Final Report: Evaluation of Physical-Chemical Methods for Rapid Assessment of the Bioavailability of Moderately Polar Compounds in Sediments

EPA Grant Number: R825513C026
Subproject: this is subproject number 026 , established and managed by the Center Director under grant R825513
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: HSRC (2001) - South and Southwest HSRC
Center Director: Reible, Danny D.
Title: Evaluation of Physical-Chemical Methods for Rapid Assessment of the Bioavailability of Moderately Polar Compounds in Sediments
Investigators: Wiesner, Mark R.
Institution: Rice University
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1998 through January 1, 2001
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (2001) Recipients Lists
Research Category: Hazardous Substance Research Centers , Land and Waste Management

Objective:

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 vegetative system. This work will focus on a matrix of moderately polar contaminants selected on the basis of the following criteria:

  • compounds which are likely to exhibit (or not exhibit) interactions with colloidal macromolecules,
  • an appropriate range of physical-chemical properties including molecular weight, Kow's, and ionization constants (where appropriate),
  • relevance to past and on-going research in the HSRC/S&SW and regional significance,
  • significance in extending past and on-going studies to a consideration of moderately polar compounds,
  • availability of radiolabeled materials and,
  • availability of commercial immunoassays.

    The bioavailability, transport, and reactivity of chemicals in aqueous environments are greatly influenced by the manner in which chemicals partition between phases. For example, sorption of polycyclic aromatic hydrocarbons to colloids decreases the bioaccumulation potential of these compounds, the transport of trace organics can be greatly "facilitated" through interactions with macromolecules, and sorption of alkylated anilines on particles has been observed to speed photolytic transformations. One premise of the proposed research is that interactions between contaminants and macromolecular/colloidal materials potentially play a key role in reducing the biotic impact of contaminants on ecosystems and ultimately public health. Related factors that affect bioavailability include compound lipophilicity and solubility, the degree of ionization of functional groups, molecular weight, and the presence of other substances that may compete for contaminant uptake or alter solution chemistry. An obvious implication of this premise is that regulated risk-based levels for contaminants, that make allowances for colloidally- or macromolecularly-bound fractions of contaminants which may not be bioavailable, will be potentially lower than those based on total concentrations. Tomson and co-workers have suggested that the reversibility of interactions such as those between colloids and contaminants may serve as a rational basis for determining regulatory endpoints.

    Presently, methods for rapidly, and inexpensively assessing the bioavailable portion of contaminants in sediments and other aquatic systems are extremely limited and relatively untested. 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 bioavailability of these contaminants.

  • Summary/Accomplishments (Outputs/Outcomes):

    The bioavailability of contaminants is clearly related to the ability of these chemicals to be transported across biological membranes. Although there are many unresolved issues related to the transport of chemical species across biological membranes, there is consensus that transport is intimately related to membrane structure. Salient features of the "fluid-mosaic" model for biological membranes include a phospholipid bilayer through which larger, hydrophobic molecules may diffuse, and in which proteins also circulate. Some of these proteins act as pores through the membrane, approximately 1 nm in diameter, and allow for the transport of small ionic species. Other proteins appear to be involved in the active transport of materials across the membrane.

    Many of the contaminants in sediments fall within the range of molecular weights, hydrophobicity, and functionality that make bioavailability difficult to assess. Moreover, the organic concentrations and abundance of colloidal materials in sediments suggest that many contaminants will exist in association with these colloidal phases. The transport and bioavailability of contaminants in sediments may also be influenced by the presence of dissolved organic matter in the overlying water column. Evidence for reduced uptake in the presence of organic matter in soils is substantial8. For example, Walker observed that the uptake of atrazine into the shoots of wheat growing in different soils decreased with increasing organic matter content in the soils. The role of dissolved organic matter in reducing uptake is less well appreciated. While bioavailability may be decreased due to contaminant scavenging by allochthonous organic matter, plants also release a wide variety of autochthonous organic compounds that appear to play a role in regulating, in this case potentially decreasing, the availability of materials to plants.

