Release Of Cd Research Articles

Biochemical mechanism of metallothionein-carbon tetrachloride interaction in vitro

To elucidate the mechanism underlying the protective effect of metallothionein (MT) against carbon tetrachloride (CCl 4) toxicity, in vitro experiments were carried out to study the interaction of metallothionein and CCl 4. Results from this study showed that incubation of Cd,Zn-MT with (CCl 4)in the presence of hepatic microsomes and NADPH resulted in a time-dependent depletion of MT thiols with a concurrent reduction in the metal-binding sites of the protein. Moreover, this reaction also released Zn and Cd from MT. Results from experiments conducted to determine whether or not the CCl 4-induced decrease in MT-thiol content was due to the scavenging of (CCl 4)metabolite(s) showed that the trichloromethyl radical, chloroform and phosgene as well as the products of (CCl 4)-induced microsomal lipid peroxidation were not directly involved. Although covalent binding of 14(CCl 4)to MT was detected following incubation in the presence of a microsomal bioactivation system, it did not account for the CCl 4-induced loss of MT thiol groups for the following reasons: (i) prior oxidation of sulfhydryl groups of MT by hydrogen peroxide did not alter the binding; and (ii) anaerobiosis did not alter the extent of covalent binding but obliterated the inhibitory effect of (CCl 4)on MT thiol content. Measurement of the thiol content of CCl 4-treated MT after treatment with 1,4-dithiothreitol revealed that all the thiol groups that were lost subsequent to CCl 4treatment could be regenerated. These data suggest that CCl 4-linked oxidation of MT, rather than the covalent binding of 14CCl 4metabolite(s), may be responsible for the CCl 4-induced loss of metal binding sites of MT with the concurrent release of Zn and Cd. However, the precise role of the metal released during the oxidation of MT in CCl 4 toxicity remains to be defined.

Environmental levels of cadmium and lead in the vicinity of a major refuse incinerator

This study examines whether the atmospheric release of Cd and Pb from a refuse incinerator in London has caused contamination of the local environment. Sampling networks were established for street dusts, surface soils, vegetation and total deposit gauges in areas up to 5 km downwind and upwind from the incinerator. Measurements of Cd and Pb indicate there is neither a marked nor an extensive contamination by these metals in the downwind area. However, dust Cd values decreased with distance from the incinerator in this area and Cd deposition rates were higher than in the upwind area. Nevertheless, most Cd values obtained in the downwind area were similar to those previously reported for other parts of London while Pb values were often lower. It is considered that the 100 m stack of the incinerator minimizes the deposition of particulate emissions in the vicinity of this source. Appreciable Cd contamination was found within the grounds of the incinerator, the values being about 4–50-fold higher than in either the upwind or downwind areas. The extent of Pb contamination in this small area was more limited, with values being about twice those found in the two study areas. The source of this contamination is ascribed to fugitive releases arising from the storage and transport of the ashes produced by the incinerator.

Microbial Mobilization of Cadmium in Soil Under Aerobic and Anaerobic Conditions

AbstractThe role of microorganisms in Cd mobilization from soils was investigated. Soils treated with Cd and washed to remove readily soluble Cd were suspended in a nutrient medium (at a ratio of 1:20 wt/v) and incubated (aerobically or anaerobically) for a period of 160 d. While no Cd was released from gamma‐irradiated sterile soils under aerobic or anaerobic conditions, a significant amount of “strongly bound” or “fixed” Cd was mobilized from nonsterile samples of all softs tested. The rate and extent of microbial Cd mobilization was dependent on the soil type, aeration, and moisture content. Among the four soils tested, Morrison sandy loam and Morrison loam soils (Ultic Hapludalfs) showed aerobically and anaerobically a greater degree and a faster rate of microbial Cd mobilization compared to Hagerstown silt loam soils (Typic Hapludaifs). In all soils but the Morrison sandy loam soil, the amount of Cd released was considerably greater under anaerobic than aerobic conditions. Although soil moisture content did not have a distinct effect in anaerobic experiments, under aerobic conditions air‐dried field soils exhibited a significantly greater rate and extent of microbial Cd mobilization than did fresh soils that had been kept moist at 5 °C. Cadmium release was much more rapid during anaerobic incubation, but upon prolonged incubation (up to 3 weeks), a continued removal of Cd from the aqueous phase occurred in anaerobic, but not the aerobic samples. In many instances, the pH of the soil suspensions decreased to an acidic level (near pH 5.5) with a concurrent release of Cd. Based on our results, mobilization of strongly bound or fixed Cd is a microbially mediated process and this is affected by soil environmental factors such as soil type, aeration, and moisture content.

