Two cage designs and fingernail clams(Sphaerium fabale) were evaluated for theirsuitability for use in in situ bioassays toassess the ecological condition of a stream andpredict ecological recovery potential. One design(referred to as tray design) was a modified plastictray about one-fourth full of small gravels andcovered with 1 mm fiberglass mesh. The second design(referred to as tube-plates) consisted of shortplexiglass tubes about one-third full of small gravelsand attached horizontally to a plexiglass plate. Oneend of each tube faced into the current; both endswere covered with mesh. Cages containing clams weredeployed at reference and impacted (test) sites forperiods of 70 to 135 d. Growth and survival were theprimary endpoints evaluated, but the tube-platesallowed isolation of individual clams so that natalityalso could be evaluated as an endpoint. Results ofbenthic macroinvertebrate surveys, performed foranother study, were included to help validate bioassayresults. Both cage designs yielded good quantitative,site-specific results for clam survival and growth;results for natality, though, were less conclusive. Clam survival and growth results were in good generalagreement with the results for the benthicmacroinvertebrate community surveys. At a site wherethe macroinvertebrate community was the mostdepauperate, clam mortality was always rapid. At asite where the condition of the macroinvertebratecommunity was only slightly less impacted than themost impacted site, clam growth was almost alwayssignificantly lower than at reference sites. Survivalof clams was significantly reduced in <25 d at thissite in some trials, but in other trials there waslittle mortality. At a minimally impacted site, clamsurvival was similar to that found at reference sites,and differences in clam growth were not detectableuntil after 40 to 50 d of exposure. The tube-platedesign was easier to use, allowed more flexibility inselection of response parameters, and required lesshandling time of test animals, thus, this was thepreferred design. Our results demonstrated thateither in situ bioassay design can be used toaugment monitoring and assessment programs. Their useas a predictor of ecological recovery, however,requires further evaluation. 相似文献
Two strains of Pseudomonas species (B2 and D5)selected from an array of lead solubilizing and accumulatingbacteria obtained from the effluent contaminated soil samples of abattery manufacturing factory were studied. Increase in pH between 4.0 and 6.0 favoured the growth of isolates: Peaklog10 cfu mL–1 values of 7.1, 7.5 and 8.5 wereobtained at pH 4, 5 and 6, respectively.Cell bound lead concentrations for B2 (0.34 mg mL–1)and D5 (0.30 mg mL–1) obtained by direct contact withPbs were greater than lead concentrations of 0.89 and 0.25 mg mL–1 for B2 and D5, respectively,obtained in dialyzed cultures. These cell bound lead concentration in undialyzed cultures were alsogreater than lead concentrations of 0.03 and 0.07 mg mL–1 for B2 and D5 in culture supernatants. Glucose addition did nor improve lead accumulation in the isolates.Exploitation of such isolates for the biotreatment of lead ladeneffluent was conducted. 相似文献
Nitrate leaching forms an important environmental problem because it causes pollution of groundwater and surface water, and adds to already problematic eutrophication. This study analyses the impact of reductions in nitrate leaching on land cover decisions of dairy farms, of which the activities make an important contribution to nitrate leaching. As the level of nitrate leaching depends on groundwater depth as well as on the supply of nitrogen, spatial variation in groundwater levels will cause a spatial variation in land cover under restrictions on nitrate leaching. A non-linear partial optimisation model for the economic and ecological aspects of the problem were used to show how land cover and dairy farms' financial balances change when nitrate losses are reduced. The model is spatially explicit, and describes nitrate leakage and yields of maize and grass as a function of groundwater depth, including the effects of various grazing systems. The model analyses the decisions of a risk neutral agent who minimises costs under the following constraints: (i) production, feed requirements and mass balances for fodder; (ii) constraints for nitrate leaching. Economic costs are attributed to increased costs of fodder and processing of manure when nitrate restrictions are tightened. An important result of the study is the variation in compliance costs and land cover for maize and grass production brought about by spatial variation in groundwater depth. While the effects are negligible for some shallow groundwater classes, it is extremely difficult in other classes – if not impossible – to obtain the EU standard of maximum admissible losses of 34 kg N ha–1 at low costs. The study shows an important reduction in land cover by maize. 相似文献
Use of sewage sludge, a biological residue produced from sewage treatment processes in agriculture is an alternative disposal technique of waste. To study the usefulness of sewage sludge amendment for palak (Beta vulgaris var. Allgreen H-1), a leafy vegetable and consequent heavy metal contamination, a pot experiment was conducted by mixing sewage sludge at 20% and 40% (w/w) amendment ratios to the agricultural soil. Soil pH decreased whereas electrical conductance, organic carbon, total N, available P and exchangeable Na, K and Ca increased in soil amended with sewage sludge in comparison to unamended soil. Sewage sludge amendment led to significant increase in Pb, Cr, Cd, Cu, Zn and Ni concentrations of soil. Cd concentration in soil was found above the Indian permissible limit in soil at both the amendment ratios.
The increased concentration of heavy metals in soil due to sewage sludge amendment led to increases in heavy metal uptake and shoot and root concentrations of Ni, Cd, Cu, Cr, Pb and Zn in plants as compared to those grown on unamended soil. Accumulation was more in roots than shoots for most of the heavy metals. Concentrations of Cd, Ni and Zn were more than the permissible limits of Indian standard in the edible portion of palak grown on different sewage sludge amendments ratios. Sewage sludge amendment in soil decreased root length, leaf area and root biomass of palak at both the amendment ratios, whereas shoot biomass and yield decreased significantly at 40% sludge amendment. Rate of photosynthesis, stomatal conductance and chlorophyll content decreased whereas lipid peroxidation, peroxidase activity and protein and proline contents, increased in plants grown in sewage sludge-amended soil as compared to those grown in unamended soil.
