Morphophysiological Characteristics of Two Duckweed Species Grown in Gold Mine Tailings and HAuCl4 for Phytomining Purpose

Abstract Background and aims Phytomining can be utilized to extract gold from low-concentration sources like gold mine tailings. Duckweeds (Lemnaceae) have been known as heavy metal hyperaccumulators. This research aimed to observe the morphological, anatomical, and physiological characteristics of two duckweed species ( Landoltia punctata and Lemna aequinoctialis ) grown in media containing tailings and gold solution (HAuCl 4 ) and their gold accumulating capability. Methods The experiment was carried out by exposing L. punctata and L. aequinoctialis to 2.5 L of Hoagland’s solution treated by 0 g (0%), 100 g (4%), 250 g (10%), 500 g (20%) of tailings suspended by aqua regia, or by 0.7 mM of HAuCl 4 (Au 138 ppm). The treatments and observation were carried out in greenhouse conditions for 7 days. The duckweeds were then harvested for anatomical and physiological measurement, and gold accumulation analysis. Results high content of tailing or Au treatment caused stunting growth in both duckweeds. Anatomical and physiological observations revealed that both duckweeds experienced heavy metal stress, indicated by increasing reactive oxygen species (ROS) and thinner fronds. L. punctata had superior ability to tolerate the stress based on the ability to increase ROS scavengers to countermeasure ROS production. In addition, under the highest tailing content (20% tailing), L. punctata was still able to accumulate gold up to 1.7 µg g − 1 and produced larger gold nanoparticles with gold content reached 2.3% in media containing Au 138 ppm. Conclusions The gold phytomining process caused stress in duckweeds. Nevertheless, both species have great potential as gold phytomining agents.