Brassica juncea as a Feasible Hyperaccumulator of Chosen Potentially Toxic Metals Under Extreme Environmental Conditions

Nowadays, many sites are considered waste, due to high potentially toxic metal (PTM) concentration. Recycling of globally critical metals requires development of environmentally friendly processes for metal recovery. To study plants response to elevated Zn and Cu concentration in soil, a greenhouse experiment was designed using hyperaccumulator Brassica juncea. Plants were irrigated daily with PTM solutions, with final mass of both Zn and Cu added to the soil reaching 104.5, 209, 313.5, and 330 mg. After 8 weeks, samples were harvested, dried, weighed, and elemental analysis was conducted using atomic emission spectrometry (Agilent Technologies 4210 MP-AES). Phytotoxicity was determined based on visual observation, biomass, and chlorophyll measurements. The highest accumulation of Zn and Cu was found in the stem and leaf material, with observed concentrations of Zn in the leaf being 16.750 mg kg⁻¹ and 7.170 mg kg⁻¹ of Cu in the stem. The highest allocated in the biomass mass of Zn and Cu was in T4 treatment reaching 25.8 mg and 9.5 mg, respectively. Treatment with 330 mg Zn and Cu application displayed a 62.3% decrease in stem mass, a 25% decrease in average root mass (LD30 reached), and a 59% decrease in leaf mass when compared with the control. With increasing PTM concentration, root, biomass (from about 0.4 to 0.1 g; from about 3.8 to 2.0 g, respectively) and chlorophyll “a” (from about 24 to 19 μg/cm²) decline was observed, which correlates with observed chlorosis. This study reaffirmed the capabilities of B. juncea to bioaccumulate Zn and Cu from an enriched soil and provided further understanding as to how Zn and Cu translocate within plant tissues.