Sequential toxicity identification evaluation (TIE) for characterizing toxicity of Venice Lagoon sediments: comparison of two different approaches.

A toxicity identification evaluation phase-I (TIE-1) procedure was carried out on five pore water samples extracted from sediments of the Venice Lagoon previously investigated to assess both chemical contamination and toxic effects on the biota. Two different sequential TIE procedures were tested. A first sequence (TIE-1) provided for adding Na2S2O3, adding Na-EDTA, filtering, elution through a C18-SPE column and removing ammonia using the macroalgae Ulva rigida Agardh 1823, while a second procedure (TIE-2) was set up using U. rigida treatment for ammonia removal as first step, keeping unchanged the sequence of the other manipulations. Two different exposure time to the macroalgae were tested (3-h and 15-h). Sperm-cell toxicity test with the echinoid Paracentrotus lividus and embryotoxicity tests with the bivalves Mytilus galloprovincialis and Crassostrea gigas were performed on pore-water samples to assess the effect of the sequential treatments on the overall toxicity. The results confirmed that ammonia contribution to toxicity is strong in most of the samples and that metals, specially Cu, are of concern at least in three sites. The TIE-2 procedure provided more reliable results for the samples characterized by high ammonia contribution to the overall toxicity, whereas the results of TIE-1 and TIE-2 were equivalent for the samples where ammonia contribution was not prevailing. Chemical analyses and test results showed that a 3-h U. rigida exposure is suitable to remove ammonia toxicity minimizing potential metal up-take.

Metal-ligand solution equilibria studied by electrospray ionization mass spectrometry: correlation between ion intensity and acid-base equilibria in solution.

Electrospray ionization mass spectrometry (ESI-MS) is increasingly used in the study of metal-ligand equilibria in aqueous solutions. However, the correlation between conditions in solution and mass spectra in the gas phase is far from being completely established. In the present work the equation i = kC(0)f was used to correlate relative ion intensity (i) in an ESI mass spectrum, the stoichiometric concentration (C(0)) in solution of the complex which produced this ion, and the fraction (f) of complex having the same protonation state as that of the ion detected in the spectrum. This equation takes into account that metal-ligand complexes have acid-base properties, and that these properties affect the efficiency by which the ions are brought from the solution to the gas phase. The equation was experimentally checked by electrospraying solutions containing aluminium(III) and any of the four ligands 3,4-dihydroxybenzoic acid, 3-hydroxy-2-(1H)pyridinone, citric acid, and ethylenediaminetetramethylenephosphonic acid at different pH values. ESI-MS experimental i values and C(0)f values calculated from literature data were plotted versus the solution pH. Values are correlated in the majority of cases, thus confirming the validity of the approach proposed. Correlation is lost, as expected, for low f or C(0) values, and when extensive gas-phase reactions occur. The equation i = kC(0)f can be used to estimate quantitative data for unknown metal-ligand solutions analyzed by ESI-MS.