Factors driving mercury variability and background values in a tropical region: The case of western Amazonia

• Published in: Journal of South American earth sciences 2019-11, Vol.95, p.102279, Article 102279
• Main Authors: Horbe, Adriana Maria Coimbra, da Costa Lima, Cyntia Beatriz, Garnier, Jeremie
• Format: Article
• Language: English
• Subjects: Lateritic duricrust; Natural sources; Sediment
• ISSN: 0895-9811; 1873-0647
• DOI: 10.1016/j.jsames.2019.102279

This study provides additional information about mercury sources and their distribution in the Amazônia regolith using a large dataset of samples collected from distinct geology, mineralogy, and tropical weathering effects. Furthermore, the Hg distribution allowed discussing the superficial dynamics and controversial question on the Hg natural or anthropogenic source. The dataset composed of 341 samples, allowed assigning Hg background values for western Amazônia of 305, 125 and 132 ppb, respectively, for lateritic duricrust and oxisol developed on Archean-Proterozoic Amazon Craton and Phanerozoic sedimentary rocks and for sediment along the Solimões and Madeira rivers compartments. The data show that natural weathering, leading to the formation of Fe/Al lateritic duricrusts and oxisols, promoted a very high Hg enrichment (up to 800%). Considering this feature, although Hg is naturally accumulated by weathering processes relative to rocks, the large enrichment may be potentially harmful and confirms studies that pointed out the key role of weathering as an efficient scavenger for metals like Hg in Amazônia. Moreover, it highlights the importance of tropical regions as a natural sink that should be better considered in the Hg cycle and as a possible natural Hg source. •Hg background value in Amazonia.•Hg behavior in Amazonia is related to weathering process.•Key role of amorphous or poorly crystalline species in Hg scavenging.•Andean Cordillera rocks are important Hg natural source.