This study describes the geochemical distribution and potential mobility of selected heavy metals in sediments affected by tanneries established in the Cadeia-Feitoria River basin, South Brazil. Surficial samples were taken at ten sites, in January 2000, during dry season. Metal contents were determined according to their association with main sediment phases by applying a sequential extraction scheme proposed by the 'Community Bureau of Reference' of the European Commission. In order to compare the results, total and partial extractions were performed, following analytical methods used by US EPA and US Geological Survey. Metals were analyzed in the silt/clay fraction, using inductively coupled plasma -optical emission spectrometry. The results indicate the following order of metal mobility: Ti (1%) < Al (5%) < Ni (6%) < Fe (10%) < Cu (20%) < Zn (28%) < Cr (49%) < Mn (76%). Manganese was highly mobile along the sampling sites, and mainly bound to exchangeable and reducible phases. Total Ti, Al, Fe, Cu, and Mn exceeded two or three times the average shale metal concentration, but generally reflected background conditions in the basin, where basalt rocks predominate. Ni and Zn were homogeneously distributed along the rivers, with concentrations comparable to the average shale and local concentration levels. Sediments affected by tanneries were enriched with chromium (geoaccumulation index = 2 and 3), preferentially associated to the oxidizable phase. The potential release of this metal and conversion to toxic forms seems closely related to the prevailing redox conditions. The relationship between data obtained from sequential extraction and from partial and total extractions are briefly discussed.

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The present study aimed to evaluate Cu, Cr, Ni, Zn, Pb, Mn, Al, and Fe contents, as well as their geochemical partitioning in Sinos River basin sediments in southern Brazil. This basin is a densely populated area with a substantial number of industries, especially metallurgy, electroplating works, steel mills, petrochemicals, and tanneries. The total metal concentrations were determined by X-ray fluorescence and the sediment phase concentrations were determined by applying the BCR-701 sequential extraction method proposed by the Community Bureau of Reference of the European Community, using ICP/OES. The contents extracted by a solution of 0.5 mol/L HCl were also considered. Metal contents were evaluated in the sediment fraction <63 µm. Results in the industrialized and densely populated region showed an increase in the total concentrations of Cu, Cr, Zn, and Pb, and in the potentially mobile fractions for Cu, Cr, Zn and Ni sequentially extracted. Cr stood out particularly in the Portão stream, showing 1,286 mg/kg as a result of the total concentration, considering the tannery region influence.

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This study evaluated the potential toxicological risk posed to human health due to the exposure to heavy metals by water ingestion in an area affected by tanneries - the Cadeia-Feitoria hydrographic basin (Brazil). River water was collected at 10 sites, every 3 months, from July 1999 to April 2000. After acid digestion, total metal concentration was determined by inductively coupled plasma optical emission spectrometry (Cd, Cu, Cr, Ni, Zn), flame atomic absorption (Al, Fe, Pb, Mn), or cold vapor atomic absorption spectrometry (Hg). Cr(VI) was complexed with diphenyl-carbazide and detected by UV-vis spectrometry. In order to quantify the risk of exposure, the risk assessment methodology employed by the Environmental Protection Agency of the United States was applied at a screening level. The assumed scenarios included extreme exposure patterns (ingestion of untreated water, conversion of Cr(III) to Cr(VI), temporal peaks of pollution). Fe, Al, Cd, Hg, and Pb were not included in the risk analysis, since they showed a low toxicity potential or were undetected in the samples. The selected metals presented Hazard Quotients < 1, in the following order of increasing risk: Cu < Cr(III) < Zn < Ni < Mn < Cr(VI). Hazard indexes, representing the additive effect of contaminants, were also low in the basin (< 1), but comparatively increased in the lower reach of Feitoria and Cadeia Rivers. Although noncarcinogenic risk levels did not suggest possible adverse toxicological effects to the human population, a considerable deviation from background conditions was observed downstream the area where tanneries are mainly located.

Selected metals were evaluated in surface sediments from Cadeia and Feitoria Rivers (Brazil), potentially affected by tanneries. Statistical factor analysis of sediment data allowed the identification of critical metals and priority areas for biological monitoring, i.e., chromium and mercury at the lower course of Feitoria River. Non-piscivorous bottom-fish from the species Rineloricaria cadeae (violinha) were collected at reference and contaminated sites. Chromium was undetected in fish tissues, and mercury accumulated in individuals living in contact with contaminated deposits. Mercury contents in fish were below World Health Organization quality standard for human consumption (0.5 μg/g). The ratio of total mercury content in fish (wet weight) to sediment (dry weight, <63 μm) was 0.5 and 0.7 at reference and contaminated sites, respectively. A risk assessment based on hazard index showed that maximum consumption of fish from contaminated site by human population should be 32 g/day, while at reference site the allowable amount could reach 140 g/day.

Recebido em 22/7/10; aceito em 15/2/11; publicado na web em 15/4/11 A rapid and low cost method to determine Cr(VI) in soils based upon alkaline metal extraction at room temperature is proposed as a semi-quantitative procedure to be performed in the field. A color comparison with standards with contents of Cr(VI) in the range of 10 to 150 mg kg -1 was used throughout. For the different types of soils studied, more than 75% of the fortified soluble Cr(VI) were recovered for all levels of spike tested for both the proposed and standard methods. Recoveries of 83 and 99% were obtained for the proposed and the standard methods, respectively, taking into account the analysis of a heavily contaminated soil sample.