水溶性羧甲基壳聚糖对Cd2+的解吸行为研究

为改善壳聚糖(CTS)的水溶性及对重金属的配位能力,合成水溶性好并能与重金属形成配位作用的水溶性羧甲基壳聚糖(WSCC),研究了WSCC对镉的增溶、解吸行为,考察了pH、离子强度、有机质含量和WSCC初始浓度对镉的解吸影响。结果表明:WSCC对碳酸镉的增溶效果显著,当其质量浓度为2g/L时溶液中Cd2+可达到275mg/L;WSCC对镉解吸能力随着土壤中有机质含量的增加而降低,pH的升高、离子强度的增加和WSCC初始浓度的增加有利于镉的解吸;WSCC对镉污染土壤的解吸更符合准二级动力学方程,该静态解吸研究可以为镉污染土壤的修复提供基础信息及依据。     

Speciation and mobility of cadmium in straw and wood combustion fly ash

Two fly ashes from biomass combustion have been analysed regarding cadmium speciation and mobility. A fly ash from straw combustion contained 10 mg Cd/kg dry matter, and around 50% of the cadmium was leachable in water. The possible main speciation of cadmium in this fly ash was CdCl2. When adding this fly ash to agricultural soil a threat for groundwater contamination and plant uptake is existing. A fly ash from wood chip combustion had 28.6 mg Cd/kg dry matter. In this fly ash, the cadmium was bound more heavily, with only small amounts of cadmium leached in mild extractants. A possible speciation of cadmium in this fly ash was as oxide or as CdSiO3. Long-term effects and accumulation of cadmium could be a problem when adding this fly ash to agricultural or forest soils.     

镉胁迫对向日葵幼苗生长和生理特性的影响

采用溶液培养方法,研究了不同浓度镉(0、0.05、0.1、0.5和1 mg/L)处理7 d对向日葵幼苗生长和生理特性的影响。结果表明：随着镉处理浓度的增加,向日葵幼苗对镉的吸收显著增加。1 mg/L镉浓度处理时,叶、茎和根中镉浓度分别为0.05 mg/L镉处理时的16.3、19.2和581倍;根中积累的镉含量明显高于叶和茎, 各浓度根部积累的镉分别为叶和茎的37.8～63倍和29.4～41倍。镉胁迫显著抑制向日葵幼苗生长和叶绿素合成,当镉浓度达1 mg/L时,整株植物生物量和总叶绿素含量分别为对照的55.9%和52.6%。镉胁迫下向日葵幼苗游离脯氨酸和丙二醛（MDA）含量显著增加,1 mg/L镉浓度时,根中含量分别为对照的4和5.8倍。向日葵幼苗可溶性蛋白含量和过氧化物酶(POD)活性变化与镉胁迫浓度呈明显的倒U字型关系,可溶性蛋白含量在0.05 mg/L镉浓度时达到最大值,叶、茎、根中的POD活性分别在0.1、0.1和0.05 mg/L镉浓度时达到最大值。     

Desorption of copper and cadmium from soils enhanced by organic acids

The adsorption/desorption behavior of copper and cadmium on soils was investigated in this study. The adsorption isotherm of copper and cadmium conformed to Langmuir equation better than Freundlich equation. The effect of ionic strength, pH, and organic acid, including ethylenediamine tetraacetic disodium acid salt (EDTA), citric acid, oxalic acid and tartaric acid, on the desorption of copper and cadmium was studied. The desorption of copper and cadmium increased with the increase of ionic strength, while the desorption decreased with the rise of pH. The desorption of copper and cadmium enhanced by organic acids was influenced by pH. EDTA showed excellent enhancement on the desorption of both copper and cadmium; citric acid demonstrated great enhancement on the desorption of copper but negligible enhancement on the desorption of cadmium; oxalic acid enhanced the desorption of copper only at pH around 6.4 and enhanced the desorption of cadmium in the pH range from 6.4 to 10.7; tartaric acid slightly enhanced the desorption of copper but negligibly enhanced the desorption of cadmium. The desorption mechanism in the presence of organic acids were explained as the competition of complexation, adsorption and precipitation. The net effect determined the desorption efficiency. This study provided guidance for the selection of organic acids to enhance the electrokinetic (EK) remediation of copper and cadmium from contaminated soils.     

