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This experimental study determined internal distributions of an array of radio-elements (54Mn, 60Co, 65Zn, 134Cs, 241Am, 109Cd, 110mAg, 75Se and 51Cr) accumulated from seawater by three chondrichthyan fish species (Scyliorhinus canicula (dogfish), Raja undulata (undulate ray) and Torpedo marmorata (spotted torpedo)) and three teleost species (Scophthalmus maximus (turbot), Sparus aurata (seabream) and Dicentrarchus labrax (seabass)). The study tested the hypothesis that the chondrichthyan (cartilaginous) fish taxon and teleost (bony) fish taxon have different patterns of bioaccumulation of these radio-elements in six body components (head, digestive tract, liver, kidneys, skin and muscle), consistent with their long period of evolutionary divergence. Comparisons of body component CFs between the two taxa for each radio-element and the full array of radio-elements showed highly significant differences (p ≤ 0.001) between cartilaginous and bony fishes in each body component, confirming the existence of a strong and pervasive phylogenetic signal; however, the subset of radio-elements most determinant of these differences were unique for each body component. Partitioning between the three individual bony species and the three individual cartilaginous species also occurred repeatedly among their body components, particularly for bony fishes. Distributions of these radio-elements among body components were typically highly heterogeneous for both fish taxa.

This article contains a dataset of the genotoxic (DNA damage, via the micronucleus frequency test) and cytotoxic (lysosomal membrane stability (cellular integrity), via the neutral red retention test) effects on the pygmy mussel, Xenostrobus securis (Bivalvia: Mytilidae) from variably contaminated sites (primarily from cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn)) in the highly urbanized Sydney Estuary, south-eastern Australia. Data were collected 15 years apart (June 2004 and June 2019) to assess any change in (i) the "health" of mussels (based on the above two toxicity endpoints) and (ii) their metal contaminant status (measured as whole soft tissue concentrations of Cd, Cr, Cu, Pb and Zn). Linear relationships between both toxicity endpoints and metal concentrations in the whole soft tissue were also investigated. Multivariate statistical techniques, including principal components analysis, multidimensional scaling and cluster analysis, were also explored to reduce dimensional data, investigate patterns and assess similarities among study sites with respect to tissue metal concentrations and toxicity effects in X. securis. Enrichment factors were calculated by dividing the mean whole soft tissue metal concentration at each site in the Sydney Estuary, by its mean baseline metal concentration from near-pristine (reference) sites in the adjacent Hawkesbury Estuary. Salinity, pH, temperature, turbidity, dissolved oxygen and chlorophyll a were measured in the surface waters at each site.

Freshwater mussels (Bivalvia: Unionida) are among the most threatened freshwater faunal groups worldwide. Metal contamination is one threat that has been linked to declining mussel population distribution and abundance. This study determined the sensitivity (valve closure) of the glochidia (larvae) of six species of Australian freshwater mussels to cadmium (Cd), cobalt (Co), copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn), key metal contaminants impacting urbanized coastal rivers in south-eastern Australia (home to ~50% of the population), in a soft reconstituted freshwater (hardness 42mgCaCO3L-1; alkalinity 22mgCaCO3L-1 and pH7.0) over 72h. The sensitivity of each mussel species to each metal increased 2.5-fold with increasing exposure time from 24 to 72h. The most sensitive mussel species (Cucumerunio novaehollandiae), across all metals and exposure times, was ~60% more sensitive than the least sensitive species (Velesunio ambiguus). The relative sensitivity of glochidia to the six selected metals, across all mussel species and exposure times, was: Cu>Cd>Pb>Co=Ni>Zn. Glochidia were most sensitive to Cu and least sensitive to Zn. Quantitatively, the toxicity of Cu was 3-fold more than Cd, 8-fold more than Pb, 14-fold more than Co or Ni and 16-fold more than Zn. The cell surface binding affinities (conditional log K values) of Cd (range 6.65-6.94), Co (6.04-6.29), Cu (7.17-7.46), Ni (6.02-6.29), Pb (6.24-6.53) or Zn (5.96-6.23), pooled for all mussel species after 72h exposure, were positively related to metal sensitivity. The chronic no effect concentrations (NECs) of Cu, Ni and Zn were below (i.e. glochidia were more sensitive than) their national freshwater guideline values, indicating that freshwater mussels may not be adequately protected for these metals in urbanized coastal rivers within south-eastern Australia.

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 400 mg CaCO(3) L(-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 (13 mg CaCO(3) L(-1)) and pH (6.2) over 7 days. A 20-fold increase in water hardness resulted in a 4-fold decrease in U toxicity (median effect concentration (EC50)=134 μg L(-1)U at 20 mg CaCO(3 )L(-1) hardness, increasing to 547 μg L(-1) U at 400 mg CaCO(3) L(-1) hardness), cell surface binding affinity (log K=6.25 at 20 mg CaCO(3) L(-1) hardness, decreasing to log K=5.64 at 400 mg CaCO(3) L(-1) hardness) and accumulation (the concentration factor decreased from 63 at 20 mg CaCO(3) L(-1) hardness to 15 at 400 mg CaCO(3) L(-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 (UO(2)(2+), UO(2)OH(+), UO(2)(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 Ca(2+)/Mg(2+) and UO(2)(2+) (and/or UO(2)OH(+)) 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 UO(2)(2+) (and/or UO(2)OH(+)) 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.

The effects of chronic uranium (U) exposure on larval Northern trout gudgeon, Mogurnda mogurnda, were assessed in two experiments using a newly-developed 28d survival and growth toxicity test. Significant effects were observed in both tests, but toxicity was markedly higher in Test 2 than Test 1. The LC50s for Tests 1 and 2 were 2090microgL(-1) and 1070microgL(-1), respectively. Larval growth IC10s for Tests 1 and 2 were 860microgL(-1) and 660microgL(-1) (dry weight), and 1160microgL(-1) and 850microgL(-1) (length), respectively. Uranium speciation modelling showed that a lower pH in Test 2 (mean of 6.0) compared to Test 1 (mean of 6.7) resulted in a greater proportion of free uranyl ion (UO(2)(2+)), the predominant bioavailable form of U. A higher dissolved organic carbon concentration (DOC) in Test 2 (4.2mgL(-1)) compared to Test 1 (2.1mgL(-1)) resulted in a higher proportion of U-DOC in Test 2, but this was insufficient to counter the effect of pH on the proportion of UO(2)(2+). The difference in U toxicity between the two tests could be explained by normalising for UO(2)(2+); the concentrations of UO(2)(2+) at the LC50s for Tests 1 and 2 were calculated to be 13.3 and 13.7microgL(-1), respectively. Finally, the results of this study, and comparisons with other studies suggest that U toxicity to M. mogurnda appears to be as much, if not more, a function of exposure water quality and feeding regime, as exposure duration.

