exotic weed that has become aggressively invasive in Nigeria. It forms dense stands and is a problem in agricultural land and commercial plantations causing great economic and biodiversity losses. It is found in disturbed areas, abandoned and waste lands, where there can be potentially high soil heavy metal contamination (Srirueang et al., 2022). It has been recorded to grow naturally in waste sites, hence it was hypothesised that it has some inherent ability for survival under toxic environment, which might include ability to absorb and sequester heavy metals without negative symptoms. The objective of the study was to assess the potential of C. odorata for phytoremediation of soil contaminated with lead (Pb) and zinc (Zn). This was hoped to contribute to the ongoing discourse surrounding sustainable and effective environmental remediation strategies. 2 Materials and Methods 2.1 Collection of soil used for planting Samples of the soil used for planting were analysed to know its physical and chemical properties. The samples were shade-dried, passed through a 2-mm sieve, and analyzed for physical and chemical properties using standard methods of the Association of Official Analytical Chemists (AOAC, 1990). 2.2 Experimental set up Uniform young seedlings of C. odorata were collected from a plantation site in Akure, Ondo State, Nigeria, and transplanted into polyethylene pots filled with top soil mixed with 0, 20, 40, 60, 80 and 100 mg ZnSO4 or PbSO4 to 1 kg soil (mg/kg Pb or Zn). The targeted concentrations fell within and above the permissible level for Pb (85 mg/kg) and Zn (50 mg/kg) in soil according to World Health Organization, WHO (1996). The experiment was conducted at the screen house of Plant Science and Biotechnology Department, Adekunle Ajasin University, Akungba-Akoko, Ondo State, Nigeria. During the experiment, the screen house had an average morning
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