The effect of citric acid on enhancing metal (Cu²⁺, Ni²⁺and Pb²⁺ ) uptake in duckweed

This study evaluated the impact of citric acid (CA) to increase metal uptake Cu²⁺, Ni²⁺, and/or Pb²⁺ in duckweed (Lemna minor). Duckweed was cultured in single or mixed metal solutions (Ni²⁺ 50 ppm, Cu²⁺50 ppm, and /or Pb²⁺ 10 ppm) with different levels of CA added (no CA 0 ppm, low-level 10 ppm, middle-level 50 ppm, or high-level 100 ppm CA) for 4 weeks. Then, the plants were harvested, oven dried, and acid-digested. The amounts of metals in plants were analysed by an inductively coupled plasma optical emission spectrometer. The results indicated that duckweed successfully survived and sequestered metals from all solutions. Different levels of CA had different impacts on different metal sequestration in duckweed. For duckweed cultured in single metal solutions, 10 ppm CA already significantly increased Pb²⁺accumulation in duckweed; 50 ppm CA and 100 ppm significantly enhanced Cu²⁺ and Ni ²⁺ levels in duckweed by more than 80%. For duckweed cultured in mixed metal solutions, middle and high levels of CA significantly increased the amounts of Cu²⁺ and Ni²⁺ in duckweed. However, CA did not have a significant impact on Pb uptake in duckweed from mixed metal solutions. More research is needed to further understand the impact of CA to enhance metal uptake in plants and its application to increase phytoremediation efficiency.