Cephalopods play a key role in many marine trophic networks and constitute alternative fisheries resources, especially given the ongoing decline in finfish stocks. Along the European coast, the eggs of the cuttlefish Sepia officinalis are characterized by an increasing permeability of the eggshell during development, which leads to selective accumulation of essential and non-essential elements in the embryo. Temperature and pH are two critical factors that affect the metabolism of marine organisms in the coastal shallow waters. In this study, we investigated the effects of pH and temperature through a crossed (3×2; pH 8.1 (pCO2, 400 ppm), 7.85 (900 ppm) and 7.6 (1400 ppm) at 16 and 19°C, respectively) laboratory experiment. Seawater pH showed a strong effect on the egg weight and non-significant impact on the weight of hatchlings at the end of development implying an egg swelling process and embryo growth disturbances. The lower the seawater pH, the more 110 mAg was accumulated in the tissues of hatchlings. The 109Cd concentration factor (CF) decreased with decreasing pH and 65Zn CF reached maximal values pH 7.85, independently of temperature. Our results suggest that pH and temperature affected both the permeability properties of the eggshell and embryonic metabolism. To the best of our knowledge, this is one of the first studies on the consequences of ocean acidification and ocean warming on metal uptake in marine organisms, and our results indicate the need to further evaluate the likely ecotoxicological impact of the global change on the early-life stages of the cuttlefish.

Semaphore crabs (Heloecius cordiformis), soldier crabs (Mictyris platycheles), ghost shrimps (Trypaea australiensis), pygmy mussels (Xenostrobus securis), and polychaetes (Eunice sp.), key benthic prey items of predatory fish commonly found in estuaries throughout southeastern Australia, were exposed to dissolved (109)Cd and (75)Se for 385 h at 30 k Bq/l (uptake phase), followed by exposure to radionuclide-free water for 189 h (loss phase). The whole body uptake rates of (75)Se by pygmy mussels, semaphore crabs and soldier crabs were 1.9, 2.4 and 4.1 times higher than (109)Cd, respectively. There were no significant (P>0.05) differences between the uptake rates of (75)Se and (109)Cd for ghost shrimps and polychaetes. The uptake rates of (109)Cd and (75)Se were highest in pygmy mussels; about six times higher than in soldier crabs for (109)Cd and in polychaetes for (75)Se - the organisms with the lowest uptake rates. The loss rates of (109)Cd and (75)Se were highest in semaphore crabs; about four times higher than in polychaetes for (109)Cd and nine times higher than in ghost shrimps for (75)Se - the organisms with the lowest loss rates. The loss of (109)Cd and (75)Se in all organisms was best described by a two (i.e. short and a longer-lived) compartment model. In the short-lived, or rapidly exchanging, compartment, the biological half-lives of (75)Se (16-39 h) were about three times greater than those of (109)Cd (5-12h). In contrast, the biological half-lives of (109)Cd in the longer-lived, or slowly exchanging compartment(s), were typically greater (1370-5950 h) than those of (75)Se (161-1500 h). Semaphore crabs had the shortest biological half-lives of both radionuclides in the long-lived compartment, whereas polychaetes had the greatest biological half-life for (109)Cd (5950 h), and ghost shrimps had the greatest biological half-life for (75)Se (1500 h). This study provides the first reported data for the biological half-lives of Se in estuarine decapod crustaceans. Moreover, it emphasises the importance of determining metal(loid) accumulation and loss kinetics in keystone prey items, which consequently influences their trophic transfer potential to higher-order predators.

Several nations have adopted hardness-modified copper (Cu) guidelines for protecting freshwater biota. However, 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 Cu to freshwater biota, particularly macrophytes. This study determined the effect of true water hardness (35, 90 and 335 mg CaCO(3)/l, added as Ca and Mg chloride in a 1:1 mole ratio) on the cell surface binding affinity (log K), accumulation and toxicity (96 h growth (biomass and stem length) and photosynthetic pigment inhibition) of Cu in the free-floating submerged macrophyte, Ceratophyllum demersum, in a synthetic freshwater with constant alkalinity (16 mg CaCO(3)/l) and pH (7.0). There were no significant (P0.05) differences in the cell surface binding affinity, accumulation or toxicity of Cu in C. demersum with a 10-fold increase in water hardness from 35 to 335 mg CaCO(3)/l. The mean 96 h EC(50) values (and 95% confidence intervals) for biomass, the most sensitive endpoint, were 8.4 (7.6-9.2), 8.9 (8.0-9.8) and 9.9 (9.1-10.7) microg/l Cu for 35, 90 and 335 mg CaCO(3)/l, respectively. Speciation calculations indicated only very small (1-6%) differences in the percentage distribution (i.e. bioavailability) of Cu over the hardness range. These collective results indicate no apparent competition between Cu and Ca/Mg for binding sites on the cell surface. Given that the mechanism of Cu uptake (via Cu-specific and Na-linked transporters) is fundamentally different to that of Cd, Ni, Pb and Zn (via Ca transporters), for which other hardness-dependent algorithms have been developed, it is doubtful whether a hardness-modified Cu guideline value will be sufficiently protective of sensitive freshwater biota, such as C. demersum, particularly in medium-hard fresh surface waters with low levels of dissolved organic carbon. The biotic ligand model offers a more flexible and mechanistic approach for deriving site-specific Cu (metal) guidelines for protecting freshwater biota.

This study determined the condition and reproductive output of a common estuarine toadfish, Tetractenos glaber, in two metal contaminated and two reference estuaries near Sydney, Australia. Female toadfish from metal contaminated estuaries were smaller and younger than in reference estuaries; however, it could not be resolved whether these differences were due to direct effects of metal contamination or differences in nutritional value of prey. Lipid content in liver and gonad tissues was inversely related with levels of As, Pb, Cd and Co in sediment. In contrast, protein content in liver, gonad and muscle tissues was positively related to sediment levels of Ni and Co. Increased levels of Pb in gonads were associated with decreased oocyte diameter and density. This suggests a reduction in egg size and fecundity, which ultimately may lead to a decline in female reproductive output. Changes in fish health and reproduction caused by chemical pollutants may alter fish population and community structure. © 2005 Elsevier Ltd. All rights reserved.

The freshwater green microalgae Chlorella sp. and Pseudokirchneriella subcapitata (P. subcapitata) were chronically (48 and 72 h, respectively) exposed to copper at various pH levels, i.e., pH 6-7.5 and pH 5.9-8.5, respectively. Concentrations resulting in 50% inhibition of exponential growth rate (EC50) were determined as dissolved Cu, estimated chemical activity of the free Cu2+ ion (as pCu = - log{Cu2+ activity as molarity}), and as external (surface-bound) Cu and internal Cu in the algal cells. With increasing pH, EC50dissolved decreased from 30 to 1.1 microg of Cu L(-1) for Chlorella sp. and from 46 to 18 microg of Cu L(-1) for P. subcapitata. The pH effect on copper toxicity was even more obvious when expressed as Cu2+ activity. The EC50pCu increased on average 1.4 pCu unit per pH unit for Chlorella sp. and 1.1 pCu unit per pH unit for P. subcapitata, thus indicating a marked increase of Cu2+ toxicity at higher pH (more than 1 order of magnitude per pH unit). In contrast, it was found that EC50 values expressed as surface bound or external copper (EC50external) and as internal copper (EC50internal) did not vary substantially when pH was increased. External Cu was operationally defined as the Cu fraction removable from the algal cell by short-term contact with ethylenediaminetetraacetic acid; internal copper was defined as the nonremovable fraction. For Chlorella sp. the EC50external varied between 5 and 10 fg of Cu/ cell (factor of 2 difference) and the EC50internal between 25 and 40 fg of Cu/cell (factor of 1.6 difference). For P. subcapitata the EC50external varied between 10 and 28 fg of Cu/cell (factor of 2.8 difference) and the EC50internal between 42 and 71 fg of Cu/cell (factor of 1.7 difference). Because the observed variation in EC50external and EC50internal is much less than the variation in EC50Cu2+, it is concluded that both external and internal copper are better predictors of copper toxicity than Cu2+ when pH is varied. From the perspective of toxicity modeling, this observation is the first step toward considering the use of the cell surface as the algal biotic ligand for Cu in a similar way as fish gills fulfill this role in the biotic ligand model for predicting metal toxicity to fish species.

