Arsenic Bioaccumulation in Freshwater Fishes

The arsenic ambient water quality criterion (AWQC) for protection of human health via ingestion of aquatic organisms is currently 0.14 μ g/L. This AWQC is derived using a bioconcentration factor (BCF) of 44, which is a consumption-weighted average based on two data points for oysters and fish that was proposed by the U.S. Environmental Protection Agency in 1980 for broad application to freshwater and marine environments. This BCF is based on the assumption that bioaccumulation is a simple linear function of the exposure concentration. In the nearly quarter of a century since this BCF was promulgated, there have been additions to the arsenic bioaccumulation database and a broader scientific understanding of bioaccumulation mechanisms and how they can be applied to estimating tissue concentrations in aquatic organisms. From this database, we identified 12 studies of arsenic bioaccumulation in freshwater fishes in order to explore differences in laboratory-generated BCFs and field-generated bioaccumulation factors (BAFs) and to assess their relationship to arsenic concentrations in water. Our analysis indicates that arsenic concentrations in tissue and arsenic BAFs may be power functions of arsenic concentration in water. A power function indicates that the highest BCF values may occur at low background levels and may decrease as environmental concentrations increase above the ambient range.     

Removal of Cr(VI) from ground water by Saccharomyces cerevisiae

Chromium can be removed from ground water by the unicellular yeast, Saccharomyces cerevisiae. Local ground water maintains chromium as CrO₄ ^2- because of bicarbonate buffering and pH and E _h conditions (8.2 and +343 mV, respectively). In laboratory studies, we used commercially available, nonpathogenic S. cerevisiae to remove hexavalent chromium [Cr(VI)] from ground water. The influence of parameters such as temperature, pH, and glucose concentration on Cr(VI) removal by yeast were also examined. S. cerevisiae removed Cr(VI) under aerobic and anaerobic conditions, with a slightly greater rate occurring under anaerobic conditions. Our kinetic studies reveal a reaction rate (V_max) of 0.227 mg h^-1 (g dry wt biomass)^-1 and a Michaelis constant (Km) of 145 mg/l in natural ground water using mature S. cerevisiae cultures. We found a rapid (within 2 minutes) initial removal of Cr(VI) with freshly hydrated cells [55–67 mg h^-1 (g dry wt biomass)^-1] followed by a much slower uptake [0.6–1.1 mg h^-1 (g dry wt biomass)^-1] that diminished with time. A materials-balance for a batch reactor over 24 hours resulted in an overall shift in redox potential from +321 to +90 mV, an increase in the bicarbonate concentration (150–3400 mg/l) and a decrease in the Cr(VI) concentration in the effluent (1.9-0 mg/l).     

The use of hollow fiber cross-flow microfiltration in bioaccumulation and continuous removal of heavy metals from solution by Saccharomyces cerevisiae

Cross-flow microfiltration was shown to retain Saccharomyces cerevisiae biomass utilized for heavy metal bioaccumulation. The passage of metal-laden influent through a series of sequential bioaccumulation systems allowed for further reductions in the levels of copper, cadmium, and cobalt in the final effluent than that afforded by a single bioaccumulation process. Serial bioaccumulation systems also allowed for partial separation of metals from dual metal influents. More than one elemental metal cation could be accumulated simultaneously and in greater quantities than when a single metal was present in the effluent (Cu(2+) 0.43 mmol, Cu(2+) + Cd(2+) 0.67 mmol, and Cu(2+) + Co(2+) 0.83 mmol/g yeast dry mass when the initial concentration of each of the metal species was 0.2 mmol.L(-1)). Co-accumulation of two different metal cations allowed higher total levels of bioaccumulation than found with a single metal. The flux rate was 2.9 x 10(2) L.h(-2)mum(-2) using a polypropylene microfiltration membrane (0.1 mum pore size) at 25 degrees C. (c) 1994 John Wiley & Sons, Inc.     

