Valéria Guimarães Silvestre Rodrigues

Sediment Geochemistry and Climatic Influences in a River Influenced by Former Mining Activities: the Case of Ribeira de Iguape River, SP-PR, Brazil

The Ribeira de Iguape River (RIR) was historically contaminated by residues from mining activities. These activities ceased in the late 1990’s, but the residues remained deposited along the river banks. This study aimed to evaluate the sediment characteristics of the RIR in different hydro-meteorological conditions and detect eventual changes in the geochemistry. Three sampling surveys were conducted, in which sediments were collected in 6 sites, and then analyzed for sediment textures and metals concentrations. Sediments were predominantly sandy, and samples collected downstream to the mining areas tended to be enriched by metals, especially Pb, Cr, Cu, Ni and Zn. Concentrations of metals in sediments tended to be higher after rainstorm episodes, evidencing the pollution sources are not totally controlled and that the stormwater runoff may carry metals to the RIR.

Uso do bivalve límnico Anodontites tenebricosus (LEA, 1834) no biomonitoramento de metais do Rio Ribeira de Iguape

USING THE FRESHWATER BIVALVE Anodontites tenebricosus (LEA, 1834) AS A BIOMONITOR OF METALS IN THE RIBEIRA DE IGUAPE RIVER. This study investigated the contamination of the Ribeira de Iguape River – RIR by Cd, Zn, Cr and Pb, using the bivalve Anodontites tenebricosus as a biomonitor. Metal concentrations in tissue samples were measured by HR-ICPMS. Bivalve tissues exhibited mean levels of 1.00 µg/g Cd; 152.89 µg/g Zn; 14.79 µg/g Cr and 4.40 µg/g Pb. Lead concentrations were comparable to those reported for moderately contaminated sites. The results showed that Pb is bioavailable to the bivalves, exhibiting high concentrations and exceeding both natural and reference values for human consumption. The freshwater bivalve Anodontites tenebricosus is a suitable biomonitor of contamination by metals.

Study of Gully Erosion in South Minas Gerais (Brazil) Using Fractal and Multifractal Analysis

Tropical countries experience intense rainfall; this natural process, associated with land use, influences or accelerates soil erosion due to changes in soil properties and water flow dynamics. Gullies are an expression of soil erosion caused by water and are considered an environmental problem, since their extents and depths reach hundreds of meters, and areas of gullies frequently become unusable. Gullies are present in most states of Brazil. The case study of this paper focuses on the watershed between the Grande River and Das Mortes River (in Nazareno, southern region of Minas Gerais). There are 96 gullies in this municipality in areas where the soil has low fertility and high erodibility; the origins of these gullies are linked to vegetation removal and gold mining in the 17th century, potentialized by non-conservationist farming practices and by runoff intensification due to inadequate road drainage systems. The studied Charuteiro stream watershed has 13 gullies within a 6.55 km2 area. Therefore, we used a box-counting method with two software packages to analyze the fractality and multifractality of these gullies. The vegetated gullies presented similar values for fractal dimension, while those with bare soil presented more variability. The multifractal spectrum for each gully in the study area was obtained; these soil erosion features do not show high complexity and heterogeneity. This analysis of watersheds with intense gully erosion is a novel and promising approach, enabling mathematical modeling and recovery projects to more closely reflect reality.

The Potential Use of Residual Soil from Ribeira Valley (Brazil) in Mitigating Metal Contamination: A Geotechnical Characterization

The incorrect disposal of hazardous waste causes serious problems around the world. For instance, mining waste is one of the main sources of potentially toxic metals in the environment. In the Ribeira Valley region of Brazil, residues generated during lead ore smelting were improperly deposited in the Ribeira de Iguape River and on the soil’s surface without protection. An alternative solution for mitigating local contamination is verifying whether a local residual soil is appropriate to use as a mining waste landfill liner. The soil is sandy silty clay, with a plasticity index of 24%, an optimum water content, wopt, of 26.3% and a maximum dry density, ρdmax, of 1.515 g/cm3 from the Standard Proctor test. Specimens molded at an optimum compaction condition showed hydraulic conductivity of 10−9 m/s and effective shear strength parameters of c′ = 22 kPa and φ′ = 26.8°. The soil is acidic (pH 4.6), exhibits low CEC (41.4 mmolc/dm3) and presents a predominance of negative charges on the particle surface (PZSE 3.6 < pH), favoring cation retention. The hydraulic and mechanical characteristics together with the chemical properties suggest that this soil is a candidate for use as a liner. Further studies are underway to characterize its chemical contaminant retention and to complete the analysis about its suitability for the desired purpose.

