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| Evaluation of Physical-Chemical Methods for Rapid Assessment of the Bioavailability of Moderately Polar Compounds in Sediments | |
| 项目编号 | R825513C026 |
| Mark R. Wiesner | |
| 项目主持机构 | University of South Carolina at Columbia |
| 开始日期 | 1998 |
| 结束日期 | 2001-01-01 |
| 英文摘要 | The goal of the project is to study the transport of contaminants across synthetic membranes and immunoassay methods as a means for assessing the bioavailability of moderately polar contaminants in sediments. This effort is composed of three interrelated tasks: 1) The transport of xenobiotic compounds across synthetic membranes will be investigated under conditions of variable solution chemistry where the concentration, nature, and conformation of dissolved organic matter will be varied. 2) Concentrations of these compounds will be measured by scintillation counting and immunoassay to determine if a portion of the contaminants is functionally inaccessible to the antibodies. 3) Plant uptake studies will be run using identical conditions of solution chemistry applied in tasks 1 and 2 to determine the fraction of contaminant which is bioavailable to a hydroponically grown vegetativesystem. The proposed effort will focus primarily on the use of synthetic membrane analogues for biological membranes as a basis for predicting bioavailability in sediment systems. Thus, one hypothesis to be tested is that synthetic membranes can be used to mimic the uptake selectivity expressed by biological membranes for specific compounds. A second hypothesis to be tested is that the antibodies used in immunoassays to bind trace organic compounds, exhibit specificity for "free" species of these compounds in a manner which can be correlated with the bioavailabilityof these contaminants.Task 1: Transport of xenobiotic compounds across synthetic membranes. This task will include examination of the contaminant/organic matter interactions and their effect on transport through dialysis membranes. Experiments to be conducted in task 1 will include the use of model solutions of macromolecular organic compounds which will serve as surrogates for natural organic matter in sediment pore waters. Contaminants will be mixed with the solution of organic matter and solution chemistries will be adjusted. Transport of contaminant through membranes, and contaminant retained will be measured as well as any residual remaining on membranes or other surfaces. Similar experiments will be conducted using concentrated solutions of fractionated natural organic matter. Again, transport of contaminant across membranes will be monitored as well as the remaining measures required to perform a rigorous mass balance on the system. A novel experimental procedure will be used to facilitate the collection of data required to obtain a mass balance on the system. The contaminated solution sample will communicate via a semipermeable membrane with a solution made up to mimic desired water column or pore water composition. A second membrane will be in contact with this solution on one side, and with a small quantity of lipid (triolein) on the other. At equilibrium, this system will allow the determination of both the unavailable and available fractions of contaminant. This work will also involve a detailed interpretation of results in the context of the underlying physical chemistry of contaminant transport across the membranes as a basis for selecting membranes with properties that might correlate wellwith biouptake. Task 2: Determination of the "immunoassay- available fraction" of contaminants. Immunoassay techniques allow for rapid determination of the relative presence of certain contaminants at even very low concentrations. Numerous investigators have observed excellent correlation between immunoassay-based measurements and those obtained by conventional methods such as GC/MS. However, while highly correlated, several researchers have produced data that suggest that in the absence of significant cross reactivity, the immunoassay methods may produce lower concentrations than those obtained from conventional methods. For example, Thurman and co-investigators found that atrazine concentrations in surface water measured using an immunoassay method were approximately 20% lower than those measured by GC/MS. Interferences associated with "bound" contaminant are typically minimized by standard sample preparation, and differences between the two techniques appear to be smaller when the samples are free of materials that might cause interferences or when similar extraction techniques are usedto prepare samples. The investigators will explore the possibility that this drawback in the immunoassay technique can be exploited in suitable