Cadmium uptake by freshwater bacterial communities

Microcosm experiments in chemostat incubated at 20°C showed that cadmium contamination does not greatly affect bacterial communities in cultures contaminated with up to 1 mg Cd l⁻¹.Bacterial productivity remains unchanged and cadmium-resistant strains arise quickly and in great number. The cadmium accumulation by bacteria depends on the bacterial productivity. The free bacteria can accumulate up to 1200 ppm cadmium whereas the adhering bacteria concentrate up to 6100 ppm. At a steady state, 11–29% cadmium is removed from the water phase of cultures.     

Chromium bioaccumulation: comparison of the capacity of two floating aquatic macrophytes

The capacity of Salvinia herzogii and Pistia stratiotes to remove Cr (III) from water and their behaviour at different Cr (III) concentrations were studied in outdoor experiments. Cr distribution in aerial parts and roots with time and the possible mechanisms of Cr uptake were analyzed. Both macrophytes efficiently removed Cr from water at concentrations of 1, 2, 4 and 6 mgCrL(-1). S. herzogii was the best adapted species. At a greater initial concentration, greater bioaccumulation rates were observed. Root Cr uptake was a rapid process that was completed within the first 24h. Cr uptake through direct contact between the leaves and the solution is the main cause of the increase of Cr in the aerial parts, Cr being poorly translocated from the roots to the aerial parts. Both mechanisms were fast processes. The Cr uptake mechanism involves two components: a fast component and a slow one. The former occurs mainly due to the roots and leaves adsorption and is similar for both species. The slow component is different for each species probably because in P. stratiotes a Cr precipitation occurs induced by the roots.     

Root uptake and reduction of hexavalent chromium by aquatic macrophytes as assessed by high-resolution X-ray emission

Aquatic macrophytes Salvinia auriculata, Pistia stratiotes and Eichhornia crassipes were chosen to investigate the Cr(VI) reduced by root-based biosorption in a chromium uptake experiment, using a high-resolution XRF technique. These plants were grown in hydroponics medium supplied with non-toxic Cr concentrations during a 27-day metal uptake experiment. The high-resolution Cr-Kβ fluorescence spectra for dried root tissues and Cr reference material (100% Cr, Cr₂O₃, and CrO₃) were measured using an XRF spectrometer. For all species of aquatic plant treated with Cr(VI), the energy of the Cr-Kβ_2,5 line was shifted around 8 eV below the same spectral line identified for the Cr(VI) reference, but it was also near to the line identified for the Cr(III) reference. Moreover, there was a lack of the strong Cr-Kβ″ line assigned to the Cr(VI) reference material within the Cr(VI)-treated plant spectra, suggesting the reduction of Cr(VI) for other less toxic oxidation states of Cr. As all Cr-Kβ spectra of root tissue species were compared, the peak energies and lineshape patterns of the Cr-Kβ_2,5 line are coincident for the same aquatic plant species, when they were treated with Cr(III) and Cr(VI). Based on the experimental evidence, the Cr(VI) reduction process has happened during metal biosorption by these plants.     

Cadmium and zinc uptake by volunteer willow species and elder rooting in polluted dredged sediment disposal sites

Salix species and Sambucus nigra L. (elder) naturally invade dredged sediment landfills and are commonly encountered on substrates contaminated with heavy metals. Foliar concentrations of Cd and Zn in four Salix species and elder were explored in the field. Metal contents in dredged sediment derived soils were elevated compared to baseline concentration levels reported for Flanders. To evaluate foliar concentrations, reference data were compiled from observations in nurseries, young plantations and unpolluted sites with volunteer willow vegetation. Willows grown on polluted dredged sediment landfills showed elevated foliar Cd and Zn concentrations (>6.6 mg Cd/kg DW and >700 mg Zn/kg DW). This was not the case for elder. For willow, a significant relation was found between soil total Zn or Cd and foliar Zn or Cd, regardless of age, species, or clone. Willows proved to be useful bioindicators. Results indicated a possible threat in long-term habitat development of willow brushwood from transfer of Cd and Zn to the food web.     

