Marco Grotti

Temporal distribution of trace metals in Antarctic coastal waters

Abstract In the framework of the Italian Research Programme in Antarctica, a nearshore station positioned inside the Gerlache Inlet (Terra Nova Bay, Western Ross Sea) was regularly sampled during the Austral Spring 1997/1998, from November to February. In order to evaluate the physical, chemical and biological variations along the water column, measurements of a large number of parameters were performed at a suitable frequency: temperature, salinity, fluorescence, suspended particulate matter, concentration of dissolved and particulate Fe, Cu and Mn, concentration of nutrients and phytoplankton pigments. Samples of pack ice and marine microlayer were also collected and analysed. Elaboration of data with regards to temporal and vertical components provided a good description of temporal distribution of trace metals in the coastal waters of Terra Nova Bay, in relation to the physical and biological processes. Concerning the surface layer, it was found that concentrations are mainly affected by the dynamic of the pack ice melting and phytoplankton activity. The first process influences both the input of metals from meltwaters and the covering of the seawater surface, allowing atmospheric dust input only when all ice has been melted or removed. Direct release from ice of particulate Fe and Cu were clearly shown by surface concentration peaks and by the high concentrations of suspended particulate matter and particulate metals detected in the ice core section interfaced with the seawater. Moreover, a quite complex dynamic dissolved/particulate partitioning was found, which can account for the temporal uncoupling between the maximum values of particulate and dissolved metals. In absence of pack ice, there is evidence of a further input of Fe and Mn due to atmospheric dust brought into the water column through the marine microlayer. This picture is complicated by phytoplankton activity, which removes micronutrients like Fe and Cu from water, incorporating them into organic particulate matter. The dynamic of metal uptake follows that of primary production which, in the studied area, shows a specific trend characterised by two distinct blooms: the first in the second half of December and the second in late summer. In intermediate and deep waters, the vertical distribution of Fe and Mn was characterised by a substantial constant profile until January; then, an increase of particulate metal concentration with depth was observed along with a corresponding decrease of the dissolved concentrations. This trend is typical of these scavenging-type elements which are removed by particulate matter during the sinking process, in the absence of well-defined water column stratification.

Trace metals distributions in coastal sea ice of Terra Nova Bay, Ross Sea, Antarctica

In an attempt to clarify the release of trace elements from the seasonal coastal sea ice, samples were periodically collected in a nearshore station inside the Gerlache Inlet (Terra Nova Bay, Western Ross Sea), during the summer 2000/01 and analysed for dissolved and particulate cadmium, copper, iron, manganese and lead, as well as salinity, suspended particulate matter, nutrients and phytoplankton pigments. In order to provide insight on the metal association with the particles included in the sea ice, the metal solid speciation was also investigated. Both vertical distributions within the ice cores and temporal variations at the seawater interface were studied, in an effort to fully characterize the system and correlation among the considered parameters. Concentrations and speciation patterns clearly indicate metal incorporation within the annual sea ice due to resuspension of sediments, followed by release of particulate metals during melting as a primary process affecting trace metal availability in the Antarctic coastal waters.

Effect of operating conditions on excitation temperature and electron number density in axially-viewed ICP-OES with introduction of vapours or aerosols

The combined effect of the power and the carrier gas flow rate on excitation temperature, electron number density, ionic-to-atomic line intensity ratios and departure from local thermal equilibrium has been studied in an axially-viewed plasma with introduction of different amounts of wet aerosols, partially desolvated aerosols or dry vapours, according to empirical modelling and experimental design methods. Under robust conditions (1500 W and a carrier gas flow rate of 0.7–0.85 L min−1), an increase in water loading led to an improvement in the plasma excitation properties, while desolvation caused degradation. In contrast, under non-robust conditions, the plasma was no longer able to tolerate an increase in water loading and desolvation resulted in an improvement in the plasma characteristics. The hydrogen formed during the hydride generation process significantly improved the plasma excitation properties, regardless of the conditions. In this instance, the plasma characteristics were primarily affected by the reductant concentration, which determined the amount of hydrogen generated, and by the carrier gas flow rate, which controlled its residence time within the plasma. In contrast, there was no relevant change in the plasma excitation conditions due to systematic variation of HCl concentration from 0.1 to 6 M.

