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Radioisotope techniques in delineation of the environmental behavior of cadmium.

Radioisotope techniques are being developed and utilized at Oak Ridge National Laboratory (ORNL) for evaluating the environmental behavior of toxic elements such as cadmium in aquatic and terrestrial ecosystems. Tracer techniques using 109Cd in microcosm, field plot, and stream systems are providing information on biogeochemical cycling and distribution of cadmium in the environment. Parameters being measured include adsorption capacity for cadmium in mineral soils and sediments; uptake rates of cadmium in various plant species from both soils and nutrient solutions as affected by pH, competing cations, and chemical form of cadmium; and distribution of cadmium in various components of both aquatic and terrestrial ecosystems following application of 109Cd to soil vegetation, or directly to streams. Food chain parameters being estimated with 109Cd include uptake, assimilation, and turnover by both aquatic and terrestrial organisms. Information obtained in these radiotracer studies is providing insight into the behavior of cadmium in aquatic and terrestrial ecosystems, especially transport rates of cadmium and potential biomagnification or dilution in food chains. The factors which influence the incorporation of cadmium into vegetative material as well as those affecting residence time in ecosystems have been identified. Use of 109Cd also has permitted evaluation of a cadmium specific electrode as a tool for rapid assay of free cadmium ions in soil solutions.

Adsorption↗

Application of substoichiometric radioisotopic dilution to extraction of trace-level cadmium.

A substoichiometric isotopic dilution method was coupled to the standard addition technique for the determination of trace-level cadmium. 109Cd carrier-free as a radiotracer and extraction with dithizone in chloroform were used. A preconcentration procedure, which also cuts down the main interferences, for tap and natural waters was suggested. The sensitivity and accuracy of the method are discussed.

Cadmium↗

Effects of 1.25 dihydroxyvitamin D3 on calcium metabolism in rats exposed to cadmium.

The radioisotopic study of calcium metabolism in the rat after chronic oral administration of cadmium (8 mg/kg) has shown two different effects: a) in the intestine cadmium inhibits the absorption of calcium by active transport; b) in the deep bone compartment, the decrease of the bone calcium used for the crystallization goes together with a reduction of the exchange rates between this compartment and the central compartment (serum extracellular and soft tissues calcium). The simultaneous oral administration of 1.25 dihydroxyvitamin D3 (80 ng/kg) even though it increases significantly the calcium intestinal absorption factor does not allow the various parameters of bone calcium metabolism to stay within normal values. In spite of the arrest of osteolysis and of an strong increase of osteogenesis (superficial bone balances and alkaline phosphatases) the loss of calcium caused by cadmium in the deep bone is not compensated.

Alkaline Phosphatase↗

Cadmium binding by bacteria: screening and characterization of new isolates and mutants.

A fast and simple methodology was developed that enables screening of microbial strains for their ability to bind cadmium. It is based on the use of a radioisotope of cadmium (109Cd) for screening colonies and for evaluation of cadmium binding. The methods described here can be used to screen new environmental isolates or to obtain mutants with altered ability to bind cadmium. Examples for the two uses are described in the paper.

Bacteriological Techniques↗

Optimal conditions for identifying 80Br and 128I in health food Angelica keiskei using rapid epithermal neutron activation analysis.

This study presents an optimal rapid epithermal neutron activation analysis (ENAA) technique, using a 1mm Cd filter in reactor neutron flux, to analyze 80Br and 128I in the roots, stems, and leaves of health food Angelica keiskei (AK). Various sample weights of lichen (IAEA-336) for each portion of AK, under various periods of irradiation and counting, were used to optimize the elemental analysis. Selecting the analytical conditions depends on the minimum detectable concentration (MDC), required sensitivities and the quantitative accuracy of Br and I elements. These findings imply that the MDCs of Br and I, measured under 10min activation and 5min counting followed by 10min decaying, using 350mg of lichen are ideal for elemental analysis. Moreover, each portions of AK were analyzed under optimal conditions. The elemental concentrations of Br, Cl, I, Mg, Mn and Na and their implications are discussed.