Cadmium adsorption by sediment in a turbulence tank.

The mechanism sediment motion that affects cadmium (Cd) adsorption on sediment particles was studied in a turbulence tank in the presence (and absence) of bed mud. The experimental results were verified by a mathematical model for heavy metal transport-transformation developed for the turbulence tank. The mathematical model includes the equations of water flow, sediment motion, heavy metal transport-transformation, heavy-metal reaction kinematics and equations for prescribing the initial conditions and boundary conditions for the experiment. The model conforms the transport-transformation of heavy-metal pollutants in surface waters to following the law of convective-diffusive of common tracers and the characteristics of fate and transport of sediment motion. Variations of dissolved Cd concentrations and suspended particulate Cd concentrations with time and in the water column were measured and computed. The experimental measurements correspond with the computed results. Both the experimental measurements and computed results show that it takes about 6 h to reach equilibrium condition for cadmium adsorption by sediment particles. This is different from the result obtained from experiments conducted in continuously stirred tank reactors (or batch reactors) in which adsorption equilibrium can be achieved in about 20 min. Determination of the model parameters for sediment adsorption-desorption of metals in the tank is discussed. The experimental and computed results obtained in this study are useful to solve practical engineering problems in surface waters.     

Cadmium adsorption by oxic sediment

To understand the strong pH dependency of cadmium adsorption by oxic sediment, we investigated the surface charge of sediment particles by potentiometric titration with acid and base. Metal adsorbed by sediment can occur by complexation of metal ions with weakly acidic functional groups or by ion exchange of metal ions. A multi-site binding model, which incorporates the effect of pH, has been applied to describe the adsorption of cadmium onto sediment. The model has been used to satisfactorily predict the extent of adsorption over the pH range of 4.5–7.0.     

浮动绞刀的正确应用

介绍了浮动绞刀的传动特点,对传动绞刀的几种联结结构进行了比较,分析了浮动绞刀的材料,从提高真空挤出机零件的制造精度和装配精度,正确设计和制作挤出绞刀和成型系统等方面分析了如何正确应用浮动绞刀。     

自由飞翔的建筑设计

1项目简介石化专家楼位于新疆乌鲁木齐市。总建筑面积约6300m2,主要功能为接待国内外专家会议、住宿的综合性宾馆,并侧重于     

伊东丰雄的浮世观

通过对伊东丰雄建筑思想的深入剖析,阐释了伊东与现代主义建筑思想的关联,日本传统审美观、自然观对其的影响以及伊东在网络信息时代的思考,探讨了以伊东丰雄为代表的日本前卫建筑师如何在当今纷繁的建筑思潮中,延续日本传统文化的精髓。     

运河日历 漂浮的空间

京杭运河是世界开挖最早、最长的人工河道。随城市路网的密布延伸,曾经承载南北交通、市井生活的运河日渐萧条。古老的运河如何在新兴城市中存活？承载着历史印记与文化传统的运河如何重新定义？     

Platinum uptake by the freshwater isopod Asellus aquaticus in urban rivers.

Platinum has been increasing in the environment as a result of emissions from catalytic converters. The platinum emitted is principally located in the vicinity of roads but might be transported to urban rivers through highway and urban run-off water. Platinum concentrations in the freshwater isopod Asellus aquaticus were measured for two urban rivers and a stormwater detention pond. Concentrations ranged from 0.04 to 12.4 micrograms g-1 for direct analysis and from 0.16 to 4.5 micrograms g-1 after depuration. Analyses of water, pore water and sediments indicate that platinum in urban rivers is mostly found in the sediments and these provide the major contribution of platinum to Asellus aquaticus. Exposure experiments showed the importance of platinum speciation for uptake.     