The concentrations of 15 metals were measured in the osteoderms (dermal bones) of 30 freshwater crocodiles (Crocodylus johnstoni) from a single population in the Lynd River, northeastern Australia (17 degrees 50'S, 144 degrees 20'E), that were well characterised with respect to site fidelity, reproductive status and age. Multiple linear regression analyses were used to determine the effects of crocodile size (snout-vent length, 25-128 cm), age (0.7-62.7 years), gender (male or female) and reproductive status (sexually mature or immature) on osteoderm metal concentrations. Gender and reproductive status were not significant (P > 0.05) co-predictors of the osteoderm concentration of any metal. In contrast, size, age and osteoderm calcium concentration were highly significant (P < 0.001) systematic predictors of the osteoderm concentrations of all metals, except Na and K. Osteoderm metal concentrations were inversely related (P < 0.001) to both size (r(2) = 0.52-0.92) and age (r(2) = 0.52-0.84), but positively related (P < 0.001) to osteoderm calcium concentration (r(2) = 0.67-0.92). Relative to calcium concentration, the rates of metal accumulation in the osteoderms of C. johnstoni were inversely related to the solubility constant (log K(sp)) of the metal as a phosphate; however this relationship was not linear. This finding is consistent with that previously established for the flesh of freshwater bivalves, which like the crocodilian osteoderm, have a calcium phosphate repository in the form of extracellular granules. The constancy of this relationship between rate of metal accumulation and relative solubility for calcium phosphate deposits, despite contrasting Ca accumulation regimes and taxonomic dissimilarity, points to a potential underlying principle that warrants investigation in a greater range of biota. The implications for using the osteoderms of C. johnstoni as an indicator of metal levels in freshwater ecosystems are also discussed.

Body size, age, and gender (male or female) are important variables influencing many aspects of the ecology, physiology, and survival of animals. However, no data are available on the influence of these variables on bivalves exposed to sublethal metal concentrations. This study tested whether the valve movement responses (measured in terms of the duration or frequency of valve opening) of the Australian tropical freshwater unionoid bivalve, Velesunio angasi, exposed to sublethal uranium (U) concentrations in a standard synthetic water (pH, 6.0; hardness and alkalinity, 4 mg/L as CaCO(3)) were influenced by body size (shell length, shell breadth, or dry tissue weight), age, and/or gender. The valve movement responses of V. angasi to U were independent of gender; the sensitivity of males to U was not significantly (p > 0.05) different from that of females. In contrast, the valve movement responses of V. angasi to U were size- and age-dependent; smaller and younger individuals (median shell length = 36.8 mm; median age = 0.7 years) were 22% more sensitive (p

The toxicity of aluminium (Al) to fish in acidic waters has been well documented. It was therefore expected that Al toxicity would be significant in fish communities in Gadjarrigamarndah (Gadji) Creek, a seasonally flowing stream in tropical northern Australia. This creek receives acidic groundwater containing elevated concentrations of Al from earlier land irrigation of treated mine tailings water from the former Nabarlek uranium mine. It was hypothesised that Al toxicity was reduced by high levels of silica (Si) in the water, and the subsequent formation of Al-silicate complexes. This prompted a laboratory assessment of the toxicity of Gadji Creek water to sac-fry of the native fish, Mogurnda mogurnda, followed by more detailed investigation of the toxicity of Al and the influence of Si in reducing Al toxicity. No mortality of M. mogurnda sac-fry was observed in two toxicity tests using Gadji Creek water collected in August 1997 and September 1998. The majority of Al (80-95%) was calculated to be complexed with humic substances and sulfate, with l1% being complexed with silicate. Assessment of the influence of silica on the acute toxicity of Al in the absence of natural organic complexants (i.e. in reconstituted freshwater, pH 5) revealed that Si reduced Al toxicity. As the molar ratio of Si:Al was increased, the percent survival of M. mogurnda sac-fry increased until there was no significant (P g 0.05) difference from the controls. However, speciation modelling again predicted that little (l3%) Al complexed with silicate, with the speciation and bioavailability of Al remaining constant as the molar ratio of Si:Al increased. Therefore, the original hypothesis that Al-silicate complexes in solution reduced the toxicity of Al to M. mogurnda could not be supported. This potential mechanism, and an alternative hypothesis, that Si competes with Al for binding sites at the fish gill surface, requires further investigation. Crown Copyright (C) 2002 Published by Elsevier Science Ltd. All rights reserved.

Knowledge of the transport pathways of metals into aquatic organisms is paramount in determining the metal's potential mechanism of toxicity. To determine the relative importance of water and food as cadmium (Cd) sources for the cladoceran Daphnia magna grazing on the algae Chlorella vulgaris, we measured cadmium accumulation and toxicity (feeding inhibition and survival) in three genetically different clones of D. magna subsequent to water, food, and water and food exposures. We found that Cd uptake from water and food was independent of source and additive in effect, with D. magna juveniles accumulating twice as much Cd from water than from food (algae). However, the efficiency with which Cd was assimilated by D. magna from its algal diet was much higher (10%) than from water (0.3%). Uptake and toxic responses were inversely related: tolerant clones accumulated more Cd. As a consequence, models based on uptake of metals from the combined routes of water and food may be reliable to predict metal dynamics in the field, but may fail to predict toxic effects since tolerance to metals is not necessarily linked to reduced total uptake of metals.

Freshwater bivalves (Velesunio angasi) were sampled in 1996 from the Finniss River in tropical northern Australia at 10 sites a priori exposed and nonexposed to acid rock drainage (ARD), containing elevated metal concentrations, from the rehabilitated Rum Jungle copper-uranium mine. Secondary ion mass spectrometry (SIMS) was used to measure Cu, Mn, Zn, U, Ni, Co, Pb, and Fe/Ca ratios across the annual shell laminations of the longest-lived bivalves found at each site, with the aim of evaluating the ability of the shells to archive measured annual metal inputs and their temporal patterns. At sites not contaminated by ARD, relatively constant and similar (baseline) SIMS signals were found for all metals in the shell laminations of V. angasi, dating as far back as 1965. At sites contaminated by ARD, relatively constant, but variably elevated, SIMS signals were evident for Cu, Mn, Zn, Ni, and Co in the shell, which extended back to the end of rehabilitation (1986) only. Since rehabilitation, the temporal patterns of Cu, Zn, and Mn observed in the shells at the most contaminated sites reflected those of the measured annual dissolved loads in the surface waters. The average concentrations of Cu, Mn, Zn, Ni, and Co in the shells decreased (3-13-fold) with increasing distance downstream of the mine site, until concentrations characteristic of the noncontaminated sites were reached. This geographic pattern of decline in pollution signal in the shell with increasing distance downstream of the pollution input is consistent with the pattern established for water and sediment chemistry. Overall, the SIMS results support the proposition that the shells of V. angasi can be used as archival indicators of metal pollution in surface waters of the Finniss River over their lifetime.

