Bv O'Grady

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.

Quantitative analysis of total resin acids by high-performance liquid chromatography of their coumarin ester derivatives

Abstract A method for the quantitative analysis of resin acids in effluent and water samples using high-performance liquid chromatography is described. Resin acids in aqueous samples are extracted by passage through C18 solid-phase cartridges at pH 9. The (7-methoxycoumarin-4-yl) methyl (MMC) and (7-acetoxycoumarin-4-yl) methyl (MAC) esters are quantitatively formed at room temperature by the reaction of resin acids with 4-bromomethyl-7-methoxycoumarin and 4-bromomethyl-7-acetoxycoumarin respectively, in the presence of potassium carbonate. The effect of potassium carbonate particle size, exposure to light, presence of residual water, and derivatisation reagent: resin acid ratio on their formation are described. The MMC esters of resin acids may be detected by UV absorption at 318 nm at concentration > 20 μg 1−1, while the (7-hydroxycoumarin-4-yl) methyl esters, obtained by post-column alkaline hydrolysis of the resin acid MAC (RAMAC) esters, enable the detection or resin acids by fluorescence spectrophotometry to levels below 1 μg 1−1. The method has been compared to gas chromatogrpahic analysis of the carboxylic acid methyl esters and shows no evidence of any interferences by other carboxylic acids. The method is routinely used by two newsprint mills for environmental monitoring of resin acids in effluent.

Theoretical Prediction of CH3O and CH2OH Gas-Phase Decomposition Rate Coefficients

Theoretical predictions are made for the pressure and temperature dependences of two reactions involved in methanol combustion: (A) CH3O → CH2O + H and (B) CH2OH → CH2O + H. The calculations are carried out by using RRKM theory with a Gorin model for the activated complexes, with fall-off effects being taken into account by using the master equation. Results for the high-pressure rate coefficients (s-1) are (A) 3×1014 exp(-108 kJ mol-1 /RT), (B) 7×1014 exp(-124 kJ mol-1 /RT) at 1000 K. For the low-pressure limiting rate coefficient (cm3 s-1) over the range 600- 1000 K (A) 8×10-9 exp(-90 kJ mol-1 /RT); (B) 2×10-8 exp(-108 kJ mol-1 /RT). At 1000 K, the pressure at which the fall-off rate coefficients are one-half of their limiting high-pressure values are 3x108 Pa for both reactions. Formulae for inclusion of these reactions (including fall- off effects) over the range 300-2000 K and 10-2-106 Pa in modelling complex kinetic schemes are presented.

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.

Frigidly Concentrated Seawater and the Evolution of Antarctic Saline Lakes

The frigidly concentrated seawater and the evolution of Antarctic saline lakes were discussed. The concentration of the major ions of the saline lakes was accurately quantified. The current state of salt mineral equilibria in the brines was determined. The analysis showed that the major ion composition of saline lakes was modified accurately using a closed-basin brine evolution model based on seawater freezing.