Am Featherstone

Antimony and Arsenic Biogeochemistry in the Western Atlantic Ocean

The subtropical to equatorial Atlantic Ocean provides a unique regime in which one can examine the biogeochemical cycles of antimony and arsenic. In particular, this region is strongly affected by inputs from the Amazon River and dust from North Africa at the surface, and horizontal transport at depth from highlatitude northern (e.g., North Atlantic Deep Water) and southern waters (e.g., Antarctic Bottom and Intermediate Waters). As a part of the 1996 Intergovernmental Oceanographic Commission’s Contaminant Baseline Survey, data for dissolved As(III+V), As(III), mono- and dimethyl arsenic, Sb(III+V), Sb(III), and monomethyl antimony were obtained at six vertical profile stations and 44 sites alongthe 11,000 km transect from Montevideo, Uruguay, to Bridgetown, Barbados. The arsenic results were similar to those in other oceans, with moderate surface depletion, deep-water enrichment, a predominance of arsenate (>85% As(V)), and methylated arsenic species and As(III) in surface waters that are likely a result of phytoplankton conversions to mitigate arsenate ‘‘stress’’ (toxicity). Perhaps the most significant discovery in the arsenic results was the extremely low concentrations in the Amazon Plume (as low as 9.8 nmol/l) that appear to extend for considerable distances offshore in the equatorial region. The very low concentration of inorganic arsenic in the Amazon River (2.8 nmol/l; about half those in most rivers) is probably the result of intense iron oxyhydroxide scavenging. Dissolved antimony was also primarily in the pentavalent state (>95% antimonate), but Sb(III) and monomethyl antimony were only detected in surface waters and displayed no correlations with biotic tracers such as nutrients and chlorophyll a. Unlike As(III+V)’s nutrient-type vertical profiles, Sb(III+V) displayed surface maxima and decreased into the deep waters, exhibitingthe behavior of a scavenged element with a strongatmospheric input. While surface water Sb had a slight correlation with dissolved Al, it is likely that atmospheric Sb is delivered with combustion byproducts and not from mineral aerosols. In the Amazon Plume, antimony concentrations dropped substantially, and an Amazon River sample had a concentration (0.25 nmol/l) that was less than one-fourth those found in other major rivers. Usingthese river data, and estimates of atmospheric fluxes based on

Determination of arsenic species in sea-water by hydride generation atomic fluorescence spectroscopy

A method for the determination of arsenate, arsenite, monomethylarsonate and dimethylarsinate was developed using hydride generation and cold trapping of the hydrides, coupled with atomic fluorescence detection at 193.7 nm. Optimisation of the signal was carried out for a number of experimental parameters, including the carrier gas flow rates, sample volume and the concentration and addition time of NaBH 4 . The detection limits for As III , As V , MMA and DMA are 2.3, 0.9, 2.4 and 3.7 ng l –1 , respectively, in a 5 ml sample. The precision for nine sample replicates was better than 3.5% for all the arsenic species. The accuracy of the method was determined by analysis of a sea-water reference material (NASS-4) and by recovery studies on natural samples. Examples of the methods application to the analysis of arsenic species in unpolluted coastal sea-water are given.

Removal of dissolved copper and iron at the freshwater-saltwater interface of an acid mine stream

The King River, Tasmania, contains elevated levels of heavy metals, in particular copper, a result of the discharge of mine tailings and acid mine water from the Mt Lyell copper mine, which operated until late 1994. Samples were collected from the lower King River in July 1994, over a 48-h period, during which time the power station at the head of the river was off for the first 24 h. Saline water was observed in the delta region during this low flow period, and dissolved iron and copper were found to exhibit nonconservative behaviour with salinity. Removal of dissolved copper, as the river enters the harbour, was confirmed by laboratory experiments. The removal mechanism appears to be dependent on rapid pH increases and the formation of amorphous iron flocs which occur in the estuary, and results in a significant proportion of dissolved copper being removed from solution.

A shipboard method for arsenic speciation using semi-automated hydride generation atomic fluorescence spectroscopy

Abstract The development of a semi-automated batch HG-AFS method for the shipboard determination of As(III), As(V), MMA and DMA is described. Procedures in the analytical sequence including addition of NaBH4 to samples, cooling and heating the U-trap used for pre-concentration and separation of the arsines, and logging the AFS output are automated. Overall control of the automated tasks into a logical analytical sequence is achieved using a commercially available data acquisition and control package, workbenchmac ™. Further modifications required for the method to be adapted to shipboard use, including the use of a hydrogen generator, are also detailed. This method shows a number of advantages over a previously reported manual HG-AFS method including, shorter sample throughput time, increased precision and most significantly, ease of use under shipboard conditions. The semi-automated method was operated on the RSV Aurora Australis during a Southern Ocean voyage in March 1998. Arsenic measurements from a surface transect between 42° and 55° S along 141° 30′ E, are presented. Application of the method to more routine laboratory use is also discussed.