Whole soft tissue concentrations of Mn, Co, Ni, Cu, Zn, Pb, Cd and U were measured in two species of freshwater (unionid) bivalves (Hyridella depressa and Velesunio ambiguus) from a minimally polluted site in the Hawkesbury-Nepean River, south-eastern Australia. Although the mean concentrations of metals in the tissue were similar for each bivalve species, their patterns of accumulation were dissimilar. For each metal, positive linear relationships between tissue concentration and shell length (r2 = 0.37-0.77; P < or = 0.001) and tissue dry weight (r2 = 0.29-0.51; P < or = 0.01) were found in H. depressa, but not in V. ambiguus. However, for both species, positive linear relationships were found between the tissue concentration of each divalent metal and Ca tissue concentration (r2 = 0.59-0.97; P < or = 0.001). For both bivalve species, the normalised rates of accumulation of the metals relative to increasing Ca concentration and/or size, were U approximately = Cd > or = Pb > or = Mn > Co > or = Zn > Cu > Ni. The differential rates of accumulation of divalent metals are interpreted as being predominantly governed by their varying loss rates, which are controlled by the differing solubilities (log Ksp values) of the metals in the phosphatic extracellular granules, the demonstrated major sites of metal deposition in the tissue of H. depressa and V. ambiguus. The rates of accumulation of Mn, Co, Zn, Cu and Ni were linearly and inversely related (r2 = 0.91-0.97; P < or = 0.001) to their solubilities as hydrogen phosphates, a finding consistent with the bioaccumulation model previously developed for the alkaline-earth metals. However, for U, Cd and Pb, this linear inverse relationship did not continue to hold, i.e. their rates of accumulation did not increase with decreasing solubility. However, these results are still consistent with the model if U, Cd and Pb are so insoluble in the granules of H. depressa and V. ambiguus over their lifetime (up to approx. 50 years) that there is effectively no loss of these metals, and hence, no differential between their rates of accumulation. The present results reaffirm the use of Ca tissue concentration to predict the tissue concentrations of other divalent metals by explaining up to 94 and 97% of the variability between individual bivalves of H. depressa and V. ambiguus, respectively. The use of Ca tissue concentration to effectively minimise the inherent variability between individuals in their metal tissue improves the ability of an investigator to discern smaller spatial and/or temporal differences in the metal tissue concentrations of these bivalves, and thus to detect metal pollution.

The concentrations of Na, K, Ca, Mg, Ba, Sr, Fe, Al, Mn, Zn, Pb, Cu, Ni, Cr, Co, Se, U, and Ti were determined in the flesh and osteoderms of estuarine crocodiles (Crocodylus porosus) captured in three adjacent catchments of Kakadu National Park, within the Alligator Rivers Region of northern Australia. This study provides, for the first-time, baseline concentrations of elements in both flesh and osteoderms of wild crocodiles. Multiple linear regression analyses were used to determine the effects of total crocodile length, estimated age, gender, inferred reproductive status, physical condition, and catchment of capture on element concentrations in both tissues. The Mg concentration (log10) in the flesh and osteoderms of C. porosus significantly (p < or = 0.001) decreased with increasing length (1.7-5.0 m) and estimated age (5-40 years). Similarly, the Ti concentration (log10) in flesh significantly (p < or = 0.01) decreased with increasing length. In contrast, Zn and Se concentration (log10) in flesh significantly (p < or = 0.001) increased with increasing length and/or age, suggesting that these relationships are mediated by biological rather than environmental chemical factors. In flesh, Fe and Na concentrations (log10) significantly (p < or = 0.05) increased as the physical condition of C. porosus deteriorated. No significant (p > 0.05) effects of gender or inferred reproductive status on element concentrations in the flesh and osteoderms were found. The mean concentrations (log10) of Al, Ba, Cr, Ni, and Pb in flesh and Co, Fe, Mg, Mn, and U in the osteoderms were significantly (p < or = 0.01) different between catchments. The significant (p < or = 0.05) effects of catchment on the concentrations of various elements indicate that C. porosus reflects the chemistry of its environmental milieu and therefore has a certain degree of catchment fidelity, even though the catchments are adjacent to one another. Such catchment-specific signals may be useful in the determination of the provenance of itinerant crocodiles. They also point to the utility of crocodiles as long-term biomonitors of their environment.

The veracity of the free ion activity model (FIAM) was tested by examining the acute (48 h) valve movement responses (VMR) (measured in terms of the duration of valve opening) of the Australian tropical freshwater unionid bivalve, Velesunio angasi to increasing concentrations of total Mn or U, in a standard synthetic water under conditions of varying pH (5.0-6.0) and/or dissolved organic carbon (model fulvic acid, FA) concentrations (0-8.9 mg l(-1)). Valve movement behaviour, measured using an automated data acquisition system, was shown to be a quantifiable and rapid, real-time endpoint for assessing the toxic effects of Mn and U exposures. For Mn, the VMR of V. angasi were independent (P>0.05) of pH and/or model FA concentration. In contrast, VMR to U exposures were highly dependent (P< or =0.05) on pH and/or model FA concentration; individuals were more sensitive to U at low pH and model FA concentrations. Valve movement responses to Mn were directly proportional to the activity of the free metal ion (Mn(2+)), which is consistent with the FIAM. In contrast, VMR to U were regarded as an 'exception' to the FIAM, since they were a weighted function of the activities of the free metal ion and the 1:1 metal hydroxide species (i.e. 1.86 x UO2(2+) + UO2OH(+)). Additionally, the effect of U on V. angasi demonstrates the importance of examining VMR at more than one pH. At a fixed pH, the results for U were consistent with the FIAM (i.e. response was directly proportional to UO2(2+)); only when pH was altered, were the results inconsistent with the FIAM. The inconsistency in the VMR of V. angasi to U exposures in this study, together with similar examples from other studies using different metals (e.g. Al or Zn), raises questions regarding the veracity of the FIAM. A detailed examination of the conceptual development of the FIAM is required to probe its apparent failure to describe several metal-organism interactions.

The ultimate aim of ecotoxicological studies is to predict how natural populations respond to contaminant exposure. Thus, it is crucial to understand how genetic and environmental factors in the field modify responses measured in the laboratory. In the present study the authors determine the genetic and environmental components of variability in acute responses among four Daphnia magna clones exposed to both essential (Zn and Cu) and non-essential (Cd and U) metals in waters with varying water hardness. The authors postulate that genotype acute responses to physiologically non-essential metals may be more variable than responses to essential metals and that this may be explained by hypothesizing that acute responses to non-essential substances are subject to intermittent selection (since the substances may not always be present in biologically significant amounts), whereas responses to essential substances are subject to continuous directional selection (since essential substances by definition co-occur with biota in biologically significant amounts). D. magna clones were exposed to single-metal solutions of varying concentration at two or three levels of water hardness (soft, moderate–hard and hard) for periods ranging from 12–96 h (12 h increments). LC50 values for each metal×genotype×water hardness×exposure period combination were determined for (i) total metal concentration and (ii) the free hydrated metal ion concentration (predicted using geochemical speciation modeling) and compared using analysis of covariance with environment (water hardness) and genotype (clone) as fixed factors and exposure time as a covariate. The results showed that Zn–Cd were consistent, but Cu–U inconsistent, with the essentiality hypothesis. In addition, the small, or even non-existent, genotype-environment interaction effect on the inheritance of metal tolerance supports the argument that genetic variability in resistance to trace metals is inherited through single major genes. Implications of these results for the prediction of population tolerance ranges are discussed in relation to the problem of predicting metal speciation and the biological effects of metals in fresh waters with varying hardness.