The remobilization of pb and cd from contaminated dredge spoil after dumping in the marine environment

Abstract Results of batch experiments on the release of Cd and Pb from dredge spoil suspended in estuarine water of different salinity show that in contrast to other published results the cation exchange reactions have no importance for the degree of mobilization. A considerable release of Cd up to 25% was observed only in long‐term experiments. A significant Pb release could not be stated in any case. The addition of antibiotics to the system caused an interruption of the remobilization process. The results are discussed with special emphasis on the role of bacteria for the release of Cd during the decomposition of organic matter.

Effect of diet on tissue retention of cadmium heavily preaccumulated in rats.

The effects of diets on the tissue retention of preaccumulated cadmium (Cd) were examined after loading Cd to a maximum concentration in the livers of rats. Two commercially available stock diets were examined; one was a normal (basal) diet and the other (low protein diet) was prepared by replacing a portion of the protein sources with starch. The low protein diet selectively enhanced the release of Cd from the livers, while it reduced the uptake of Cd by the kidneys. Cd in the spleen increased even after the cessation of Cd loading in both diet groups and it was explained by the decrease of Cd in the RBC and liver. Significant differences in copper concentration and content in the kidneys and glutathione concentration in the liver were observed between the two diet groups of the saline-injected rats.

Formation of the metal-thiolate clusters of rat liver metallothionein.

The isoforms of rat liver apo-metallothionein (MT) were reconstituted in vitro with Cd and Zn ions to study the order of binding of the seven metal sites. Reconstitution with seven Cd ions resulted in a metalloprotein similar to induced Cd,Zn-MT by the criteria of electrophoretic mobility, insensitivity to proteolysis by subtilisin and the pH-dependent release of Cd. Proteolytic digestion of MT reconstituted with sub-optimal quantities of Cd followed by separation of Cd-containing polypeptide fragments by electrophoresis and chromatography revealed metal ion binding initially occurs in cluster A. Upon saturation of the four sites in cluster A, binding occurs in the three metal center, cluster B. Samples reconstituted with one to four Cd or Zn ions per protein molecule, followed by digestion with subtilisin, yielded increasing amounts of a proteolytically stable polypeptide fragment identical with the alpha fragment domain encompassing the four metal center. Samples renatured with five to seven Cd ions per MT molecule showed decreasing quantities of alpha fragment and increasing amounts of nativelike MT. The binding process in each domain is cooperative. Reconstitution of apo-MT with two Cd ions followed by proteolysis yields a 50% recovery of saturated Cd4-alpha cluster. Likewise, when Cd5-renatured MT was digested with subtilisin, 30% of the molecules were identified as Cd7-MT with the remainder as Cd4-alpha fragment.

Formation of the Metal-Thiolate Clusters of Rat Liver Metallothionein

The isoforms of rat liver apo-metallothionein (MT) were reconstituted in vitro with Cd and Zn ions to study the order of binding of the seven metal sites. Reconstitution with seven Cd ions resulted in a metalloprotein similar to induced Cd,Zn-MT by the criteria of electrophoretic mobility, insensitivity to proteolysis by subtilisin and the pH-dependent release of Cd. Proteolytic digestion of MT reconstituted with sub-optimal quantities of Cd followed by separation of Cd-containing polypeptide fragments by electrophoresis and chromatography revealed metal ion binding initially occurs in cluster A. Upon saturation of the four sites in cluster A, binding occurs in the three metal center, cluster B. Samples reconstituted with one to four Cd or Zn ions per protein molecule, followed by digestion with subtilisin, yielded increasing amounts of a proteolytically stable polypeptide fragment identical with the alpha fragment domain encompassing the four metal center. Samples renatured with five to seven Cd ions per MT molecule showed decreasing quantities of alpha fragment and increasing amounts of nativelike MT. The binding process in each domain is cooperative. Reconstitution of apo-MT with two Cd ions followed by proteolysis yields a 50% recovery of saturated Cd4-alpha cluster. Likewise, when Cd5-renatured MT was digested with subtilisin, 30% of the molecules were identified as Cd7-MT with the remainder as Cd4-alpha fragment.