Engineered nickel bioaccumulation in Escherichia coli by NikABCDE transporter and metallothionein overexpression

Mine wastewater often contains dissolved metals at concentrations too low to be economically extracted by existing technologies, yet too high for environmental discharge. The most common treatment is chemical precipitation of the dissolved metals using limestone and subsequent disposal of the sludge in tailing impoundments. While it is a cost-effective solution to meet regulatory standards, it represents a lost opportunity. In this study, we engineered Escherichia coli to overexpress its native NikABCDE transporter and a heterologous metallothionein to capture nickel at concentrations in local effluent streams. We found the engineered strain had a 7-fold improvement in the bioaccumulation performance for nickel compared to controls, but also observed a drastic decrease in cell viability due to metabolic burden or inducer (IPTG) toxicity. Growth kinetic analysis revealed the IPTG concentrations used based on past studies lead to growth inhibition, thus delineating future avenues for optimization of the engineered strain and its growth conditions to perform in more complex environments.     

五台山山地草甸自然保护区11种化学元素生物积累的研究

五台山山地草甸自然保护区可划分为亚高山草甸带、山地五花草甸带、常绿针叶林草甸带。本文研究了各生态带土壤和植被中１１种化学元素的含量、分布及生物积累特征。研究表明：（１）各带土壤中化学元素含量均在全国同类型土壤含量范围之内,就平均含量而言,Ｃｏ＇Ｎｉ含量较高,其它元素含量较低,整体属清洁理想水平,合乎自然保护区土壤环境标准。（２）各带植被中营养元素含量较高,营养丰富。尤其是亚高山草甸带是饲用价值很高     

Experimental silver bioaccumulation in the polychaetePomatoceros triqueter (L.)

Summary The tubicolous polychaetePomatoceros triqueter was exposed for 6–7 weeks to 200 or 400 g · l^–1 silver introduced as the nitrate into sea water. Survival conditions and mortality were evaluated and silver bioaccumulation analysed by atomic absorption spectrometry. Characteristic morphological lesions were recognized. Histopathologic examination was performed on paraffin or semi-thin sections and at the ultrastructural level. Histochemical examination mainly concerned the metals, reducing groups and sulfur-containing proteins. Microanalytical study involved the use of a wavelength-dispersive X-ray spectrometry microprobe and ion microanalyzer, and the use of an energy-dispersive X-ray spectrometry microprobe at the ultrastructural level. Our results emphasize the role of the branchial crown for metal penetration. Its cuticle accumulates silver as a metal, in particulate form. The internal accumulation of mainly extracellular deposits concerns the basement membranes and connective tissue present in the axis of the branchial crown filaments, or surrounding the nephridial pouches and the gut sinus. The carrier role of the closed vascular system is suggested by ultrastructural observations. The silver route from transepithelial uptake to nephridial excretion involves at least two intracellular transits, plus the vascular mesothelium. Nephridia play a role in silver storage (lysosomes) and elimination (concretions). In all parts internal to the crown cuticle, silver is at least partly associated with protein SH-groups (metallothionein-like); deposits can be enriched with silver sulfide and metallic silver.     

Arsenic Resistance and Bioaccumulation of an Indigenous Bacterium Isolated from Aquifer Sediments of Datong Basin,Northern China

To obtain bacteria with arsenic accumulation potential that can be used to remove arsenic from contaminated waters, experiments were made to investigate the tolerance and accumulation to arsenic of an indigenous bacterium XZM002 isolated from aquifer sediments of Datong Basin, northern China. The results showed that strain XZM002 belongs to the genus Bacillus and has evolved defense mechanisms to reduce arsenic injury: the change of cellular shape from initial rod to oval and then to round with increment of arsenic toxicity. The effect of arsenate or arsenite on the bacterial growth was also investigated. Results showed that growth of the strain was inhibited under As(III) and high concentration As(V) (over 1200 μg l^?1) conditions in the first 2 days and promoted under low concentration As(V) (under 400 μg l^?1) condition. Its arsenic bioaccumulation potential was surveyed by monitoring the concentration changes of total arsenic and arsenic speciation in the medium and in the cytoplasm, and those of total arsenic on the membrane. Methylated arsenic species were not detected throughout the experiment. The results indicated that 11.5% of arsenic was removed from liquid medium into the bacterial cells and 9.22% of As(V) in the medium was transformed gradually to As(III) during 4 d of incubation. Approximately 80% of the total accumulated arsenic was adsorbed onto the membrane instead of into cytoplasm; and the arsenic accumulation almost approached saturation after incubation for 72 h.     

