Phytoremediation of mildly contaminated, wastewater-irrigated soils using mixed planting of <i>Brassica juncea</i> and <i>Urtica dioica</i>

Soil contamination with toxic heavy metals is a critical concern in areas irrigated with industrial and domestic wastewater. This study assessed the phytoextraction potential of <i>Brassica juncea</i> (Indian mustard) and <i>Urtica dioica</i> (stinging nettle) under mixed planting for the remediation of cadmium (Cd), lead (Pb), and nickel (Ni). Surface soils (0-15 cm) were collected, filled into 8-kg pots, and planted at a density of 50 plants m^-2 (35 <i>B. juncea</i>, 15 <i>U. dioica</i>), followed by 60 days of wastewater irrigation. Metal accumulation exhibited a root > stem > leaf distribution in both species, with <i>B. juncea</i> recording higher concentrations (Cd: 634.36 mg/kg; Pb: 563.54 mg/kg; Ni: 445.68 mg/kg) compared to <i>U. dioica</i> (Cd: 317.18 mg/kg; Pb: 305.92 mg/kg; Ni: 222.84 mg/kg). Soil mass balance revealed reductions of 74.8% for Pb, 38.0% for Cd, and 39.2% for Ni, corresponding to removals of 307.30 mg/m². Phytoremediation indices (bioconcentration factor (BCF), translocation factor (TF), and efficiency) confirmed Pb as the most effectively removed element, with <i>B. juncea</i> extracting ∼68.5% of soil Pb in one cycle. Statistical analysis (mean ± SD; 95% CI) validated these reductions. Mixed planting improved uptake by combining high biomass with efficient extraction, highlighting a cost-effective, sustainable approach for remediating wastewater-irrigated soils.