Comparative effectiveness of organic and inorganic amendments on cadmium bioavailability and uptake by Pelargonium hortorum

PURPOSE: The aim of this study was to compare organic and inorganic amendments namely citric acid, ammonium nitrate, compost, and titanium dioxide nanoparticles (TiO₂ NPs) with ethylenediaminetetraacetic acid (EDTA) in enhancing the bioavailability of cadmium (Cd) in assisted phytoextraction. MATERIALS AND METHODS: Uncontaminated soil was spiked with different levels of Cd (25–150 mg kg⁻¹) by using CdSO₄ salt. Different levels of five amendments used were as follows: EDTA (0–5 mmol kg⁻¹), citric acid (0–10 mmol kg⁻¹), ammonium nitrate (0–10 mmol kg⁻¹), TiO₂ NPs (0–100 mg kg⁻¹), and compost (0–10%). Pelargonium hortorum plants were grown on amended soils for a period of 6 months and different parameter were considered to evaluate bioavailability of Cd upon application of amendments. RESULTS AND DISCUSSION: The bioavailability of Cd in soil was increased by 1.2-, 0.8-, 0.4-, and 0.2-fold in EDTA, citric acid, ammonium nitrate, and TiO₂ NPs, respectively. However, Cd bioavailability was decreased by 0.5-fold in compost-amended soils. The efficiency of amendments for mobilizing Cd followed the order: EDTA > citric acid > ammonium nitrate > TiO₂ NPs > compost. The maximum accumulations of Cd in root (350 mg Cd kg⁻¹) and shoot (943 mg Cd kg⁻¹) were observed upon EDTA application and minimum concentrations in root (125 mg Cd kg⁻¹) and shoot (104 mg Cd kg⁻¹) were observed in compost-amended soils. The maximum (2.7 g) and minimum (1.5 g) plant biomass was observed upon compost and EDTA application, respectively. The maximum Cd uptake per plant (1.44 mg) and metal extraction ratio (4.4%) were observed in citric acid-amended soils due to better biomass produced. CONCLUSIONS: Among all amendments, citric acid can be recommended as an environmentally friendly and effective substitute to EDTA for assisted phytoextraction of Cd to decontaminate polluted soil as Cd uptake per plant and metal extraction ratio were the highest upon application of citric acid.