G. Scarponi

Speciation of trace metals in seawater by anodic stripping voltammetry : critical analytical steps

The speciation of trace metals in seawater based on the voltammetric (DPASV) titration of ligands by metal addition is considered. The method allows the determination of the total metal amount, the “labile” fraction, the ligand concentration and the related conditional stability constant. Analytical problems related to sample contaminations during sampling, filtration and storage, displacement of complexing equilibria in freeze storage, the kinetics of the reaction of complexation and the potential kinetic lability of organic complexes are discussed and possible solutions presented. Data on quality control tests carried out to verify the accuracy of the laboratory procedure for trace metal determination in seawater are reported.

Recent decrease in the lead concentration of Antarctic snow

Differential Pulse Anodic Stripping Voltammetry (DPASV) was applied to determine the lead concentration in recent snow at two sites in the Victoria Land region, East Antarctica. Snow samples were collected during the 6th Italian Scientific Expedition to Antarctica (austral Summer 1990-91) along the wall of 2.5 m-deep hand-dug pits and by coring to a depth of about 1 m. The measurements revealed that lead content in Antarctic snow increased continuously from 1965 (about 3 pg/ g) to the early 1980s (maximum about 8 pg/g), after which a marked, rapid decrease took place during the second half of 1980s, down to 2-4 pg/g in 1991. Estimates of the lead contributions from rocks and soils, volcanoes and the marine environment, together with analysis of statistical data on non-ferrous metal production and gasoline consumption, and the corresponding lead emissions into the atmosphere of the Southern Hemisphere, show that a net anthropogenic component is present and support the hypothesis that the trend observed in Antarctic snow may be related to lead consumption in gasoline, which firstly was on the rise, then declined owing to the increased use of unleaded gasoline.

Copper complexation in the surface seawater of Terra Nova Bay (Antarctica)

Abstract Speciation of copper in the surface seawater of Terra Nova Bay is studied by Differential Pulse Anodic Stripping Voltammetry using samples collected during the 1987–88, 1988–89 and 1989–90 Italian expeditions. Total copper concentration ranges between 0.5 and 4.8 nM and shows uniform spatial distribution without evident differences between the three campaigns. The mean value for the labile fraction is 4% of the total for the first two expeditions, while it is below the detection limit for the last one. Results show the presence of two classes of ligands, one stronger (mean concentration 1.5 nM) which shows considerable variability due to seasonal and spatial factors, and one weaker (mean concentration 31 nM, average conditional stability constant 2.8×108 M−1) which shows homogeneous distribution in the studied area.

Analytical quality control : Sampling procedures to detect trace metals in environmental matrices

The problem of contamination during the collection of samples of environmental interest to detect trace metal is discussed. Attention is focused on the leaching of metals from sampling devices used to collect surface and deep seawater. A procedure to test metal release is applied to emphasize the importance of conditioning samplers before use. The procedure for checking the contamination extent and decontamination of firn and ice cores to detect ultratrace elements (particularly Cd and Pb) is presented and applied to some firn cores collected in Antarctica during the 1990–1991 Italian expedition.

Chemometric studies in the Lagoon of Venice, Italy. 1. The environmental quality of water and sediment matrices

Water, particulate, and sediments were collected at a few sites in the Venice Lagoon (Italy) in order to evaluate the quality of these components through a number of mainly chemical measurements. Trace elements (mainly heavy metals), nutrients, PCBs, a toxicity test, and other general constituents were the main features considered. Principal component analysis was applied as a multivariate statistical technique for dimensionality reduction, for the formulation of a multivariate quality criterion, and for identification of the most significant variables. The first few (2−3) principal components have proven useful in summarizing the information available in all the observed variables, supplying a link between the different classes of chemical substances detected in the water matrix and the different polluting inputs (industrial, agricultural, urban) to which the Venice Lagoon is subject (water matrix) and between the chemical composition (speciation of trace elements) of the sediment matrix and its toxicity.

Statistical evaluation of the group structures of five Venetian wines from chemical measurements

Exploratory statistical methods are used to elucidate the group structures pertaining to a chemical data set obtaned from 184 samples of five typical white wines from the Venetian Region: Soave Classico, Presecco di Conegliano-Valdobbiadene, Verduzzo del Piave, Tocai di Lison, Tocai delle Grave del Friuli. Analytical data included 19 classical parameters and 9 aroma components. Correlation matrices showed that the same three sets of intercorrelated variables were present in all the groups, and that aroma components were nearly uncorrelated with classical parameters. Principal components analysis allowed a subspace of reduced dimensionality to be derived for each group. However, because of similar pattern of the correlation matrices, a high degree of similarity was also observed among the subspaces. An efficient differentiation of the groups was obtained by canonical variates analysis. The most important chemical parameters were potassium, ash content, total nitrogen, cis-3-hexen-1-o1 and 1-hexanol. Classification of samples by the Euclidean distances from the centroids in the canonical space gave on average 94% correct results.

Concentration Changes in Cadmium and Lead in Antarctic Coastal Seawater (Ross Sea) During the Austral Summer and Their Relationship with the Evolution of Biological Activity

Studies were made of the seasonal evolution of cadmium and lead distribution in the water column of Wood Bay (Ross Sea, Antarctica) during the 1993–94 austral summer. Anodic stripping voltammetry was used to carry out on-site measurements, immediately after the collection and filtration of samples. Before the phytoplankton bloom, the concentrations of both metals were uniform along the water column, with mean values of 0.64 (SD 0.07) and 0.031 (SD 0.006) nmoll−1 for cadmium and lead, respectively. A subsequent depletion in metal concentration was observed in shallow waters. By the end of the season, the surface concentration of cadmium had decreased to about 0.1 nmoll−1. As regards lead, vertical distribution was less affected by season and the mean surface concentration decreased to about 0.01 nmoll−1 over the same period. Results are evaluated in relation to the evolution of biological activity in the area, and are examined and compared with those obtained during a similar study carried out in the Terra Nova Bay area (Gerlache Inlet) 3 years previously.

An integrated study of the chemical composition of Antarctic aerosol to investigate natural and anthropogenic sources

Environmental context Owing to its remoteness, Antarctica is an excellent natural laboratory for conducting studies on the behavior of marine aerosols and for monitoring the impact of global human activities. The aim of this study is to provide an extensive chemical characterization of Antarctic aerosol and to investigate its sources. A distinction among anthropogenic, crustal, and biogenic sources was defined using several chemical markers. Abstract During the 2010–11 austral summer, an aerosol sampling campaign was carried out at a coastal Antarctic site (Terra Nova Bay, Victoria Land). In this work, previously published data about water-soluble organic compounds and major and trace elements were merged with novel measurements of major ions, carboxylic acids and persistent organic pollutants (polychlorobiphenyls, polycyclic aromatic hydrocarbons, polychlorinated naphthalenes, polybrominated diphenylethers and organochlorine pesticides) in order to provide a chemical characterisation of Antarctic aerosol and to investigate its sources. The persistent organic pollutants were determined using a high-volume sampler, able to collect both particulate and gaseous fractions, whereas remaining compounds were determined by performing an aerosol size fractionation with a PM10 cascade impactor. Ionic species represented 58% (350ng m–3) of the sum of concentrations of all detected compounds (596ng m–3) in our Antarctic PM10 aerosol samples due to natural emission. Trace concentrations of persistent organic pollutants highlighted that the occurrence of these species can be due to long-range atmospheric transport or due to the research base. Factor analysis was applied to the dataset obtained from the samples collected with the PM10 sampler in order to make a distinction between anthropogenic, crustal and biogenic sources using specific chemical markers.