Angelica↗

Cationic radioisotope delivery to loose connective tissue in vivo using ion-exchange resin beads.

Ion-exchange resin beads, implanted into connective tissue, were used as the vehicle for the delivery of radiolabelled cations to determine the local distribution of lead, silver and cadmium in loose connective tissue. The system was devoid of systemic toxicity, permitted a predictable release, enabled location of released cations in respect to the site of bead implantation, afforded safety and could be used with several other cations. The radiolabels released into the tissue formed an immediate relationship with inflammatory cells and a more protracted relationship with the matrix elements of the local connective tissue. The lesion induced by the presence of the bead was complicated by the particular cation.

Animals↗

In vivo K-shell X-ray fluorescence bone lead measurements in young adults.

The (109)Cd K-shell X-ray fluorescence (XRF) technique was used to measure in vivo tibia lead concentrations of 34 young adults living in the state of Vermont (USA) and the province of New Brunswick (Canada). The subjects ranged in age from 18 to 35 years, and had no known history of elevated lead exposure. Measurement parameters were varied, using the same XRF system for both populations. Tibia lead concentrations were low for both groups, with mean values of 0.7 microg lead g(-1) bone mineral (Vermont) and 0.5 microg g(-1)(New Brunswick). No individual measurement exceeded 7 microg g(-1). Mean uncertainty values obtained for the Vermont and New Brunswick subjects were 4.1 microg g(-1) and 2.6 microg g(-1), respectively. Improved measurement uncertainty in the New Brunswick group was attributed to the use of a reduced source-to-skin distance (approximately 5 mm) and a longer measurement time (3600 seconds) using a weaker radioisotope source (< or =0.42 GBq). Measurement uncertainty tended to increase with body mass index. For a given body mass index, female subjects returned a measurement uncertainty approximately 1 microg g(-1) greater than males.

Adolescent↗

Radioisotope x-ray fluorescence analysis of ancient pottery from Tel Kouzama site in Damascus, Syria.

The radioisotope X-ray fluorescence method has been utilized in the analysis of thirty nine archaeological pottery fragment samples from Tel Kouzama site, Damascus city, Syria. The samples were irradiated by a 109Cd radioisotope source (-9 10(8) Bq) for 1000 s. 17 chemical elements were determined. These elemental concentrations have been processed using two multivariate statistical methods, cluster and factor analysis in order to determine similarities and correlation between the various samples. Factor analysis confirms that samples were correctly classified by cluster analysis. These two methods suggest that samples can be considered to be manufactured using four different sources of raw material.

Archaeology↗

Identification of lead and other elements in ceramic glazes and housewares by 109Cd-induced X-ray fluorescence emission spectrometry.

Radioisotope x-ray fluorescence spectrometry was investigated as a potential screening method for Pb and other elements in housewares. Thirty-six commercial houseware items and 87 ceramic test tiles (85 fired with hobby glazes and 2 blank bisques) were examined qualitatively for the presence of Pb by using 109Cd-induced L x-ray fluorescence emission spectrometry. For the housewares, the technique provided fast, nondestructive analysis of areas with about 10 cm diameters (general regions) to about 4 mm diameters (isolated design regions). Pb was found in 25 of 28 ceramicware items, in all 8 other housewares, and in all the test-tile glazes above the limit of detection of 1 count per second (cps) for Pb L beta x-rays. For housewares, Pb identification did not always correspond to Pb leachability. For 68 test-tile glazes labeled as containing Pb (39 of which were also labeled 'dinnerware safe' or 'safe for food containers'), count rates ranged from 290 to 730 cps, whereas for the other 17 glazes labeled (with one exception) 'non-toxic,' much lower count rates (5-61 cps) were obtained. Other elements found in the housewares or test glazes were As, Au, Ca, Co, Cr, Cu, Fe, Mn, Nb, Ni, Rb, Sr, Y, Zn, and Zr.

Cadmium Radioisotopes↗

Combined treatment with a new biscarbodithioate C9G2DTC and BGDTC for mobilizing cadmium deposits in rats.