Meridional distribution of arsenic species in the subantarctic zone of the Southern Ocean, south of Australia

Distribution of the arsenic species total inorganic arsenic [As(V+III)], arsenite [As(III)], monomethyl arsenic (MMA), and dimethyl arsenic (DMA) was studied in the Subantarctic Zone (SAZ) of the Southern Ocean, south of Australia, during the austral autumn (March 1998). As(V) was the dominant arsenic species in both vertical profiles and surface waters along the meridional transect 42°–55°S, 141°30′E. It was also the only species observed at depths >600 m. Concentrations of the reduced arsenic species (As(III), MMA, and DMA) were low in these waters compared with other oceanic sites with similar concentrations of chlorophyll a. As(III) concentrations could not be reliably quantified at any sites (<0.04 nM). The greatest conversion of As(V) to “biological” species was found at the surface in the Subtropical Convergence Zone (2.5%) and decreased heading southward to 1% in the Polar Front (PF). While the decline in methyl arsenic concentrations was broadly associated with water temperature and measures of biological production, slightly different trends were found in the SAZ and PF. North of the Subantarctic Front (SAF), methyl arsenic concentrations were well correlated with water temperature, while south of the front, no such relation existed. In addition, the ratio DMA/MMA increased south of the SAF, associated with a change in the microalgal community composition. Low water temperature, phosphate-replete conditions, and low biological productivity in the Southern Ocean all contribute to the concentrations of biologically produced arsenic species in this region being among the lowest reported for oceanic waters.

Seasonal cycling of arsenic species in a stratified, microtidal estuary (Huon River, Tasmania)

A detailed study of arsenic cycling in the Huon estuary, south-east Tasmania, was undertaken October 1996–September 1998. Arsenic species data were obtained during eight 3-monthly spatial surveys, and a time-series study at a single site in the estuary over a 7-mo period. The data have been correlated with other chemical measurements, including nutrients, salinity, and dissolved oxygen, and also with biological information about the microalgal species present. In the Huon estuary, arsenic cycling is almost entirely biologically influenced. The seasonal cycle of reduced, methylated, and hydride refractory arsenic species was similar to that found in other temperate estuaries of the Northern hemisphere, with greatest production occurring during summer months. Inorganic arsenic concentrations in the Huon River were very low [As(V+III): 0.023–0.057 μg l−1], even when compared with other pristine systems. Concentrations at the seaward end of the estuary were typical of those found in unpolluted coastal seawater. The behavior of As(V+III) in the estuary was nearly conservative in all surveys except those conducted during summer (February), when significant depletion was observed at higher salinity. During these surveys, up to 60% of inorganic arsenic was apparently depleted from the water column with only a small proportion (20–25%) recycled as methylated and UV-labile arsenic species. This was particularly the case in a high salinity side-arm of the estuary, Port Cygnet. The extent of inorganic arsenic depletion correlated with cell numbers of the phytoplanktonPseudo-nitzschia. The fate of the missing inorganic arsenic is unclear, but the co-existence ofPseudo-nitzschia blooms with commercial mussel leases in Port Cygnet could provide one explanation for the loss.

Selenium status in Southern Tasmania

Objective:To assess the selenium status of Southern Tasmanians.Design:Cross-sectional.Settings:One thousand and five hundred adults randomly selected from the electoral roll living in the Greater Hobart region of Southern Tasmania, Australia, were invited to participate.Subjects:The overall response rate was 22% (335/1500).Interventions:A venous blood sample was collected and a questionnaire administered (consisting of brief demographic details and health questions) to subjects who granted informed consent. A previously validated assay using magnetic sector ICP-MS was employed for plasma analysis.Results:Total plasma selenium levels for this sample population were normally distributed with a mean level of 110 μg/l (range 67–268 μg/l) indicating that the majority of the subjects were not selenium-depleted (71% with levels greater than 100 μg/l). Adjustment for differential age/gender response rates produced similar values. More women under 50 (42%) and men over 50 (32%) had selenium levels <100 μg/l with the potential for sub-optimal selenoprotein activity. Low education attainment was associated with low total selenium level (P<0.02).Conclusions:The majority of participants were not deficient in selenium. Given the narrow therapeutic window of supplementation, dietary advice to increase foods rich in selenium, particularly to higher risk groups, may be an effective means of increasing plasma selenium toward target levels.Sponsorship:This project was funded by the University of Tasmania and the Royal Hobart Hospital Research Foundation.

Selenoprotein P analysis in Human Plasma: A Discrepancy Between HPLC Fractionation of Human Plasma with Heparin-Affinity Chromatography and SDS-PAGE with Immunoblot Analysis

Several recent analytical methods for determination of Se and seleno-protein P have involved high-performance liquid chromatography (HPLC) using heparin-affinity columns coupled to inductively coupled plasma-mass spectrometry (ICP-MS) for Se detection. HPLC-ICP-MS chromatography using tandem HPLC columns with ICP-MS detection was used to detect the major selenium-containing proteins in plasma (glutathione peroxidase, albumin, and selenoprotein P). The efficiency of HPLC separation of plasma selenoprotein P was investigated by analyzing HPLC fractions using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with immunoblot analysis. The HPLC fraction corresponding to selenoprotein P contained 25.1% of total selenoprotein P as measured by immunoblot analysis. The majority (74.9%) of total seleno-protein P found by immunoblot analysis was contained in the early HPLC fractions, consistent with either poor heparin affinity, which was not evident based on the HPLC-ICP-MS technique alone or nonspecific binding of the antibody. Immunoblot analysis of selenoprotein relies on antibodies binding to a selenoprotein P epitope, which might be preserved when selenoprotein P is broken down to release selenocysteine residues. Immunoblot methods overestimate selenoprotein P and are not suitable for determinations of intact selenoprotein P.

Determination of inorganic selenium species in marine waters by hydride generation-AFS

A method based on hydride generation with cryogenic trapping and atomic fluorescence detection was developed that is capable of determining both inorganic Se species (SeIV and SeVI) while at sea. Evaluation of the system for optimal performance was made for each stage of the analysis and detection sequence, as well as for the SeVI reduction step. A detection limit of 0.4 ng L−1 Se in a 10 mL sample was achieved using this method. Precision was better than 3.5% for 25, 100, and 1000 ng L−1 SeIV standard solutions. Accuracy was determined by recovery studies using natural samples and a certified reference seawater (NASS-5).