A microautoradiographic method for fresh-frozen sections to reveal the distribution of radionuclides at the cellular level in plants.

Microautoradiography (MAR) is a conventional imaging method based on the daguerreotype. The technique is used to visualize the distribution of radionuclide-labeled compounds within a tissue section. However, application of the classical MAR method to plant tissue sections is associated with several difficulties. In this study, we report an MAR method applicable to fresh-frozen plant sections. Our method had two features: (i) the sample was kept frozen from plant tissue collection to radioisotope detection, making it possible to fix solutes without solvent exchange; and (ii) 1.2 µm thick polyphenylene sulfide film was inserted between the fresh-frozen plant section and the photosensitive nuclear emulsion to separate the section from the emulsion before autoradiography was conducted, which significantly improved the quality of the section until microscopic detection, the quality of the MAR image and the success rate. Then, the passage of cadmium (Cd) through vegetative rice stem tissue after 24 h of (109)Cd absorption was described for the first time using the MAR method. MAR clearly revealed the distribution of (109)Cd at the tissue level with high resolution. The (109)Cd concentration in phloem cells was found to be particularly high, whereas the xylem cells contained only small amounts of (109)Cd. The MAR method was also applicable for detecting (109)Cd and [(33)P]phosphate in roots. The MAR method developed here is expected to provide distribution images for a variety of compounds and ions in plant tissue.

Characterization of rapid intervascular transport of cadmium in rice stem by radioisotope imaging.

Participation of the intervascular transport system within the rice stem during cadmium (Cd) partitioning was investigated by characterizing (109)Cd behaviour in the shoot. In addition, (45)Ca, (32)P, and (35)S partitioning patterns were analysed for comparison with that of (109)Cd. Each tracer was applied to the seedling roots for 15 min, and the shoots were harvested either at 15 min (i.e. immediately after tracer application) or at 48 h. Distribution patterns of each element at 15 min were studied to identify the primary transport pathway before remobilization was initiated. (32)P was preferentially transported to completely expanded leaf blades having the highest transpiration rate. The newest leaf received minimal amounts of (32)P. In contrast, the amount of (35)S transported to the newest leaf was similar to that transported to the other mature leaf blades. Preferential movement towards the newest leaf was evident for (109)Cd and (45)Ca. These results directly indicate that elemental transport is differentially regulated in the vegetative stem as early as 15 min before the elements are transported to leaves. Cd behaviour in the stem was investigated in detail by obtaining serial section images from the bottom part of shoots after (109)Cd was applied to a single crown root. At 30 min, the maximum amount of (109)Cd was distributed in the peripheral cylinder of the longitudinal vascular bundles (PV) and, interestingly, some amount of (109)Cd was transported downwards along the PV. This transport manner of (109)Cd provides evidence that Cd can be loaded on the phloem at the stem immediately after Cd is transported from the root.

In situ analysis of cadmium uptake in four sections of the gastro-intestinal tract of rainbow trout (Oncorhynchus mykiss).

This study links results from past in vitro and in vivo experiments, by implementing an in situ experiment in order to determine the relative importance for cadmium (Cd) uptake of different sections of the gastro-intestinal tract (GIT) of rainbow trout. Transport of Cd from four sections of the GIT of adult rainbow trout (~220 g) was individually examined by infusing ligated sections of the GIT in live, free-swimming fish with 50 µM Cd spiked with radiolabelled (109)Cd (0.5 µCi ml(-1)). Fish were exposed for an 8-h period. The percentage of the total injected (109)Cd which was internalized from the different segments was only between ~0.1 and ~7%, indicating low uptake efficiency. The stomach is the most important GIT segment for Cd transport into the internal compartment of the animal, while the posterior intestine also plays a significant role. The majority of (109)Cd recovered at the end of the flux period was detected within gut material (ranging from 28 to 95%); the portion of Cd which was internalized was largely found in the carcass (32 to 60%). Distribution between the measured organs varied with uptake from the various GIT sections. Our results also confirm that the GIT acts as a protective barrier against Cd uptake from dietary exposure.

Inclusion of a GaAs detector model in the Photon Counting Toolkit software for the study of breast imaging systems.

