1,720,999 research outputs found
Heavy metals in surface sediments of the lagoon of Venice: evaluation of selectivity and efficiency of extraction procedures
No full textIn this study new procedures for the extraction of heavy metals from sediments were developed. Microwave heating was used as an alternative to conventional digestion techniques, allowing to shorten considerably the time required for extraction and to improve the reproducibility of the various procedures. The study concerned both single step acid extractions, used to evaluate the anthropogenic and total content of metals, and sequential selective extractions, used to determine the partitioning of heavy metals among the different components of sediments. Optimization of microwave digestion procedures was carried on by investigating the use of different conditions and by comparing the results with those obtained by conventional extraction techniques.
Attention has been focused on the evaluation of efficiency and selectivity of the newly developed procedures. To this purpose, X-ray diffraction, Mössbauer spectroscopy, FTIR spectroscopy and scanning electron microscopy were used to determine the composition both of the sediment and of the residues of extractions; the results were then compared, in order to identify which geochemical phases have been solubilized by each extraction procedure. The results pointed out the main factors that are likely to affect efficiency and selectivity. In particular, the extraction used for determining the anthropogenic fraction of metals yielded an incomplete solubilization of authigenic sulphides and a partial attack of residual phases. Sequential extractions showed some indetermination due to non efficient solubilization of carbonates. Moreover, the effect of the presence of organic matter coatings on the surface of sediment particles was underline
Messa a punto e ottimizzazione di tecniche di speciazione dei metalli in diverse matrici ambientali e loro applicazione nello studio dell’inquinamento presente nella laguna di Venezia
No full text
"Clam harvesting methods in the Venice lagoon: changes in metal and metalloids partitioning after seabed disturbance by different fishing gears"
No full textCharacterization of heavy metal pollution in the sediments of the lagoon of Venice by sequential selective extractions
No full textIn this study heavy metal pollution in surface sediments of the lagoon of Venice (Italy) has been investigated. A new procedure of sequential selective extractions has been developed to determine the partitioning of heavy metals among the different components of sediments; it provides metal concentrations in five fractions: 1) exchangeable, 2) bound to carbonates, 3) bound to Fe-Mn oxides/hydroxides, 4) bound to organic matter and sulphides, 5) bound to resistant authigenic phases and 6) residual. Microwave heating has been used as an alternative to conventional heating techniques, allowing to shorten considerably the time required for extraction; the perfect control of experimental conditions, such as temperature and pressure, improved greatly the reproducibility of the various extraction procedures. A particular attention has been posed to the evaluation of efficiency and selectivity. to this purpose, the composition of the sediment and of the residue of each extraction has been determined by means of x-ray diffraction, mossbauer and ir spectroscopy and scanning electron microscopy; the comparison of the results was used to identify the geochemical phases affected by each extractant.The analytical procedure has been applied to sediment samples collected in various areas of the lagoon of Venice, characterized by different morphological, hydrodinamical and physicochemical conditions. The use of sequential extractions can provide information on the amounts of heavy metals that can be potentially released to the overlying water column under particular environmental conditions, becoming thus bioavailable. This approach is useful to assess the risk posed to the lagoon ecosystem by metal contaminated sediments and permits to estimate anthropogenic heavy metal conten
Halophytes for Phytoremediation of Lead in a Salt Marsh in the Venice Lagoon
No full textA small but important area on the Venice lagoon was used as a shooting range for more than thirty years. As a result of this activity, this sensitive salt marsh area is now dangerously contaminated by Pb, Cu, Sb and As. This extremely dynamic and complex ecosystem can promote the accumulation of metals and metalloids in both soil and sediment, and favours their conversion into more reactive compounds by physicochemical and biochemical transformations. Changes in redox and pH conditions can promote the mobility of these metals/metalloids, thus increasing their potential bioavailability.
The characterization of contamination in this area pointed out a markedly variable Pb concentration (100-6700 mg Kg-1 dw), while Cu (about 60 mg Kg-1 dw) and metalloids (As and Sb < 20 mg Kg-1 dw) showed homogeneous distributions. As, Cu and Sb concentrations were below regulatory limits (they do not represent a serious risk), while Pb concentration was above the established limit. Geochemical speciation showed that a high percentage of total Pb content can be potentially mobilized and become thus phytoavailable in the particular conditions of this ecosystem. In the salt marsh the most abundant plant species are Limonium vulgaris, Salicornia, Spartina and Puccinellia). Preliminary analysis for Pb accumulation showed that all these plants have a low translocation factor (TF); nonetheless Limonium and Salicornia showed a bioaccumulation factor (BAF) in the roots greater than one. These results point out the possibility of using natural chelating agents to improve uptake and translocation efficiency of Pb in these plant
- …
