The IAEA handbook on radionuclide transfer to wildlife.

An IAEA handbook presenting transfer parameter values for wildlife has recently been produced. Concentration ratios (CRwo-media) between the whole organism (fresh weight) and either soil (dry weight) or water were collated for a range of wildlife groups (classified taxonomically and by feeding strategy) in terrestrial, freshwater, marine and brackish generic ecosystems. The data have been compiled in an on line database, which will continue to be updated in the future providing the basis for subsequent revision of the Wildlife TRS values. An overview of the compilation and analysis, and discussion of the extent and limitations of the data is presented. Example comparisons of the CRwo-media values are given for polonium across all wildlife groups and ecosystems and for molluscs for all radionuclides. The CRwo-media values have also been compared with those currently used in the ERICA Tool which represented the most complete published database for wildlife transfer values prior to this work. The use of CRwo-media values is a pragmatic approach to predicting radionuclide activity concentrations in wildlife and is similar to that used for screening assessments for the human food chain. The CRwo-media values are most suitable for a screening application where there are several conservative assumptions built into the models which will, to varying extents, compensate for the variable data quality and quantity, and associated uncertainty.

The accumulation of lead and mercury from seawater and their depuration by eggs of the spotted dogfish Scyliorhinus canicula (Chondrichthys).

Radiotracer experiments using (210)Pb and (203)Hg demonstrated that eggs of the spotted dogfish Scyliorhinus canicula absorbed lead and inorganic mercury directly from seawater over 21 days of experimental exposure, attaining total egg concentration factors (CFs) relative to water of approximately 400 for Pb and 180 for Hg, predominantly (> or =98%) due to their accumulation by the collagenous egg case. The rates of accumulation of both Pb and Hg by the total egg were significantly (P < 0.0001) reduced by its increasing age since parturition, whereas only the rate of depuration of Pb was reduced (P < 0.0001) with increasing age; these effects indicate a declining chemical reactivity of the egg case that may be due to the continued tanning of the case following parturition. The egg case per se, attained average CFs of about 1,500 and 850 for Pb and Hg, respectively. Both Pb and Hg showed declining concentration gradients from the exterior to the interior membranes of the wall of the egg case; CFs for Pb declined from 3,500 to 2,000 and for Hg from 5,000 to 500. Comparison of concentrations in separate membranes also demonstrated significant (P < or = 0.01) depurations of Hg from the external and internal membranes during the loss experiments. The presence of radiotracers of Pb and Hg in the internal components of the egg at the end of uptake phase, and prior to the opening of the apertures, confirmed the permeability of the egg case wall to them, consistent with their observed gradients in it. The average CFs for all embryos at the end of the uptake experiment were 34 and 44 for Pb and Hg, respectively, but were significantly (P < 0.001) enhanced for Hg by a factor of 6 in the older eggs. The accumulatory and kinetic characteristics of the egg-case may operate to optimize the exposure of embryos to Pb and Hg following episodic contaminant events in coastal habitats.

Experimental study of blood lead kinetics in estuarine crocodiles (Crocodylus porosus) exposed to ingested lead shot.

A previous study of lead (Pb) contamination in estuarine crocodiles (Crocodylus porosus) in Kakadu National Park, Australia, found elevated Pb levels in bone and flesh from individuals caught in habitats where hunting with lead ammunition had occurred. Lead shot was suspected as the potential source of Pb in these animals. An investigation was designed to determine if crocodiles are capable of retaining and dissolving lead shot in their stomachs and absorbing the ionic Pb into the blood. Four of the six juvenile crocodiles (C. porosus) used in the experiment were fed an initial dose of five or ten lead shot each. Most of the lead shot were retained in the stomach over the 20-week experimental period, as confirmed by stomach lavage and radiography of the stomach region. From 13 to 30% of the original weight of individual lead shot had been eroded in that time. In vitro experiments confirmed that lead shot could be dissolved under conditions simulating those known for the crocodilian stomach. Blood Pb concentrations increased by an order of magnitude within a week after dosing three crocodiles with five lead shot each, and then attained steady-state equilibrium 5-20 weeks after dosing, with blood Pb steady-state levels ranging from 278 to 363 microg/dL. The blood Pb concentration-time curves in these crocodiles followed a one-compartment model with first-order loss kinetics that yielded an apparent biological half-life for Pb in blood of about 3.4 days. Throughout the experiment, the crocodiles remained in apparent good physical condition and displayed no clinical signs of Pb toxicosis. These observations, together with the very high blood Pb levels that were sustained for several months, suggest that crocodilians may possess a relatively high degree of resistance to Pb toxicity.

The effects of pH and dissolved organic carbon on the toxicity of cadmium and copper to a freshwater bivalve: further support for the extended free ion activity model.