A Comparison of Two Methods of Sequential Extraction in a Former Mining Waste Deposit of Pb—Adrianópolis (Brazil)

Sequential extraction methods (SEM) have been developed to study potentially toxic metal (PTM) fractionation in soil. Although many procedures have been suggested in literature, these methods are usually developed for temperate soils. Thus, the objective of this study was to compare a SEM developed for temperate soils with a SEM developed for tropical soils. The soil samples chosen for this comparison were collected in a former deposit of slag enriched in lead (Pb) and zinc (Zn), located in Adrianopolis (Brazil—tropical soil). These samples were collected in profile to verify metal mobility in depth. Since it is known that soil characteristics affect metal mobility, the soil pH, the soil organic matter content (SOM), the cation exchange capacity (CEC) and the pseudo-total concentration of Pb and Zn were determined. Zn and Pb were predominantly associated with Fe–Mn oxides and the residual fraction. Using methodology developed for tropical soils, it was possible to distinguish Fe–Mn oxides and verify that Pb and Zn were mainly associated with the less mobile form (crystalline Fe oxides). Metal associated with the mobile fraction varied significantly, being more abundant when using the temperate soil method. It is concluded that the procedure for tropical soils is more adequate for distinguishing different forms of Fe–Mn oxides in soil, but the temperate soils procedure was more effective in extracting exchangeable and organic matter fractions.

Preliminary Study of the Adsorption Capacity of Pb, Zn and Cd Through Zeolite and Organic Compost

Reactive materials have been used as a solution to prevent potentially toxic metal contamination stemming from mining waste disposal. These materials are characterized by a high cation exchange capacity (CEC) and a predominance of negative charges, favoring their potential utilization in metal cation immobilization. Therefore, the aim of this study is to compare the sorption capacity of common metals in mining areas (Pb, Zn and Cd) with zeolite, an inorganic material traditionally studied and used for this purpose, and compost, a low-cost organic material, that in comparison to zeolite, has been sparsely researched. Two Cuban commercial clinoptilolite zeolites were evaluated: natural zeolite (NZ) and NaCl treated zeolite (TZ). Two municipal solid waste-derived composts were also assessed with differences in the composting method: windrow (WC) and static pile (SPC). Batch equilibrium experiments showed that the selectivity of removal of TZ, WC and SPC followed the order Pb > Cd > Zn. The only exception was NZ (Pb > Zn > Cd). In general, all materials presented higher performances than Pb (with adsorption efficiency more than 95%). The SPC was revealed to be the best adsorbent of Pb, but with a similar removal percentage for the TZ. The TZ was significantly more efficient in retaining Zn. In the case of the Cd, the WC and TZ showed the highest removal percentage. These results suggest that compost, a low-cost byproduct, can adsorb a considerable concentrations of metals, and thus is able to compete with zeolites for use, isolated or combined with other materials, as an effective sorbent in metal contamination.

The Characterization of Tropical Peats for Potentially Toxic Metals Adsorption Purposes in an Abandoned Mine Area

Peat has been used as an alternative, low-cost and efficient material capable of retaining metals. Most studies of adsorption have tended to focus on the characterization and adsorption mechanisms of temperate peats rather than tropical ones, therefore there is insufficient data about their characteristics and subsequent use in contaminated areas. The purpose of this study is to assess the chemical characteristics of tropical peats from the Mogi-Guacu river Basin (Brazil), to evaluate their ability to capture potentially toxic metals in a contaminated mine area in Brazil. The peats were classified as H5–H6 on the Von Post scale of humification and had 48% ash content. The \( {\text{pH}}_{{{\text{H}}_{{\text{2}}} {\text{O}}}} \), ∆pH and the point of zero salt effect (PZSE) for peat 1 was 5.1, −1.0 and 3.6, while for peat 2, the values were 5.9, −2.4 and 3.1, respectively. These data showed materials with low acidity characteristic and a predominance of negative charges, which allows great cation retention. The cation exchange capacity (CEC) was considered high (91.0 and 116.0 cmolc kg−1), especially when considering the organic matter content (520.43 and 510.06 g kg−1). The removal of lead (Pb II) ions from the aqueous solution, investigated under different experimental conditions, revealed a satisfactory efficiency of 1/50, peat/solution ratio. Metals were removed in the descending order Pb > Zn > Cd, and both peats showed similar efficiency of lead sorption in high concentrations. The results show that the tropical peats have good characteristics to be used as alternative adsorbent materials in abandoned and contaminated mining areas.