Phytoremediation potential of Spirulina (Arthrospira) platensis: biosorption and toxicity studies of cadmium

This study examines the possibility of using Spirulina (Arthrospira) platensis TISTR 8217 to remove low concentrations of cadmium (less than 100 mg/l) from wastewater. The cyanobacteria were exposed to six different cadmium concentrations for 96 h, and the growth rate was determined using an optical density at 560 nm. The inhibiting concentration (IC50) was estimated using probit analysis. The IC50 at 24, 48, 72, and 96 h were 13.15, 16.68, 17.28, and 18.35 mg/l Cd, respectively. Cellular damage was studied under a light microscope and a transmission electron microscope. Swollen cells and fragmented filaments were observed. Cell injury increased with increasing concentrations of cadmium. Ultrastructural changes were observed in the algae exposed to cadmium concentrations both close to IC50 (14.68 mg/l) and at IC50 (18.35 mg/l). The alterations induced by cadmium were disintegration and disorganization of thylakoid membranes, presence of large intrathylakoidal space, increase of polyphosphate bodies, and cell lysis. In addition, the cadmium adsorption by algal cells was studied. Environmental factors were found to have an effect on biosorption. The uptake of cadmium was not affected by the temperature of the solution, but the sorption was pH dependent. The optimum pH for biosorption of algal cells was 7. The cadmium uptake process was rapid, with 78% of metal sorption completed within 5 min. The sorption data fit well to the Langmuir isotherm. The maximum adsorption capacity for S. platensis was 98.04 mg Cd per g biomass.     

Variation in the development of cadmium resistance in Daphnia magna straus; effect of temperature, nutrition, age and genotype

The extent to which responses to toxicants can be modified by the environment and genotype of Daphnia magna is important for interpreting the results from ecotoxicity tests. Variation in the development of cadmium resistance and its relevance for survivorship has been investigated in two genetically distinct clones of D. magna. Cadmium resistance was induced by pre-exposing daphnids to a sublethal concentration of a Cd/Zn mixture and thereafter cadmium tolerance was assessed in standard acute tests. The results showed that the ability to develop cadmium resistance is affected by temperature, but there is no consistent pattern for maternal nutrition. The age of the daphnids had no apparent effect on the development of cadmium resistance. Differences in the induction of cadmium resistance between clones were seen only under resource depression.     

Simultaneous removal of phenanthrene and cadmium from contaminated soils by saponin, a plant-derived biosurfactant

Batch experiments were conducted to evaluate the performance of saponin, a plant-derived biosurfactant, for simultaneously removing phenanthrene and cadmium from the combined contaminated soils. Results showed that phenanthrene was desorbed from the contaminated soils by saponin with the partition of phenanthrene into surfactant micelle, meanwhile cadmium was effectively removed from the contaminated soils by the complexation of cadmium with the external carboxyl groups of saponin micelle. The efficiencies of saponin for the removal of phenanthrene and cadmium from the contaminated soils were greater than that of Triton X100 and citric acid, respectively. At concentration of 3750 mg/L, saponin has a removal rate of 87.7% and 76.2% of cadmium and phenanthrene, respectively, from the combined contaminated soil. The removals of cadmium and phenanthrene from the soils were not obviously constrained each other. Thus, saponin has the potential for the removal of heavy metal and PAHs from the combined contaminated soils.     

Metabolic rate and uptake and loss of cadmium from food by the fish Noemacheilus barbatulus L. (stone loach)