We present an upgraded version of the Photon Counting Toolkit (PcTK), a freely available by request MATLAB tool for the simulation of semiconductor-based photon counting detectors (PCD), which has been extended and validated to account for gallium arsenide (GaAs)-based PCD(s). The modified PcTK version was validated by performing simulations and acquiring experimental data for three different cases. The LAMBDA 60 K module planar detector (X-Spectrum GmbH, Germany) based on the Medipix3 ASIC technology was used in all cases. This detector has a 500-µm thick GaAs sensor and a 256 × 256-pixel array with 55 µm pixel size. The first validation was a comparison between simulated and measured spectra from a 109Cd radionuclide source. In the second validation study, experimental measurements and simulations of mammography spectra were generated to observe the performance of the GaAs version of the PcTK with polychromatic radiation used in conventional x-ray imaging systems. The third validation study used single event analysis to validate the spatio-energetic model of the extended PcTK version. Overall, the software provided a good agreement between simulated and experimental data, validating the accuracy of the GaAs model. The software could be an attractive tool for accurate simulation of breast imaging modalities relying on photon counting detectors and therefore could assist in their characterization and optimization.

Real-time imaging and analysis of differences in cadmium dynamics in rice cultivars (Oryza sativa) using positron-emitting 107Cd tracer.

BACKGROUND: Rice is a major source of dietary intake of cadmium (Cd) for populations that consume rice as a staple food. Understanding how Cd is transported into grains through the whole plant body is necessary for reducing rice Cd concentrations to the lowest levels possible, to reduce the associated health risks. In this study, we have visualized and quantitatively analysed the real-time Cd dynamics from roots to grains in typical rice cultivars that differed in grain Cd concentrations. We used positron-emitting 107Cd tracer and an innovative imaging technique, the positron-emitting tracer imaging system (PETIS). In particular, a new method for direct and real-time visualization of the Cd uptake by the roots in the culture was first realized in this work. RESULTS: Imaging and quantitative analyses revealed the different patterns in time-varying curves of Cd amounts in the roots of rice cultivars tested. Three low-Cd accumulating cultivars (japonica type) showed rapid saturation curves, whereas three high-Cd accumulating cultivars (indica type) were characterized by curves with a peak within 30 min after 107Cd supplementation, and a subsequent steep decrease resulting in maintenance of lower Cd concentrations in their roots. This difference in Cd dynamics may be attributable to OsHMA3 transporter protein, which was recently shown to be involved in Cd storage in root vacuoles and not functional in the high-Cd accumulating cultivars. Moreover, the PETIS analyses revealed that the high-Cd accumulating cultivars were characterized by rapid and abundant Cd transfer to the shoots from the roots, a faster transport velocity of Cd to the panicles, and Cd accumulation at high levels in their panicles, passing through the nodal portions of the stems where the highest Cd intensities were observed. CONCLUSIONS: This is the first successful visualization and quantification of the differences in whole-body Cd transport from the roots to the grains of intact plants within rice cultivars that differ in grain Cd concentrations, by using PETIS, a real-time imaging method.

Characterization of basolateral-to-apical transepithelial transport of cadmium in intestinal TC7 cell monolayers.

Cadmium (Cd) is a toxic metal with an extremely long half-life in humans. The intestinal absorption of Cd has been extensively studied but the role the intestinal epithelium may play in metal excretion has never been considered. The basolateral (BL)-to-apical (AP) transepithelial transport of Cd was characterized in TC7 human intestinal cells. Both AP and BL uptakes varied with days in culture, and BL uptake was twofold higher compared to AP in differentiated cultures. A 50% increase in the BL uptake of 0.5 µM (109)Cd was observed at pH 8.5 in a chloride but not nitrate medium, suggesting the involvement of a pH-sensitive mechanism of transport for chloro-complexes. Fe and Zn inhibited the BL uptake of Cd whereas complexation by albumin had no effect, but the stimulatory effect of pH 8.5 was lost in the presence of albumin. The BL uptake of [(3)H]-MPP(+) and (109)Cd were both inhibited by decynium22 without reciprocal inhibition. MRP2 and MDR1 mRNA levels increased as a function of days in culture. A 25 and 20% decrease in the cellular AP efflux of Cd was observed in the presence of verapamil and probenecid, respectively. In cells treated with BSO, which lowered by 26% the total cellular thiol content, the inhibitory effect of verapamil increased, whereas that of probenecid decreased. These results reveal the existence of a decynium22-sensitive mechanism of transport for Cd at the BL membrane, and suggest the involvement of MDR1 and MRP2 in cellular Cd efflux at the AP membrane. It is conceivable that the intestinal epithelium may contribute to Cd blood excretion.