Adult Silver Perch ( Bidyanus bidyanus ) were exposed to 137 Cs and 85 Sr for 8 weeks to determine radionuclide concentration factors (CFs) for use in a dose assessment model database for sub-tropical and tropical ecosystems. At equilibrium, the fresh weight CFs for 137 Cs and 85 Sr in the flesh of B. bidyanus were 12.6 ± 5.2 kg 1 −1 (mean ± S.E.) and 0.73 ± 0.21 kg 1 −1 , respectively. The mean CFs were considerably lower than those expected for temperate freshwater fish, but were consistent with recently reported values for other sub-tropical and tropical freshwater fish. The results indicate that the use of recommended CFs for radiological dose assessment models, based on temperate freshwater fish, may provide overestimates of dose when applied to sub-tropical and tropical fish. The biological half-lives of 137 Cs (19 ± 2 days) and 85 Sr (5 ± 1 days) in the flesh of B. bidyanus , estimated from a one-compartment exponential uptake model, were lower than reported values for four other species of sub-tropical and tropical freshwater fish. Cesium-137 was distributed in B. bidyanus as follows: flesh (63%) > skin/scales (22%) > bone (15%). Conversely, 85 Sr showed similar activities in the bone and skin/scales that were still increasing after eight weeks, while the levels in the flesh remained relatively low. Analysis of the skin/scales component showed that the majority of 85 Sr (∼ 94%) was located in the scales.

A theoretical and experimental study was performed to determine the kinetics of 45Ca, 60Co, 210Pb, 54Mn and 109Cd in the whole soft tissue of the unionid bivalve Velesunio angasi. This investigation further tested the hypothesis, developed previously for the alkaline-earth metals, that the biological half-life of a metal in soft tissue is related to its solubility when deposited in the extracellular granules of the bivalve. This hypothesis was tested for the above radionuclides (tracers of the stable metals) by a comparison of (a) a qualitative a priori prediction of their biological half-lives in bivalve tissue, based on critically evaluated log Ksp values for their respective hydrogen phosphate salts, and calibrated to previous experimentally determined rates of loss for 45Ca and 226Ra, with (b) their empirical biological half-lives that were investigated experimentally using the radionuclides 45Ca, 60Co, 210Pb, 54Mn and 109Cd. The results of the experimental investigation showed that the mean values calculated for the biological half-lives of 45Ca and 60Co in the tissue were 106 and 121 days, respectively, but there was no significant (P > 0.05) loss of 210Pb, 54Mn or 109Cd from the soft tissue over 160 days, when bivalves were exposed to radionuclide-free water. A chemical model was developed from first principles that quantitatively explains the kinetic mechanisms that underlie the differential rates of loss of divalent metals from the extracellular granules of V. angasi. The experimental results were consistent with the predictions of the model; however, some investigational limitations were evident, and these are discussed. The uptake of each radionuclide into the bivalve tissue tended to be linear, but the variation in tissue concentration, between individual bivalves, increased with the period of exposure. Significant (P < 0.001) positive correlations were found between tissue concentrations of each radionuclide pairing in both the uptake and loss phases of the experiment, indicating that individual bivalves were internally consistent in the way that they metabolised these radionuclides.

The influence of dissolved organic carbon (DOC), in the form of Suwannee River fulvic acid (SRFA), on uranium (U) toxicity to the unicellular eukaryote, Euglena gracilis (Z strain), was investigated at pH 6. In a background medium without SRFA, exposure of E. gracilis to 57 μg L(-1) U resulted in a 50% reduction in growth (IC(50)). The addition of 20 mg L(-1) DOC (as SRFA), reduced U toxicity 4 to 5-fold (IC(50) increased to 254 μg L(-1) U). This reduction in toxicity was also evident at more sensitive effect levels with a 10% reduction in growth (IC(10)) occurring at 5 μg L(-1) U in the background medium and at 17 μg L(-1) U in the SRFA medium, respectively. This amelioration of toxicity with the addition of SRFA was linked to a decrease in the bioavailability of U, with geochemical speciation modelling predicting 84% of U would be complexed by SRFA. The decrease in bioavailability of U in the presence of SRFA was also evident from the 11-14 fold reduction in the cellular concentration of U compared to that of E. gracilis in the background medium. Stepwise multiple linear regression analyses indicated that UO(2)(2+) alone explained 51% of the variation in measured U toxicity to E. gracilis. Preliminary U exposures to E. gracilis in the presence of a reactive oxygen species probe, suggest exposure to ≥60 μg L(-1) U may induce oxidative stress, but this endpoint was not considered to be a sensitive biological indicator.

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.

The influence of dissolved organic carbon (DOC) on the toxicity of aluminum (Al) at pH 5 (relevant to acid mine drainage conditions), to the tropical green hydra (Hydra viridissima), green alga (Chlorella sp.), and cladoceran (Moinodaphnia macleayi) was assessed. Two DOC sources, a natural in situ DOC in soft billabong water (SBW) and Suwannee River fulvic acid (SRFA) standard, were compared. The order of sensitivity of the test organisms to dissolved Al (0.1 µm fraction) was Hydra viridissima > Moinodaphnia macleayi > Chlorella sp. with DOC reducing dissolved Al toxicity most for Hydra viridissima. However, colloidal or precipitated Al may contribute indirectly to the toxicity for M. macleayi and Chlorella sp. The toxicity of dissolved Al was up to six times lower in test waters containing 10 mg L−1 DOC (in the form of SRFA), relative to toxicity observed at 1 mg L−1 DOC. In contrast, the toxicity of Al was up to two times lower in SBW containing 10 mg L−1 DOC, relative to water containing 1 mg L−1 DOC. The increased ability of SRFA in reducing Al toxicity was linked to its greater affinity for complexing Al compared with the in situ DOC. This has important implications for studies that use commercial standards of humic substances to predict Al toxicity in local environments. Speciation modeling demonstrated that Al3+ and AlOH2+ provided a strong relationship with toxicity. An empirical relationship is provided for each organism that can be used to predict Al toxicity at a given Al and DOC concentration. Environ. Toxicol. Chem. 2012;31:427–436. © 2011 SETAC

The influence of dissolved organic carbon (DOC) on the toxicity of uranium (U) to three Australian tropical freshwater species, the Northern Trout Gudgeon (Mogurnda mogurnda), green hydra (Hydra viridissima) and unicellular green alga (Chlorella sp.) was assessed. Exposures were conducted in synthetic soft water without DOC and with DOC added in the form of standard Suwannee River Fulvic Acid (SRFA). Organisms were exposed to a range of U concentrations at a range of DOC concentrations (0-20 mg L(-1)). U toxicity was up to 20 times less in water containing 20 mg L(-1) DOC, relative to DOC-free test waters. U toxicity was also assessed using natural water from a tropical Australian billabong containing 10 mg L(-1) DOC. U toxicity was up to ten times less in the billabong water, relative to DOC--free test waters. SRFA was twice as effective at reducing U toxicity as the billabong water at equivalent DOC concentrations. Geochemical speciation modeling confirmed the decreased U toxicity that resulted from both DOC sources was primarily due to a decrease in the free uranyl ion (UO2(2+)) through complexation with DOC. A predictive model is presented for each of the organisms that can be used to predict U toxicity at a given U and DOC concentration.

Few data are available on the comparative accumulation of metal(loid)s from water and food in estuarine/marine fish. Smooth toadfish ( Tetractenos glaber ), commonly found in estuaries in south-eastern Australia, were separately exposed to radio-labelled seawater (14 kBq L −1 of 109 Cd and 24 kBq L −1 of 75 Se) and food (ghost shrimps; Trypaea australiensis : 875 Bq g −1 109 Cd and 1130 Bq g −1 75 Se) for 25 days (uptake phase), followed by exposure to radionuclide-free water or food for 30 days (loss phase). Toadfish accumulated 109 Cd predominantly from water (85%) and 75 Se predominantly from food (62%), although the latter was lower than expected. For both the water and food exposures, 109 Cd was predominantly located in the gut lining (60–75%) at the end of the uptake phase, suggesting that the gut may be the primary pathway of 109 Cd uptake. This may be attributed to toadfish drinking large volumes of water to maintain osmoregulation. By the end of the loss phase, 109 Cd had predominantly shifted to the excretory organs – the liver (81%) in toadfish exposed to radio-labelled food, and in the liver, gills and kidney (82%) of toadfish exposed to radio-labelled water. In contrast, 75 Se was predominantly located in the excretory organs (gills, kidneys and liver; 66–76%) at the end of the uptake phase, irrespective of the exposure pathway, with minimal change in percentage distribution (76–83%) after the loss phase. This study emphasises the importance of differentiating accumulation pathways to better understand metal(loid) transfer dynamics and subsequent toxicity, in aquatic biota.

Copper and zinc toxicity to the freshwater alga Chlorella sp. was determined at a range of pH values (5.5-8.0) in a synthetic softwater (hardness 40-48 mg CaCO(3)/L). The effects of the metals on algal growth (cell division) rate were determined after 48-h exposure at pH 5.5, 6.0, 6.5, 7.0, 7.5, and 8.0. The toxicity of both metals was pH dependent. As pH decreased from 8.0 to 5.5, the copper concentration required to inhibit the algal growth rate by 50% (IC50) increased from 1.0 to 19 microg/L. For zinc, the IC50 increased from 52 to 2,700 microg/L over the same pH range. Changes in solution speciation alone did not explain the increased toxicity observed as the pH increased. Modelled Cu(2+) and Zn(2+) concentrations decreased with increasing pH, whereas toxicity was observed to increase. Measurements of extracellular (cell-bound) metal concentrations support the biotic ligand model (BLM) theory of competition between protons (H(+)) and metals for binding sites at the algal cell surface. Higher extracellular metal concentrations were observed at high pH, indicating reduced competition. Independent of pH, both extracellular and intracellular copper were directly related to growth inhibition in Chlorella sp., whereas zinc toxicity was related to cell-bound zinc only. These findings suggest that the algal cell surface may be considered as the biotic ligand in further development of a chronic BLM with microalgae. Conditional binding constants (log K) were determined experimentally (using measured intracellular metal concentrations) and theoretically (using concentration-response curves) for copper and zinc for Chlorella sp. at selected pH values. Excellent agreement was found indicating the possibility of using concentration-response data to estimate conditional metal-cell binding constants.

The bioaccumulation of selected heavy metals and radionuclides ( 241 Am, 109 Cd, 57 Co, 51 Cr, 134 Cs, 54 Mn and 65 Zn) from seawater was experimentally compared in the Chondrichthyan Scyliorhinus canicula (spotted dogfish) and the Actinopterygian Teleost Psetta maxima (turbot), of comparable size, age and benthic feeding habits. The speciation of these elements in seawater (salinity 38‰, pH 8.1, temperature 16.5 °C) was also calculated to determine their potential bioavailability. The uptake rates, measured over 14 days, varied greatly among isotopes and between species. Concentration factors (CFs) in P. maxima varied 5-fold between ca. 0.2 for 51 Cr and 2.5 for 65 Zn and 134 Cs, whereas in S. canicula they varied by a much greater factor of 350, with CFs for 51 Cr and 241 Am ranging from ca. 0.4 to 140, respectively. With the exception of 134 Cs, all radiotracers were accumulated at a faster rate in S. canicula than in P. maxima , particularly for 241 Am and 65 Zn where the CFs attained during the uptake phase were, two and one order of magnitude greater in S. canicula , respectively. In contrast, 134 Cs reached a CF of about 2.5 in P. maxima, which was 5-fold greater than in S. canicula . Patterns of loss from the experimental depuration phase over 29 days showed greater similarities between species, compared to the uptake phase that highlighted the greater differences between elements. The distributions of these seven radioisotopes among six body components indicated that between the two species the skin of the dogfish displayed a greater bioaccumulation potential, particularly for 241 Am, 57 Co and 65 Zn. However 65 Zn was also distinctive from 241 Am and 57 Co in its pattern of bioaccumulation in dogfish, with its other body components attaining concentrations of 65 Zn that were comparable to the levels found in its skin. The heightened uptake of 134 Cs in turbot was characterised by a more even percentage distribution among its tissues compared to 241 Am and 57 Co, but every tissue of turbot had a higher concentration of 134 Cs, compared to dogfish, particularly the muscle and liver. The elevated uptake rates and higher CFs for most radioisotopes indicate that S. canicula is more susceptible than P. maxima to exposure and contamination by these metals and radionuclides in seawater. These experimentally-determined differences between dogfish and turbot in their bioaccumulation characteristics were assessed against a set of criteria erected to evaluate the working hypothesis that they were taxonomically based. The outcomes of this initial assessment were supportive of this hypothesis that warrants further investigation.

This study determined the metal levels in sediments and tissues of a common estuarine fish, Tetractenos glaber (smooth toadfish), from two metal contaminated and two reference estuaries near Sydney, Australia. Metal levels were highest in sediments and fish from contaminated estuaries. Gonads contained the highest metal levels followed by muscle, gill and liver. Metal accumulation was gender-dependant (e.g. male gonads were >20 times higher in As than females; female gills were >30 times higher than males for Pb). Cadmium, Pb and Ni levels in fish tissues reflected sediment levels, indicating sediment and/or dietary metal uptake. Levels of As, Co, Cd & Pb in gills showed similar patterns to other tissues, suggesting that metals may have been taken up by gills through contaminated water. Similar metal patterns in tissues and sediments suggest more than one uptake pathway. This study indicates that multiple factors influence metal accumulation in fish. © 2005 Elsevier Ltd. All rights reserved.