Fish, Noemacheilus barbatulus (stone loach), of different body weights were used to study rates of uptake and loss of cadmium during and after dietary exposure. Fish were kept singly in a continuous-flow system, and fed tubificid worms. The worms had a range of cadmium levels, but all levels were below that needed to cause acute lethal toxicity in the fish. Body weight affected both the maintenance ration and the amount of food consumed ad libitum, but the exponent for body weight (0.78+/-0.04), relating body weight to food consumption, was unaffected by either temperature or the size of feeding ration. The cadmium content of the worms did not affect the size of the maintenance ration. Metal burden in fish changed rapidly both during and after exposure. After exposure, the cadmium burden of starved fish usually declined more rapidly than in fed fish. A 58-fold increase in cadmium content in the food produced a 28% increase of body burden in the fish, and there was no evidence for biomagnification. Maintenance ration and ration ad libitum and rates of uptake and loss of cadmium increased with temperature within the range 8-18 degrees C, but exposure to cadmium at 16 degrees C yielded a higher asymptotic body burden than either 8 degrees C or 18 degrees C. Rate constants for loss of cadmium after exposure appear to be lower than for loss during exposure. Rates of uptake and loss of cadmium vary with metabolic rate. A maximum in the rate of oxygen consumption was measured at 16 degrees C, above which the rate dropped, presumably due to stress. The exponent for body weight was unaffected by activity or temperature. Body weight of fish appeared to affect both the rates of uptake and loss of cadmium, and feeding rations and respiration to the same extent: body weight exponents were not dissimilar.     

Cadmium availability to the cyanobacterium Synechocystis aquatilis in solutions containing chloride

Availability of cadmium to Synechocystis aquatilis (estimated by 109Cd sorption and cadmium toxicity-14C method) in solutions containing cadmium and complexing (KCl) or non-complexing (KNO3) salts, in the range of 0-0.5 m was investigated. Both cadmium surface adsorption and transport into the cells were lower in solutions containing cadmium chloride complexes (CdCl+, CdCl2, CdCl3-) than in those containing cadmium in the form of Cd2+. Also, cadmium toxicity in solutions of higher KCl concentrations, in which CdCl+ and CdCl2 forms predominated, was significantly limited.     

Cadmium as a possible cause of bladder cancer: a review of accumulated evidence

Bladder cancer is a significant disease, the rates of which have increased over the few last years. However, its etiology remains as yet undefined. Cadmium, a widespread environmental carcinogen that has received considerable interest, presents evidence as a possible cause of bladder cancer. A literature review was conducted from the years 1984–2013 to study the accumulated evidence for cadmium as a possible cause of bladder cancer, including routes of cadmium exposure, accumulation, toxicity, carcinogenicity, and evidence from epidemiological and experimental studies. Special reference is devoted to cadmium nephrotoxicity, which illustrates how cadmium exerts its effects on the transitional epithelium of the urinary tract. Mechanisms of carcinogenesis are discussed. The effects of cadmium on gene expression in urothelial cells exposed to cadmium are also addressed. Despite different methodologies, several epidemiologic and nephrotoxicity studies of cadmium indicate that occupational exposure to cadmium is associated with increased risk of bladder cancer and provide additional evidence that cadmium is a potential toxic element in urothelial cells. In vitro studies provide further evidence that cadmium is involved in urothelial carcinogenesis. Animal studies encounter several problems such as morphology differences between species. Among the complex mechanisms of cadmium carcinogenesis, gene expression deregulation is the subject of recent studies on bladder cadmium-induced carcinogenesis. Further research, however, will be required to promise a better understanding of the mechanisms underlying cadmium carcinogenesis and to establish the precise role of cadmium in this important malignancy.     

Sources and fates of lead and cadmium in municipal solid waste

Lead and cadmium enter the municipal solid waste stream as components of a variety of consumer products. Average empirical data from several resource recovery plants were analyzed to obtain an estimate of the source and fate of the subject elements. The total amounts of lead and cadmium found in municipal solid waste, determined from empirical data sources, were found to agree closely with those based on materials flow data. It was determined that most of the cadmium enters the waste stream in the combustible fraction and can account for a major share of the cadmium observed in fly ash and in atmospheric particulates. The most likely sources of cadmium are plastics and pigments. The lead emissions appeared to be derived from both combustible and noncombustible discards of batteries, plastics, and pigments. The data suggests that it would be useful to perform mass balance studies to provide primary data for the determination of the most effective methods for managing discards containing lead and cadmium. The purpose of the suggested research is the reduction of lead and cadmium emissions into the environment from resource recovery plants.     