Order of metal binding in metallothionein.

Purified isoforms of rat liver apometallothionein were reconstituted in vitro with Cd and Zn ions to study the order of binding of the 7 metal sites in the two separate metal clusters, one containing four metal ions (cluster A) and the other containing three (cluster B). Reconstitution with 7 Cd ions resulted in a metalloprotein similar to induced Cd,Zn-metallothionein by the criteria of electrophoretic mobility, insensitivity to proteolysis by subtilisin, and the pH-dependent release of Cd. Proteolytic digestion of metallothionein reconstituted with suboptimal quantities of Cd followed by separation of Cd-containing polypeptide fragments by electrophoresis and chromatography revealed metal ion binding initially occurs in the 4-metal center, cluster A. Upon saturation of the 4 sites in cluster A, binding occurs in the 3-metal center, cluster B. Samples reconstituted with 1 to 4 Cd ions per protein molecule, followed by digestion with subtilisin, yielded increasing amounts of a proteolytically stable polypeptide fragment identical with the alpha fragment domain that is known to encompass the 4-metal center. Samples renatured with 5 to 7 Cd ions per metallothionein molecule showed decreasing quantities of alpha fragment and increasing amounts of native-like metallothionein. Similar results were obtained in reconstitution studies with Zn ions. Samples reconstituted with 7 Cd eq followed by incubation with EDTA revealed that cluster B Cd ions were removed initially. The binding process in each domain is cooperative. Reconstitution of apometallothionein with 2 Cd ions followed by proteolysis yields a 50% recovery of saturated Cd4 alpha cluster. Likewise, when Cd5-renatured metallothionein was digested with subtilisin, 30% of the molecules were identified as Cd7 metallothionein with the remainder as Cd4 alpha fragment.

Sorption and Release of Cadmium by Some Sewage Sludges

AbstractSorption and release of Cd were determined in nine sewage sludges from Tuscany, Italy. The Cd adsorption data were in agreement with both the linear sorption isotherm and the Langmuir equation. The average of calculated adsorption maxima was about 50% of the mean CEC value, indicating that exchangeable cations present in the sludges were more effective in competing with the Cd ion for exchange sites. The calculated Langmuir adsorption maxima were found significantly correlated with fulvic acid C content and carboxyl and phenolic hydroxyl groups of fulvic acids.The release of Cd retained at two initial concentrations as a function of different extraction solutions was indagated. Extraction experiments showed that Cd may be held in sludges by more than one type of site and that the strength of bonding decreases as the total Cd increases. Cadmium was retained mainly by exchange and complexing sites, the former assuming a relatively more important role as cadmium adsorption increased.The effect of different exchangeable cations on the sorption of Cd by sludges was also studied. The amounts of Cd sorbed on the sludge surfaces decreased in the order: Ca‐sludge > untreated sludge > Fe‐sludge = Al‐sludge.

SOLUBILITY AND SORPTION OF CADMIUM IN SOILS AMENDED WITH SEWAGE SLUDGE

SummaryThe mechanisms governing the retention and release of Cd in two soils, a loam and a loamy sand, pretreated with anaerobically digested sewage sludges or with chemical fertilizers, were studied using batch equilibration in 0.05 m Ca(NO3)2 solution containing up to 6 μg Cd/ml. Adsorption rather than precipitation as Cd3(PO4)2 limited solution Cd2+ concentration. With the addition of 50 μg Cd/g, however, precipitation as CdCO3 was likely at pH 7.6. Cadmium adsorption increased with increasing soil pH. The differences in Cd adsorption between different soil treatments were attributed mainly to the soil pH (6.9 to 7.9) induced by sludge application. About 82 to 92 per cent of adsorbed Cd was retained by cation exchange and complexing sites. Soils treated with sludge increased the amount of exchangeable Cd but reduced the amount of complexed Cd compared with the fertilized soil. Cadmium retention by cation exchange became more dominant as the amount of Cd in the soil was increased.