    Transport in synthetic membranes has been tested repeatedly with a variety of solutes, yielding trends that greatly resemble those observed with biological membranes. However, synthetic membranes can be made with a wide range of pore sizes, often resulting in diffusive or convective transport through pores as the dominant mechanism of transport. In these cases, the membranes serve as molecular sieves, that is, preferential solute transport occurs via steric rejection. The factors governing rejection by synthetic membranes are apparently quite complex. However, the following trends in removal of organic solutes have been observed and often mirror those noted previously for uptake by biological membranes:

  • Merten and coworkers11 analyzed data reported previously by Sourirajan and co-workers and concluded that rejection of organic compounds increases with increased molecular weight in a homologous series and with increased branching for molecules of equal molecular weight.
  • Compounds without ionizable groups are rejected by RO (and probably NF) membranes to a lesser extent than are compounds with ionizable groups.
  • Compounds with ionizable groups are rejected to a greater extent when these groups are ionized.
  • Phenolic compounds are, as a class, poorly rejected. Low molecular weight chlorinated hydrocarbons (e.g. some insecticides and herbicides) also tend to be poorly rejected.
  • Compounds that are capable of significant hydrogen bonding tend to be removed to a lesser extent (e.g. alcohols, aldehydes, acids, urea).
    Interactions with natural organic materials may significantly affect the rejection of specific SOCs.
  • Organic acids and amines are rejected better when present as a salt.
  • Low MW polar organics tend to be removed better by nonpolar membranes.

    One premise of the proposed research is that the same physical-chemical factors which control the association between natural organic matter and compounds like atrazine and thereby reduce the passage of contaminants across synthetic membranes, may also inhibit the passage of these materials across cell membranes. In other words, we hypothesize that mobility of a contaminant across a carefully chosen synthetic membrane might be correlated with the bioavailability of that contaminant. If this hypothesis proves to be true, this work will open up a number of methods for very rapidly assessing bioavailability, and end-points for contaminant remediation, including instantaneous, on-line monitoring. If false, this work will nonetheless contribute significantly to the "how clean is clean" dialogue by extending experimental evaluation to include moderately polar compounds and consideration of the role of dissolved macromolecules.

    The proposed use of membranes as a surrogate for the biological membrane is not new. Most notably, Huckins and co-workers have explored the use of semipermeable 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.

    The proposed matrix of contaminants for this study is summarized in Table 1.

    Compound MW Log Kow Polarity
    RDX 222 0.86 Slightly polar at neutral pH
    Atrazine 215 2.56 Slightly polar at neutral pH
    2,4-Dichlorophenol 163 2.80 pKa 7.85
    Napthalene 128 3.36 Non-polar
    Pentachlorophenol 266 5.01 pKa 4.85

    The matrix of contaminants and choice of plant systems is designed to leverage results from previous and on-going Center activities. For example, this work will be coordinated with work on reversible adsorption and bioavailability proposed by Hughes, Reible, Tomson, Kan, Fleeger, Pardue and Valsaraj. However, this proposed effort will extend previous Center efforts to include a consideration of moderately polar compounds and the use of an entirely different methodology for estimating bioavailability.

    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 well with 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 used to prepare samples.

    We 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 contaminants benchmarked 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 and 14C content determined using a biological oxidizer that converts 14C-labeled plant tissue to 14CO2. 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 from measurement and by mass balance.


