Andrew J. Seen

A comparison of an optimised sequential extraction procedure and dilute acid leaching of elements in anoxic sediments, including the effects of oxidation on sediment metal partitioning.

The effect of oxidation of anoxic sediment upon the extraction of 13 elements (Cd, Sn, Sb, Pb, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, As) using the optimised Community Bureau of Reference of the European Commission (BCR) sequential extraction procedure and a dilute acid partial extraction procedure (4h, 1 molL(-1) HCl) was investigated. Elements commonly associated with the sulfidic phase, Cd, Cu, Pb, Zn and Fe exhibited the most significant changes under the BCR sequential extraction procedure. Cd, Cu, Zn, and to a lesser extent Pb, were redistributed into the weak acid extractable fraction upon oxidation of the anoxic sediment and Fe was redistributed into the reducible fraction as expected, but an increase was also observed in the residual Fe. For the HCl partial extraction, sediments with moderate acid volatile sulfide (AVS) levels (1-100 micromolg(-1)) showed no significant difference in element partitioning following oxidation, whilst sediments containing high AVS levels (>100 micromolg(-1)) were significantly different with elevated concentrations of Cu and Sn noted in the partial extract following oxidation of the sediment. Comparison of the labile metals released using the BCR sequential extraction procedure (SigmaSteps 1-3) to labile metals extracted using the dilute HCl partial extraction showed that no method was consistently more aggressive than the other, with the HCl partial extraction extracting more Sn and Sb from the anoxic sediment than the BCR procedure, whilst the BCR procedure extracted more Cr, Co, Cu and As than the HCl extraction.

Nafion: an excellent support for metal-complex catalysts

Abstract A number of studies over the past 20 years have demonstrated that the perfluorinated ion-exchange polymer Nafion is an excellent support for metal-complex catalysts. A variety of cationic metal-complex catalysts have been successfully immobilized in Nafion with little if any leaching occurring during catalysis, and in several instances the supported catalyst has been re-used with little loss in activity. Whilst the activity of Nafion-supported catalysts has been shown to be dependent upon catalyst loading, suggesting diffusion limitations, activities comparable with homogeneous activities have been observed by increasing the dispersion of Nafion. The physical structure and chemical properties of Nafion offer the additional benefits of providing protection to the supported catalyst from deactivation and the potential to increase the activity of the supported catalyst compared with its homogeneous analogue. Although diffusion limitations and the high cost of Nafion have potentially limited its application as a metal-complex catalyst support, the recent development of high surface area Nafion–silica nanocomposites provides the opportunity to solve these issues.

Historical lead isotope record of a sediment core from the Derwent River (Tasmania, Australia): A multiple source environment

A 105 cm sediment core from the Derwent River (Tasmania, Australia) was collected in 2004 and was characterised considering both physical (loss on ignition at 550 °C and grain size) and chemical (Fe, Cu, Zn, Cd and Pb concentrations, Pb isotope ratios and (210)Pb dating) properties. The core was analysed to (i) investigate the historical profiles of some important elements associated with the Risdon zinc refinery adjacent to the Derwent River, (ii) determine Pb isotopic signatures of sediment samples, and (iii) assess the veracity of Pb isotope ratios as indicators of contaminant Pb input. Extractable metal concentrations were (all values as mgkg(-1), non-normalised for grain size) Fe: 20,000-35,000, Zn: 42-4500, Pb: 5-1090, Cu: 13-141, and Cd: 1-31; with a close correlation between Cu, Zn, Cd and Pb. Metal enrichment factors (normalised to Al) were Pb: 0.9-144, Zn: 0.8-93, Cd: 0.8-30, Cu: 0.8-8.9 and Fe: 0.9-1.3, confirming anthropogenic contributions of Cu, Zn, Pb and Cd to the sediments. The onset of metal contamination above background levels occurred at a depth between 43 and 49 cm, with maximum concentrations noted near 20 cm for Cu, Zn, Cd and Pb. Lead isotope ratios were determined in sediments using sector field ICP-MS, and were found to be 36.5-38.8, 16.5-18.7 and 1.07-1.20 for (208)Pb/(204)Pb, (206)Pb/(204)Pb and (206)Pb/(207)Pb ratios, respectively. Major Australian ores processed at the refinery over the previous ~90 years include those from Broken Hill, Rosebery, Mt Isa, Elura, Hellyer and Century deposits. Anthropogenic impact by Pb with Broken Hill type isotopic ratio was initially evident in the core at 43-49 cm. The introduction of Rosebery and Elura ores to the refinery was also clearly noted. Pb isotope ratios further highlight that the Derwent River has been exposed to a greater impact by anthropogenic Pb in comparison to other major Tasmanian rivers, namely the Huon and Tamar.