The study clearly shows that increase in heavy metal concentration in foliage of plants grown in sewage sludge-amended soil caused unfavorable changes in physiological and biochemical characteristics of plants leading to reductions in morphological characteristics, biomass accumulation and yield. The study concludes that sewage sludge amendment in soil for growing palak may not be a good option due to risk of contamination of Cd, Ni and Zn and also due to lowering of yield at higher mixing ratio. 相似文献
Background, Aim and Scope
Numerous herbicides and xenobiotic organic pollutants are detoxified in plants to glutathione conjugates. Following this enzyme
catalyzed reaction, xenobiotic GS-conjugates are thought to be compartmentalized in the vacuole of plant cells. In the present
study, evidence is presented for long range transport of these conjugates in plants, rather than storage in the vacuole. To
our knowledge this is the first report about the unidirectional long range transport of xenobiotic conjugates in plants and
the exudation of a glutathione conjugate from the root tips. This could mean that plants possess an excretion system for unwanted
compounds which give them similar advantages as animals.
Materials and Methods:
Barley plants (Hordeum vulgare L. cv. Cherie) were grown in Petri dishes soaked with tap water in the greenhouse.
- Fluorescence Microscopy. Monobromo- and Monochlorobimane, two model xenobiotics that are conjugated rapidly in plant cells
with glutathione, hereby forming fluorescent metabolites, were used as markers for our experiments. Their transport in the
root could be followed sensitively with very good temporal and spatial resolution. Roots of barley seedlings were cut under
water and the end at which xenobiotics were applied was fixed in an aperture with a thin latex foil and transferred into a
drop of water on a cover slide. The cover slide was fixed in a measuring chamber on the stage of an inverse fluorescence microscope
(Zeiss Axiovert 100).
- Spectrometric enzyme assay. Glutathione S-transferase (GST) activity was determined in the protein extracts following established
methods. Aliquots of the enzyme extract were incubated with 1-chloro-2,4-dinitrobenzene (CDNB), or monochlorobimane. Controls
lacking enzyme or GSH were measured.
- Pitman chamber experiments. Ten days old barley plants or detached roots were inserted into special incubation chambers, either
complete with tips or decapitated, as well as 10 days old barley plants without root tips. Compartment A was filled with a
transport medium and GSH conjugate or L-cysteine conjugate. Compartments B and C contained sugar free media. Samples were
taken from the root tip containing compartment C and the amount of conjugate transported was determined spectro-photometrically.
Results:
The transport in roots is unidirectional towards the root tips and leads to exsudation of the conjugates at rates between
20 and 200 nmol min-1. The microscopic studies have been complemented by transport studies in small root chambers and spectroscopic
quantification of dinitrobenzene-conjugates. The latter experiments confirm the microscopic studies. Furthermore it was shown
that glutathione conjugates are transported at higher rates than cysteine conjugates, despite of their higher molecular weights.
This observation points to the existence of glutathione specific carriers and a specific role of glutathione in the root.
Discussion:
It can be assumed that long distance transport of glutathione conjugates within the plant proceeds like GSH or amino acid
transport in both, phloem and xylem. The high velocity of this translocation of the GS-X is indicative of an active transport.
For free glutathione, a rapid transport-system is essential because an accumulation of GSH in the root tip inhibits further
uptake of sulfur. Taking into account that all described MRP transporters and also the GSH plasmalemma ATPases have side activities
for glutathione derivatives and conjugates, co-transport of these xenobiotic metabolites seems credible.
- On the other hand, when GS-B was applied to the root tips from the outside, no significant uptake was observed. Thus it can
be concluded that only those conjugates can be transported in the xylem which are formed inside the root apex. Having left
the root once, there seems to be no return into the root vessels, probably because of a lack of inward directed transporters.
Conclusions:
Plants seem to possess the capability to store glutathione conjugates in the vacuole, but under certain conditions, these
metabolites might also undergo long range transport, predominantly into the plant root. The transport seems dependent on specific
carriers and is unidirectional, this means that xenobiotic conjugates from the rhizosphere are not taken up again. The exudation
of xenobiotic metabolites offers an opportunity to avoid the accumulation of such compounds in the plant.
Recommendations and Perspectives:
The role of glutathione and glutathione related metabolites in the rhizosphere has not been studied in any detail, and only
scattered data are available on interactions between the plant root and rhizosphere bacteria that encounter such conjugates.
The final fate of these compounds in the root zone has also not been addressed so far. It will be interesting to study effects
of the exuded metabolites on the biology of rhizosphere bacteria and fungi. 相似文献
There is growing interest in the development of more cost-effective and retrofit technologies for the upgrade and expansion of existing wastewater treatment plants with extreme space constraints. A free-floating sponge media (BioCube) process, using a 24L lab scale reactor, was operated to study the nitrification profiles and microbial community. The COD removal efficiencies were maintained, at an average of 95%, with the mixed liquor suspended solids (MLSS) inside the BioCube sponge media maintained at 12,688mg/L. The nitrification removal efficiencies were between 92% and 100%, with an average value of 99%. From the results of microelectrode measurements, the ammonium ion concentration was found to rapidly decrease from the surface of the BioCube sponge media to a depth of 2mm due to chemical reactions carried out by ammonia oxidizing bacteria (AOB) species. Multi-fluorescence in situ hybridization (FISH) has been used to investigate the spatial distributions of various microbial activities within reactors. Microbial communities were targeted using different oligonucleotide probes specific to AOB and nitrite oxidizing bacteria (NOB). There were a large number of AOB populations, but these were not uniformly distributed in the biofilm compared to the NOB populations. 相似文献