Michael Ridd

The use of transplanted cultured tropical oysters (Saccostrea commercialis) to monitor Cd levels in North Queensland coastal waters (Australia).

Bivalves are commonly used to detect metal pollution in the marine environment. Commercially cultured Milky oysters (Saccostrea commercialis) were transplanted in various sites along the North Queensland coast and analyzed for two metals of potentially anthropogenic origin (Cd, Zn). To provide additional information, naturally occurring Black Lip oysters (Saccostrea echinata) were also collected at the transplantation sites. The study demonstrated that the oysters species transplanted are good bioindicators of these metal concentrations in tropical waters, sensitive to variations in the environment at concentrations which are much smaller than pollution signals commonly reported for temperate waters. Three transplant experiments were carried out from May 1999 to February 2000. Milky oysters transplanted to offshore areas (Orpheus Is., Kelso Reef) accumulated Cd in the soft parts whereas oysters sampled from cages placed in Ross Creek and the Herbert River estuaries showed a decrease in Cd concentration, which resulted from an increase in dry weight. Dry weight appeared to be an important covariant affecting Cd concentration in the oysters whereas it does not unambiguously affect Zn concentrations. For the duration of the experiments, oysters sampled from the Magnetic Is. reference site showed effectively constant Cd concentrations and total Cd contents which indicates that any seasonal cycle affecting metal concentration is weak. It was found that Cd accumulation in oysters increased as ambient dissolved Cd concentration decreased, from which it was concluded that for these oysters, the predominant source of Cd was from the particulate phase rather than the dissolved phase.

Chronic herbicide exposures affect the sensitivity and community structure of tropical benthic microalgae

The effects of prolonged exposure to low concentrations of herbicides on tropical periphyton (biofilm) communities are largely unknown. Tropical estuarine biofilms established in microcosms were therefore exposed to diuron (photosystem-II-inhibitor) at 2-16μg L(-1) for 4 weeks. The biofilms, consisting of diatoms, filamentous brown algae and cyanobacteria, developed a tolerance to diuron during this period as measured by Phyto-PAM fluorometry. Microscopy and pigment analysis revealed that this decrease in sensitivity was accompanied by a shift in species composition towards communities dominated by diatoms. The combination of techniques enabled the first identification of pollution-induced community tolerance (PICT) in tropical estuarine periphyton in response to chronic herbicide exposures. Community composition changed compared to controls at environmentally relevant concentrations of 1.6μg L(-1), while development of PICT was evident at 6.5μg L(-1) diuron, with no recovery (over 2 weeks) in uncontaminated water, indicating chronic pollution induced shifts in community structure.

Pesticide contamination and phytotoxicity of sediment interstitial water to tropical benthic microalgae

Many organic compounds including some herbicides concentrate in sediment, thus it may be expected that interstitial waters contain higher concentrations of these contaminants than the water column. To estimate benthic microalgal exposure to pesticides, sediment and interstitial water sampled in the dry season from four major rivers in north Queensland, Australia, were analysed for these contaminants. Interstitial water extracts from the sediments were tested for acute phytotoxicity to benthic microalgae using PAM fluorometry and the results were compared with chemical analyses of the same water samples. A range of pesticides were detected in both sediment and interstitial waters from all sites, notably the herbicide diuron at concentrations ranging from 0.3 to 11 μg kg(-1) dry weight sediment, and up to 68 ng L(-1) in interstitial waters. Herbicide concentrations estimated from partition coefficients and the sediment concentrations typically overestimated analytically determined concentrations present in interstitial water by an order of magnitude. The analytically determined herbicide concentrations in the interstitial water explained most of the phytotoxicity measured with the bioassay; however, photoinhibition was slightly higher than expected based on analytical results, indicating the presence of unidentified phytotoxins. These results demonstrate the presence of pesticides in interstitial waters in the Tropical dry season, sometimes at concentrations that may affect sensitive benthic organisms, and supports the use of the I-PAM bioassay as a valuable tool in exposure- and environmental risk- and impact-assessments.

Natural and Enhanced Concentrations of Trace Metals in Sediments of Cleveland Bay, Great Barrier Reef Lagoon, Australia

Natural variation in concentrations of Cd, Co, Cu, Ni, Pb, and Zn in sediments of Cleveland Bay can be modelled by linear regression by using the concentration of Al recovered by strong acid digestion as an independent variable. Samples that exceed the upper 95% prediction interval of regression models are classified as enhanced. Enhancement of trace metals occurs in the intertidal zone and near-shore sediments of western Cleveland Bay, in sites that are characterized by high accumulation rates of fine grained terrigenous sediment. There is a strong positive relationship between increasing enhancement of Cu and Pb and the recovery of these metals by weak HCl digestion, which suggests that for these metals the modelled enhancement is environmentally meaningful. In contrast, at least 60%, and generally greater than 80% of Cd is recovered by weak HCl digestion irrespective of modelled enhancement, and suggests that the statistically modelled enhancement of Cd may be more meaningful than weak HCl soluble concentrations.

