Accumulation Potential Cadmium and Lead by Sunflower (Helianthus annuus L.) under Citric and Glutaric Acid-Assisted Phytoextraction

TL;DR

Citric and glutaric acid amendments were tested to enhance Cd/Pb phytoextraction by sunflower, with citric acid generally promoting growth and metal uptake and glutaric acid showing treatment-dependent, sometimes inhibitory, effects. The authors conclude organic acids may assist sunflower phytoextraction, but outcomes depend on metal type, concentration, and organic acid.

Key findings

• Citric acid improved sunflower growth, with maximum shoot/root biomass promotions of 20.97%/15.21% in Cd10 and 16.38%/12.33% in Pb50 (p < 0.05); the highest complex-treatment PRB was in Cd10+Pb50 (21.55% aerials; 24.60% roots).
• In single treatments, 30 mg·L⁻¹ citric acid produced the highest Cd and Pb accumulations in Cd10 and Pb100, respectively: Cd 14.48 mg·kg⁻¹ in aerials and 75.32 mg·kg⁻¹ in roots; Pb 31.06 mg·kg⁻¹ in aerials and 140.71 mg·kg⁻¹ in roots.
• In complex treatments, citric acid gave the highest Cd (78.40 mg·kg⁻¹ root; 16.18 mg·kg⁻¹ aerials) and Pb (153.28 mg·kg⁻¹ root; 36.27 mg·kg⁻¹ aerials) in Cd10+Pb100, while glutaric acid inhibited metal uptake in some complex treatments and showed no obvious Pb effect except in Pb100.
• For translocation, 30 mg·L⁻¹ citric acid enhanced Cd TF in Cd5+Pb100 and Cd10+Pb100; 30 mg·L⁻¹ glutaric acid gave the highest Cd TFs of 0.20 and 0.21 in Cd10+Pb50 and Cd10+Pb100, and maximum Pb TFs of 0.25 and 0.26 in Cd5+Pb100 and Cd10+Pb100.

Methods

• Pot experiment with Helianthus annuus L. grown for 45 days; ten sterile seedlings were transplanted into pots containing 5.0 kg polluted or control soil, with soil properties reported as organic matter 14.72 g·kg⁻¹, CEC 159.70 mmol·kg⁻¹, and pH 6.80.
• Treatments included CK; Cd5, Cd10; Pb50, Pb100; and Cd5+Pb50, Cd10+Pb50, Cd5+Pb100, Cd10+Pb100; citric and glutaric acids were applied at 10, 20, and 30 mg·L⁻¹ in 500 mL solution, homogenized 1 day before the experiment, with triplicate replication and watering twice per week.
• Plant aerials and roots were collected every 15 days, dried, digested with concentrated HNO₃, and analyzed by flame atomic absorption spectroscopy for Cd at 228.8 nm and Pb at 283.3 nm; quality control recovery was 93.6–107.7%, and data were analyzed by ANOVA and Pearson correlation in SPSS with p < 0.05 as significant.

Limitations

• The paper states that more research is needed to verify the effectiveness of organic acids in phytoremediation and that relationships between organic acid dosage and heavy-metal translocation require further study.
• The paper notes that organic acid performance depended on factors such as joint metal toxicity, chemical structures of organic acids and organo-metals, and plant physiological characteristics, limiting generalization.
• Evident from the text: this is a 45-day pot study using one sunflower species, one soil type, and limited metal/organic-acid concentrations, with no field validation; the provided text also refers to Equations (1) and (2) but does not display the PRB and TF formulas.