ISSN:1522-6514    

DOI:10.1080/15226519908500001

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A method is described to assess the toxicity of selected volatile organic compounds (VOCs) in poplar trees. The method is illustrated for a specific aqueous mixture of VOCs that contaminates the groundwater at a site for which phytoremediation was being considered. The VOC mixture contained a variety of aromatic compounds, chlorinated aliphatics, and alcohols. Poplar tree cuttings planted in 50-gallon barrels in the greenhouse were watered via subirrigation. The subirrigant contained either a low (42 mg/L), medium (85 mg/L), or high (169 mg/L) dose of the VOC mixture, or water only (experimental control). Phytotoxicity was evaluated by measuring the physiological parameters of stomatal conductance, shoot elongation, and biomass production. Two experiments are briefly described: (1) The poplar tree cuttings were allowed to become established in the barrels and then treated to gradually increasing concentrations of the VOC mixture until the final dose was reached. The objective was to establish a detailed dose-response relationship. (2) The poplar tree cuttings were given the low, medium, or high dose of the VOC mixture immediately after planting. The aim of this experiment was to determine if the VOC mixture would be inhibitory to root development. Phytotoxic effects were not observed in either experiment.

ISSN:1522-6514    

DOI:10.1080/15226519908500002

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Many reports have documented wetlands removing a wide variety of contaminants in mine drainage, including aluminum, arsenic, cadmium, cobalt, copper, cyanide, iron, lead, manganese, nickel, selenium, uranium, and zinc. This article reviews biogeochemical processes responsible for their ability to transform and retain metals into insoluble forms. Shallow depth and large inputs of organic matter are key characteristics of wetlands that promote chemical and biological processes effecting metal removal. Aquatic macrophytes play an essential role in creating and maintaining this environment, but their uptake of metals usually accounts for a minor proportion of the total mass removed. Sorption onto organic matter is important in metal removal, particularly for copper, nickel, and uranium. Aluminum, iron, and manganese are often removed by hydrolysis, with the resulting acidification of water buffered by alkalinity produced in wetland sediments by anaerobic bacteria. Bacterial sulfate reduction accounts for much of this alkalinity. It can also contribute significantly to metal removal by formation of insoluble sulfides. Other important processes include the formation of insoluble carbonates, reduction to nonmobile forms, and adsorption onto iron oxides and hydroxides. Examples from field studies are presented throughout the review to illustrate these processes.

ISSN:1522-6514    

DOI:10.1080/15226519908500003

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We have compared the growth rates and cadmium binding capacity of wild-type and transgenicChlamydomonas reinhardtiicells expressing a foreign class-II metallothionein. We observed that cells expressing metallothionein grew to significantly higher cell densities than wild-type cells in the presence of a toxic cadmium concentration (40 μM). When grown at a low (5 μM) cadmium concentration, cells expressing metallothionein bound twofold more cadmium (0.43 μg Cd)mg Ch1) than wild-type. At cadmium concentrations (40 μM), which induce phytochelatin synthesis in wild-type cells the cadmium binding capacity of both wild-type (79.6 μg Cd)mg Ch1) and transformed cells (86.4 μg Cd)mg Ch1) was similar; however, the transformed cells grew to higher densities than the wild type. These results suggest that under conditions that apparently induce phytochelatin expression, the presence of metallothionein in the cytoplasm reduces heavy metal toxicity. Furthermore, because cells expressing metallothionein grow to higher densities than wild-type cells at a toxic cadmium concentration (40 μM), the transgenic cells sequester more total cadmium (9% of total Cd) from the medium than the wild type (5.5% of total Cd). These results indicate that the trace-metal binding properties of Chlamydomonas can be enhanced through the expression of trace-metal-specific binding proteins.

ISSN:1522-6514    

DOI:10.1080/15226519908500004

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

By accumulating Cd from solution, roots of hydroponically grown Indian mustard (Brassica junceaL.), a high biomass crop plant, were able to cause substantial reductions in the concentration of Cd in solution. The removal of Cd from solution was linearly correlated with Cd accumulation by roots. Screening of 300 different rhizobacterial isolates identified several that, when inoculated onto roots of Indian mustard, significantly enhanced the total amount of Cd removed from solution. Further investigations revealed that this enhancement was because of an overall increase in root biomass in the rhizobacterial-treated plants. Rhizobacteria were found to accumulate Cd from solution, and ultrastructural observations suggested that rhizobacteria promote the precipitation of Cd on the root surface. By precipitating Cd at the root surface, rhizobacteria reduce the amount of Cd taken up into roots, thereby protecting the plants, and in particular the roots, from the toxic effects of Cd. This reduced Cd toxicity allows for the increased proliferation of roots observed when plants are inoculated with certain rhizobacteria.

ISSN:1522-6514    

DOI:10.1080/15226519908500005

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

There has been much interest recently in central California for reusing drainage water to grow trees. A sand-culture study was conducted to investigate the accumulation of boron (B) and selenium (Se) in eight hybrid poplar (Populus) clones irrigated with synthetic agricultural effluent containing increasing levels of chloride salt, B, and Se. Electrical conductivity (EC) ranged from 1.5 to 15 dS m-1, B levels from 1 to 5 mg L-1, and Se levels from 100 to 500 μg L-1. Compared with all tree organs, the leaves accumulated the greatest concentrations of B and Se at the time of harvest. The results show that pooled leaf B concentrations were positively correlated with EC levels (r = 0.78, P < 0.001) and negatively correlated (r = -0.53, P < 0.001) with leaf dry matter for all clones at all tested B levels. Combined leaf and stem Se data show, respectively, a significant decrease (P < 0.05 level) in tissue accumulation of Se with increased salinity. Toxicity symptoms (e.g., burning leaf margins, shoot die back) occurred in most clones grown at 12 and 15 dS m-1treatments leading to leaf abscission. Based on the data, clone 49177 (Populus trichocarpa×P. deltoidus) best tolerated the tested parameters among the clones and accumulated the greatest amount of B and Se. The moderate ability of the Populus species to remove and accumulate B and Se from saline effluent is most effective at salinity levels less than 7 dS m-1.

ISSN:1522-6514    

DOI:10.1080/15226519908500006

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The uptake and transformation of perchlorate in the presence ofMyriophyllum aquaticum(parrot-feather) were examined in sand and aqueous treatments with concentrations between 0.2 to 20 ppm. Controls were included without plants to confirm the uptake of perchlorate by parrot-feather. The kinetic data followed a first-order reaction mechanism with rate constants ranging from 0.004 to 0.090, resulting in half-lives between 7 to 173 days. Uptake rates were five times higher in aqueous treatments than in sand treatments. The intermediates detected in the plant tissue suggest that perchlorate transformed in a step-wise fashion to form chloride. Accumulation of perchlorate in the plant tissues (1.2 g/kg) suggests that parrot-feather has a high capacity for accumulating this contaminant.

ISSN:1522-6514    

DOI:10.1080/15226519908500007

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor