Distribution and Early Diagenesis of Antimony Species in Sediments and Porewaters of Freshwater Lakes

Abstract

The study identifies the role played by different components of natural aquatic systems on the poorly known geochemistry of antimony. Different chemical forms of antimony were measured in porewaters and sediments of two Sudbury lakes characterized by contrasting redox conditions at the sediment-water interface. In porewaters, Sb(III) was present under reducing conditions where it could exist as SbS2- according to thermodynamic calculations. Sb(V) was detected mainly under oxic and mildly reducing environments where its presence was attributed to the oxidizing effect of iron and manganese oxyhydroxides or to the slow kinetics of reduction by dissolved sulfide or possible complexation by it. A third form of Sb identified as refractory was obtained after UV irradiation of the water samples, suggesting an association of Sb to low molecular weight natural organic matter. The distribution of Sb in sediments of the two lakes revealed (through the comparison of profiles and statistical correlations) the importance of iron and manganese oxyhydroxides in controlling the behavior of Sb, particularly in the lake where the interface was clearly oxic. Porewater profiles indicate that the dissolution of manganese and iron oxyhydroxides under anoxic conditions leads to the simultaneous release of dissolved Sb previously sorbed onto those compounds. In reducing sediments, the control of the solubility of Sb by iron sulfides is suggested.

Contrasting geochemistry of antimony in lake sediments

“…In a previous study, we have identified a fraction of dissolved Sb associated with NOM. In this work, major portions of Sb in porewater were present in a refractory fraction, partially or entirely made of NOM [9]. In Clearwater L., good statistical correlations were observed between DOC and dissolved Sb species in porewaters.…”

Antimony in aquatic systems

“…A few studies [8][9][10] report significant Sb-NOM interactions but most authors do not (Figure 3b). We have observed [11] that a significant proportion of Sb in two Sudbury lakes was associated with a refractory fraction (operationally defined by UV irradiation) consisting partially or entirely of organic matter (Figure 4). Our recent results [15] on Sb (III) oxidation by H202 in NaCI solutions over a wide range of pH, ionic strength and oxidant concentrations show that the oxidation reaction is first order with respect to Sb (Ill) and H202.…”

Microbial Antimony Biogeochemistry: Enzymes, Regulation, and Related Metabolic Pathways

“…1B) (67). In nature, Sb(III) is thermodynamically predicted to be dominant in anoxic environments, while Sb(V) is dominant in oxic environments (72,98). Thus, any Sb(III) molecules that enter oxic environments tend to be oxidized to Sb(V), a situation that is similar to As(III).…”