The use of statistical methods to separate natural background and anthropogenic concentrations of trace elements in radio-chronologically selected surface sediments of the Venice Lagoon.

A new method has been developed that predicts the natural background concentrations of microelements of interest in sediments using the concentrations of various components present in the sample. This is done by developing multiple linear regressions using a dataset which has been selected, using radiochronological dating and statistical methods, to reflect the concentration distributions of natural levels of a large number of sediment constituents. This method is demonstrated in Venice Lagoon, using data generated in a lagoon-wide sampling effort. A quantitative assessment is carried out of the variability of natural background levels at the lagoon scale for the main inorganic microelements, and distribution maps of the background and anthropogenic concentrations of a selected metal (Ni) in sediments at the lagoon scale are presented. With sufficient data, this method can be applied in other areas, allowing for a site-specific separation of natural background and anthropogenic levels of microconstituents in sediments, providing insights into regional geochemistry and aiding in the risk-based management of coastal sediments.

Measurement of environmental trace-metal levels in Mediterranean coastal areas with transplanted mussels and DGT techniques.

Mussels (Mytilus galloprovincialis) and diffusive gradients in thin films (DGT) devices were deployed together for three one-month periods in coastal waters of Sardinia (Italy), in order to assess the levels of Cd, Cu, Ni, and Pb in areas differently affected by anthropogenic activities. DGT devices were more sensitive than mussels in detecting differences in metal concentrations between sites, while interpretation of the biomonitoring data revealed difficulties related to the biotic and abiotic factors that can influence the measurements. Regression analysis showed a significant correlation between Cd and Pb concentrations measured in the mussel tissues and bioavailable metal levels in seawater. Moreover transplanted mussels did not accumulate Cu and Ni following pre-exposure, although DGT showed significant concentrations of bioavailable forms of these metals in seawater. The results provided an estimate of the water quality with respect to dissolved metals and pointed out the usefulness of a combination of biomonitoring and DGT techniques for a better understanding of trace metal availability in coastal waters.

Field validation of autometallographical black silver deposit (BSD) extent in three bivalve species from the Lagoon of Venice, Italy (Mytilus galloprovincialis, Tapes philippinarum, Scapharca inaequivalvis) for metal bioavailability assessment.

The autometallographic approach was applied to three filter-feeder bivalves from differently polluted sites of the Lagoon of Venice. The area density (AD) values of black silver deposits (BSDs) were therefore seasonally quantified by image analysis in digestive cell lysosomes. Sediments were characterised in terms of grain size, organic content and metal concentrations (Cd, Cu, Ni, Pb, Zn). The physiological status of the bivalves was also evaluated by applying the "survival in air" test as a generic stress index. Chemical results showed that Zn contributed to the total metal load for more than 60% in sediments and for 85%-94% in mussel and clam digestive glands, respectively (data processed from published results obtained on the same samples). Regression analyses between extent of BSDs and both total metal and Zn concentrations in digestive gland followed a linear pattern in mussels and clams, but not in arks. Similarly, in mussels and clams only, BSD amount was significantly correlated with total metal concentrations in sediments according to a logarithmic model. Consequently, results obtained from autometallography can discriminate sites on the basis of their metal pollution levels, like chemical analyses on both sediments and digestive glands, evaluations being supported by the results of the physiological stress index. As a conclusion, it is suggested that autometallography in bivalves may provide overall estimates of metal fractions moving from sediments towards organisms through the ingestion of metal-enriched particles. Future work is needed to define the bioaccumulation model in arks and to clarify their possible use as metal biomonitors.

Critical analysis of radiochemical methodologies for the assessment of sediment pollution and dynamics in the lagoon of Venice (Italy).

Aquatic sediments are the ultimate sink of wastes dispersed in freshwater and soil. They are therefore a useful tool for investigating polluted ecosystems. Lagoon environments are very difficult to study due to their unstable morphology. Under these circumstances, even an excellent environmental investigation of a restricted lagoon area would still be inadequate to appreciate the characteristics of the entire system. The Venice lagoon is a very complex ecosystem whose morphology is complicated further by extensive anthropic intervention. A good environmental representation of the area was obtained with a preliminary radiochemical survey of airborne radionuclides, a unique tool in evaluating the homogeneity of the entire sedimentary system. It must be stressed, however, that the significance of the data depends substantially on the use of qualified procedures. Based on this, a detailed study was carried out on selected homogeneous areas, reconstructing the inventories and fluxes of pollutants in the sediments. In this work the radiochemical approach to the environmental study of the Venice lagoon is examined.