The cadmium mobilizing efficiency of a combined treatment with a novel cadmium chelating agent disodium N,N'-bis(D-glucosyl)-1,9-nonanediamine-N,N'-biscarbodithioate++ + (C9G2DTC) and with sodium N-benzyl-D-glucamine-N-carbodithioate (BGDTC) was evaluated in albino rats. They received 109Cd intraperitoneally once and 1 week later chelation therapy six times over 12 days at 2-day intervals. The treatment groups were: 1, control; 2, BGDTC six times; 3, C9G2DTC six times; 4, C9G2DTC three times followed by BGDTC three times; 5, C9G2DTC twice followed by BGDTC four times; 6, C9G2DTC once followed by BGDTC five times. The radioactivity in liver, kidney and brain was determined 19 days after 109Cd administration. Results were expressed as a percentage of the 109Cd dose and differences were analyzed by Duncan's multiple range test (P < 0.05). Treatment with C9G2DTC resulted in higher Cd reduction in the liver and lower in the kidney than with BGDTC, which is in agreement with our previous findings. Combined treatment resulted in a greater reduction of Cd in the liver and kidney than by using either chelating agent alone, irrespective of the number of C9G2DTC or BGDTC treatments, and without causing redistribution to the brain. The important aspect of this work is that C9G2DTC--the novel cadmium chelating agent which is extremely efficient in reducing Cd liver deposits and about three times more toxic than BGDTC--has to be used only once at the beginning of the treatment to obtain optimal reduction of aged organ cadmium deposits.

Animals↗

113Cd NMR and fluorescence studies of multiple binding mechanisms of Cd(II) by the Suwannee River fulvic acid.

The binding of Cd (II) by the fulvic acid from a Suwannee River (FA) was investigated at various pH values and reactants ratios by 113Cd NMR and fluorescence spectroscopy. The NMR results provided evidences that the FA-Cd interactions occur through a variety of binding modes and mechanisms. Different kinds of organically bound Cd-species were detected in the 1.8-10.8 pH range depending on the FA/Cd ratios. Labile complexes (amenable to Cd-aminoacidic and Cd-hydroxy interactions or outer-sphere complexes) were observed at low pH and FA/Cd levels while stronger interactions (of carboxylate-type or inner-sphere complexation) took place as the pH and/or the FA concentration were increased. At pH ca. 6 insoluble FA-Cd adducts were primarily produced but, at relatively large FA concentration, only soluble complexes, stable in the whole pH 1.8-10.8 range, were formed. A complementary analysis, by fluorescence spectroscopy, provided clear evidences of FA-Cd association/aggregation phenomena. While no noticeable effects occurred with soluble samples, the formation of insoluble adducts led to significant enhancements of the emission fluorescence spectra. Although other explanations could not be excluded, this result was accounted for by modifications of the optical properties of the ligand itself due to sedimentation of the heavier components. Fluorescence enhancement was also observed on samples before the effective precipitation and interpreted as spectroscopic evidence of the onset of aggregation phenomena.

Benzopyrans↗

Influence of age and time of administration of dithiocarbamate analogues on cadmium retention in rats.

In the present study the influence of age and time of chelation therapy on cadmium retention in 6-, 11-and 14-day-old rats and in 6-week-old rats has been investigated. Chelating agents N-benzyl-dithiocarboxy-D-glucamine (BDCG), sodium N-(metho-xybenzyl)-D-glucamine dithiocarbamate monohydrate (MeOBDCG) and N-methyl-N-dithiocarboxy-D-glucamine (MDCG) were administered intraperitoneally to three different groups at a dose of 1 mmol kg-1 body weight on two occasions following 115mCd intraperitoneal administration; immediately and after 24 h; after 24 h and 48 h; or after 48 h and 72 h. The 115mCd retention in the whole body and organs was determined 6 days after cadmium administration. Chelation therapy very effectively reduced cadmium retention in the whole body and organs, MeOBDCG being the most effective. The effects of chelating agents were significantly more pronounced in older than younger animals and in the case of early rather than late administration. The highest fraction of cadmium administered was retained in the liver, where also the strongest effect of chelation therapy was observed. Mobilized cadmium was excreted almost exclusively by the faecal route.