cases based on the hypothesis that the same factors which inhibit transport of atrazine across synthetic membranes may also limit binding by antibodies. In an immunoassay measurement a sample, containing for example triazines (O), is added to a test well, followed by a triazine-enzyme conjugate (O-E). The triazine-enzyme conjugate competes with triazines for the same antibody binding site. After a brief incubation period any unbound molecules are washed away and clear solutions of substrate (S) and chromogen (C) are then added to each well. In the presence of bound triazine-enzyme conjugate, the substrate is converted to a compound which causes the chromogen to turn blue (B). One enzyme molecule can convert more than one substrate molecule. A stop solution is added after a prescribed period to each well to arrest the blue color development and turn the reaction solution yellow. A calibrated spectrophotometric measurement at 450 nanometers (nm) can then be done to obtain the triazine concentration. Contaminants bound up in a macromolecular "trap" may not be accessible from the standpoint of antibody binding. If this is the case, comparison of immunoassay-based measurements with a benchmark such as total extractable (or scintillation counting in a laboratory setting) might be used as an index of contaminant availability. Experiments performed in task 1 will be complemented with immunoassay measurements of radio-labeled contaminantsbenchmarked by scintillation counting. Task 3: Plant uptake studies. The fractions of contaminants which are able to pass through synthetic membranes under the conditions applied in task 1 and those available to bind with a immunoassay-specific antibody will be compared with the apparent fractions available for biouptake by plants. Plants common to Regions 4 and 6, and typically found in wetlands will be used in this study. Candidate plants include parrot feather, water hyacinth, and alligator weed. These plants have been the subject of previous bioaccumulation work undertaken within the HSRC/S&SW. Plants will be grown hydroponically in modified Hoagland's nutrient solutions adjusted to produce identical initial compositions to those used for tasks 1 and 2, only without contaminants. Plants will be acclimated for approximately 3 days in a controlled exposure chamber (photon flux and temperature) which will allow for mixing using a magnetic stirrer. The uptake experiment will be initiated by injecting contaminants into the hydroponic solution and mixing. Plants will be removed periodically, weighed and14C content determined using a biological oxidizer that converts14C-labeled plant tissue to14CO2. Samples of the hydroponic solution will also be monitored over time. The primary focus of the plant measurements will be on the roots tissues, which are likely to equilibrate within 1 day. The amount of bioavailable contaminant will then be calculated directly frommeasurement and by mass balance.The proposed use of membranes as a surrogate for the biological membrane is not new. Most notably, researchers have explored the use of semi-permeable membrane devices (SPMDs) to predict the biouptake of organic compounds by fish. Their SPMDs essentially consist of a lipid phase sandwiched between membranes. Selectivity of transport is determined by the membrane and the lipophilic contaminant of interest is accumulated in the lipid phase and later analyzed. Although some correlation has been observed between chemical concentrations accumulated in their SPMDs and the bioavailable concentration back-calculated from concentrations in fish tissues, interpretation of their results is complicated by numerous factors including variability in the aqueous environment, possible metabolic transformations in fish, uptake of contaminants from multiple sources (food intake as well as transport across the gill membrane), and metabolic changes induced by stress. Moreover, for many other reasons stated in the previous section, the physical chemistry of interactions between membranes and contaminants are likely to be affected by solution chemistry and may be specific for a given contaminant/membrane combination. |
| 英文关键词 | immunoassays;synthetic membranes;chemical partitioning;environmental chemistry;environemental engineering;remediation;contaminated sediments;bioremediation;phytoremediation;plant uptake studies. |
| 学科分类 | 09 - 环境科学;08 - 地球科学 |
| 资助机构 | US-EPA |
| 项目经费 | 0 |
| 国家 | US |
| 语种 | 英语 |
| 文献类型 | 项目 |
| 条目标识符 | http://gcip.llas.ac.cn/handle/2XKMVOVA/73006 |
| 推荐引用方式 GB/T 7714 | Mark R. Wiesner.Evaluation of Physical-Chemical Methods for Rapid Assessment of the Bioavailability of Moderately Polar Compounds in Sediments.1998. |
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