Cadmium background content in meat,liver and kidney from cattle and its consequences to cadmium tolerance levels (x)

The natural background of cadmium content in meat, liver and kidney from 287 cattle from a non polluted area in the subalpine region of Bavaria has been analyzed during the period from 1972 to 1975. The cadmium content in meat was always below the detection limit of 0.005, in liver between < 0.005 to 1.65 (median 0.050) and in kidney 0.008 to 1.95 (median 0.229) ppm Cadmium in fresh weight. The cadmium contents are discussed and compared with preliminary suggestions for cadmium tolerance levels and their consequence for food inspection.     

Physiological mechanism of plant roots exposed to cadmium

Physiological experiments on plant roots exposed to cadmium were conducted on carrot and radish using a liquid culture and a pot experiment with a series of cadmium applications. Activities of four enzymes (catalase, peroxidase, polyphenol oxidase, superoxide dismutase), and concentrations of free proline and malonaldehyde in the roots of both plants were investigated. Results showed that the germination rate and growth of roots of both plants were inhibited at the concentration of 20 mg Cd/l, and the inhibition was increased with the increasing concentrations of cadmium, both in the liquid culture and in the pot experiment; activities of the four enzymes declined similarly in both species. The concentration of proline in roots reached the maximum when the application of cadmium was at the level of 20 mg/l in the liquid culture (or 20 mg/kg in soil), and then it declined slowly with the increasing concentration of cadmium. However, the reverse trend was observed for the concentration of malonaldehyde. All of bio-indicators measured here was quite sensitive to the addition of cadmium.     

Dual-continuum analysis of a cadmium tracer field experiment

Cadmium penetration into a sandy-loam soil during the field ponded infiltration at Kralovska luka site in Southern Slovakia was observed in a controlled experiment. Adsorption of cadmium was examined using the radioactive tracer techniques in laboratory batch tests. Quite deep (115m)Cd penetration during the field experiment (65 cm beneath the soil surface) gives evidence of the particle-facilitated transport of cadmium through preferential pathways. More than 40% of the applied cadmium moved deeper than 10 cm. The field experiment was analyzed using both conventional single-continuum approach (based on Richards' equation for water flow and advection-dispersion equation for Cd transport) and dual-continuum approach. The latter approach allowed us to simulate more adequately the observed movement of cadmium.     

Accumulation and egestion of dietary copper and cadmium by the grasshopper Locusta migratoria R & F (Orthoptera: Acrididae)

Copper and cadmium budgets were studied for a model insect herbivore/host plant system comprising the oligophagous leaf-chewing grasshopper (Locusta migratoria) feeding on Zea mays (Gramineae). Fifth instar larvae were fed, for between 5 and 20 days, on maize foliage contaminated with either copper, cadmium or on control foliage containing no excess metal. Male and female locusts fed on copper-treated maize retained 45 and 42% of ingested copper respectively, figures not significantly different from the 41 and 33% retained on untreated maize. Remaining copper was egested with the faeces. Locusts fed on copper-treated maize showed an increase of 27% in body copper burden compared with those on the control diet: the increase was independent of time on the diet. Female locusts retained 33% and males 21% of ingested cadmium. Faecal cadmium levels were elevated, and accumulation in both sexes was proportional to time on the Cd-enriched diet. For both copper and cadmium, some ingested metal probably passed directly through the locust gut, bound to undigested food material. Results suggest that grasshoppers may effectively regulate excess dietary copper, but are unable efficiently to regulate cadmium.     

Effect of cadmium on ATPase activities in rats fed on iron-deficient and sufficient diets

Male Sprague-Dawley rats were fed on different levels of cadmium mixed with purified diets containing iron or no iron for 8 weeks. The body weight gain, tissue weights, hemoglobin, hematocrit, liver and brain ATPase were measured at 2, 4 and 8 weeks after feeding. The hemoglobin and hematocrit values were the same in all rats fed on cadmium. The rats fed on iron-deficient diets mixed with cadmium showed a significant decrease in body weight gain. However, the rats receiving only the 100 ppm of cadmium in iron-sufficient diet showed a significant decrease in body weight gain. There were no significant changes in the weights of thymus, spleen, kidney, heart, brain and testes. However, the liver weights were decreased in the highest treatment of cadmium but the liver weight/body ratios were uneffected. Na+-K+ activated ATPase activity in brains of rats fed on cadmium were significantly decreased at 2, 4 and 8 weeks of treatment. The decrease was more pronounced in rats fed on iron-deficient diets. Oligomycin-sensitive (Mitochondrial) Mg2+ ATPase activity was also significantly decreased in liver and brain tissues of rats fed on cadmium. Oligomycin-insensitive Mg2+ ATPase activity, however, was not altered in any tissues tested. It appears that cadmium may be interfering with energy (ATP) production and utilization processes in rat brain and liver tissues.     

