Short-term changes in water chemistry in the Baccu Locci stream (Sardinia,Italy) affected by past mining

Short-term changes in water chemistry, and especially in dissolved trace element concentrations, associated with diel cycles during base-flow conditions at a specific sampling station in the Baccu Locci stream draining the homonymous old mine area in Sardinia (Italy) were investigated. Diel fluctuations in pH and alkalinity were correlated with the temperature-dependent CO₂ solubility and the biologically-induced CO₂ production, both of which were higher during the night. Adsorption/desorption to/from streambed material, in particular ferrihydrite, is believed to be the main in-stream mechanism causing the observed diel variations in dissolved concentrations of As and Zn. Arsenic was mainly affected by the dual action of temperature and competing carbonate ions, whereas pH seemed less important. Temperature acted in accordance with the exothermic feature of anion sorption onto hydrous metal oxide surfaces; aqueous carbonate species exerted their competitive effect in relation to alkalinity variation. Zinc was primarily affected by temperature, in accordance with the endothermic feature of metal cation sorption onto hydrous metal oxide surfaces, and secondly by pH. Co-precipitation of As and Zn with calcite is another possible mechanism, which requires further investigation involving examination of inorganic and biological materials coating the streambed. All these processes potentially controlling the diel cycles of trace elements should be carefully considered to assess the effectiveness of remediation actions currently in progress at Baccu Locci. A normalization method for data from asynchronous sampling has been developed and proposed in order to eliminate or at least attenuate the effect of sampling time and provide an additional tool to identify the processes/mechanisms involved in trace element concentration fluctuations observed along a contaminated stream during base-flow conditions.     

Environmental monitoring of magnetic iron phases of urban water reservoir lake sediments (Taiaçupeba Lake,metropolitan region of São Paulo,Brazil) by using Mössbauer spectroscopy

In the present work, we investigate the iron oxides and oxyhydroxides behavior and evolution, related to the geochemical behavior of some metals, which could be retained as solid phases in the sediments from an urban water reservoir lake, placed in Taiaçupeba, Great São Paulo, Brazil. These tasks were performed by the establishment of a proceduring setting for environmental monitoring analysis through Mössbauer spectroscopy measurements associated to hysteresis loops measurements and chemical analysis [X-ray fluorescence (XRF)]. We inferred the possibility of goethite occurrence in broad particle size distribution (5–50 nm), and related to ferrihydrite, and small grain-size hematite (about 8 nm). The magnetometry results pointed to the paramagnetic/superparamagnetic behavior of the magnetic phases present in the samples and also suggested the occurrence of small grain-size magnetite. We also verified the presence of clay minerals related to Fe, as well as the occurrence of Fe³⁺ and/or Fe²⁺ in short-range structural order. Through a straight correlation among Mössbauer spectra data gained at T = 77 K and Al-metal, metal-Fe molar ratios, provided through XRF data, we found remarkable indications of interference on meta-stable phases evolution to its final products. Such results can be pointing for evidences about the possible isomorphic replacing and/or adsorption of Al and other metals in goethite and hematite.