Retrospective analysis of an archived soil collection. II. Cadmium

Soil samples collected and stored since the mid-1800s to the present day have been analysed recently for Cd. The samples from long-term experiments under permanent grassland or arable crops at Rothamsted Experimental Station (U.K.) were selected to investigate time trends in elemental composition, due either solely to atmospheric deposition or to a combination of atmospheric deposition and various soil treatments. Increases in soil Cd of 27-55% since the 1850s due to atmospheric deposition were observed. This corresponds to an increase in the soil plough layer Cd concentration of between 0.7 and 1.9 micrograms kg-1 year-1 and is equivalent to an increase of 1.9-5.4 g Cd ha-1 year-1. The changes in soil Cd concentrations since 1846 at one control site corresponded well to predicted increases in the plough layer Cd burden based on assumptions about the temporal trends in atmospheric Cd emissions. In addition, sub-samples of a selection of rock phosphates of known origin and superphosphates, mainly from one supplier, collected and stored in the archive from 1925 onwards were also analysed for Cd. The concentrations ranged from 3.6 to 92 (mean 36) mg Cd kg-1 for rock phosphates and from 3.3 to 40 (9.7) mg kg-1 for superphosphates. On the basis of these data and known application rates the estimated input of Cd to P-treated plots at Rothamsted was 2 g ha-1 year-1, but there was little further increase in soil Cd due to this addition in three long-term arable experiments where soil pH was greater than 6.5. On P-treated plots the mean increase in soil Cd was 1.2 micrograms kg-1 year-1, which is equivalent to an increase in the plough layer burden of 3.1 g Cd ha-1 year-1. By contrast, P-treated soils under permanent grassland with a higher organic matter content and lower pH have increased their Cd content by 7.2 g ha-1 year-1. When permanent grassland soils ranging in pH from 5 to 7 were examined it was found that organic matter had a larger effect on Cd concentration than pH and the effects of pH were not consistent. Farmyard manure applied to some experimental plots at Rothamsted appears to have been a more significant source of Cd than combined atmospheric and phosphate fertiliser inputs.     

用科学发展观分析中国浮法玻璃工业状况

平板玻璃及加工玻璃工业已成为我国国民经济发展和提高人民生活水平不可缺少的重要材料工业。在世界能源、资源短缺,国内煤、电、油、运力紧张环境下,用科学发展观分析中国浮法玻璃工业状况,找出存在的主要问题并提出解决的办法与措施十分必要。一、中国浮法玻璃工业存在的问题     

Flow controls on lowland river macrophytes: a review

We review the current status of knowledge regarding the role that flow parameters play in controlling the macrophyte communities of temperate lowland rivers. We consider both direct and indirect effects and the interaction with other factors known to control macrophyte communities. Knowledge gaps are identified and implications for the management of river systems considered.The main factors and processes controlling the status of macrophytes in lowland rivers are velocity (hence also discharge), light, substrate, competition, nutrient status and river management practices. We suggest that whilst the characteristics of any particular macrophyte community reflect the integral effects of a combination of the factors, fundamental importance can be attributed to the role of discharge and velocity in controlling instream macrophyte colonisation, establishment and persistence. Velocity and discharge also appear to control the relative influence of some of the other controlling factors.Despite the apparent importance of velocity in determining the status of macrophyte communities in lowland rivers, relatively little is understood about the nature of the processes controlling this relationship. Quantitative knowledge is particularly lacking. Consequently, the ability to predict macrophyte abundance and distribution in rivers is still limited. This is further complicated by the likely existence of feedback effects between the growth of macrophytes and velocity.Demand for water resources increases the pressure on lowland aquatic ecosystems. Despite growing recognition of the need to allocate water for the needs of instream biota, the inability to assess the flow requirements of macrophyte communities limits the scope to achieve this. This increases the likelihood of overexploitation of the water resource as other users, whose demands are quantifiable, are prioritised.     