Lead isotopic signatures in Antarctic marine sediment cores: A comparison between 1 M HCl partial extraction and HF total digestion pre-treatments for discerning anthropogenic inputs

Sensitive analytical techniques are typically required when dealing with samples from Antarctica as even low concentrations of contaminants can have detrimental environmental effects. Magnetic Sector ICP-MS is an ideal technique for environmental assessment as it offers high sensitivity, multi-element capability and the opportunity to determine isotope ratios. Here we consider the Pb isotope record of five marine sediment cores collected from three sites in the Windmill Islands area of East Antarctica: Brown Bay adjacent to the current Australian station Casey, Wilkes near the abandoned US/Australian Station and McGrady Cove lying midway between the two. Two sediment pre-treatment approaches were considered, namely partial extraction with 1M HCl and total dissolution involving HF. Lead isotope ratio measurements made following sediment partial extraction provided a more sensitive indication of Pb contamination than either Pb concentrations alone (irrespective of sample pre-treatment method) or isotope ratios made after HF digestion, offering greater opportunity for discrimination between impacted and natural/geogenic samples and sites. Over 90% of the easily extractable Pb from sediments near Casey was anthropogenic in origin, consisting of Pb from major Australian deposits. At Wilkes impact from discarded batteries with a unique isotopic signature was found to be a key source of Pb contamination to the marine environment with ~70-80% of Pb being anthropogenic in origin. The country and source of origin of these batteries remain unknown. Little evidence was found suggesting contamination at Wilkes by Pb originating from the major US source, Missouri. No definitive assessment could be made regarding Pb impact at McGrady Cove as the collected sediment core was of insufficient depth. Although Pb isotope ratio signatures may indicate anthropogenic input, spatial concentration gradients at nearby Brown Bay suggest contamination at McGrady Cove is unlikely. We recommend Pb isotopic analysis following 1M HCl partial extraction pre-treatment as a powerful and sensitive method for tracing Pb contamination in marine sediments.

Determining the history and sources of contaminants in the Tamar Estuary, Tasmania, Australia, using 210Pb dating and stable Pb isotope analyses

Environmental Context. Dating estuary sediments provides insights into the materials entering the estuary and can pinpoint when the contamination occurred. Heavy metal contamination is a known health risk but attributing it to a source can be contentious. For a sample sourced downstream of a city and a mining region, lead-210 dating and stable lead isotope analyses uncovered the sources of lead inputs. These methods quantified the extent that upstream mining activities and, for the first time, the extent that non-mining inputs (vehicles, industry) contributed to the estuarys pollution. Abstract. 210Pb dating and heavy metal analyses (Cd, Cu, Pb, Zn) have been combined to establish an historical profile of pollutant levels in sediments in the Tamar Estuary (Tasmania, Australia) over the past century. Heavy metal profiles through the core show a strong correlation with mining activities and industrialization during the past century, reflecting catchment disturbance in one of Australias earliest settled areas. A source apportionment of Pb in the sediment core using stable Pb isotope ratios (204Pb, 206Pb, 207Pb, 208Pb) shows that mine pollution has been contributing 10-25 mg kg-1 to Tamar Estuary sediments since the start of mining in the early 1890s, whilst non-mining inputs were not significant until post-1930 and became increasingly significant post-World War II. Since the 1950s-1960s, non-mining anthropogenic Pb inputs have become as significant as Pb from mining activities, although there does appear to be a decline in non-mining inputs during the past 20 years, which is consistent with findings elsewhere where reductions in atmospheric Pb levels have been observed and are attributed to the phasing-out of leaded gasoline. The source apportionment does, however, suggest that Pb from mine pollution at Storys and Aberfoyle Creeks continues to impact upon upper Tamar Estuary sediment quality.