The effects of sodium chromate and carbon tetrachloride on the urinary excretion and tissue distribution of cadmium in cadmium-pretreated rats

Rats were administered nontoxic doses of Cd 2+ by the oral or intraperitoneal routes. They were subsequently treated with either Na 2CrO 4 (10 or 20 mg/kg, sc) or CCl 4 (0.5 or 1 ml/kg, intragastric). Evidence of renal damage was obtained from the determination in urine of total protein and amino acids and from the analysis of the urinary proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Liver damage was evaluated by determining the serum activities of sorbitol dehydrogenase and glutamate pyruvate transaminase. The effects of CCl 4 on the urinary excretion and the tissue distribution of Cd 2+ vary depending on whether liver damage is associated or not with extensive renal lesions. When renal function was not or only moderately altered, induction of liver damage by CCl 4 resulted in a transfer of Cd 2+ from the liver to the kidney. This transfer was evidenced by a decrease of total Cd 2+ as well as metallothionein-bound Cd 2+ in the liver and an increase of the same parameters in the kidney. The urinary excretion of Cd 2+ was only slightly increased. When liver damage induced by CCl 4 was associated with extensive kidney lesions, the accumulation of Cd 2+ released from the liver in the kidney was considerably reduced and large amounts of Cd 2+ were excreted in urine. Administration of Na 2CrO 4 to Cd 2+-pretreated rats gave rise to a sharp and reversible increase in the urinary excretion of Cd 2+. This increase was proportional to the amount of Cd 2+ stored in kidney and to the dose of Na 2CrO 4 administered. The Cd 2+ excreted in urine originated mainly from the kidney in which total Cd 2+ and metallothionein-bound Cd 2+ were reduced in proportion to the dose of Na 2CrO 4 administered. These results suggest that two mechanisms may lead to an increased urinary excretion of Cd 2+; a direct release of Cd 2+ into urine from damaged kidney (i.e., Na 2CrO 4) or a decreased tubular reabsorption of plasma circulating Cd 2+ evidenced when large amounts of Cd 2+ are released into blood from damaged liver (i.e., CCl 4). These results tend to support the hypothesis that kidney damage due to chronic Cd 2+ poisoning may lead to an increased loss of the Cd 2+ stored in the kidney.

The interaction of cadium-induced rat renal metallothionein with bivalent mercury in vitro

Addition of Hg 2+ in vitro to metallothionein (Cd : Cu : Zn = 6.5 : 4 : 1) from the kidneys of Cd 2+ exposed rats appears to result initially in the replacement of Zn 2+, then Cd 2+ and finally copper. The ionic stoichiometries between Hg 2+-binding and the release of Cd 2+ (or Zn 2+) and copper are 3 : 2 and 1 : 1 respectively. After treatment with amounts of Hg 2+ sufficient to displace completely either the bound Zn 2+ and Cd 2+, or all of the original cations, the metallothionein has little or no negative charge at pH 8.0 and is not resolved into the two isometallothioneins, which characterize the (Cd, Cu, Zn)-thionein, by ion exchange chromatography at this pH. Cation substitution occurs in both isometallothioneins and there is no evidence that Hg 2+ interacts preferentially with one of them. Treatment of the metallothionein with increasing amounts of Hg 2+, equivalent to approx. 25% and 50% of the bound cations gives rise to a range of molecular species of progressively decreasing negative charge. The consistent stiochiometry between Hg 2+ uptake and Cd 2+ or Zn 2+ release at all concentrations of Hg 2+ indicates that free thiol groups are not formed during the substitution reaction.