The extended free ion activity model (FIAM) was developed by integrating concepts from the original FIAM into biological receptor theory, to obtain a conceptual model that more precisely quantifies the interaction of chemical species at biological receptor sites. The extended FIAM was tested by determining the acute (48 h) valve movement behavior (VMB) (measured in terms of the duration of valve opening) of the Australian freshwater bivalve, Hyridella depressa, to increasing concentrations of total Cd or Cu, in a standard synthetic water under conditions of varying pH (6.5-7.5) and/or dissolved organic carbon (as model fulvic acid (FA)) concentrations (0-11.2 mg L(-1)). Valve movement behavior, measured using an automated data acquisition system, was shown to be a quantifiable and rapid, real-time endpoint for assessing the toxic effects of Cd and Cu exposures. The VMB of H. depressa to Cd was independent (p > 0.05) of pH and/or model FA concentration. In contrast, the VMB of H. depressa to Cu was highly dependent (p < 0.001) on pH and/or model FA concentration; individuals were more sensitive to Cu at low pH and model FA concentrations. The VMB of H. depressa was directly proportional to the activity of the free metal ion (Cd2+), for the linear region of the concentration-response curves. In contrast, the VMB of H. depressa was a weighted function of the activities of the free metal ion and the 1:1 metal hydroxide species (i.e. 2.02 x Cu2+ + CuOH+), whereby Cu2+ had a two-fold greater binding affinity than CuOH+ at the cell membrane surface. Moreover, the results for Cd and Cu are consistent with the extended FIAM, as opposed to the original FIAM, where the result for Cu would be regarded as an exception. The extended FIAM explained 98% of the variability in VMB, whereas the original FIAM explained only 63% (i.e. an improvement of 35%). The improved predictability of organism response to Cu is relevant to advancing water quality guidelines for protecting aquatic biota.

Divalent metal accumulation in freshwater bivalves: an inverse relationship with metal phosphate solubility.

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.

Recovery of fish communities in the Finniss River, northern Australia, following remediation of the Rum Jungle uranium/copper mine site.

The Finniss River in the wet-dry tropics of northern Australia has received acid rock drainage (ARD) contaminants from the Rum Jungle uranium/copper mine site over more than four decades. Annual-cycle loads of Cu, Zn, Mn, and sulfate, calculated from daily water and flow measurements, have been determined both prior to and following mine-site remediation, that began in the early 1980s. The effects of varying contaminant loads on the relative abundances of seven fish species, sampled by enmeshing nets during dry seasons, were determined by nonmetric multidimensional scaling (nMDS), in combination with cluster-analysis and other nonparametric statistical techniques. These analyses showed that (i) prior to remediation, the impacted region of the Finniss River in 1974 had significantly dissimilar (P < 0.001) and more heterogeneous fish communities, generally characterized by reduced diversity and abundance, compared to sites unexposed to elevated contaminant water concentrations and (ii) postremediation, recovery in fish communities from the impacted region was indicated because they were not significantly dissimilar from those sampled at contemporary (P = 0.16) unimpacted sites, that were also similar to preremedial unimpacted sites. Even though considerable contaminant loads are still being delivered to the impacted region of the Finniss River over the annual cycle, the recovery in fish diversity and abundances is consistent with (a) reductions of in situ contaminant water concentrations at the time of fish sampling, (b) reductions in annual-cycle contaminant loads of sulfate, Cu, Zn, and Mn by factors of 3-7, (c) greatly reduced frequencies of occurrence and magnitude of elevated contaminant water concentrations over the annual cycle, that was most pronounced for Cu, and (d) the absence of extensive fish-kills during the first-flushes of contaminants into the Finniss river proper at the beginning of the wet season, that were observed prior to remediation. As such, the results indicate that there has been ecological benefit to the Finniss River attributable to remedial works undertaken at the Rum Jungle mine site. Recovery in abundances of these fishes may also be due to their time-dependent evolution of tolerance to mine-waste contaminants over their long period of exposure.

Element concentrations in the flesh and osteoderms of estuarine crocodiles (Crocodylus porosus) from the Alligator Rivers Region, Northern Australia: biotic and geographic effects.

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.

Valve movement responses of Velesunio angasi (Bivalvia: Hyriidae) to manganese and uranium: an exception to the free ion activity model.

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.

Accumulation of radiocalcium from the aquatic medium via the cloaca and bucco-pharynx of Australian freshwater turtles (Chelidae).

1. The cloacal and bucco-pharyngeal regions of three species of Australian freshwater turtles were experimentally compared for their ability to take up radiocalcium directly from the aquatic medium. 2. The cloacal route was at least 4 times more important than the bucco-pharyngeal route for radiocalcium uptake, in each of the three species investigated. 3. Histological examination of anatomical regions in the cloaca showed that the cloacal bursae of three species (E. dentata, C. longicollis and E. signata) had abundant villi and infolded mucosal epithelia that increase the surface area of the epithelium exposed to the aquatic medium. 4. Electron microscopic studies on the mucosal epithelium of the cloacal bursae showed that it contained many structural characteristics indicative of an exchange function and consistent with the cloacal bursae being an important site of radiocalcium uptake within the cloaca.