Edward C. V. Butler

Saccharides enhance iron bioavailability to Southern Ocean phytoplankton

Iron limits primary productivity in vast regions of the ocean. Given that marine phytoplankton contribute up to 40% of global biological carbon fixation, it is important to understand what parameters control the availability of iron (iron bioavailability) to these organisms. Most studies on iron bioavailability have focused on the role of siderophores; however, eukaryotic phytoplankton do not produce or release siderophores. Here, we report on the pivotal role of saccharides—which may act like an organic ligand—in enhancing iron bioavailability to a Southern Ocean cultured diatom, a prymnesiophyte, as well as to natural populations of eukaryotic phytoplankton. Addition of a monosaccharide (>2 nM of glucuronic acid, GLU) to natural planktonic assemblages from both the polar front and subantarctic zones resulted in an increase in iron bioavailability for eukaryotic phytoplankton, relative to bacterioplankton. The enhanced iron bioavailability observed for several groups of eukaryotic phytoplankton (i.e., cultured and natural populations) using three saccharides, suggests it is a common phenomenon. Increased iron bioavailability resulted from the combination of saccharides forming highly bioavailable organic associations with iron and increasing iron solubility, mainly as colloidal iron. As saccharides are ubiquitous, present at nanomolar to micromolar concentrations, and produced by biota in surface waters, they also satisfy the prerequisites to be important constituents of the poorly defined “ligand soup,” known to weakly bind iron. Our findings point to an additional type of organic ligand, controlling iron bioavailability to eukaryotic phytoplankton—a key unknown in iron biogeochemistry.

A compact flow injection analysis system for surface mapping of phosphate in marine waters

The design, construction and validation of a compact, portable flow injection analysis (FIA) instrument for underway analysis of phosphate in marine waters is described. This portable system employs gas pressure for reagent propulsion and computer controlled miniature solenoid valves for precise injection of multiple reagents into a flowing stream of filtered sample. A multi-reflection flow cell with a solid state LED photometer is used to detect filterable reactive phosphate (0.2 mum) as phosphomolybdenum blue. All the components are computer controlled using software developed using the Labviewtrade mark graphical programming language. The system has the capacity for sample throughput of up to 380 phosphate analyses per hour, but in the mode described here was operated at 225 analyses per hour. Under these conditions, the system exhibited a detection limit of 0.15 muM, reproducibility of 1.95 % RSD (n=9) and a linear response (r(2)=0.9992) when calibrated in the field with standards in the range 0.81-3.23 muM. The system was evaluated for the mapping of phosphate concentrations in Port Phillip Bay, south eastern Australia, and during the course of a 150 km cruise, 542 analyses were performed automatically. In general, good agreement was observed between analyses obtained using the portable FIA system and those obtained from manual sampling and laboratory analysis.

Modern preconcentration methods for the determination of selenium species in environmental water samples

Modern methods of preconcentration are investigated with regard to the determination of selenium species in natural (especially ocean) waters. The low concentration of selenium in surface waters means that it is often present at levels below the limits of detection (LODs) of traditional analytical methods. This article investigates preconcentration methods that can be used to improve the LOD for selenium and discusses their suitability with respect to the different selenium species.

Flow-injection analysis with fluorescence detection for the determination of trace levels of ammonium in seawater

A method using flow-injection, gas-diffusion, derivatisation and then fluorescent detection has been established for ammonium ion determination in seawater. The fluorescent derivative formed by reacting ortho-phthaldialdehyde (OPA) and sulfite with ammonia gives high sensitivity while removing potential interferences. This is required to measure the low concentrations of ammonium often seen in the open ocean. The experimental conditions (flow-rate, reagent concentrations, membrane configurations, etc.) were manipulated to improve performance. For a sample throughput of 30 samples h(-1), the limit of detection was 7 nM, the coefficient of variation was 5.7% at 800 nM, and the calibration curve was linear to at least 4 micromol L(-1). Interferences were minimised by a gaseous diffusion step. Volatile small molecular-weight amines as interferents were discriminated against by this method. They neither passed through the membrane as efficiently as ammonia, nor reacted as readily with OPA when sulfite was the reductant. Contamination by ammonia from laboratory and shipboard sources complicates application of the method to natural waters, especially measurement of low concentrations (<100 nM) in open-ocean waters. Steps to overcome contamination are described in detail. Some results are presented for ammonium determination in Southern Ocean and Huon Estuary (Tasmania) waters.

Speciation of dissolved iodine in the waters of a humic-rich estuary

Abstract This paper reports the findings of a study into iodine speciation in the humic-rich waters of the Huon Estuary, Tasmania, Australia. Water samples were taken from the estuary at various locations during both summer and winter. The samples were analysed for a range of parameters including iodate, iodide, total iodine, nutrients, chlorophyll a , dissolved organic carbon (DOC) and salinity. Total iodine behaved conservatively within the estuary irrespective of season. Iodate concentrations varied linearly with salinity but became undetectable in the low salinity end of the estuary. Iodide concentrations showed no correlation with salinity, but showed a positive correlation with total dissolved phosphorus during summer suggesting iodide concentrations within the estuary are controlled by biological activity during, or immediately after, periods of high productivity. “Organic” iodine is produced within the estuary and the fraction of iodine present in this form increases in the low salinity waters where DOC concentrations are highest.