Bioconcentration of cadmium in water hyacinth (Eichhornia crassipes) in relation to thiol group content

To study the bioconcentration of cadmium in water hyacinth, the plants were exposed to water containing 2 microg Cd2+/ml for extended periods of time. Three strains from several exposures during a 30-day period were sampled for the analyses of cadmium and thiol group. The data showed that the plant concentrates cadmium mainly in the roots and that the cadmium uptake is proportional to the increase of the thiol group content. The latter suggests the possibility of using the thiol group content to assess the bioconcentration of heavy metal ions in water hyacinth and as a general parameter for monitoring the heavy metal pollution of water. A simple two-compartmental model was used to simulate the kinetics of cadmium uptake. The calculated bioconcentration factor matches the one derived directly from experimental data, indicating the adequacy of the model.     

Cadmium concentration and distribution in corn (Zea mays L.) grown on a calcareous soil for three years after three annual sludge applications.

The disposal of digested sewage sludge on crop-producing land appeals to municipalities as an option but may pose a hazard to human and animal health if the plant material contains elevated levels of some heavy metals. This paper reports the levels of cadmium in corn grain and stover for six years -- three years with sludge applied annually and for three years after sludge applications were terminated. The cadmium concentration in corn grain from the sixth year was similar to values found in corn grown on non-sludged plots. In corn stover from treated plots the cadmium concentration was greater than from untreated plots. Our study indicated that phytotoxic levels of cadmium did not exist even though elevated levels occurred in the corn stover.     

Single and double metallothionein knockout in the nematode C. elegans reveals cadmium dependent and independent toxic effects on life history traits

The genome of the nematode Caenorhabditis elegans contains two metallothionein genes, both involved in metal homeostasis and/or detoxification. Single metallothionein knockout mutants have been created and now, for the first time, a double mutant has been isolated. Life history studies in the presence or absence of cadmium showed that all metallothionein mutants are viable. Although cadmium did not influence longevity, a dose dependent reduction in total brood size and volumetric growth was observed in wild type animals, which was magnified in single knockouts and further exacerbated in the double knockout. However, the metallothionein deletion caused two effects that are independent of cadmium exposure, namely all knockout strains displayed a reduced total brood size and the deletion of both metallothionein loci caused a significant reduction in volumetric growth. In summary, metallothionein is undoubtedly an important player in cadmium detoxification, but evidently also an important factor in cadmium independent pathways.     

The current status of osteoporosis after 15 years of reduced cadmium exposure among residents living in cadmium-contaminated areas in northwestern Thailand

The purposes of this study were to determine the prevalence of osteoporosis after 15 years of reduced cadmium exposure and to determine the association between urinary cadmium (U-Cd) and osteoporosis. The study was conducted with 937 participants (109 males, 828 females) living in a cadmium-contaminated area in northwestern Thailand. All participants were required to respond to a questionnaire. Bone mineral density (BMD) was investigated by measurements taken at the calcaneus by dual-energy X-ray absorptiometry. U-Cd, which reflects the amount of cadmium contained in the body, was measured by atomic absorption spectrophotometry (AAS). The geometric mean of U-Cd was significantly higher in males than in females (p < 0.001). The mean level of BMD for females was found to be statistically significantly lower than that for males (p < 0.001). Increasing U-Cd levels were correlated with decreasing levels of BMD. The association between U-Cd and osteoporosis appeared to exist only at concentrations of U-Cd ≥ 10 μg/g creatinine (OR = 2.7, 95% CI = 1.2–5.9). It can be concluded that despite discontinued or reduced cadmium exposure for more than 10 years, the effect of cadmium toxicity on bone, which is stronger in women, continues, as cadmium, once absorbed, will accumulate in the human body for a long time due to its extremely long half-life.