Christine Bourotte

Natural occurrence of hexavalent chromium in a sedimentary aquifer in Urânia, State of São Paulo, Brazil

Anomalous concentrations of hexavalent chromium have been detected in ground-water of the Adamantina Aquifer inat least 54 municipalities located in the northwestern region of the State of Sao Paulo, southeast Brazil, occasionallyexceeding the permitted limit for human consumption (0.05 mg.L-1). An investigation was conducted in the municipality of Urânia, where the highest concentrations of chromium were detected regionally. It was defined that the originof this contamination is natural, since high concentrations of chromium were detected in aquifer sandstones (averageof 221 ppm) and also in pyroxenes (6000 ppm), one of the main heavy minerals found in the sediments. Besides, noother possible diffuse or point sources of contamination were observed in the study area. Stratification of ground-waterquality was observed and the highest concentrations of Cr6+ were detected at the base of the aquifer (0.12 mg.L-1),where ground-water shows elevated values for redox potential (472.5 mV) and pH (8.61). The origin of Cr6+ in water may be associated with the weathering of pyroxene (augite), followed by the oxidation of Cr3+ by manganese oxides. The highest concentrations of Cr6+ are probably related to desorption reactions, due to the anomalous alkaline pHfound in ground-water at the base of the aquifer.

Comparison of Polycyclic Aromatic Hydrocarbon (PAHs) concentrations in urban and natural forest soils in the Atlantic Forest (São Paulo State)

Studies about pollution by Polycyclic Aromatic Hydrocarbons (PAHs) in tropical soils and Brazil are scarce. A study was performed to examine the PAHs composition, concentrations and sources in red-yellow Oxisols of remnant Atlantic Forest of the Sao Paulo State. Sampling areas were located in an urban site (PEFI) and in a natural one (CUNHA). The granulometric composition, pH, organic matter content and mineralogical composition were determined in samples of superficial soils. The sum of PAHs (HPAs) was 4.5 times higher in the urban area than in the natural one. Acenaphthylene, acenaphthene, fluorene, phenanthrene and fluoranthene have been detected in the soils of both areas and presented similar concentrations. Acenaphthene and fluorene were the most abundant compounds. Pyrene was twice more abundant in the soils of natural area (15 µg.kg-1) than of the urban area and fluoranthene was the dominant compound (203 µg.kg-1) in urban area (6.8 times higher than in the natural area). Some compounds of higher molecular weight, which are tracers of vehicular emissions showed significant concentrations in urban soils. Pyrene represented 79% of PAHs whereas it has not been detected in natural soils. The results showed that forest soils in urban area are characterized by the accumulation of high molecular weight compounds of industrial and vehicular origin.

Chemical composition of atmospheric particulate matter soluble fraction and meteorological variables in São Paulo state, Brazil

The objective of this work was to characterize and compare the chemical composition of the PM10 soluble fraction in relation to meteorological variables such as wind direction and air masses backward trajectories. The PM10 was collected during winter of 1999 in two contrasting sites: the Sao Paulo city and the State Park of Serra do Mar (Cunha) inside the Atlantic Forest Reserve. The aqueous extracts of PM10 were analyzed by Ion Chromatography for major ions (Na+, K+, Mg2+, Ca2+, NH4+, Cl-, NO3-, SO42-) and by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for trace elements (Al, Mn, Fe, Pb, Zn, etc.). In Sao Paulo, the dominant chemical species were SO42-, NO3-, NH4+, Zn, Fe, Al, Ba, Cu, Pb, Mn and Ni while in Cunha, Na+, K+, Cl-, SO42-, Zn and Ni were dominant. The chemical composition related to the wind direction during sampling reflected short-range influence due to soil occupation and anthropic activities.

Relações Água-Rocha e a Hidrogeoquímica do Cromo na Água Subterrânea de Poços de Monitoramento Multiníveis de Urânia, SP, Brasil

Anomalous natural concentrations of chromium, sometimes exceeding the potability limit (0.05 mg.L-1), have been detected in the groundwater of Adamantina Aquifer in the municipality of Urânia, and in a wide region of the western part of the State of Sao Paulo. In order to identify the possible geochemical reactions that may explain the occurrence of chromium in groundwater, chemical and mineralogical analyses were conducted in rock samples collected from deep boreholes drilled in the city of Urânia. Multilevel monitoring wells were installed in the boreholes, and stratified groundwater samples were collected for chemical analyses. The analyses of the borehole samples indicated the occurrence of a geochemical anomaly of chromium (average concentrations of 221 ppm) and pointed to chrome-diopside containing from 1,000 to 6,000 ppm Cr as the main reactive mineral that contributes to this anomaly. Groundwater chemical analyses indicated the occurrence of a hydrochemical stratification of the aquifer: waters from the base of the aquifer are alkaline (pH higher than 10) whereas in the shallow zone of the aquifer, pH is neutral to mildly acid. Chromium has been identified in its hexavalent form, and prevails in the aquifer, reaching the maximum concentration of 0.13 mg.L-1. The geochemical reactions that explain the release of chromium from the solid phase to the water probably involve the dissolution of Cr3+ minerals such as diopside, followed by a redox reaction that oxidizes Cr3+ to Cr6+ and reduces manganese oxide minerals. Additionally, adsorption reactions may take place, and desorption and mobilization of Cr6+ may be favored in some portions of the deep aquifer where pH is anomalously alkaline