Calibration of (109)Cd KXRF systems for in vivo bone lead measurements: the guiding role of the assumptions for least-squares regression in practical problem solving.

The use of least-squares regression to probe the level of lead contamination of plaster of Paris standards in the calibration of (109)Cd KXRF systems for bone lead measurement, as well as the use of iteratively reweighted least-squares (IRLS) in the case of violation of the assumptions for ordinary least-squares (OLS), is discussed here. One common violation is non-uniform residual variance, which makes the use of OLS inappropriate due to strong influence of points with large variance on the calibration line and variance of the slope and intercept. Comparison between OLS and IRLS in that case showed that IRLS estimates of the intercept are significantly smaller and more precise than OLS estimates, while a less marked increase in the calibration slope is observed when IRLS is used. Moreover, OLS underestimates bone lead concentrations at low levels of lead exposure and overestimates those concentrations at higher levels. These discrepancies are smaller in magnitude than the measurement uncertainty of conventional systems, except for high concentrations. For the newly developed cloverleaf systems, the suggested differences at bone lead concentrations below 17 ppm are comparable to the minimum detection limit, but are larger than the measurement uncertainty for bone lead concentrations above 60 ppm.

Calibration of (109)Cd KXRF systems for in vivo bone lead measurements: weighted least-squares regression with different weighting functions.

The use of iteratively reweighted least squares (IRLS) has recently been described as an alternative to ordinary least squares with heteroscedastic data, in the calibration of (109)Cd KXRF systems for in vivo bone lead measurements. This work addresses the use of weighted least squares (WLS) with two different weighting functions and no iteration, with that same data set. The functions are defined as the inverse of the variance of observed ratios of lead to coherent peak amplitudes and the inverse of the square of the error reported by the Marquardt fitting program for these ratios. The results show that if no iteration is implemented when using WLS, then the two weighting functions are highly inefficient in homogenizing the residual variance. Moreover, both methods estimate much more imprecise calibration intercepts and slopes than did the IRLS method. Work is in progress to investigate the implementation of IRLS with these weighting functions, with the focus on the selection of the best function for residuals to be used in each iteration stage.

Characterization of cadmium uptake and translocation in a cadmium-sensitive mutant of rice (Oryza sativa L. ssp. japonica).

To understand the physiological mechanism that confers Cd sensitivity/tolerance, Cd uptake and translocation by Cd-sensitive mutant and wild-type rice seedlings were characterized using radioactive tracer. Time-dependent Cd accumulation during 210 min was 1.8-fold higher in roots of the mutant than of wild-type rice. The kinetics of Cd uptake showed that two processes were involved: a first, fast, probably passive process and a second, slower, possibly physiological process. After 96 h, more Cd was translocated to the shoot of mutant compared with wild-type rice. Low temperature (2 degrees C), carbonyl cyanide m-chlorophenylhydrazone, and dicyclohexylcarbodiimide inhibited Cd accumulation to a greater extent in mutant than wild-type rice, suggesting that metabolism plays a more important role in Cd uptake for the rice mutant. Cd uptake into the symplasm is linked to Ca2+ transport, as revealed by the inhibition of Cd accumulation by La and high Ca by equal percentages in both mutant and wild-type rice. Cd uptake and root-to-shoot translocation in the mutant were inhibited more markedly by Zn and Mn than in wild-type rice. This indicates that transport sites other than entry into the root symplasm are also stimulated in the mutant. The results suggest that enhanced absorption into the root and further accumulation in the shoot is one of the mechanisms involved in Cd accumulation and sensitivity, and the difference in Cd uptake and root-to-shoot translocation between mutant and wild-type rice may be mediated partly by energy supply and transporters for Zn and Mn.