Nafion supported cationic palladium complexes as catalysts

Abstract The three cationic palladium species; Pd(1,10-phen) 2+ 2 , Pd(2,2′-bipy) 2+ 2 and Pd(1,10-phen) (py) 2+ 2 have been immobilized in Nafion-H + and Nafion-Na + by ion-exchange. Characterization of the Nafion supported species has been achieved by UV, IR and 13 C-NMR spectroscopies. Both Pd(1,10-phen) 2+ 2 and Pd(2,2′-bipy) 2+ 2 are unchanged when immobilized in Nafion, however, it appears that partial decomposition of Pd(1,10-phen) (py) 2+ 2 to give 1,10-phen and pyridine occurs in Nafion-H + . The ability of the immobilized species to dimerize ethene has been tested and the dimerization activity was found to be dependent upon the basicity of the nitrogen donor ligand and the counterion in Nafion.

Direct colorimetric detection of copper(II) ions in sampling using diffusive gradients in thin-films

A novel binding phase was developed for use in diffusive gradients in thin-film (DGT) sampling for Cu(II) by employing methylthymol blue as a chelating and chromogenic agent. Methylthymol blue was adsorbed onto beads of Dowex 1 x 8 resin (200-400 mesh) and the resin beads were then immobilised onto an adhesive disc. Analysis of exposed binding discs by either UV-vis spectrophotometry or computer imaging densitometry provided robust quantification of adsorbed Cu(II) in the 0.2-1 microg cm(-2) range, allowing detection at microg L(-1) concentrations in the test solution (ca. 17 microg L(-1) for a 24 h deployment), and in good agreement with established DGT theory. The method was shown to be a potential replacement for binding phases based on Chelex 100 where a colorimetric response to a specific metal is desired.

Increased catalytic activity of cationic palladium(II) complexes on immobilisation in Nafion-H+

Abstract Catalytic dimerisation of ethene by [Pd(1,10-phen)2]2+ supported in three forms of Nafion has confirmed that diffusion of reactants and/or products through Nafion is rate-limiting. However, a combination of low catalyst loading and high dispersion of Nafion has resulted in extraordinary increases in ethene dimerisation activities when compared with the homogeneous analogue. Initial activities as high as 760,000 turnovers h−1 have been obtained for the supported complex compared with a homogeneous activity of 32,000 turnovers h−1. These increases in activity most likely result from the very polar, strongly acidic environment in Nafion which ensures effective anion–cation separation and promotes labilisation of the nitrogen donor ligands. Enhancements in activities for co-polymerisation of ethene and carbon monoxide, and carbomethoxylation of ethene have also been observed using Nafion supported Pd(II) catalysts in methanol.

Naƒon® supported cationic palladium complexes as catalysts (II)

Abstract A comprehensive investigation of the ability of Naƒon to influence catalytic reactions has been undertaken using the [Pd( 1,10-phen) 2 ] 2+ species immobilized in Naƒon—H + . The effects of catalyst loading, solvent, substrate, temperature and pressure on catalytic activity have been studied. We have found that whilst the homogeneous [Pd(1,10-phen) 2 ][ p -tolyl-SO 3 ] 2 model complex dimerizes ethene and propene, and isomerizes 1-butene, Naƒon supported [Pd(1,10-phen) 2 ] 2+ effectively dimerizes ethene only. The ethene dimerization activity of the supported catalyst has been found to be highly dependent on catalyst loading and solvent. Rate limitations are overcome at very low catalyst loadings and activities as high or higher than homogeneous activities were obtained. It appears likely that ethene solubility in the reaction solvent, ethene diffusion through Naƒon, Naƒon morphology, and possible steric constraints on the catalyst at high loadings are important factors. The use of water as the reaction solvent resulted in a dramatic increase in the activity of the supported catalyst and adds weight to the argument that cation-anion separation and a non-coordinating anion are important aspects of catalysis using cationic Pd(II) species. Tests with propene and 1 -butene as the feed indicate that the activity of the supported catalyst is limited by the diffusion of these substrates in Naƒon.

Ab initio studies of molecular X-ray emission processes : methanol

The energies and intensities of X-ray emission diagram lines associated with the methanol molecule have been determined using ab initio molecular orbital procedures. Absolute transition probabilities are sensitive to the inclusion of electronic relaxation effects and inter-atomic moment contributions. Relative intensities determined from frozen orbital and relaxed orbital models are in better agreement with one another than are the absolute values. To achieve a realistic basis for comparison with experiment, calculations for molecules containing first-row atoms must be undertaken at least at the multi-centre relaxed Hartree-Fock level. Good agreement is obtained between the theoretical and experimental O-K spectra for the CH3OH molecule. A significant discrepancy is reported in the C-K spectral comparison. It is concluded that the most probable causes for the differences are satellite contributions and contamination in the experimental spectrum from other molecular species.