Sustainable management of mixed soil contaminants through integrated biosystems: Efficacy of biochar and humic acid amendments in marigold phytoremediation

Abstract

A study investigated the fate and transport of mixed contaminants—chromium (Cr), cadmium (Cd), and perfluorooctanoic acid (PFOA)—in soil using an integrated biosystem. Known concentrations of contaminants and organic amendments (biochar and humic acid) were introduced into unpolluted soil to assess degradability, mobility, bioavailability, and phytoremediation potential using marigold plants. Contaminants reduced plant physiological traits, including photosynthetic rate (33%), stomatal conductance (58%), and transpiration rate (74%) compared to control plants. Root traits and the effectiveness of biochar and humic acid were evaluated using “GiA Roots” software. Root architecture varied significantly due to contamination, with seven traits analyzed through principal component analysis (PCA). PC1 accounted for 79% variance, highlighting amendment effects, while PC2 (21%) grouped mixed contaminant treatments, indicating that biochar and humic acid enhanced root growth in contaminated soil. Additionally, untreated contaminated soil produced the root growth inhibitor 2-methyl cortisol, identified via GC/MS analysis. Scanning electron microscope analysis showed that roots in control soil had well-defined stele structures, whereas contaminated soil led to severe structural collapse. Post-harvest soil analysis revealed that humic acid treatments reduced Cr, Cd, and PFOA by 48.5%, 40.1%, and 88%, respectively, while biochar treatments achieved reductions of 68.3%, 52.7%, and 92%. These results highlight the effectiveness of biochar and humic acid in reducing contamination through sorptive properties and chemical binding. Applying biochar at 5 t ha⁻¹ or humic acid at 20 kg ha⁻¹, combined with phytoremediation, effectively mitigated soil toxicity, improving crop productivity by lowering contaminant levels.