Formation of 107Cd radionuclide impurities during 18F production.

Cd isotopes (107Cd and 109Cd) are generated from the silver target body during the bombardment of [18O]water in the routine production of 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG) for PET (Positron Emission Tomography) diagnosis. Cadmium isotopes contribute significantly to the total activity of generated impurities and, due to being potentially radiotoxic to living organisms, they should be effectively reduced from FDG to prevent accidental injection of even small concentrations into patients. Purification of the final [18F]FDG can be based on a set of columns, fulfilling various functions in the cleaning process. To assess cadmium impurities and the efficiency of the purification process, a low background gamma spectrometry system with high resolution has been applied. Even activity of 3.5 kBq and 290 kBq has been measured on QMA (Sep-Pak Light Accell Plus QMA) columns for 109Cd and 107Cd isotopes, respectively. 107Cd activity in the five column set was higher than that of 109Cd. The rate of 18F production process was about 1 GBq/min, while that of 107Cd and 109Cd radionuclides was about 4.2 kBq/min and 50 Bq/min respectively. The same purification efficiency of both isotopes has been obtained at each step of the process. The production rate of 107Cd and 109Cd radionuclides was insignificant compared to the 18F production rate. Therefore [18F]FDG final product for use in injections before PET diagnostics was efficiently purified from cadmium radionuclide impurities.

Using isotopes to trace freshly applied cadmium through mineral phosphorus fertilization in soil-fertilizer-plant systems.

Applications of mineral phosphorus (P) fertilizer can lead to cadmium (Cd) accumulation in soils and can increase Cd concentrations in edible crop parts. To determine the fate of freshly applied Cd, a Cd source tracing experiment was conducted in three soil-fertilizer-wheat systems by using a mineral P fertilizer labeled with the radio isotope 109Cd and by exploiting natural differences in Cd stable isotope compositions (δ114/110Cd). Source tracing with stable isotopes overestimated the proportion of Cd in plants derived from the P fertilizer, because the isotope ratios of the sources were not sufficiently distinct from those of the soils. Despite indistinguishable extractable Cd pools between control and treatments, the addition of P fertilizer resulted in a more negative apparent isotope fractionation between soil and wheat. Overall, the radio isotope approach provided more robust results and revealed that 6.5 to 15% of the Cd in the shoot derived from the fertilizer. From the introduced Cd, a maximum of 2.2% reached the wheat shoots, whilst 97.8% remained in the roots and soils. The low recoveries of the fertilizer derived Cd suggest that continuous P fertilizer application in the past decades can lead to a build-up of a residual Cd pool in soils.

Dietary metal bioavailability in razor clam Sinonovacula constricta under fluctuating seston environments.

To understand the potential risks of dietary metals to marine bivalves, it is important to study the interaction between dietary metal bioaccumulation and bivalve feeding behavior. Key processes in affecting the dietary metal influx are the selection of different particles during the ingestion process as well as the differential assimilation of metals during the digestion process. In this study, we quantified the influences of seston quality and quantity on the dietary assimilation of Cd and Zn as well as pre-ingestion particle selectivity in a razor clam Sinonovacula constricta following feeding on radiolabeled diatoms and sediments with different mixtures at four food concentrations. Bioavailability of 109Cd and 65Zn from seston was measured by assimilation efficiency (AE) using a pulse-chase feeding technique. The AEs of Cd and Zn were significantly affected by the seston quantity and quality (higher for Zn than they were for Cd and higher for diatoms than for suspended sediments), but were independent of the presence of other particles during the feeding process. Dual gamma radiotracer technique was further employed to study pre-ingestion particle selectivity. Particle selectivity was weak during pre-ingestion in razor clams, although there was evidence that clams might be able to differentiate particles during the process of pseudofeces production. Our study demonstrated that seston composition and quantity substantially affected the bioavailability of Cd and Zn to the razor clams. The results are important to understand the bioaccumulation of metals in clams living in dynamic food environments of estuary.

