Mercury (Hg) poses significant risks to human health, the environment, and plant physiology, with its effects influenced by chemical form, concentration, exposure route, and organism vulnerability. This study evaluates the physiological impacts of Hg on Handroanthus impetiginosus (Ipê Roxo) seedlings through SPAD index measurements, chlorophyll fluorescence analysis, and Hg quantification in plant tissues. Four-month-old seedlings were exposed for eight days to distilled water containing Hg at 0, 1, 3, 5, and 7 mg L⁻¹. The SPAD index decreased by 28.17% at 3, 5, and 7 mg L⁻¹, indicating reduced photosynthetic capacity. Chlorophyll a fluorescence analysis revealed a 50.58% decline in maximum efficiency (Fv/Fm) and a 58.33% reduction in quantum yield (ΦPSII) at 7 mg L⁻¹, along with an 83.04% increase in non-photochemical quenching (qn), suggesting oxidative stress and PSII damage. Transpiration decreased by 26.7% at 1 mg L⁻¹ and by 55% at 3, 5, and 7 mg L⁻¹, correlating with Hg levels and leaf senescence. Absorption, translocation, bioconcentration, and bioaccumulation factors varied among treatments. Hg accumulated mainly in stems (40.23 μg g⁻¹), followed by roots (0.77 μg g⁻¹) and leaves (2.69 μg g⁻¹), with limited translocation to leaves. These findings highlight Hg’s harmful effects on H. impetiginosus, an ecologically and commercially valuable species, addressing a gap in research on its Hg tolerance and phytoremediation potential.

Spontaneous plants have significant potential for phytoremediation of metal-contaminated soils. This study evaluated Tridax procumbens L. for mercury (Hg) decontamination. The plant was cultivated in a sand and vermiculite (1:1) substrate with Hg concentrations of 0, 1, 3, 5, and 7 mg kg–1. After 90 days, biometric growth and total Hg uptake by the aerial and root tissues were analyzed. Bioconcentration (BCF), translocation (TF), and bioaccumulation (BAF) factors, along with the elongation ratio (RER), tolerance (TI), and absorption (AI) indices, were used to assess the phytoremediation potential. BAF ranged from 1.46 to 11.04, BCF ranged from 6.07 to 30.31, and TF averaged 0.72, showing high Hg accumulation in roots and shoots. Vegetative development was affected by the concentration of Hg in the substrate (Hgs), with TI varying from 97 to 6.62% at Hgs of 1 and 7 mg kg–1, respectively. AI increased proportionally to Hgs, ranging from 8.12 to 17.81 μg, indicating that the mass of Hg absorbed by the plant increased even with a reduction in biomass production. T. procumbens, despite the reduction in its biomass, did not show any visual signs of chlorosis or necrosis, demonstrating resistance to Hg toxicity. These findings suggest that T. procumbens is a promising phytoremediator for soil decontamination and bioindication of Hg contamination, contributing to global efforts to protect, restore, and promote the sustainable use of terrestrial ecosystems and to halt and reverse land degradation and biodiversity loss.