Major aspects of the mercury cycle in the Negro River Basin, Amazon

Abstract

Embora com pouca atividade humana, as concentrações de Hg na bacia do Rio Negro são relativamente altas. A presença natural de Hg em solos e a deposição atmosférica são as principais fontes deste metal. O balanço entre fluxos invasivos e evasivos sugerem o seu acúmulo no interior da bacia em 39.9 t ano -1. O tipo de solo, fonte de metal para os rios, e o ciclo hidrológico com períodos de cheia e seca atuam sobre a química redox das águas. A conjunção sazonal de fatores como a natureza da matéria orgânica, pH ácido e radiação solar permitem que as águas pretas oscilem de redutora a oxidante, onde, por sua vez, ocorre o consumo de Hg 0 e degradação do metilmercúrio. Deste modo, o fluxo do mercúrio pode ser invasivo ou evasivo. Embora a metilação seja mais favorecida em águas pretas, a fotodegradação do metilmercúrio se contrapõe ao seu acúmulo, contribuindo para regular o estoque deste composto na coluna água.Despite the low level of industrial activity and human density, Hg concentration in the Negro River basin is relatively high. Soil enriched with naturally high Hg concentrations and atmospheric deposition are the main sources of the metal in this watershed. Differences between invasive and evasive fluxes at the water/air and soil/air interfaces indicate Hg accumulation in the basin at a rate of 39.9 t y -1 . The type of soil, which is the main source of mercury for the water bodies, the hydrological cycle with floods and dry periods, act markedly on the water redox chemistry. A complex interaction between many seasonable variables such as solar intensity, water pH, age of the naturally occurring organic matter and the hydrological cycle alter the redox characteristics of these black water bodies, thus markedly affecting the consumption of Hg 0 and the degradation of methylmercury present in the water. Although methylation is favored in black waters, photodegradation counterpoints this formation, thus regulating the methylmercury burden in the water column.

Sulfetos volatilizáveis por acidificação e metais extraídos simultaneamente na avaliação de sedimentos de água doce

“…69 Por analogia, se a presença de sulfetos pode ser utilizada como indicador de quantidades seguras de prata, já que a sua solubilidade nessa situação seria de 2,2 x 10 -17 mol L -1 , a mesma regra deveria valer para o mercúrio, que apresenta uma constante do produto de solubilidade igual a 1,6 x 10 -54 e solubilidade de 1,6 x 10 -27 mol L -1 , que é dez ordens de magnitude menor do que a da prata. No entanto, o mercúrio, um metal que apresenta um ciclo biogeoquímico complexo, [70][71][72][73] apresenta particularidades que tornam esta avaliação bastante intrincada.…”

Influence of seasonality on the interaction of mercury with aquatic humic substances extracted from the Middle Negro River Basin (Amazon)

“…2 The nature of OM is influenced by the alternating flood and low water regime, 3 and its interaction with mercury influences the biogeochemical cycle of the metal in terms of its transport, speciation, solubility and bioavailability. 1,2,4,5 An important characteristic of the biogeochemical cycle of mercury is the variety of routes that it can take in the environment, including its release at the soil/atmosphere and water/atmosphere interfaces, atmospheric transport, and deposition to soil and water surfaces. In contact with soils and sediments, sorption of mercury in insoluble form may be followed by methylation/ demethylation.…”

Photochemical Dissolved Gaseous Mercury (DGM) formation/consumption in the Negro River Basin, brazilian Amazon

“…1 In water bodies, DGM undergoes bidirectional fluxes at the water/air interface, in a mechanism that helps to regulate the mercury pool in these compartments. 2 Mercury flux across this interface involves both kinetic and thermodynamic aspects, which may be evaluated with the help of Fick's law and Henry's law, respectively. 3 Both approaches have been widely applied to both continental and oceanic environments.…”