Comparative accumulation of (109)Cd and (75)Se from water and food by an estuarine fish (Tetractenos glaber).

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 (14kBqL(-1) of (109)Cd and 24kBqL(-1) of (75)Se) and food (ghost shrimps; Trypaea australiensis: 875Bqg(-1)(109)Cd and 1130Bqg(-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.

Effects of ocean acidification on 109Cd, 57Co, and 134Cs bioconcentration by the European oyster (Ostrea edulis): Biokinetics and tissue-to-subcellular partitioning.

The uptake and depuration kinetics of dissolved 109Cd, 57Co and 134Cs were determined experimentally in the European flat oyster Ostrea edulis (Linnaeus, 1758) under different pH conditions (i.e., 8.1, 7.8 and 7.5) for 59 days. Uptake and depuration rates were variable within these elements; no effects were observed under different pH conditions for the uptake biokinetics of 109Cd and 57Co and depuration of 109Cd and 134Cs in oyster. The uptake and depuration rate constants of 134Cs differed during the exposure phase between treatments, while the steady state concentration factors (CFss) were similar. The resulting Cs activity that was purged during short- and long-term depuration phases differed, while the remaining activities after thirty-nine days depuration phase (RA39d) were similar. Co-57 depuration was affected by pCO2 conditions: RA39d were found to be significantly higher in oysters reared in normocapnia (pCO2 = 350 µatm) compared to high pCO2 conditions. Co-57 tissue distribution did not differ among the variable pCO2 conditions, while 109Cd and 134Cs accumulated in soft tissue of oysters were found to be higher under the highest pCO2. Additionally, Cd, Co and Cs were stored differently in various compartments of the oyster cells, i.e. cellular debris, metal-rich granules (MRG) and metallothionein-like proteins (MTLP), respectively. The subcellular sequestration of the elements at the end of the depuration phase did not differ among pH treatments. These results suggest that bioconcentration and tissue/subcellular distribution are element-specific in the oyster, and the effects of higher pCO2 driven acidification and/or coastal acidification variably influence these processes.

A 4 x 500 mm2 cloverleaf detector system for in vivo bone lead measurement.

A 4 x 500 mm2 "cloverleaf" low energy germanium detector array has been assembled for the purpose of in vivo bone lead measurement through x-ray fluorescence. Using 109Cd as an exciting source, results are reported from a leg phantom simulating measurement of lead in a human tibia. For high activity (4.0-4.4 GBq) and low activity (0.18-0.19 GBq) sources, measurement results are reported for both the cloverleaf system and a conventional single detector system of equivalent surface area (2000 mm2). The mean uncertainty and reproducibility of measurement were both significantly improved for the cloverleaf system with a high activity 109Cd source. When using a source activity of 4.4 GBq, measurement of the phantom resulted in an average bone lead uncertainty of 0.79 microg/g and a reproducibility of 0.84 microg/g. These results represent the highest precision yet reported from a bone lead x-ray fluorescence system.

Influence of food quality and salinity on dietary cadmium availability in Mytilus trossulus.

Surficial sediments (a combination of re-suspended and suspended sediments denoted as RSS) were collected from two distinct marine intertidal habitats. The two habitats differed with respect to salinity (25ppt versus 15ppt) and RSS % organic carbon content (24% versus 15%). Feeding experiments were conducted simulating the conditions in the two habitats to determine if salinity and RSS % organic carbon content affected cadmium accumulation in the pacific blue mussel Mytilus trossulus. Eleven different treatments including pure phytoplankton, collected RSS and control clay were radiolabeled with (109)Cd and pulse-fed to M. trossulus under both high (25ppt) and low salinities (15ppt). Metal uptake and accumulation was determined using the DYMBAM biodynamic metal bioaccumulation model. Although M. trossulus ingestion rates (IR) were significantly higher at 25ppt as compared to 15ppt, assimilation efficiencies (AEs) and [(109)Cd] tissue levels were significantly lower at high as compared to low salinity exposures. Of the abiotic and biotic parameters examined and in contrast to other studies, differences in salinity rather than ingestion rate or food quality (as defined by % organic carbon content) seemed to best define the observed differences in (109)Cd AE by M. trossulus.