Heated-spray chamber-based low sample consumption system for inductively coupled plasma spectrometry

A systematic study about the effect of the heating of a modified version of the so-called Torch Integrated Sample Introduction System (TISIS) has been performed. The results showed that when working at liquid flow rates of 20–40 µl min−1, it was possible to raise the chamber wall temperature up to 100 °C without degradation of plasma thermal characteristics. Furthermore, a sheathing gas stream was added to the spray chamber so as to improve the aerosol transport towards the plasma. Under these conditions, sensitivity enhancements ranging from 8 to 15 with regard to those found under standard conditions (i.e., with neither chamber heating nor sheathing gas inlet) were reached for the different ionic and atomic emission lines studied. As a result, limits of detection at 20 µl min−1 were improved by a factor between 2.5 and 13. These LODs were only 1.7 to 2 times lower than for a cyclonic spray chamber at an uptake rate of 1 ml min−1. Two direct injection nebulizers were used for comparison: the conventional direct injection high efficiency nebulizer (DIHEN) and its demountable version (d-DIHEN). When TISIS was used under standard conditions quite similar results were found as those provided by d-DIHEN, although at low nebulizer gas flow rates (i.e., 0.1 l min−1), the DIHEN gave rise to higher sensitivities. However, by heating the TISIS chamber at 100 °C, sensitivities were enhanced by a factor up to one order of magnitude with respect to both the DIHEN and d-DIHEN. The result was ascribed both to the production of a finer tertiary aerosol and to the improved plasma excitation conditions. Furthermore, lower limits of detection were encountered for the hot chamber as compared to direct injection nebulizers. Hence, the developed system could be considered to be very promising for the analysis of very low liquid sample volumes through ICP techniques.

Natural variability and distribution of trace elements in marine organisms from Antarctic coastal environments

Abstract In an attempt to improve the understanding of the natural variability and distribution of trace elements in Antarctic organisms, the concentrations of arsenic, cadmium, cobalt, chromium, copper, manganese, nickel, vanadium and zinc in representative benthic species from two pristine coastal environments were measured and compared with literature data for other uncontaminated coastal ecosystems. Correlations between the elements, differences between the species and between the sampling sites were examined by principal component analysis. Metal accumulation was particularly evident in the tissues of the sea star Odontaster validus, the bivalve mollusc Laternula elliptica and in the red alga Phyllophora antarctica. However, metal accumulation was not the same for all the analytes, but, rather, depended on the organism characteristics. In particular, the soft tissues of Odontaster validus were characterized by high concentrations of cadmium, zinc and copper, those of Phyllophora antarctica by high concentrations of manganese and nickel, and the tissues of Laternula elliptica by high concentrations of all measured elements, particularly in its digestive gland. The Antarctic data as well as those reported for other pristine coastal ecosystems showed remarkably high natural variability in metal content, which must be taken into account when interpreting results from biomonitoring programmes.

Selection of internal standards in inductively coupled plasma atomic emission spectrometry by principal component analysis

A systematic procedure for the selection of optimal internal standards in ICP-OES has been developed. According to the procedure, a preliminary set of measurements is performed before analysis and processing by principal component analysis. The result is a plot (score plot) in which the emission lines of analytes and potential internal standards are grouped according to their empirical behaviour with respect to the considered matrix. The analysis of the score plot makes it possible to choose the optimal reference line, for each analytical line or group of analytical lines. In order to verify the efficiency of the method, trace element determination in marine sediments was considered and the procedure applied to compensate for the matrix effects due to large amounts of iron, aluminium, calcium, sodium and potassium. A robust axially viewed ICP with multichannel detection based on a coupled charge device was used in order to provide real-time internal standardization and to permit the simultaneous measurement of several emission lines. By the analyses of both synthetic and real samples, it was verified that the proposed procedure is suitable for choosing the optimal reference lines, allowing the full effectiveness of the internal standard method.

Determination of sub-nanomolar levels of iron in sea-water using reaction cell inductively coupled plasma mass spectrometry after Mg(OH)2 coprecipitation

A new procedure for the determination of iron in sea-water at sub-nanomolar concentration levels was developed. The method applied the low-blank magnesium hydroxide co-precipitation procedure in combination with quadrupole ICP-MS and used the dynamic reaction cell technique to resolve the polyatomic interferences arising from the residual matrix and the solvent. Although the interference-free determination at m/z = 56 could be obtained by using methane as the reaction gas, the best signal-to-background ratio was achieved by using ammonia and performing the measurements at m/z = 54. Accurate quantification of low levels of iron at m/z = 54 also required the mathematical correction for the isobaric interference due to the occurrence of chromium. The main analytical figures of the optimized method were evaluated, with special attention to the determination of the procedural, reagent and field blanks. A detection limit as low as 0.09 nM was achieved, using a pre-concentration ratio of 10. The accuracy of the analytical procedure was evaluated by the analysis of the sea-water reference materials CASS-4, NASS-5, SAFe D2 and SAFe S1, having certified concentration values ranging from 12.8 nM to about 0.1 nM. The analytical precision for replicated analyses of the CRMs ranged from 1.3% to 14% (n = 7). Finally, the developed procedure was applied to a number of open-ocean sea-water samples from the Ross Sea (Southern Ocean, Antarctica)