Aging↗

Indirect and lactation-associated changes in renal alkaline phosphatase of newborn rats prenatally exposed to cadmium chloride.

Pregnant Sprague-Dawley rats were intraperitoneally injected with physiological saline solution (vehicle) or cadmium chloride (CdCl2) at 2.5 mg kg-1 body wt. on days 8, 10, 12 and 14 of gestation. Offspring were examined for renal alkaline phosphatase activity (ALP) on postnatal days (PND) 3 and 12, and for kidney metallothionein (MTh) and for liver, kidney and entire gastrointestinal tract 109Cd content at birth and on PND 3 and 12. No effects were observed on neonatal survival or on body, liver and kidney weights of pups up to PND 12. Newborns born and fed by mothers exposed to CdCl2 during pregnancy exhibited a significant decrease in ALP activity on PND 3. Conversely, no significant changes were observed in newborns lactated by surrogate non-treated mothers. Renal MTh increased with age but was not influenced by maternal treatment. Traces of 109Cd were present in the liver at birth (5-7 ng). Thereafter, 109Cd was mainly found in the gastrointestinal tract of newborns lactated by their biological mothers (610-690 ng on PND 12), with a marginal uptake in the liver (10-12 ng on PND 12). 109Cd was not detectable in the kidneys at any age (less than 4 ng). These results show that prenatal exposure to Cd cannot be the sole aetiological agent in the induction of the subtle and transitory changes in renal biochemistry observed in offspring born and fed by female rats intraperitoneally injected with 2.5 mg CdCl2 kg-1 body wt. on days 8, 10, 12 and 14 of gestation. The results also contradict the role of a direct effect on the kidney.

Alkaline Phosphatase↗

Quantification of oxidized metallothionein in biological material by a Cd saturation method.

A rapid and easy to perform method for determining oxidized metallothionein (MT) is described. The main features of the procedure are that oxidized MT is converted into native MT with 2-mercaptoethanol as reducing agent and Zn2+ as metal donor, and MT is subsequently quantified via Cd saturation. The procedure was effective in recovering MT oxidized either by Cu2+ or by neutralization of apothionein at pH 3, independent of the amount of MT, the origin of sample, degree of oxidation, and oxidation method. As demonstrated by HPLC analysis, the method is highly specific for MT. The described procedure provides information on both the total concentration of MT independent of its thiol redox state and the metal binding capacity of the protein; thus, it is of particular interest in studying the role of MT in metal metabolism and toxicity.

Animals↗

Evidence for cadmium uptake through Nramp2: metal speciation studies with Caco-2 cells.

The specific uptake of 0.3 microM (109)Cd by the TC7 clone of the human enterocytic-like Caco-2 cells increased 4-fold as the pH(out) was lowered from 7.5 to 5.5; the stimulatory effect of acidic media being more pronounced when the level of the free ion (109)Cd(2+), relative to total (109)Cd, was increased. The initial uptake rate was 12-fold higher under conditions, optimizing (109)Cd(2+) accumulation over that of (109)CdCl(2-n)(n) (NO(-)(3)/pH(out) 5.5); a saturable system of transport has been characterized (K(m) = 1.1 +/- 0.1 microM, V(max) = 87 +/- 3 pmol/3 min/mg protein). An excess of Fe(2+) failed to affect (109)Cd uptake when the pH(out) was 7.4, whereas a strong inhibition was observed under NO(-)(3)/pH(out) 5.5 conditions. In contrast, the maximal inhibitory effect of Zn(2+) was observed under Cl(-)/pH(out) 7.4 conditions. This results strongly suggest that Fe(2+) may compete with Cd(2+) for Nramp2, whereas Zn and CdCl(2-n)(n) compete for another system of transport that has yet to be identified.

Acids↗