Banca de DEFESA: Julia Mançano Quintarelli

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Julia Mançano Quintarelli
DATE: 27/04/2023
TIME: 14:00
LOCAL: Sala de videoconferência do IG e Teams
TITLE:

Origin and dynamics of mercury in sediments from the upper Madeira basin

KEY WORDS:

garimpo; amazon; Mercury; environmental geochemistry; risk assessment.

PAGES: 76
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SPECIALTY: Geoquímica
SUMMARY:

The Madeira River basin has been the target of gold exploration through artisanal and small-scale gold mining/garimpo since the early 19th century. In this work, samples of sediment (margin and center) and water (dissolved and particulate) from the Madeira River, upstream of the city of Jaci-Paraná (Rondônia, BR) and its main contributors (Beni, Madre de Diós, and Mamoré rivers) were analyzed, as well as samples from a garimpo dredge in the Madeira River. The elemental composition of solid samples has a low variation between natural samples, with variations only in the enrichment or depletion degree (especially in the center sediment samples). The mineralogical assemblage of the fine fraction consists of 2:1 and 1:1 phyllosilicates, oxides and hydroxides of Fe, Al, and Ti, and quartz, in different proportions. The chemical composition and isotopic analysis of dissolved Sr allowed differentiating the different tributaries and the provenance of these dissolved elements, where 87Sr/86Sr ≈ 0.71 in rivers draining Andean rocks and 87 Sr/86Sr ≈ 0.72 in rivers with Central Brazil Shield contribution. The dissolved Hg results were below the detection limit of the method. In natural solid samples, the concentration of Hg varies from 17.6 - 547.8 ng g-1, while in contaminated samples collected in the dredge, the concentration of Hg reaches up to 1447.4 x 10³ ng g-1. The total Hg concentration has a 2x increment between MPS>margin>center. The main carrier phases in margin sediments are aluminous phyllosilicates and Fe and Al oxides and hydroxides. In MPS Hg does not seem to be closely associated with mineral phases and may be linked to functional S groups of organic matter. The solid tailings sample of the garimpo dredge is extremely enriched in Hg (EF=91.27) when compared to the concentration of the upper continental crust (0.05 ng g-1) and extremely polluted by Hg (Igeo = 10.95). The health risk assessment indicates that the tailings are extremely dangerous (HI>1) for adults (HI=8.1) and children (HI=15.6). About 26% of the Hg present in the tailings has higher lability and can be quickly mobilized and accessible in the environment, according to the sequential extraction procedure applied. Although the concentration of Hg in the tailings is very high and offers an enormous environmental and human health risk, when this material enters the Madeira River, it undergoes a large dilution due to the huge volume of water and sediment transported. This dilution is seen in the results obtained and hinders the characterization of background and the characterization of the origin of Hg in the environment. However, despite the dilution, a Hg hotspot was found in a sediment sample from the center in a waterfall area, with concentrations 25x higher than the average of this compartment. It indicates that heavy minerals can also carry anthropic Hg.

BANKING MEMBERS:
Interna - 1210338 - ADRIANA MARIA COIMBRA HORBE
Presidente - 1852544 - JEREMIE GARNIER
Interno - 418662 - ROBERTO VENTURA SANTOS
Externo à Instituição - WANDERLEY R. BASTOS - UNIR