Atmospheric mercury in forests: accumulation analysis in a gold mining area in the southern Amazon, Brazil.

The spatial distribution and dispersion of mercury (Hg) is associated with the structural conditions of the environment, primarily land use and vegetation cover. Man-made emissions of the metal from activities such as artisanal and small-scale gold mining (ASGM) can influence this distribution. Forest ecosystems are of particular importance as they constitute one of the most active environments in the biogeochemical cycle of Hg, and understanding these dynamics is essential to better understand its global cycle. In this study, we determined the content of Hg present in different forest strata (soil, leaf litter, herbaceous, underwood/bush, and arboreal), as well as the relationship between the presence of Hg and the landscape heterogeneity, percentage of gold mines, and ground slope. This study was carried out in tropical forest areas of the southern Brazilian Amazon. Accumulation and transport of Hg between forest strata was assessed in order to understand the influence of these forest environments on Hg accumulation in areas where ASGM occurs. We verified that there is a difference in Hg content between forest strata, indicating that atmospheric Hg is accumulated onto the arboreal stratum and transported vertically to strata below the canopy, i.e., underwood/bush and herbaceous, and subsequently accumulated in the leaf litter and transferred to the soil. Leaf litter was the stratum with the highest Hg content, characterized as a receptor for most of the Hg load from the upper strata in the forest. Therefore, it was confirmed that Hg accumulation dynamics are at play between the areas analyzed due to the proximity of ASGMs in the region. This indicates that the conservation of forest areas plays an important role in the process of atmospheric Hg deposition and accumulation, acting as a mercury sink in areas close to man-made emissions.

Biomass of the macrophyte remedies and detoxifies Cd(II) and Pb(II) in aqueous solution.

Aquatic plants are considered to be important remedial agents in aquatic environments contaminated by metals. The Salvinia biloba macrophyte was evaluated in relation to its removal kinetics, adsorption capacity, and toxicology, aiming at its application in the removal of Cd+2 and Pb+2 ions from aqueous solutions. A batch-type system was used, in which the plants were cultivated in microcosms containing nutritive solution and metallic ions, stored in a controlled environment (pH, temperature, and luminosity). The removal kinetics consisted in the analysis of efficiency, varying the concentrations of the metals, and time of cultivation of plants in solution. To describe the process, adsorption isotherms were constructed with the equilibrium data, which were later adjusted to Langmuir and Freundlich models. The toxicological trial was performed by sub-acute exposure test of Caenorhabditis elegans nematode to phytoremediated solutions. The results highlight the remedial effect of the plant in solutions contaminated with both metals. The kinetic study demonstrated that the plant responds differently to metals, and physical-chemical and biological processes can be attributed to the removal of metals from the solution by the plant. The equilibrium time obtained was 48 h for both metals, and the adsorption capacity was higher for Cd2+. The toxicological evaluation indicates that there was a reduction in toxicity after the remediation of the solutions by S. biloba, for all times and concentrations evaluated. Salvinia biloba was efficient for the removal of Cd2+ and Pb2+ metals from aqueous solution. The plant is a low-cost metal biosorbent and can be considered promising for phytoremediation strategies in liquid effluents and water bodies.

Assessment of the Cu(II) and Pb(II) removal efficiency of aqueous solutions by the dry biomass Aguapé: kinetics of adsorption.

Plant-based materials are promising adsorbents for treating liquid effluents. This study describes the kinetic and equilibrium parameters that best represent the copper(II) and lead(II) removal process by Eichhornia crassipes (Aguapé) dry biomass from aqueous solution, using a batch adsorption system. The plants were washed, dried, and reduced to small particles. The adsorption kinetics were assessed by varying the metal concentrations in 5, 10, and 20 mg L-1 and a control treatment (without metals) with a mixture contact time of between 5 and 720 min. Equilibrium data were fitted to the Langmuir and Freundlich models. Kinetic assay revealed fast adsorption: kinetic equilibrium was attained within 2 h with a removal efficiency of ~ 60%. The results demonstrated a fast recovery cycle of metals using the biosorbent. The biomass of E. crassipes is low cost with potential for use as a biosorbent to remove metals from solutions.