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Trenfield M.A.,Environmental Research Institute of the Supervising Scientist | Trenfield M.A.,University of Queensland | McDonald S.,Curtin University Australia | Kovacs K.,University of Szeged | And 7 more authors.
Environmental Science and Technology | Year: 2011

Fulvic acid (FA) from a tropical Australian billabong (lagoon) was isolated with XAD-8 resin and characterized using size exclusion chromatography, solid state cross-polarization magic angle spinning, 13C nuclear magnetic resonance spectroscopy, elemental analysis, and potentiometric acid-base titration. Physicochemical characteristics of the billabong FA were comparable with those of the Suwannee River Fulvic Acid (SRFA) standard. The greater negative charge density of the billabong FA suggested it contained protons that were more weakly bound than those of SRFA, with the potential for billabong water to complex less metal contaminants, such as uranium (U). This may subsequently influence the toxicity of metal contaminants to resident freshwater organisms. The complexation of U with dissolved organic carbon (DOC) (10 mg L-1) in billabong water was calculated using the HARPHRQ geochemical speciation model and also measured using flow field-flow fractionation combined with inductively coupled plasma mass-spectroscopy. Agreement between both methods was very good (within 4% as U-DOC). The results suggest that in billabong water at pH 6.0, containing an average DOC of 10 mg L-1 and a U concentration of 90 μg L-1, around 10% of U is complexed with DOC. © 2011 American Chemical Society.


Markich S.J.,Aquatic Solutions International
Science of the Total Environment | Year: 2013

There is a lack of good quality data and mechanistic understanding on the effects of true water hardness (calcium (Ca) and magnesium (Mg)) on the bioavailability and toxicity of uranium (U) to freshwater biota. This study determined the effect of true water hardness (20, 75, 150, 275 and 400mgCaCO3L-1) on the cell surface binding affinity (log K), accumulation and toxicity (growth inhibition) of U in a submerged, rootless, macrophyte (Ceratophyllum demersum) in a synthetic freshwater with constant alkalinity (13mgCaCO3L-1) and pH (6.2) over 7days. A 20-fold increase in water hardness resulted in a 4-fold decrease in U toxicity (median effect concentration (EC50)=134μgL-1U at 20mgCaCO3L-1 hardness, increasing to 547μgL-1 U at 400mgCaCO3L-1 hardness), cell surface binding affinity (log K=6.25 at 20mg CaCO3L-1 hardness, decreasing to log K=5.64 at 400mgCaCO3L-1 hardness) and accumulation (the concentration factor decreased from 63 at 20mgCaCO3L-1 hardness to 15 at 400mgCaCO3L-1 hardness) of U. Calcium provided a 4-fold greater protective effect against U accumulation and toxicity compared to Mg. Speciation calculations indicated negligible differences in the percentages of key U species (UO2 2+, UO2OH+, UO2(OH)2) over the range of water hardness tested. The inhibition of U binding at the cell surface, and subsequent uptake, by C. demersum, with increasing Ca and/or Mg concentration, may be explained in terms of (i) competition between Ca2+/Mg2+ and UO2 2+ (and/or UO2OH+) for physiologically active sites at the cell surface, and/or (ii) reduced negative charge (electrical potential) at the cell surface, resulting in a decrease in the activity of UO2 2+ (and/or UO2OH+) at the plant/water interface (boundary layer), and consequently, less U bound to physiologically active cell surface sites. In the absence of a biotic ligand model for U, the results of this study (together with previous work) reinforce the need for a more flexible, hardness-dependent, U guideline for the protection of selected freshwater biota. © 2012 Elsevier B.V.


Jeffree R.A.,University of Technology, Sydney | Markich S.J.,Aquatic Solutions International | Twining J.R.,Austral Radioecology
PLoS ONE | Year: 2014

Bony bream (Nematalosa erebi) and black catfish (Neosilurus ater) were sampled from the fresh surface waters of the Finniss River in tropical northern Australia, along a metal pollution gradient draining the Rum Jungle copper/uranium mine, a contaminant source for over five decades. Paradoxically, populations of both fish species exposed to the highest concentrations of mine-related metals (cobalt, copper, lead, manganese, nickel, uranium and zinc) in surface water and sediment had the lowest tissue (bone, liver and muscle) concentrations of these metals. The degree of reduction in tissue concentrations of exposed populations was also specific to each metal and inversely related to its degree of environmental increase above background. Several explanations for diminished metal bioaccumulation in fishes from the contaminated region were evaluated. Geochemical speciation modeling of metal bioavailability in surface water showed no differences between the contaminated region and the control sites. Also, the macro-nutrient (calcium, magnesium and sodium) water concentrations, that may competitively inhibit metal uptake, were not elevated with trace metal contamination. Reduced exposure to contaminants due to avoidance behavior was unlikely due to the absence of refugial water bodies with the requisite metal concentrations lower than the control sites and very reduced connectivity at time of sampling. The most plausible interpretation of these results is that populations of both fish species have modified kinetics within their metal bioaccumulation physiology, via adaptation or tolerance responses, to reduce their body burdens of metals. This hypothesis is consistent with (i) reduced tissue concentrations of calcium, magnesium and sodium (macro-nutrients), in exposed populations of both species, (ii) experimental findings for other fish species from the Finniss River and other contaminated regions, and (iii) the number of generations exposed to likely selection pressure over 50 years. © 2014 Jeffree et al.