Copper (Cu) and uranium (U) are of potential ecotoxicological concern to tropical freshwater biota in northern Australia, as a result of mining activities. Few data are available on the toxicity of U, and no data are available on the toxic interaction of Cu and U, to freshwater biota. This study determined the toxicity of Cu and U individually, and in combination, to a tropical freshwater macrophyte, Lemna aequinoctialis (duckweed), in a synthetic soft water (27°C; pH, 6.5; hardness, 40 mg CaCO3 l-1, alkalinity, 16 mg CaCO3 l-1), typical of many fresh surface waters in coastal northern Australia. The growth rate of L. aequinoctialis decreased with increasing Cu or U concentrations, with the concentration of Cu inhibiting growth by 50% (EC50) being 16 ± 1.0 μg l-1, with a minimum detectable effect concentration (MDEC) of 3.2 μg l-1. The concentration of U inhibiting growth by 50% (EC50) was 758 ± 35 μg l-1 with a MDEC of 112 μg l-1. The EC50 value for the exposure of L. aequinoctialis to equitoxic mixtures of Cu and U was significantly (P ≤ 0.05) higher than one toxic unit (1.35; 95% confidence interval, 1.18-1.52), indicating that the combined effects of Cu and U are less than additive (antagonistic). Therefore, inhibition of the growth rate of L. aequinoctialis was reduced when Cu and U were present in equitoxic mixtures, relative to individual metal exposures. Since non-additive (e.g. antagonistic) interactions of metal mixtures cannot be predicted using current mixture models, these results have important potential implications for the protection of freshwater ecosystems through the derivation of national water quality guidelines. © 2005 Elsevier Ltd. All rights reserved.

The chronic toxicity (72-h cell division rate) of uranium (U) to the unicellular alga, Chlorella sp., was assessed in natural Magela Creek water (NMCW) to provide data for the derivation of a site-specific water quality trigger value for U in Magela Creek, NT, Australia. In addition, the data were compared to those for Chlorella sp. when tested for U toxicity using synthetic Magela Creek water (SMCW), which simulates the inorganic composition of Magela Creek water and contains no organic component. Based on one rangefinder and four definitive toxicity tests, concentrations causing a 50% inhibition of algal growth after 72 h exposure (72 h IC50s) ranged between 137 and 238 microg/LU, no-observed-effect concentrations (NOECs) from 72 to 157 microg/LU and lowest-observed-effect concentrations (LOECs) from 120 to 187 microg/LU. Based on these data, Chlorella sp. was the second most sensitive organism to U of five local species that have been assessed using NMCW. The U toxicity data for Chlorella sp. were incorporated with existing data for the four other species to derive a site-specific guideline value for Magela Creek that is protective of 99% of species of 6 microg/L. The toxicity of U to Chlorella sp. in NMCW was approximately two to four times lower than in SMCW. Based on geochemical speciation modelling, this difference corresponded to a four-fold decrease in the proportion of free uranyl ion (UO2(2+)) in NMCW compared to SMCW, most likely due to the presence of dissolved organic carbon (DOC) in NMCW. Relatively, large variability in U toxicity across the tests conducted in NMCW was found to be inversely related to DOC concentration (r2 = 0.996, n = 4, P = 0.002). Speciation modelling indicated that the increase in DOC was associated with an increase in the proportion of U complexed with DOC (r2 = 0.986, n = 4, P < 0.001) and a decrease in the proportion of the UO2(2+) (r2 = 0.989, n = 4, P = 0.006). When the proportion of UO2(2+) was regressed against U toxicity, a very strong, positive relationship was observed (r2 = 1, n = 4, P < 0.001). The results indicate that the bioavailability and toxicity of U is highly influenced by dissolved organic matter and that the relationship should be further quantified.

Toxicity testing using a freshwater alga (Chlorella sp.), a bacterium (Erwinnia sp.) and a cladoceran (Ceriodaphnia cf. dubia) exposed to copper in synthetic and natural freshwaters of varying hardness (44-375 mg CaCO3/l), with constant alkalinity, pH and dissolved organic carbon concentration, demonstrated negligible hardness effects in the pH range 6.1-7.8. Therefore, the use of a generic hardness-correction algorithm, developed as part of national water quality guidelines for protecting freshwater biota, is not recommended for assessing the toxicity of copper to these, and other, sensitive freshwater species. Use of the algorithm for these sensitive species will be underprotective because the calculated concentrations of copper in water that cause a toxic effect will be higher.

Uranium (U) derived from mining activities is of potential ecotoxicological concern to freshwater biota in tropical northern Australia. Few data are available on the effects of water hardness (Ca and/or Mg), which is elevated in U mine wastewaters, on the toxicity and bioavailability of U to freshwater biota, particularly algae. This study determined the effect of water hardness (8, 40, 100 and 400 mg CaCO3 l-1, added as calcium (Ca) and magnesium (Mg) sulphate) on the toxicity (72 h growth rate inhibition) of U to the unicellular green alga, Chlorella sp., in synthetic freshwater, at constant pH (7.0) and alkalinity (8 mg CaCO3 l-1), similar in chemical composition to sandy coastal streams in tropical northern Australia. A 50-fold increase in water hardness resulted in a 5-fold decrease (P≤0.05) in the toxicity of U to Chlorella sp. (i.e. the 72 h EC50 increased from 56 to 270 μg U l-1). Possible explanation for the ameliorative effect of water hardness includes: (i) competition between U and Ca and/or Mg for binding sites on the cell surface; and (ii) a change in U speciation, and hence, bioavailability. Results showed that extracellular (cell-surface) and intracellular U concentrations significantly (P0.05) differences in the predicted speciation (% distribution) of U amongst the four water hardness levels. The reduction in U toxicity with increasing water hardness was most likely due to competition between U and Ca and/or Mg for binding sites on the algal cell surface. The minimum detectable effect concentrations of U were approximately 3 and 24 times higher (at 8 and 400 mg CaCO3 l-1 hardness, respectively) than the national interim U guideline value (0.5 μg l-1) for protecting aquatic ecosystems. Overall, the results reinforce the need for a more flexible U guideline based on a hardness-dependent algorithm, which may allow environmental managers to relax the national guideline for U on a site-specific basis. © 2002 Elsevier Science B.V. All rights reserved.

To date, studies on genetic variability in the tolerance of aquatic biota to chemicals have focused on exposure to single chemicals. In the field, metals occur as elemental mixtures, and thus it is essential to study whether the genetic consequences of exposure to such mixtures differs from response to single chemicals. This study determined the feeding responses of three Daphnia magna Straus clones exposed to Cd and Zn, both individually and as mixtures. Tolerance to mixtures of Cd and Zn was expressed as the proportional feeding depression of D. magna to Cd at increasing zinc concentrations. A quantitative genetic analysis revealed that genotype and genotype x environmental factors governed population responses to mixtures of both metals. More specifically, genetic variation in tolerance to sublethal levels of Cd decreased at those Zn concentrations where there were no effects on feeding, and increased again at Zn concentrations that affected feeding. The existence of genotype x environmental interactions indicated that the genetic consequences of exposing D. magna to mixtures of Cd and Zn cannot be predicted from the animals' response to single metals alone. Therefore, current ecological risk assessment methodologies for predicting the effects of chemical mixtures may wish to incorporate the concept of genetic variability. Furthermore, exposure to low and moderate concentrations of Zn increased the sublethal tolerance to Cd. This induction of tolerance to Cd by Zn was also observed for D. magna fed algae pre-loaded with both metals. Furthermore, in only one clone, physiological acclimatization to zinc also induced tolerance to cadmium. These results suggest that the feeding responses of D. magna may be related to gut poisoning induced by the release of metals from algae under low pH conditions. In particular, both induction of metallothionein synthesis by Zn and competition between Zn and Cd ions for uptake at target sites on the gut wall may be involved in determining sublethal responses to mixtures of both metals.