Sample preparation for the determination of 241Am in sediments utilizing gamma-spectroscopy.

This paper describes a procedure developed to separate americium-241 from the bulk of a sample by coprecipitation followed by high sensitivity gamma-counting of the concentrate in a well-type detector. It enables the measurement of 241Am at low concentrations, e.g. fallout levels in soils and sediments, or where large sample sizes are not available. The method is much faster and more reliable than those involving separation from other alpha-emitters, electroplating and alpha-spectrometry. A number of tracer experiments was performed in order to optimize the conditions for coprecipitation of 241Am from sediment leachates. The general outline of the determination of americium is also given.

Civilian and military uses of depleted uranium: environmental and health problems.

Depleted uranium is a by-product of the process of enrichment of natural uranium and is classified as a toxic and radioactive waste; it has a very high density (approximately 19 g cm-3), a remarkable ductility and a cost low enough to be attractive for some particular technical applications. Civilian uses are essentially related to its high density, but the prevailing use is however military (production of projectiles). From the radioactive point of view, the exposure to depleted uranium can result from both external irradiation as well as internal contamination. The associated risks are however mainly of chemical-toxicological kind and the target organ is the kidney. In the present note the recent military uses and the possible effects of its environmental diffusion are discussed.

Transfer of Chernobyl fallout radionuclides from feed to growing rabbits: cesium-137 balance.

Intake, excretion and retention of gamma-emitting radionuclides were assessed in male rabbits fed a radioactive pelleted diet (137Cs = 858 Bq kg-1 as fed) containing 40% dehydrated alfalfa meal contaminated by Chernobyl fallout. In order to evaluate radionuclide retention, an experiment was carried out on 33 animals as follows: nine rabbits were slaughtered at the beginning of the trial, six were fed a radioactive diet for 42 days, six a radioactive diet for 21 days, six a radioactive diet for 21 days and a normal diet (137Cs = 112 Bq kg-1 as fed) for the following 21 days and six a normal diet for 42 days. All the animals were housed in individual metabolism cages throughout the trial. All faeces and urine were collected and analyzed separately and live weight and feed intake were measured on a weekly basis. At the end of the trial all the animals were slaughtered and the activities of net body and muscles were determined. Cesium-137, 134Cs, 103Ru, 106Ru, 125Sb, 110mAg and 40K were measured by gamma spectroscopy. More than 85% of ingested cesium was excreted through faeces and urine (fecal much greater than urinary) and the retained 137Cs in the carcass of the more contaminated animals was only 3% of the total ingested. The concentration of total cesium in muscle reached a maximum value of 156 Bq kg-1, much lower than the EEC guideline (600 Bq kg-1), and the biological half-life for 137Cs was calculated to be 11 days. The feed-body accumulation factors were determined in net body and muscle.

The use of 210Pb and 137Cs in the study of sediment pollution in the Lagoon of Venice.

The activity of 137Cs per unit area in sediments of the central part of the Lagoon of Venice was determined with the aim of identifying boundaries of homogeneous depositional zones. The 210Pb dating technique was used to date vertical profiles of cores from the same area. A comparison of the total amounts of 137Cs and non-supported 210Pb present in each core and the atmospheric input allows us to identify different depositional areas inside the basin and to outline the possible drainage effect of industrial solid wastes used in past reclaiming operations.

Rapid determination of milligram amounts of uranium in organic complexes with pyridine-2,6-dicarboxylic acid as titrant and arzenazo I as indicator after oxygen-flask combustion.

A method is described which allows the determination of uranium in organic complexes following decomposition by the oxygen-flask procedure. Uranium is quantitatively determined by a direct titration with 0.01M pyridine-2,6-dicarboxylic acid, arsenazo I being used as the indicator. The end-point is sharp and the equilibrium is rapidly attained, so the titration can be carried out rapidly. The method is simple, rapid and highly reproducible.

Gravimetric determination of uranium(VI) with pyridine-2,6-dicarboxylic acid.

Uranium(VI) can be quantitatively precipitated from aqueous solution in the pH range 2.1-6.9 with pyridine-2,6-dicarboxylic acid in the presence of tetraphenylarsonium chloride. This provides a new rapid gravimetric method for uranyl ion as an organic chelate complex of high molecular weight. Sodium, aluminium, copper and nickel as well as nitrate, chloride, sulphate and acetate ions, do not interfere, but iron(III) and thorium(IV) do.