Electron Microscopy Evidence of Zn Bioauthigenic Sulfides Formation in Polluted Organic Matter-Rich Sediments from the Chicamocha River (Boyacá-Colombia)

Abstract

Electron microscopy and sediment geochemical data from a river basin (the upper Chicamocha river basin, UCRB, Boyacá province, Colombia) affected by anthropogenic activities (wastewater discharges, smelting and agricultural activities) showed the existence of heterogeneously distributed Zn particles in the sediments and sediments with Zn contents above the regional background (42 mg/kg). The objective of this study was to evidence the ZnS sedimentary neoformation in organic matter rich sediments deposited in anthropogenic reservoirs to reveal the processes involved in the sedimentary uptake of Zn from potential pollution sources. The highest Zn concentrations are found in clay minerals and organic matter-rich sediments (up to 427 mg/kg) deposited in slow-flowing reaches of the river associated to La Playa dam. Quartz-rich sediments poor in organic matter deposited in fast flowing segments of the river show very low Zn contents (1–12 mg/kg). Electron microscopy images showed ZnS nanoparticles forming cell-shaped aggregates suggesting that sulfate-reducing microorganisms acted as templates for the partial binding of Zn and for the nucleation and growth of zinc sulfide minerals. A good correlation of Zn with total organic carbon (r = 0.936) and the low potential redox of these sediments (−233 mV) suggest that organic matter was able to maintain oxygen depleted conditions appropriate to the Zn accumulation in the sediments. Our results demonstrate that potentially toxic Zn, originating from anthropic activities, was partially immobilized in organic matter-rich sediments through the precipitation of sulfides.

Low Temperature Illitization through Illite-Dioctahedral Vermiculite Mixed Layers in a Tropical Saline Lake Rich in Hydrothermal Fluids (Sochagota Lake, Colombia)

“…The Sochagota Lake accumulates saline waters of hydrothermal origin [24]. These waters are periodically discharged through the north exit of the dam into the Chicamocha River (flowing from east to west), in which basin the Sochagota Lake is included (Figure 2) [25,26]. The climate of the area can be classified as Cfb by the Köppen system, corresponding to a climate of subtropical highland (height, 2496 m) under oceanic conditions.…”

“…From the geological perspective, the Sochagota Lake belongs to an important geothermal area that develops hydrothermal systems associated to volcanoes of the Andean Cordillera intruding cretaceous sediments rich in silicates (Figure 2). The most important outcrops as a source of sediments to the lake are rocks from the following formations: (a) Plaeners Formation (Cretaceous), made of intensely deformed radiolarites; (b) Los Pinos Formation (Cretaceous), formed by siltstones and quartz sandstone beds; (c) Labor-Tierna Formation (Cretaceous), made of coarse to fine-grained quartz sandstones; (d) Guaduas Formation (Maastrichtian-Paleocene), with clays and siltstones that include abundant intercalations of quartz sandstones; other siliceous cretaceous formations such as (e) Conejo Formation, (f) Churuvita Formation, (g) Une Formation, and (h) Tibasosa Formation; (i) Bogotá Formation (Late Paleocene-Early Eocene), consisting of quartz sandstones, siltstones and clays; (j) Tilatá Formation (Pliocene-Pleistocene) that discordantly overlies the Cretaceous and Paleogene materials and is predominantly made of quartz-rich sandy levels with beds of siltstones and clays; (k) Quaternary deposits of sands, silts, clays, and conglomerates overlying the Tilatá Formation corresponding to the most recent alluvial, lacustrine, and fluvio-lacustrine activity also deposited in the Chicamocha River Basin, mainly made of kaolinite and quartz [25,26]. The southern part of the Sochagota Lake basin is occupied by the Pliocene-Pleistocene acid pyroclastic deposits of the Paipa volcano (l in Figure 2) [20].…”

Formation of Zn and Pb sulfides in a redox-sensitive modern system due to high atmospheric fallout

“…Zinc, Cd, Cu, Pb, and Hg sulfides were confirmed to precipitate at contaminated sites rich in natural organic matter. These include freshwater canal and river sediments, wetlands, soils, and flooded mines (Sobolewski, 1996;Gammons and Frandsen, 2001;Large et al, 2001;Sonke et al, 2002;Moreau et al, 2004;Myagkaya et al, 2016;Ciszewski et al, 2017;Lazareva et al, 2019;Mantha et al, 2019;Quevedo et al, 2020). Experimental studies confirm the importance of organic matter in facilitating metal sulfide formation and persistence in water fluctuating systems (Lau and Hsu-Kim, 2008;Weber et al, 2009;Hofacker et al, 2013;Hoffmann et al, 2020).…”