Daniel Ferreira Araújo

Geological and anthropogenic influences on sediment metal composition in the upper Paracatu River Basin, Brazil

This work reports a geochemical study of sediments from the upper Paracatu River Basin. The objective is to define the influences of Au, Zn, and Pb mineral deposits and mining activities on the sediment metal sources, distribution, and accretion. The samples were analyzed using ICP/OES, AAS, and XRD techniques and were treated with principal components analysis and the geo-accumulation index. The main geochemical processes that control the sediment composition are pyrite oxidation, muscovite weathering, carbonate dissolution, and the erosion of oxisols enriched with Zn and Pb. The upper Rico Stream has high Al, Fe, Cu, Cr, Co, and Mn concentrations due erosion of oxisols and pyrite oxidation and muscovite alteration present in the parental rock. The artisanal alluvial gold mining increased the primary rock-minerals’ weathering and Hg sediment concentration. The lower Escuro River and Santa Catarina Stream are enriched with Zn and Pb due the erosion of metal-rich soils formed over galena, sphalerite, calamine, and willemite mineral deposits located upstream. Elements such as Ca, Mg, and Ba have low concentrations throughout the sampled area due the high solubility of these metals-bearing minerals. The dispersion of metals is limited by the basin geomorphology and their affinity to silt-clayey minerals and Fe and Mn oxides and hydroxides in circumneutral pH waters.

Ion Exchange Chromatography and Mass Bias Correction for Accurate and Precise Zn Isotope Ratio Measurements in Environmental Reference Materials by MC-ICP-MS

Precise and accurate d66/64Zn data for environmental reference materials (RMs) including rocks, sediments, soils and plants are presented in order to improve the metrological traceability and analytical control of Zn isotope ratio determinations in future environmental studies. Previously developed ion exchange chromatography protocols were adjusted to enable faster sample throughput and instrumental mass bias processes were investigated. The improved chromatographic protocol yielded precise and quantitative recoveries (99 ± 7%, σ, n = 16), while the mass bias correction using Cu as external dopant provided precisions better than 0.02‰, 2σ, n = 7. Investigations into spectral and non-spectral interferences identified significant formation of Cr and Ti oxides and hydroxide ionic species. Analysis of six RMs (BHVO-2 basalt (USGS), BCR-2 basalt (USGS), AGV-2 andesite (USGS), 2709 San Joaquin soil (NIST), 1646a estuarine sediment (NIST) and 1573a tomato leaves (NIST)) showed good reproducibility (< 0.01‰, 2s, 5 ≤ n ≥ 1).

Biogeochemical mechanisms controlling trophic state and micropollutant concentrations in a tropical artificial lake

Lake Paranoá is a human-made water reservoir created in 1959 together with the new capital of Brazil (Brasilia). With the demands of urban development, population growth, and land use changes, the lake presented severe deterioration of water quality due to the disposal of wastewater with a high concentration of nutrients. To better elucidate the natural and anthropogenic sources controlling the water quality from Lake Paranoá, this study aimed to (1) investigate the main geochemical processes controlling water quality of the lake and its tributaries; (2) evaluate Lake Paranoá’s trophic state; and (3) determine the occurrence and fate of organic micropollutants in Lake Paranoá waters and WWTPs effluents. The waters from Lake Paranoá tributaries are naturally acidic due to the nature of the extremely weathered ferralsols and the crustal material composition. The main processes linked with anthropogenic activities that affect the water quality from the tributaries are the input of untreated domestic wastewater and the dissolution of carbonate minerals arising from construction material residues. Generally, the waters of Lake Paranoá presented low nutrient and chlorophyll-a concentrations, indicating a low trophic state (oligo-mesotrophic). A significant increase in the trophic state (super-eutrophic) was observed at specific regions of the lake that have high nutrient input from tributaries, caused by the continuous disposal of untreated domestic sewage. In Lake Paranoá waters, the organic micropollutants that were identified and quantified (caffeine, bezafibrate, bisphenol A, diethyl phthalate, and nonylphenol) presented concentrations consistent with previous studies and within the threshold of toxicity, except bisphenol A.