Kinetics of uptake and release of Cd by potato tissue

Abstract. The absorption of Cd by potato tissue was studied. No enhancement of the absorption capacity for Cd was observed by storage of the sliced potato tissue in aerated doubly distilled water for a period of 48 h. Cd absorption as a function of the external Cd concentration followed a typical hyperbolic isotherm. A two‐phase uptake process for the absorption of Cd was found: a rapid initial phase terminating after 30 min, was followed by a slower phase with a constant rate. Efflux, studied by means of compartmental analysis, of Cd showed three phases. The two first were shown to be extracellular in origin. The third phase, involving Cd remaining in the discs after efflux, probably involved Cd in different forms. Metabolic processes, however, did not seem to contribute to this phase.

SORPTION AND RELEASE OF CADMIUM IN SOME CANADIAN SOILS

Sorption and release of Cd was determined in 10 Canadian soils. Experimental results showed that soils exhibit large capacities to adsorb Cd; however, a major portion of adsorbed Cd was released by NaCl extraction. The amount of Cd not released by NaCl (fixed Cd) was correlated to the cation exchange capacity, pH and organic carbon content of soils. The "fixation" reactions of Cd did not have priority over adsorption reactions.

Aufnahme von Cadmium durch Chlorella fusca

Summary Labelled Cd is taken up by C. fusca by adsorption, by diffusion and by energy-dependent transport. Release of Cd from loaded cells is also possible by diffusion. Transport shows saturation kinetics with two components, one of which, however, is possibly transformed into the other by Cd allosterically. With dead cells, adsorption is faster, while energy-dependent transport is not observed. Transport of Cd and Zn inhibit each other mutually. Transport of labelled Cd is strongly enhanced by pretreatment with nonlabelled Cd. No analogous result is obtained in the case of Zn.

Leaching of Pewterware by Organic Acids

Abstract Three pewter goblets were repeatedly leached by acetic, citric, lactic, malonic, and tartaric acid solutions. The leach solutions were periodically analyzed for Pb, Cd, Cu, Bi, Sb, and Sn by atomic absorption spectrophotometry. Analysis of the leach solutions showed that, without the addition of nitric or perchloric acid to the acetic and malonic acid leach solutions, Pb precipitated from the solutions on standing. Addition of the mineral acids redissolved the precipitate. Pb, Cd, and Bi were found in higher concentrations in the leach solution than in the metal; Cu and Sb were less concentrated in the leach, while the amount of Sn was approximately equal in both. Tartaric acid solution dissolved about 9 times as much metal from the pewter as the other organic acids but removed less Pb than acetic or malonic acids. None of these samples tested exceeded the Food and Drug Administration standards for Pb or Cd release.

Trace Metals in Open Water Disposal of Dredged Material

Upon addition of sediment/seawater mixture to the seawater column, most trace metals were found to display a pattern of immediate release. These released metals were subsequently removed. The removal is gradually under reducing environments and almost immediately under oxidizing environments. The degree of release was significant for Fe, Mn, and Ni. The Cr, Cu, Pb, and Zn were moderately released. The release of Ag, Cd, and Hg was negligible. After resedimentation, the migration of trace metals between the sediment/seawater interface were found to be influenced by the redox conditions of the overlying water. In general, three patterns of metal behavior were observed: (1)The release amount increases as the redox conditions become more reducing (Fe and Mn); (2)the release amount increases as the environment becomes more oxidizing (Cd, Cu, Ni, Pb, and Zn); and (3)no significant release (Cr and Hg). The soluble metal concentrations during and after open water disposal of dredged materials were found to be in the range of sub-ppb to ppb with the exception of Fe, under reducing condition.

Release of Cadmium from Clays and Plant Uptake of Cadmium from Soil as Affected by Potassium and Calcium Amendments

AbstractThe effects of percent K and/or Ca saturations on the release of Cd from Cd‐treated H‐clays (kaolinite and illite) and on the Cd availability to plants from Cd‐treated Canfield silt loam soil were determined. The concentration of Cd in the dialyzates from both kaolinite and illite clays increased as the percent Ca or K saturation of the clays in the suspension decreased. The release of Cd from both clays was greater in the presence of Ca than K. In a separate experiment, the concentration of Cd in soybean shoots (Glycine max L. Merr.) ‘Corsoy’ decreased with increasing percent Ca or K saturation of the soil. The results indicated that Cd uptake by soybean shoots could be impaired to a great extent by K application.