Determining metal assimilation efficiency in aquatic invertebrates using enriched stable metal isotope tracers.

We employ a novel approach that combines pulse-chase feeding and multi-labelled stable isotopes to determine gut passage time (GPT), gut retention time (GRT), food ingestion rate (IR) and assimilation efficiency (AE) of three trace elements for a freshwater gastropod. Lettuce isotopically enriched in (53)Cr, (65)Cu and (106)Cd was fed for 2h to Lymnaea stagnalis. The release of tracers in feces and water was monitored for 48 h, during which unlabelled lettuce was provided ad libidum. The first defecation of (53)Cr occurred after 5h of depuration (GPT), whereas 90% of the ingested (53)Cr was recovered in the feces after 22.5h of depuration (GRT). (53)Chromium was not significantly accumulated in the soft tissues upon exposure. In contrast, (65)Cu and (106)Cd assimilation was detectable for most experimental snails, i.e., (65/63)Cu and (106/114)Cd ratios in exposed snails were higher than those for controls. Food IR during the labelled feeding phase was 0.16+/-0.07 g g(-1)d(-1). IR was inferred from the amount of (53)Cr egested in the feces during depuration and the concentration of (53)Cr in the labelled lettuce. Assimilation efficiencies (+/-95% CI) determined using mass balance calculations were 84+/-4% for Cu and 85+/-3% for Cd. The ratio method yields similar AE estimates. Expanding the application of this novel stable isotope tracer technique to other metals in a wide variety of species will provide unique opportunities to evaluate the interplay between digestive processes and dietary influx of metals. Understanding the biological processes that modulate dietborne metal uptake is crucial to assess the toxicity of dietborne metals.

Uptake and loss of dissolved 109Cd and 75Se in estuarine macroinvertebrates.

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.

Fate of cadmium in Elodea canadensis.

Elodea canadensis is a submersed macrophytes, widely distributed in stormwater treatment ponds and able to remove heavy metals from water. This study examines the Cd uptake, translocation, and efflux patterns in Elodea. Several experiments were set up in a climate chamber. To study the root and shoot Cd uptake, living and dead roots and shoots were treated with (109)Cd in one- and two-compartment systems. Furthermore, to examine Cd translocation and distribution, either roots or shoots were treated with (109)Cd. Finally, the efflux of Cd from roots and shoots, respectively, to the external solution was studied after loading whole plants with (109)Cd. Results from the two compartment studies show that Cd is accumulated via direct uptake by both roots and shoots of Elodea. The Cd accumulation proved not to be metabolically dependent in Elodea, and the apoplastic uptake in particular was decreased by Cd pretreatment. In one week, up to 23% of the root uptake was translocated to the shoots, while about 2% of the Cd accumulated by shoots was translocated to the roots. Thus, slight dispersion of Cd is possible, while metal immobilization will not be directly mediated via the Elodea plant. The efflux experiment proved that both shoots of dead plants and roots of living plants had a faster efflux than did shoots of living plants. This information is relevant for an understanding of the fate of Cd in stormwater treatment ponds with Elodea.

EDXRF analysis of municipal solid waste using (109)Cd source.

Elemental compositions of municipal solid waste (MSW) samples have been analyzed using the non-destructive energy dispersive X-ray fluorescence (EDXRF) technique. The samples were collected from three different dumping sites of urban and suburban areas of the city of Kolkata, West Bengal, India. The EDXRF spectrometer consisted of a (109)Cd radioactive source and a Si (Li) detector. To check the reliability of the system, NIST Standard Reference Material-1648 UPM had been analyzed and it was found that within the experimental errors, our results agree quite well with the certified and non-certified values. The elemental compositions of all the three MSW samples were subsequently estimated using the same procedure. The matrix effects were estimated following the emission-transmission method. It was observed that except Fe, all the elements from Ti to Pb show concentration levels higher by a factor of 2-7 than the ecological screening values where as in the case of Fe, this factor varies from 100 to 200.