The concentrations of Na, K, Ca, Mg, Ba, Sr, Fe, Al, Mn, Zn, Pb, Cu, Ni, Cr, Co, Se, U and Ti were determined in the osteoderms and/or flesh of estuarine crocodiles (Crocodylus porosus) captured in three adjacent catchments within the Alligator Rivers Region (ARR) of northern Australia. Results from multivariate analysis of variance showed that when all metals were considered simultaneously, catchment effects were significant (P < or = 0.05). Despite considerable within-catchment variability, linear discriminant analysis (LDA) showed that differences in elemental signatures in the osteoderms and/or flesh of C. porosus amongst the catchments were sufficient to classify individuals accurately to their catchment of occurrence. Using cross-validation, the accuracy of classifying a crocodile to its catchment of occurrence was 76% for osteoderms and 60% for flesh. These data suggest that osteoderms provide better predictive accuracy than flesh for discriminating crocodiles amongst catchments. There was no advantage in combining the osteoderm and flesh results to increase the accuracy of classification (i.e. 67%). Based on the discriminant function coefficients for the osteoderm data, Ca, Co, Mg and U were the most important elements for discriminating amongst the three catchments. For flesh data, Ca, K, Mg, Na, Ni and Pb were the most important metals for discriminating amongst the catchments. Reasons for differences in the elemental signatures of crocodiles between catchments are generally not interpretable, due to limited data on surface water and sediment chemistry of

Nuclear milli and microprobes at the Australian Nuclear Science and Technology Organisation (ANSTO) were used to determine lead accumulation in native Australian plants and animals. Three species of eucalypt plants (Eucalyptus camaldulensis, Eucalyptus globulus and Eucalyptus lesouefii), one species of salt bush (Atriplex burbhanyana) and one species each of acacia (Acacia saligna) and estuarine crocodiles (Crocodylus porosus) were investigated. Experimentally grown plants were subjected to a nutrient solution with a pH of 5 and spiked with a 200 μmol concentration of Pb. Lead concentrations in leaves of both E. globulus and E. camaldulensis showed an almost exponential decrease from the base of the main vein to the tip. Similarly, Pb concentrations decreased from the main vein to secondary veins. Concentrations of essential elements such as K, Fe, Zn and Br in the main and secondary veins were constant within experimental uncertainty. In contrast, the concentrations of Pb in the leaf veins of E. lesouefii were much lower and showed no systematic pattern. In stem and root samples the highest concentration of Pb was found in roots and stem of E. globulus and A. burbhanyana followed by E. camaldulensis. Some Pb was found in roots of A. saligna and only very low concentration in stem of the same plant. More detailed analysis of thin cross-sectional samples of roots and stem showed that Pb is present in much higher concentration in the growth area of the plant structure (i.e. meristemic region) and in relatively low concentration within the pith region and outer cortex. The osteoderms (dermal bones) of estuarine crocodiles, exposed to lead ammunition in food from the hunting activities of traditional Aboriginal owners, were sampled at two sites in Kakadu National Park, northern Australia. PIXE analyses showed enhanced, but relatively constant, ratios of Pb/Ca in the annual laminations. This was consistent with both their history of long term exposure to elevated anthropogenic Pb sources and the hypothesis that the osteoderm can be used as an archive of the crocodile's exposure to Pb during its life.

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.

This study is the first report on anthropogenically enhanced Pb exposure in wild crocodiles, as recorded in their dermal bones (osteoderms). Riverine habitats of the estuarine crocodile, Crocodylus porosus, in Kakadu National Park, northern Australia, have been exposed to anthropogenic Pb since the mid-1950s, due mainly to replacement of traditional spear by guns using lead ammunition for the hunting of wildlife by the Aboriginal owners. Resident crocodiles ingest waterfowl, flying foxes, and pigs killed or crippled by Pb ammunition, also commonly found in crocodile stomachs. Among 40 wild crocodiles sampled, the osteoderms from five residents of two intensively hunted habitats each had enhanced Pb (19−44 μg/g dry weight), relative to all others. Enhanced ratios of Pb:Ca in the annual laminations of their osteoderms are consistent with their history of continual long-term exposure to elevated anthropogenic Pb sources. These Pb levels are presently of undefined toxicological significance in crocodiles but ...

Fish (dusky flathead – Platycephalalus fuscus and luderick – Girella tricuspidata) and shellfish (Anadara trapezia and Saccostrea commercialis) samples from Lake Illawarra in south-eastern Australia were collected in 1993 and 2000 and analysed for a range of metals. Sediments with which the shellfish were in contact were also examined. The results were compared with shellfish data collected in 1976 and in an independent study in 1993. No reported data were available for comparison with the fish metal results. The results showed that trace metal concentrations in both fish and shellfish were generally low and represented minimal health risk. The dusky flathead, a predator species, had detectable concentrations of mercury, while the luderick, a herbivore, had values below detection limits. Metal concentrations in shellfish were in general agreement with those found in other studies, and showed that no apparent changes were occurring over time, except those that could be explained by changes in the age of the shellfish. Only copper in Lake Illawarra oysters showed greater concentrations than found in other south-eastern Australian estuaries. It is recommended that future studies focus on organic and microbial contamination.

This study determined the influence of key water chemistry parameters (pH, alkalinity, dissolved organic carbon [DOC], and hardness) on the aqueous speciation of copper and zinc and its relationship to the acute toxicity of these metals to the cladoceran Ceriodaphnia cf dubia. Immobilization tests were performed for 48-h in synthetic or natural waters buffered at various pH values from 5.5 to 8.4 (other chemical parameters held constant). The toxicity of copper to C. cf dubia decreased fivefold with increasing pH, whereas the toxicity of zinc increased fivefold with increasing pH. The effect of DOC on copper and zinc toxicity to C. cf dubia was determined using natural fulvic acid in the synthetic water. Increasing DOC was found to decrease linearly the toxicity of copper, with the mean effect concentration of copper that immobilized 50% of the cladocerans (EC50) value 45 times higher at 10 mg/L, relative to 0.1 mg/L DOC at pH 6.5. In contrast, the addition of 10 mg/L DOC only resulted in a very small (1.3-fold) reduction in the toxicity of zinc to C. cf dubia. Copper toxicity to C. cf dubia generally did not vary as a function of hardness, whereas zinc toxicity was reduced by a factor of only two, with an increase in water hardness from 44 to 374 mg CaCO3/L. Increasing bicarbonate alkalinity of synthetic waters (30-125 mg/L as CaCO3) decreased the toxicity of copper up to fivefold, which mainly could be attributed to the formation of copper-carbonate complexes, in addition to a pH effect. The toxicity of copper added to a range of natural waters with varying DOC content, pH, and hardness was consistent with the toxicity predicted using the data obtained from the synthetic waters.