Metallothionein induction in mice by CCL4: Hepatic Zn‐status and distribution of administered Cd∗

Induction of metallothionein (MT), Zn status and the subcellular distribution of administered Cd were studied in liver after single administration of CC1₄ to mice. Hepatic MT was increased up to 153±16 μMT/g liver 18 h after injection of 2ml CCl₄/kg body weight. The observed decrease in Zn bound to cytosolic high molecular weight proteins from 25.5 ± 0.6 to 19.8±1.1 resp. 19.0 ± 1.7 μgZn/g and the increase in MT bound Zn from 4.0±0.5 to 9.5 ± 1.1 resp. 10.9±1.1 μgZn/g compensate each other.

Zn content of whole liver and hepatic cytosol remained unchanged. Hepatic subcellular distribution of 4 mg Cd/kg body weight, administered 2 h prior termination was also influenced by CC1₄. Cd bound to high molecular weight proteins decreased from 10.0±1.0 to 7.2±1.6 resp. 3.7 ± 2.6 μg Cd/g and Cd bound to MT increased from 12.5 ± 1.4 to 18.0 ± 3.8 resp. 23.1± 6.4 μgCd/g. Cd content of both, whole liver and cytosol was not significantly different from control. The induction of MT has been suggested to be beneficial due to its role in the sequestration of toxic metals. The depletion of Zn from cytosolic high molecular weight proteins however might adversively influence essential physiological processes.     

The cadmium adsorption capacity of contaminated marine sediments from Hong Kong

The binding capacity of Cd to the sediment particles determines the potential of Cd release from the sediments. An experiment was performed to evaluate the adsorption of Cd by contaminated sediments collected from three different locations in Hong Kong, i.e. Kwun Tong, North Point and Nam Tam Wan, having different degrees of pollution. Langmuir and Freundlich equations were used to evaluate the adsorption of Cd by the sediments. Adsorption isotherms obtained from the Freudlich and Langmuir equations were generally linear and the adsorption of Cd by the sediments was significantly correlated with the adsorption maximum and binding energy constant of the Langmuir equation, and equilibrium partition constant of the Freundlich equation. All sediments had a high Cd adsorption capacity and the highly organic contaminated sediments from Kwun Tong had the highest adsorption capacity of 24,272 mg kg^‐1 at pH8. The adsorption of Cd for all sediments increased with a rise in pH of the equilibrium solution and the total organic carbon content of the sediments. Therefore, a change in the sediment chemical equilibrium is likely to reduce the binding capacity.     

Project Tocoen. the fate of selected pollutants in the environment. Part XIX. the phytotoxicity of organic and inorganic pollutants‐cadmium. The effect of cadmium on the growth of germinating maize plants

The effect of increasing cadmium concentration (10, 100 and 1000 μmol dm^‐3) on the growth, leaf area, content of assimilation pigments, cadmium content and the regulatory ability of the tissue of maize plants was investigated.

The results obtained document, already after 6 days, a significant decrease of dry weight, reduction of leaf area, chlorophyll a and b as well as carotenoids in plants grown in the nutrient solution containing 1000 μmol dm ^‐3 of cadmium. A highly significant inhibition of growth, leaf area and assimilation pigments in plants growing in the nutrient solutions with 100 and 10 μmol dm^‐3 of cadmium was registered after 17 days of cultivation. In plants growing in the nutrient solution containing 100 μmol dm^‐3 of cadmium a demonstrable reduction of the content of assimilation pigments was registered after 11 days of culture.

With increasing cadmium concentration in the nutrient solution as well as in the plant tissue after 6 and 17 days of culture both the range of the regulatory zone and the extent of optimum pH increased into the acid region. The pH values of the isoelectric point decreased with increasing cadmium content in the solution.     

Determination of traces of fluorine,chlorine, bromine,cadmium and lead in plastic materials

This paper describes the quantitative determination of F, Cl, Br, Cd and Pb in plastic materials. The concentration of the elements Cl, Br, Cd and Pb is first semiquantitatively measured by X‐ray fluorescence spectrometry (XRF) directly in the solid sample with a detection limit of approximately 10 μg/g. Afterwards, F and any of the other elements which exceed the limit values for materials which are disposable without special precautions are measured after the digestion of the material. The samples are digested either under pressure in an oxygen atmosphere for F, Cl and Br or under pressure with nitric acid for Cd and Pb. The digestion converts the halides to the anions which are measured potentiometrically (F^‐, Br^‐) or with ion chromatography (Cl^‐). Cd and Pb are measured by graphite furnace atomic absorption spectrometry (GF‐AAS). The determination limits achieved are 20 μg/g for F and Br, 250 μg/g for Cl, 0.01 μg/g for Cd and 0.2 μg/g for Pb, all below the limit values set by current regulations in Switzerland.     

大型海藻对重金属镉、铜的富集动力学研究

以人工培育的龙须菜(Gracilaria lemaneiformis)活体为实验材料,在低浓度Cu2+、Cd2+污染水体中,进行龙须菜对Cu、Cd富集的模拟实验,探索龙须菜对Cu、Cd的污染水体的修复,以及龙须菜食品的安全性.应用两箱动力学模型,对实验结果进行了曲线拟合,对拟合优度进行检验.结果表明,在本实验条件下,龙须菜对重金属Cu、Cd的生物累积符合两箱动力学模型,并获得龙须菜富集Cu、Cd的吸收速率常数(Ku)和排出速率常数(Kc).当Cu2+的浓度￡50mg/L、Cd2+的浓度￡20mg/L时,经过28 d的暴露,随Cu2+、Cd2+的暴露浓度以及暴露时间增大,龙须菜中Cu、Cd的含量升高.龙须菜对Cu、Cd的吸收速率常数分别为15.4~51.1和13.9~55.7,基本随实验水体中元素的暴露浓度升高而降低;排出速率常数分别为0.023~0.070和0.030~0.050,与暴露浓度无明显相关性.理论平衡状态下龙须菜中Cu、Cd含量(质量分数)随水体中暴露浓度升高而增加.龙须菜对Cu、Cd的生物富集因子分别为663~1008和463~1113,Cu、Cd的生物半衰期分别为23.1 d和20.1d.     