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.

Matrix-elimination ion chromatography with post-column reaction detection for the determination of iodide in saline waters

An ion chromatographic method has been developed for the determination of traces of iodide in saline waters. A Dionex IonPac AS11 anion-exchange column was used with a mobile phase containing sodium chloride in order to remove interferences of the sample matrix in both the chromatographic separation and detection. This matrix-elimination procedure was reinforced by a post-column reaction detection that was both selective and sensitive for iodide and was based on the reaction of iodide with 4,4′-bis(dimethylamino)diphenylmethane in the presence of N-chlorosuccinimide. Detection was carried out at 605 nm. The detection limit for iodide in seawater is at about 0.8 ppb for a 150-μl injection, and the relative standard deviation at 5 ppb is better than 4%. Bromide is a potential interference, but is well separated from iodide. No interferences from dissolved organic matter in natural samples have been observed.

Iodide and iodate concentrations in eastern Australian subtropical waters, with iodide by ion chromatography☆

Abstract Iodide and iodate concentrations were measured in the subtropical waters along the continental shelf and slope waters of eastern Australia. A thermocline between 50–100 m separated Coral Sea waters from Subtropical Lower Water on all transects. There was a sharp change in the iodide and iodate concentrations at the thermocline. The concentration of iodide in the shelf waters between 0 and 50 m ranged from 0.07 to 0.18 μM and ranged from 0.01 to 0.03 μM below a depth of 100 m. Iodate concentrations showed the inverse trend to iodide, ranging from 0.32 to 0.39 μM in the top 50 m, increasing to 0.46 μM below a 100 m. The ratio of iodate to phosphate in the Coral Sea waters was about eight times greater than deeper Subtropical Lower Water. This suggested that either (1) processes other than biological assimilation dominate in the Coral Sea, or (2) biological assimilation is greater in the Coral Sea, and more iodate is reduced to iodide, but this form of iodine does not enter the uptake cycle again as readily as phosphate, or (3) disparate paths for the biological cycling of iodine operate in different water bodies. Iodate was reduced to iodide in Coral Sea surface waters in the presence of both low concentrations of phosphate and nitrate. However, the reduction was for the most part effected before nitrate departed appreciably from its Redfield relationship with phosphate to become nutrient limiting.

Liquid chromatography—electrochemistry procedure for the determination of chlorophenolic compounds in pulp mill effluents and receiving waters

Abstract An isocratic, reversed-phase liquid chromatography procedure is described for the separation and determination of chlorophenolic compounds, including several priority pollutant chlorophenols. The separation was experimentally optimised, and selective and sensitive detection was obtained by dual electrode amperometry. The most suitable combination was a silica-based column with phenyl functional groups, and a mobile phase of acetonitrile-acetate buffer (40:60, pH 5). Dual glassy-carbon electrodes were used in a parallel configuration in a thin-layer flow cell, with differential current measurement (+0.90 V relative to +0.60 V). A solid-phase extraction scheme using a polymeric sorbent (Chromosorb 102) was devised for the extraction and preconcentration of selected chlorophenols, chloroguaiacols, and a chlorosyringol from aqueous samples. Use of tribromophenol as an internal standard was also investigated. The total procedure —preconcentration and chromatography— was applied to the analysis of effluents discharged by a paper mill, and a pulp mill.

An ICP-MS procedure to determine Cd, Co, Cu, Ni, Pb and Zn in oceanic waters using in-line flow-injection with solid-phase extraction for preconcentration

An automated procedure including both in-line preconcentration and multi-element determination by an inductively coupled plasma mass spectrometer (ICP-MS) has been developed for the determination of Cd, Co, Cu, Ni, Pb and Zn in open-ocean samples. The method relies on flow injection of the sample through a minicolumn of chelating (iminodiacetate) sorbent to preconcentrate the trace metals, while simultaneously eliminating the major cations and anions of seawater. The effectiveness of this step is tested and reliability in results are secured with a rigorous process of quality assurance comprising 36 calibration and reference samples in a run for analysis of 24 oceanic seawaters in a 6-h program. The in-line configuration and procedures presented minimise analyst operations and exposure to contamination. Seawater samples are used for calibration providing a true matrix match. The continuous automated pH measurement registers that chelation occurs within a selected narrow pH range and monitors the consistency of the entire analytical sequence. The eluent (0.8M HNO3) is sufficiently strong to elute the six metals in 39 s at a flow rate of 2.0 mL/min, while being compatible for prolonged use with the mass spectrometer. Throughput is one sample of 7 mL every 6 min. Detection limits were Co 3.2 pM, Ni 23 pM, Cu 46 pM, Zn 71 pM, Cd 2.7 pM and Pb 1.5 pM with coefficients of variation ranging from 3.4% to 8.6% (n=14) and linearity of calibration established beyond the observed concentration range of each trace metal in ocean waters. Recoveries were Co 96.7%, Ni 102%, Cu 102%, Zn 98.1%, Cd 92.2% and Pb 97.6%. The method has been used to analyse ~800 samples from three voyages in the Southern Ocean and Tasman Sea. It has the potential to be extended to other trace elements in ocean waters.