耐镉马克思克鲁维酵母重金属镉吸附特性的研究

菌株YS-K1是从镉污染土壤中筛选获得的一株耐镉马克思克鲁维酵母Kluyveromyces marxianus YS-K1,对其镉吸附特性研究结果表明,该菌对镉具有良好的耐受性和吸附性,即使在镉浓度高达140mg/L的培养基中也能生长,当镉浓度在30mg/L以下时,24h后能吸附溶液中90%以上的镉,且最佳吸附条件为pH6.0,温度30℃。该菌所吸附的镉大部分集中在细胞壁上,占总吸附镉的76%,细胞膜上的占9%,细胞质中的占15%;能量抑制剂2,4-二硝基苯酚(DNP)和二环己基碳二亚胺(DCC),分别能降低菌株15%和22%的镉吸附量。在Kluyveromyces marxianus YS-K1细胞中,锌离子与镉离子有共用的结合位点,锌离子不仅会与镉离子竞争细胞表面的结合位点,减少其对镉的吸附量,而且也会与镉离子竞争进入细胞的通道位点,减少其对镉的积累量,同时能部分恢复镉离子对菌株生长的抑制作用。     

Phytoextraction of trace elements by water hyacinth in contaminated area of gold mine tailing

The ability of water hyacinth (Eichhornia crassipes) to uptake Ag, Ba, Cd, Mo, and Pb from waters in gold mine tailing area was studied. All experiments were carried out in the field conditions without using of model system. Bioconcentration (BCF) and translocation factors (TF) as well as elements accumulation by plant in different points of tailings-impacted area were evaluated. It has been shown that water hyacinth demonstrates high ability to accumulate Mo, Pb, and Ba with BCF values 24,360 ± 3600, 18,800 ± 2800 and 10,040 ± 1400, respectively and is efficient in translocation of Mo and Cd. The general trend of the plant accumulation ability in relation to the studied elements corresponds to their concentration in the medium. As the distance from tailings increases, concentration of Ag, Ba and Pb in plant decreases more clearly than that of Cd, while the amount of Mo accumulated by plant doesn't drop significantly in accordance with its concentration in water. Under the conditions of the confluence of river Ur and drainage stream Ba and Ag can be considered as potential candidates for phytomining.     

Growth and nutrients accumulation potentials of giant reed (Arundo donax L.) in different habitats in Egypt

Arundo donax L. has a high biomass production and a tendency toward community dominance in many habitats and thereby a tolerance to a wide range of environmental conditions. Therefore, the present study investigated the potentiality of A. donax to accumulate nutrients and trace metals in its biomass. Six main habitats (Nile Bank, Drain Bank, Canal Bank, Field Edges, Railways and Roadsides) were recognized. At each habitat, six quadrats (each 1 m²), distributed equally in two sites, were selected for growth measurements (e.g., density, shoot height, diameter, leaf area and biomass), plant and soil analyses. Plants from Nile, Canal and Drain Banks had the highest values of most growth measurements, while those from Railways and Roadsides had the lowest. Canal Bank plants accumulated the highest concentrations of P, Cu and Pb in their leaves; Zn in the stem; and Mg, Cd and Fe in the rhizome. The bioaccumulation factor (BF) of A. donax, for Cd, Fe, Mn and Zn, was greater than 1, while the translocation factor (TF) of most trace metals was less than unity in most habitats. In conclusion, A. donax showed morphological plasticity in response to habitat heterogeneity, and its growth was most vigorous in the riparian habitats. The high BF, as well as the significant positive correlations between trace metals, especially Cd, in soil and plant, renders A. donax a powerful phytoremediator.