移动式起重机船用安装的设计

大型建筑工程有时需要进行岸边或水中的起重作业,例如水面上桥梁结构的建造、海洋运输项目的部分工程、水上船只之间的货物转移等。陆上作业和水上作业之间有一条界线,一旦跨过这个界线,就需要使用浮式起重机或甲板起重机进行作业。当然有现成的重型浮式起重机可用,但现场常见的是将移动式起重机安装到驳船上使用。本文所关注的就是这类浮式起重机的安装和使用。     

污水池HDPE膜浮动覆盖技术研究

介绍了采用HDPE膜做污水池浮动盖的设计和施工原则，浮动盖的构成、材料选用和施工安装要点等。     

Environmental tobacco smoke uptake by clothing fabrics

The uptake of cigarette smoke by a variety of clothing fabrics was determined. The tested fabrics included wool, linen, cotton, silk, rayon, acetate and polyester. While a variety of factors effect such absorption, polyester fabrics were found to significantly take up less smoke than all the other tested cloths. A simple and rapid technique is described for measuring such absorption.     

Evaluation of pesticide uptake by Lupinus seeds

Pesticide uptake by seeds depends on the properties of the chemical, such as structure, stability, log k(ow) and diffusion rate, type of water, pH, temperature, content of organic matter and composition, and on seed characteristics such as permeability of the seed coat. The efficiency with which Lupinus angustifolius seeds retain different herbicides (simazine, atrazine, isoproturon, linuron,) and insecticides (carbaryl, fenamiphos, permethrin) was evaluated using both a batch and a continuous system. Factors which affect pesticide uptake by seeds, such as flow rate, seed biomass, pesticide concentration, contact time, pH, seed saturation and also the speed of the retention process for 17 days, were tested. L. angustifolius showed a high retention capacity for the above mentioned pesticides. The extraction of pesticides from seeds using different organic solvents, such as methanol, acetonitrile, ethyl acetate and n-hexane was evaluated and no pesticide residues were detected in any of the solvents tested. This could be attributed to the capacity of the seed to degrade the pesticides. From the results obtained, L. angustifolius seems to be a promising seed to be applied for phytoremediation of industrial effluents or contaminated water.     

Cadmium and lead in infant cereals--electrothermal-atomic absorption spectroscopic determination.

Because infant cereals are an important component of the infant diet from the fourth month of life onwards and therefore contribute to the dietetic intake of metals by infants, cadmium and lead were measured in samples of cereals commercially available in Spain. For this purpose an electrothermal atomic absorption (ET-AAS) method for determining cadmium and lead in these products was studied. The ET-AAS instrumental conditions and temperature/time furnace program were selected. The analytical parameters of the method (linearity, detection and quantification limits and precision) show its usefulness in measuring cadmium and lead in infant cereal products. The method was applied to eight different types of infant cereals from four different manufacturers, in all 29 different infant cereal products commercially available in Spain. The cadmium and lead contents of milk-free infant cereals range from 6.6 to 35.8 ng/g and from 36.1 to 305.6 ng/g, respectively, while the ranges corresponding to milk-added infant cereals are 2.9-40.0 ng/g for cadmium and 53.5-598.3 ng/g for lead. The cadmium and lead contents of cereal products of the same type from different manufacturers is responsible for the large confidence intervals and made it impossible to detect significant differences among the different products. Given the values found for lead and the correlation between chronic exposure to low lead doses and neuropsychological damage in early childhood, efforts should be made to reduce lead contamination.     

Luxury uptake of phosphorus by sediment bacteria

This note reports the results of experiments aimed at confirming the luxury uptake of phosphorus (P) by sediment bacteria as polyphosphate (Poly-P). Aerobic suspensions of sediments from two different sites were spiked with 1 mg P/L as orthophosphate and augmented with acetate (a fermentation product) or glucose. The orthophosphate was rapidly taken up over a period of a few hours. When these aerobic uptake experiments were made anaerobic and additional organic carbon added, only the acetate-amended sediment released a significant amount of the added phosphorus. It was hypothesised that during the aerobic stage, and with the addition of acetate, some of the phosphorus was accumulated as Poly-P by sediment microorganisms, which was released during the subsequent anaerobic stage (provided acetate was still present). Two lines of evidence--transmission electron microscope analysis of sediment bacteria and 31P-NMR analysis of sediment extracts--are presented to support the hypothesis that a portion of the phosphorus taken up during the aerobic experiments was stored as Poly-P.