Ari Roisenberg

Petrology of Serra Geral (Paran) continental flood basalts, southern Brazil: crustal contamination, source material, and South Atlantic magmatism

The Serra Geral (Paraná) continental flood basalt (SG-CFB) province in Brazil is associated with the Jurassic-Cretaceous breakup of Gondwanaland and the transition of continental to oceanic magmatism during the opening of the South Atlantic Ocean. A suite of 24 samples representative of the SG-CFB in Rio Grande do Sul, southern Brazil, shows a compositional continuum from basalt (50–53 wt% SiO2, Mg# 60-45), to basaltic andesite, to andesite, rhyodacite, and rhyolite (73 wt% SiO2). Certain compositional aspects of the mafic rocks (e.g., TiO2, K2O, CaO, Zr/Nb, Zr/Y, Ti/Zr) resemble those of basaltic dikes and flows associated with the opening of the North Atlantic Ocean.Fractionation trends are apparent in MgO variation diagrams and calculations show that basalt-basaltic andesite continuums are largely due to removal of plagioclase and clinopyroxene. These mafic rocks can be categorized as (i) having higher or lower incompatible-element contents (e.g. K2O 0.6–1.5 wt%; Rb 12–43 ppm; Ba 125–240 ppm) due to incorporation of Brazilian Archean crust or rhyolitic magma by basalt from a particular source material or to partial-melting differences of that source, and (ii) as having higher or lower TiO2, Sr, Ba, and P contents due to source heterogeneities. Crustal components are “obvious” in certain basaltic samples, as where K2O > 1 wt%, SiO2 > 51%, and TiO2 ∼ 1%, but are insignificant in others (e.g., compositions close to those of South Atlantic basin basalts). Calculations indicate origins for intermediate and silicic rocks by removal of pl, cpx, and Ti-magnetite from basaltic andesite, but crust and magma-mixing affecting basaltic-andesite fractionates were likely also involved. Where contamination is insignificant, Zr, Nb, and Y abundances indicate T-type MORE source material like that for certain S. Atlantic Ocean basalts. Source material was essentially a 9∶1 hybrid of N-type and P-type MORB components. N-type MORB lithosphere followed SG-CFB because decompression due to rifting crust enabled partial melting of uppermost (depleted) mantle.

Anomalous fluoride concentration in groundwater - is it natural or pollution? A stable isotope approach.

Fluoride anomalies (up to 11 mg/l) have been detected in groundwater of the central region of Rio Grande do Sul State, Southern Brazil, in an area where fluorosis is endemic. Two hypotheses are investigated concerning the fluoride origin: lithochemical affiliation from regional rock or contamination by fertilisers application. These hypotheses are discussed based on the stable isotope data of water, nitrate, and sulphate, which indicates that the local precipitation is the main groundwater recharge source. The isotopic composition of groundwater sulphate is similar to that of fertiliser sulphate. However, a conclusive assignment of groundwater sulphate to fertiliser origin is not indicated because further possible sulphate sources fall into the same isotopic range. In contrast, the isotopic composition of dissolved nitrate suggests that there is no direct relationship to the use of NPK fertilisers. Hence, an origin of the high fluoride content in groundwater related to long-term rock–water interactions seems likely.

Fluoride in the Serra Geral Aquifer System: Source Evaluation Using Stable Isotopes and Principal Component Analysis

Groundwater with anomalous fluoride content and water mixture patterns were studied in the fractured Serra Geral Aquifer System, a basaltic to rhyolitic geological unit, using a principal component analysis interpretation of groundwater chemical data from 309 deep wells distributed in the Rio Grande do Sul State, Southern Brazil. A four-component model that explains 81% of the total variance in the Principal Component Analysis is suggested. Six hydrochemical groups were identified. δ18O and δ2H were analyzed in 28 Serra Geral Aquifer System samples in order to identify stable isotopes patterns and make comparisons with data from the Guarani Aquifer System and meteoric waters. The results demonstrated a complex water mixture between the Serra Geral Aquifer System and the Guarani Aquifer System, with meteoric recharge and ascending water infiltration through an intensive tectonic fracturing.

Utilização de solos locais para tratamento de efluentes do refino de petróleo contendo metais

The employment of local soils for extraction of metallic elements was evaluated through batch tests to treat wastewaters generated in a petroleum refinery plant in southern Brazil. Clay and organic carbon content and clay mineralogy provide these soils, in principle, with moderate metal retention capacity. The following retention order was established: Cr3+ > Pb2+ > Cu2+ > Hg2+ > Cd2+, with total amount of metals retained varying from 36 to 65 meq kg-1. The results show the high efficiency of local soils for extracting metals from liquid effluents through sorption and precipitation processes under acid pH conditions.