The chronopotentiometric reduction of proteins adsorbed on mercury

Abstract The constant current chronopotentiometric reduction of five disulphide-containing proteins (bovine serum albumin, insulin, ribonuclease A, transferrin and trypsin), adsorbed on a hanging mercury drop electrode has been investigated. All five proteins showed a reduction peak at approximately −0.6 V vs. SCE due to the reduction of the disulphide groups. A linear relationship between protein molar mass and the adsorption area of the protein at monolayer coverage was observed, indicating that the proteins spread to a uniform thickness of approximately 10 A on the mercury surface.

Predicting the number of electroactive disulphide bonds in proteins adsorbed on mercury electrodes

Abstract A method for estimating the number of electroactive disulphide bonds in proteins was developed based on the assumption that the electroactive disulphides are located in the more hydrophobic regions of the protein. The method used literature values for the relative hydrophobicity of amino acids to arrive at a measure of the relative hydrophobicity of regions containing disulphide bonds. Threshold values for the calculated hydrophobicity were identified which gave a good correlation between the number of observed and predicted electroactive disulphide bonds in a variety of proteins.

The barnacle Balanus amphitrite as a biomonitor for Cd: Radiolabelled experiments

Radiolabelled experiments were carried out to measure necessary parameters in the development of a biodynamic ecotoxicological simulation model of Cd accumulation in the barnacle biomonitor Balanus amphitrite. The Cd uptake rate constant from the dissolved phase, the Cd assimilation efficiency (AE) from suspended particulate matter (SPM) and the efflux rate constant were obtained using (109)Cd. A Cd uptake rate constant from the dissolved phase (k(u)) of 0.0072 Lg(-1)h(-1) was determined for the barnacle under environmentally realistic dissolved Cd concentrations (maximum of 400 ng L(-1)). Cd AE from SPM was determined from the barnacle feeding on SPM with low and high chl a concentrations, resulting in AEs of 39.0% and 48.7%, respectively, and an efflux rate of 0.0072 d(-1). The difference between the AEs resulted from differences in chl a:SPM ratios suggesting a general tendency of higher AE when SPM is enriched with chl a. These results reinforce that the accuracy of ecotoxicological models for metal accumulation in organisms depends on how representative the selected food items are of the organisms natural diet.

Hydrodynamic Modeling of Copper Electrodeposition at a Vertical Rotating Cylinder Electrode

The hydrodynamics of a rotating cylinder electrode were modeled to predict tertiary current distributions during electrodeposition of copper from acidic sulfate media, and to evaluate the effects of the resulting density gradients close to the electrode. Assuming no such density variations, then predictions of transport-limited current densities were in good agreement with Mizushina’s empirical law and with Leveque’s theoretical description, but not with measured values. Assuming a linear density variation with copper concentration, predictions of concentration profiles agreed to within 3 % of experimentally measured limiting current densities at the rotating cylinder electrode. For solution compositions relevant to copper electrowinning, a diffusion coefficient for cupric ions of 1.2×10 -9 m 2 /s at 45 o C, was inferred by solving the continuity, Navier-Stokes and mass balance equations with Fluent® computational fluid dynamics software.

Mechanism of oxidative dehydrogenation of alcohols co-ordinated to ruthenium

The oxidative dehydrogenation of the complexes [Ru(bipy)2(NC5H4CH2OH)]2+, [Ru(bipy)2(NC5H4CD2OH)]2+ and [Ru(bipy)2{NC5H4CH(CH3)OH}]2+ to the corresponding carbonyl species [bipy = 2,2′-bipyridine; NC5H4CH2OH = 2-(hydroxymethyl)pyridine; NC5H4CD2OH = 2-(dideuteriohydroxymethyl)pyridine; NC5H4CH(CH3)OH = 2-(1-hydroxyethyl)pyridine] has been studied in aqueous solution by kinetic and electrochemical techniques. The mechanistic scheme was found to involve the intermediacy of a ruthenium(IV)–alkoxide species, formed by disproportionaton of the ruthenium(III) complex produced in the initial step of the oxidation process. The rate-determining removal of the proton from the α-carbon atom of the chelate ring is general-base catalysed.