M. Teresa Sevilla

Study of fractionation and potential mobility of metal in sludge from pyrite mining and affected river sediments: changes in mobility over time and use of artificial ageing as a tool in environmental impact assessment.

Sludge from mining exploitation can be a source of land and water contamination in the adjacent zone. Accidents such as the break of waste mining pools in the Aznalcollar Mine (Seville, Spain) in 1998 produce important ecological disasters. In this work is presented a study of the evolution of aqua regia leachable concentration and mobility of metals in sediment samples of Guadiamar River basin from the accident date up to 2001. The application of BCR standard extraction procedures provides valuable information about the mobility and toxicity of the spill and the metal mobility in Guadiamar River polluted sediments. As a rule, themobility of several metals in the initial sludge (sulphides) is low, except for copper. Otherwise, the results of aqua regia leachable concentration and mobility of metal obtained for sediments samples indicate that the cleaning and inertisation works carried out in the zone have been adequate but insufficient, being the metal levels observed in the zone are higher than natural levels. To establish the initial impact of the spill and the mobility changes with time, mineralogical composition of the pyritic sludge and its evolution after the natural weathering and after the induction, of accelerated ageing processes by light and temperature was studied in the laboratory. Oxidation of initial sulphides to sulphates was observed. Both environmental and laboratory oxidation of the metallic sulphides increase the mobility of all metals, especially of copper, zinc and lead. The proposed laboratory procedure allows to predict the changes in mobility and therefore in toxicity that can occur at short or long term after exposure of sludge at environ-mental conditions. The mobility results in sludge and sediment samples are interpreted in terms of the mineral composition of the samples.

Synthesis, spectral and electrochemical properties of divalent metal complexes containing thiohydrazone and thiosemicarbazone ligands

Abstract The L1H4 and L2H6 complexes of metal halides MX2 (M = Cu, Ni, Co, Zn, Cd or Hg, X = Cl, Br or I) have been prepared. The complexes were characterized on the bases of 1H NMR, IR, electronic and mass spectra, magnetic studies, conductance and analytical data. The stoichiometry and the spectroscopic data indicate that the complexes 1–8, 11, 12 and 15 the metal ions are coordinated by ligand anions and the complexes 9, 10, 13, 14 and 16 contain the neutral ligand. Electrochemical behaviour of nickel and cobalt complexes was determined by cyclic voltammetry. The reduction of complexes are related to metal-centred reductions. In addition, complexes 3, 11 and 12 show irreversible waves associated to Ni(II)/Ni(III) process. The reduction/oxidation potentials depend on the unsaturation grade present in the complexes.

Cathodic stripping voltammetry of paraquat on a carbon paste electrode modified with Amberlite XAD-2 resin

Abstract A carbon paste electrode chemically modified with Amberlite XAD-2 resin was used for the determination of paraquat by cathodic stripping voltammetry. A previous study on the electrochemical behaviour of paraquat showed that the cathodic peak at −0.70 (vs. Ag/AgCl) permits adequate quantification of the analyte. The response was characterized in terms of preconcentration period, bulk concentration, pH, paste composition, supporting electrolyte and other parameters. The procedure exhibits good linearity for concentration of paraquat lower than 1.08 μg ml −1 with a detection limit of 0.10 gmg ml t-1 . The proposed method is suitable for the determination of paraquat in river water.

Macrocyclization of cyclic thiosemicarbazones with mercury salts

Abstract A new cyclic Schiff base L1H3 derived from benzil and thiosemicarbazide has been prepared in the presence of NaBH4. Reactions of the new molecule and the cyclic 5-methoxy-5,6-diphenyl-4,5-dihydro-2H-[1,2,4]triazine-3-thione L2H2 with mercury chloride and nitrate are reported. Complexes of 1:2 stoichiometry are obtained from L1H3, but the reactions from L2H2 yield complexes of the macrocyclic Schiff base 5,6,11,12-tetraphenyl-1,2,4,7,8,10-hexaaza-cyclododeca-4,6,10,12-tetraene-3,9-dithione L3H2, which indicates the macrocyclization of L2H2. A mechanism for the cyclization reaction based on the rupture of the C–N single bond in L2H2 is proposed. The electrochemical results of complex L3Hg makes it and its precursors, L2H2 and L3H2, outstanding candidates for mercury determination by appropriate electrode modification.

Direct and rapid determination of ultratrace heavy metals in solid plant materials by ET‐AAS ultrasonic‐assisted slurry sampling

INTRODUCTION Plants can be used as bioindicators in the study of contamination processes by heavy metals. Most of the analytical methodologies used for determination of metals in plants are based on atomic techniques with previous wet digestion of the solid samples. Methodologies that allow direct metal measurements in solid samples are very attractive alternatives. OBJECTIVE To develop a new procedure for direct analysis of copper, nickel, cadmium and lead at very low concentration levels in leaves based on electrothermal atomic absorption spectroscopy (ET-AAS) with introduction of samples as a slurry. METHODOLOGY In order to obtain accurate and precise results even at very low concentrations, the different parameters that influence the sample slurry preparation such as acid percentage, presence of stabilising agents and ultrasonic probe operation were studied. Instrumental parameters such as chemical modifier and temperature and times for drying, pyrolysis and atomisation steps that influence ET-AAS measurement were optimised. RESULTS Optimal slurry conditions for copper and nickel determination were 0.5% Tween 85 with 5% nitric acid. For lead and cadmium analysis the best results were obtained in 5% nitric acid without stabilising agents. The achieved detection limits were 0.023 mg/kg for copper, 0.018 mg/kg for nickel, 0.0002 mg/kg for cadmium and 0.009 mg/kg for lead. For validation purposes, the method was applied to metal analysis in a pine needles reference material. CONCLUSION According to our knowledge, the detection limits obtained are the best reported in the literature. The methodology was successfully used in metal determinations in actual leaf samples.