The potential of four legume trees for mercury phytoremediation and the role of arbuscular mycorrhizal fungi

Artisanal and small-scale gold mining (ASGM) in low- and middle-income countries often lack adequate safety measures, leading to significant health risks and environmental mercury pollution. Phytoremediation, a plant-based method that utilizes plants to accumulate soil-borne contaminants such as heavy metals, has been verified to restore land for ecosystem services or even future farming. Therefore, this study evaluates the potential of four legume species typically found in Ghana, the world's second largest gold exporter - Acacia mangium , Gliricidia sepium , Leucaena leucocephala and Senna siamea - for the removal of mercury from contaminated soils, as well as potential trade-offs related to eco-physiological processes. It was further investigated whether arbuscular mycorrhizal fungi (AMF) inoculation could enhance mercury removal capacity. Predominantly, A. mangium consistently exhibited the highest mercury uptake and did not show signs of mercury toxicity. G. sepium showed moderate mercury uptake but suffered considerable physiological damage. L. leucocephala was resistant to mercury but accumulated only small amounts. S. siamea exhibited moderate mercury accumulation without physiological impairment. AMF inoculation did not significantly increase mercury uptake but appeared to mitigate physiological stress under mercury exposure. These results indicate that reforestation of abandoned gold mines with A. mangium may be a suitable starting point for phytoremediation of mercury and inoculation with AMF can provide additional protection against mercury toxicity.