Hyperaccumulator Thlaspi caerulescens (Ganges ecotype) response to increasing levels of dissolved cadmium and zinc

Hyperaccumulation of metals by plants involves at least three processes: efficient absorption by roots, efficient root-to-shoot translocation and hypertolerance through internal detoxification. In this study, Thlaspi caerulescens was separately exposed to Cd and Zn at 0, 50, 100 and 200 μ M for 7 d to monitor plant responses in hydroponics. Significant dose-dependent accumulation was observed for both metals, mainly in roots (up to 3.2 and 9.2 mg g ^?1 for Cd and Zn, respectively). However, Cd was more phytotoxic in terms of plant growth and photosynthesis. This higher toxicity was also evidenced by MetPLATE bioassay. Root exudation was significantly correlated to Cd and Zn translocation (r>0.85) proving its involvement in facilitating metal uptake. As for antioxidative responses, plants reacted to Cd and Zn by broadly exhibiting an elevation of glutathione reductase activity before declining at 200 μ M due to higher phytotoxicity. By contrast, superoxide dismutase activity was unlikely to be affected by both metals. Root-to-shoot apoplastic flow was traced using a fluorescent dye (trisodium-8-hydroxy-1,3,6-pyrenetrisulfonic acid; PTS), whose concentration in leaves increased to a certain extent with Cd and Zn accumulation, indicating that heavy metals have a comparable effect to drought or salinity in promoting the passive diffusion of water and solutes. Nevertheless, Cd at 200 μ M hindered the diffusion of PTS and consequently affected the apoplastic transport in plants.     

Rice seedlings under cadmium stress: effect of silicon on growth,cadmium uptake,oxidative stress,antioxidant capacity and root and leaf structures

In this study, the effect of silicon (Si) addition on cadmium (Cd) toxicity in rice seedlings was investigated. After a series of screening experiments, 50 μmol·L^?1 of Cd and 10 μ mol·L^?1 of Si were selected. Treatment of rice seedlings with Cd (50 μ mol·L^?1) resulted in significant accumulation of this metal in roots and shoots. The data revealed that accumulation of Cd resulted in oxidative stress in rice seedlings as evidenced by increased accumulation of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA; a peroxidation product of lipids). However, addition of Si (10 μ mol·L^?1) together with Cd prevented accumulation of Cd, H₂O₂ and MDA. Antioxidant capacity was decreased by Cd but enhanced by Si addition. Cd decreased the length and frequency of root hairs, stomatal frequency, and distorted leaf mesophyll cells and vascular bundles. However, addition of Si together with Cd reduced these abnormalities. The results showed that addition of exogenous Si protected rice seedlings against Cd toxicity by preventing Cd accumulation and oxidative stress (H₂O₂ and MDA accumulation) by increasing Si accumulation and antioxidant capacity, which maintained the structure and integrity of leaf and root.     

Dispersive liquid–liquid microextraction of cadmium(II) for preconcentration prior to flame atomic absorption spectrometric detection in water

A dispersive liquid–liquid microextraction procedure for cadmium(II) as its 2-(5-bromo-2-pyridylazo)-5-diethylamino-phenol chelate is presented. Carbon tetrachloride and methanol were used as extraction and dispersive solvents, respectively. After phase separation, the preconcentrated-separated cadmium(II) is determined by flame atomic absorption spectrometry with a microinjection technique. The factors which affected the extraction efficiency, i.e. the pH of the sample solution and the volumes of reagent and sample were investigated. The effects of some alkali, alkali earth, and transition metal ions, and of some anions on the recovery of cadmium were also studied. A preconcentration factor of 250 was obtained for a sample volume of 50?mL under optimum conditions. The method was validated by analysis of certified reference materials and applied to some water samples from Turkey.     

Interrelation of Cd‐lon concentrations and the growth and activities of microorganisms in two growth media†

Partitioning of native or anthropogenic heavy metals in solid and solution phases of soil is a result of network of several physico‐chemical reactions. The attainment of equilibrium between two phases is also regulated by biochemical processes. For practical purposes, the bioavailability of metal present in soil is predominantly regulated by the soil solution phase which is in dynamic equilibrium with the solid phase. The results of a model laboratory and greenhouse growth experiments have been used to investigate the effect of Cd‐ion concentrations (either in soil solution or in nutrient solution) on the growth and activities of microorganisms. The soil solution has been simulated by preparing a suspension of soil with 0.1 M NaNO₃ (1: 2.5) equilibrated for two hours. Important conclusions are as follows:

Increase in Cd‐ion concentration in soil solution or in nutrient solution induces corresponding adverse effect on the growth and activities of microorganisms. Thus, it seems that Cd‐ion concentration is a more sensitive indicator for assessing the effect of metal pollution upon the growth and activities of soil microorganisms in comparison to total Cd contents.

During active microbial growth phase, a large part of the organically bound Cd was released in the soil solution which is largely bioavailable. This process is termed as mobilisation. There was momentary increase of Cd‐ion concentration in soil solution which intoxicated the growing organisms. After this stage, the Cd ions from the solution phase were removed by the newly formed solid phase (nonviable biomass) and were transformed in non‐available form. This process is termed as immobilisation.

The consequences and importance of these results for practical agriculture and in deciding the limits or guidelines on the maximum tolerable metal load in soils are discussed.