Markich S.J.,Aquatic Solutions International
Radioactivity in the Environment | Year: 2012

Radionuclides in (sub-) tropical freshwater systems generally behave in a predictable manner, based on what is known from lakes and streams in the better studied temperate climes. Within the water column, the fate and behaviour of radionuclides and their stable element analogs are typically governed by key physicochemical variables such as pH, redox potential, the concentrations of dissolved ions and the presence and type of organic matter. The chemical form (or speciation) of a radionuclide or stable element is generally of greater biological importance (i.e. bioavailability) than the total concentration. This concept is currently being integrated into mechanistic frameworks (e.g. biotic ligand and bioaccumulation models) by national regulators for protecting freshwater ecosystems. Given that the volume of fresh surface waters (i.e. rivers and lakes) is relatively small (0.01%) in comparison to seas and oceans, then the biota living within them can also substantially influence the chemistry of a radionuclide, by effectively acting as " large particles" available for surface complexation. For example, wetlands serve as effective biofilters to remove radionuclides from the water column. Once radionuclides have been accumulated by organisms, their behaviours generally reflect their similarities to essential (macro and micro nutrients) and non-essential elements. Metabolic mechanisms tending toward homeostasis typically make internal organism chemistry less dynamic than that in the external water column. Again, this is to be expected and radionuclide biokinetics generally follow the patterns observed for freshwater organisms in temperate climates. This constancy has enabled models to be developed to describe the rate and extent of radionuclide bioaccumulation. These models can be adapted to include various uptake pathways (from water, food or sediment) via gills, skin or gut and modes of excretion or dilution (e.g. diffusion, egestion, moulting and growth) and different parameters can be estimated for each radionuclide and organism. Key biotic factors known to influence radionuclide bioaccumulation are size, age and gender. There are also differences within and between species that reflect the natural variability within any system. Despite the similarities that exist between tropical and temperate freshwater systems, it should be noted that there is still a paucity of data for (sub-) tropical freshwater organisms and systems, and hence there is the chance for exceptions to the consistency to exist. Data are presented that show that the uptake of Sr and Cs by tropical freshwater fishes is much lower than would be expected based on the studies of freshwater temperate fishes. These observations point to the need to undertake additional site- and species- specific investigations on the radioecology of key radionuclides, whenever future nuclear developments in tropical systems are initiated. © 2012 Elsevier Ltd.


Van Dam R.A.,Environment | Trenfield M.A.,Environment | Markich S.J.,Aquatic Solutions International | Harford A.J.,Environment | And 3 more authors.
Environmental Toxicology and Chemistry | Year: 2012

The present study reanalyzed 46 existing uranium (U) chronic toxicity datasets for four freshwater species to generate consistent toxicity measures and explore relationships between U toxicity and key physicochemical variables. Dissolved organic carbon (DOC) was consistently the best predictor of U toxicity based on 10% inhibitory concentration (IC10) and median inhibitory concentration (IC50) values, with water hardness also being a significant co-predictor of IC50 concentrations for one species. The influence of DOC on acute and chronic U toxicity was further characterized using existing data for five species, and was found to vary depending on species, DOC source, and exposure duration (acute vs chronic). The slopes of the relationships between DOC and (normalized) acute and chronic U toxicity were modeled using cumulative probability distributions. From these, slopes were selected for which to correct acute or chronic U toxicity values or hazard estimates based on the aquatic DOC concentration. The fifth percentiles of these cumulative probability distributions for acute and chronic exposure data were 0.064 and 0.090, respectively, corresponding to a 6.4 and 9.0% reduction in U toxicity relative to the toxicity at the base DOC concentration for each 1mg/L increase in DOC concentration (over the DOC range 0-30mg/L). Algorithms were developed to enable the adjustment of U toxicity values and U hazard estimates, depending on DOC concentrations. These algorithms will significantly enhance the environmental relevance of water quality/risk assessments for U in fresh surface waters. © 2012 SETAC.

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