Arsenobetaine is a significant arsenical constituent of the red Antarctic alga Phyllophora antarctica

Environmental context. Although arsenic occurs in marine animals at high concentrations, the pathways by which it is biotransformed and accumulated remain largely unknown. The observation that some species of algae can contain significant concentrations of arsenobetaine, a major marine arsenic species, is relevant to explanations of the source of this compound to marine animals and its transport through the marine food web. Abstract. Significant amounts of arsenobetaine (up to 0.80 μg As g–1 dry mass, representing 17% of the extractable arsenic) were found in the extracts of all four samples of the red alga Phyllophora antarctica collected from two sites in Antarctica (Terra Nova Bay and Cape Evans). The assignment was made with high performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC-ICPMS) based on exact cochromatography with a standard compound with two chromatographic systems (cation-exchange and ion-pairing reversed-phase), each run under two sets of mobile phase conditions. Particular care was taken during sample preparation to ensure that the arsenobetaine was of algal origin and did not result from epiphytes associated with the alga. Another red alga, Iridaea cordata, collected from Terra Nova Bay, did not contain detectable concentrations of arsenobetaine. For both algal species, the majority of the extractable arsenic was present as arsenosugars. Confirmation that marine algae can contain significant amounts of arsenobetaine allows a simpler explanation for the widespread occurrence of this arsenical in marine animals.

Comparison of inductively coupled plasma spectrometry techniques for the direct determination of rare earth elements in digests from geological samples

Inductively coupled plasma quadrupole mass spectrometry (ICP-QMS), ICP sector field mass spectrometry (ICP-SFMS) and ICP atomic emission spectrometry (ICP-AES) were compared with regard to the direct determination of rare earth elements (REEs) in geological samples. In order to reduce the polyatomic interferences occurring in ICP-QMS, the use of a cooled spray chamber was optimized, obtaining a significant decrease of the oxide ions formation (about 50%) and a consequent mitigation of the interfering effects. Precision and accuracy of the method were demonstrated by the analyses of sediment and soil certified reference materials. ICP-SFMS working in high-resolution mode also provided accurate results, with similar precision to ICP-QMS (RSD%: 3-8%) and comparable or better limits of detection. Quantification limits of the procedures were 18-52 ng g(-1) and 10-780 ng g(-1) for sector field- and quadrupole-ICP-MS, respectively. Accurate and precise determination of most REEs was also achieved by ICP-AES using both pneumatic and ultrasonic nebulization, after a careful selection of the emission lines and compensation for non-spectral interferences by internal standardization. The three techniques were finally applied to glaciomarine sediment samples collected in Antarctica, providing comparable analytical data on REE abundance and depth pattern.

Effects of Ice Melting on Cu, Cd and Pb Profiles in Ross Sea Waters (Antarctica)

Abstract In the framework of the Italian Research Programme in Antarctica, evolution of dissolved and particulate Cu, Cd and Pb profiles in the coastal waters of Gerlache Inlet (Terra Nova Bay, Western Ross Sea) was studied during the Austral Summer 1997/98. In order to relate the distributions of trace metals with the physical and biological processes, a series of temperature and salinity measures were made, and water samples were collected to determine nutrients and chlorophyll. Samples of pack ice and marine microlayer (50–150 μm) were also collected and analysed. Concerning the surface layer, it was found that metal concentrations are mainly affected by the dynamic of the pack ice melting and phytoplankton activity. The first process influences both the input of metals from meltwaters and the covering of the seawater surface, allowing atmospheric dust input only when all ice has been melt or removed. Direct release of particulate Cu from ice was clearly shown by surface maxima and by the high concentrations of suspended particulate matter and particulate metals found in the ice core section interfaced with the seawater. Differently, the high amount of Cd in the particulate included in the pack ice seems not to affect the concentration in surface particulate; on the contrary, the corresponding increase of dissolved Cd indicates that it isreleased in dissolved form when the pack ice melts. Surface distribution is further complicated by the effect of phytoplankton activity, which removes Cu and Cd from water, incorporating them into organic particulate. Finally, in absence of pack ice, there is evidence of inputs of Pb and Cu due to atmospheric dust brought into the column water through marine microlayer. In intermediate and deep waters, the vertical distribution of Pb and Cd was characterised by substantially constant profiles, while Cu shown, during the end of the summer and in absence of a well-defined water column stratification, a “scavenging-type” distribution which overlaps its “nutrient-type” behaviour.