Nitrogen and oxygen isotopes as indicators of pollution sources in the Faxinal Dam watershed, Southern Brazil

Isotopic signatures of δD-H2O, δ18O-H2O, δ15N-NO3−, δ18O-NO3− and δ15NFertilizer isotopes were used in order to evaluate the impact of agricultural inputs (fertilizers and calcium nitrate) and sewage effluents on the water of tributaries of the Faxinal Dam, which supply the city of Caxias do Sul in Southern Brazil. δ2H and δ18O were identified by spectroscopy laser absorption tunable diode-type cavity ring-down spectroscopy, while the isotopic ratios of 15N and 18O in nitrate were determined by isotopic ratio mass spectrometry, applying the chemical denitrification method. The results showed that most of the analyzed samples are compatible with the Global Meteoric Water Line, Local Meteoric Water Line and Carlos Barbosa Wells and Fountains Tendency Line, except for the Fx-07 sample that presented greater similarity to δ18O values for groundwater. The isotopic signatures of δ15N-NO3− versus δ18O-NO3−, in the great majority of the samples, pointed out the influence and the contribution of the fertilizers. In a monitored affluent, the results show the impact of the direct discharge of domestic sewage, while in the sewage treatment plant there is clear evidence of denitrification. This study demonstrated that isotope application of δ15N-NO3− and δ18O-NO3− is efficient tools for identification of N-NO3− of synthetic fertilizers and domestic sewage.

Radon emissions related to the granitic Precambrian shield in southern Brazil.

The equivalent uranium (eU) activity concentration was analysed in selected granite samples at several sites in Porto Alegre, Southern Brazil, to obtain information on the radon (222Rn) generation by the aquifer rock matrices. Radon analyses of ground water and soil samples were also performed. Several samples exhibited a dissolved 222Rn activity concentration exceeding the World Health Organization maximum limit of 100 Bq l−1. The dissolved radon content in ground waters from the Fractured Precambrian Aquifer System exhibited a direct significant correlation with the eU in the rock matrices, which is a typical result of water–rock interactions. Variation in the soils porosity was confirmed as an important factor for 222Rn release, as expected, due to its gaseous nature. Thus, although the calcic-alkaline to alkaline Precambrian granitoid rocks of the study area are important reservoirs for underground resources, they can release high amounts of radon gas into the liquid phase.

Definição de níveis aceitáveis baseados no risco para hidrocarbonetos no Município de Porto Alegre segundo a metodologia RBCA

This study defined RBSL (Risk Based Screening Levels) values to hydrocarbons in Porto Alegre, Southern Brazil. The values were obtained through the RBCA methodology, using hydrogeological data from the Crystalline Altered Basement and the Quaternary Sedimentary Deposits. The exposure parameters appropriate to the urban population, as well as toxicity data of selected compounds, were obtained from bibliographical sources and toxicological databases. The reference tables demonstrated that the Crystalline Altered Basement values, in general, are more restrictive than those from the Quaternary Sedimentary Deposits. In comparison to Cetesbs reference tables, the values in Porto Alegre are lower, resulting in the need of more detailed environmental investigations in hydrocarbons polluted areas.

Origin of high fluoride contents in groundwater of the Santa Maria Formation, Guarany Aquifer System, southern Brazil

A comprehensive assessment of man-made impact on the environment is much kept behind because of missing unified systems of environmental monitoring. They represent sources of reliable information on the current status of the environment, as well as the absence of approaches to assess the impact of chemical pollution by different anthropogenic sources. Vegetation, being the component of environmental systems, is very sensitive to atmospheric man-made load. However, permissible concentrations of elements in plants, causing deflection in their development are differently estimated in different regions and vegetation species. As to the Baikal region, it is commonly the sanitary state of woods, that is primarily assessed. Coniferous trees, in particular pine, represent the main tree species in the region. In the Olkhon region we investigated the trace element compositions in pine needles to obtain the background contents of toxic metals. This region of the National park lies 300 km away from the industrial sources of pollutants, beyond the zone of wind effect, and has no industry. The research was made on the healthy (green) and dried up (red) pine needles. The elements like Zn, A1, Mn, Fe, Cr, Cu, Co, Ni, Sr, Cd, Pb, Li, Rb, Sb and As were measured by atomic absorption and flame emission photometry. The samples were decomposed in autoclaves with the mixture of nitric acid and hydrogen peroxide. Distinct differences were found in a series of elements contained in the green and dried needles. The red needles are characterized by higher contents of Zn, A1, Cu and low Mn, Fe, Pb with similar contents of other elements. It is proposed to use the ratio Fe/Mn for evaluating the ecological status and characterization of the damage to trees. In the study region in the green needles Fe/Mn=0.5, in red ones it is 0.7 (for comparison the ratio Fe/Mn in the zone of industry influence the ratio is 1.1-2.0). The obtained values of metal concentrations in the green pine needles can be accepted as background in the assessment of the sanitary state of the Prebaikalian woods, and reddening of the needles most likely reflects the natural serial level of tree stands.