  • Journal Articles on this Report : 3 Displayed | Download in RIS Format

    Other subproject views: All 3 publications 3 publications in selected types All 3 journal articles
    Other center views: All 392 publications 154 publications in selected types All 106 journal articles
    Type Citation Sub Project Document Sources
    Journal Article Devitt EC, Wiesner MR. Dialysis investigations of atrazine-organic matter interactions and the role of a divalent metal. Environmental Science & Technology. 1998;32(1):232-237. R825513C026 (Final)
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  • Journal Article Devitt EC, Ducellier F, Cote P, Wiesner MR. Effects of natural organic matter and the raw water matrix on the rejection of atrazine by pressure-driven membranes. Water Research. 1998;32(9):2563-2568. R825513C026 (Final)
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    Journal Article Wiesner MR, Chellam S. The promise of membrane technologies. Environmental Science & Technology.1999;33(17):360A-+. R825513C026 (Final)
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  • Supplemental Keywords:

    immunoassays, synthetic membranes, and chemical partitioning., RFA, Scientific Discipline, Waste, Water, Chemical Engineering, Contaminated Sediments, Environmental Chemistry, Analytical Chemistry, Hazardous Waste, Bioremediation, Ecology and Ecosystems, Hazardous, Environmental Engineering, hazardous waste management, hazardous waste treatment, risk assessment, sediment treatment, environmental technology, decontamination of soil and water, soil and groundwater remediation, bioavailability, biodegradation, risk management, contaminated sediment, decontamination of soil, chemical contaminants, contaminated soil, plant uptake studies, contaminants in soil, remediation, bioremediation of soils, biotransformation, phytoremediation, technology transfer, anaerobic biotransformation, waste mixtures, CERCLA

    Progress and Final Reports:

    Original Abstract
  • 1998
  • 1999

  • Main Center Abstract and Reports:

    R825513    HSRC (2001) - South and Southwest HSRC

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R825513C001 Sediment Resuspension and Contaminant Transport in an Estuary.
    R825513C002 Contaminant Transport Across Cohesive Sediment Interfaces.
    R825513C003 Mobilization and Fate of Inorganic Contaminant due to Resuspension of Cohesive Sediment.
    R825513C004 Source Identification, Transformation, and Transport Processes of N-, O- and S- Containing Organic Chemicals in Wetland and Upland Sediments.
    R825513C005 Mobility and Transport of Radium from Sediment and Waste Pits.
    R825513C006 Anaerobic Biodegradation of 2,4,6-Trinitrotoluene and Other Nitroaromatic Compounds by Clostridium Acetobutylicum.
    R825513C007 Investigation on the Fate and Biotransformation of Hexachlorobutadiene and Chlorobenzenes in a Sediment-Water Estuarine System
    R825513C008 An Investigation of Chemical Transport from Contaminated Sediments through Porous Containment Structures
    R825513C009 Evaluation of Placement and Effectiveness of Sediment Caps
    R825513C010 Coupled Biological and Physicochemical Bed-Sediment Processes
    R825513C011 Pollutant Fluxes to Aquatic Systems via Coupled Biological and Physicochemical Bed-Sediment Processes
    R825513C012 Controls on Metals Partitioning in Contaminated Sediments
    R825513C013 Phytoremediation of TNT Contaminated Soil and Groundwaters
    R825513C014 Sediment-Based Remediation of Hazardous Substances at a Contaminated Military Base
    R825513C015 Effect of Natural Dynamic Changes on Pollutant-Sediment Interaction
    R825513C016 Desorption of Nonpolar Organic Pollutants from Historically Contaminated Sediments and Dredged Materials
    R825513C017 Modeling Air Emissions of Organic Compounds from Contaminated Sediments and Dredged Materials title change in last year to "Long-term Release of Pollutants from Contaminated Sediment Dredged Material"
    R825513C018 Development of an Integrated Optic Interferometer for In-Situ Monitoring of Volatile Hydrocarbons
    R825513C019 Bioremediation of Contaminated Sediments and Dredged Material
    R825513C020 Bioremediation of Sediments Contaminated with Polyaromatic Hydrocarbons
    R825513C021 Role of Particles in Mobilizing Hazardous Chemicals in Urban Runoff
    R825513C022 Particle Transport and Deposit Morphology at the Sediment/Water Interface
    R825513C023 Uptake of Metal Ions from Aqueous Solutions by Sediments
    R825513C024 Bioavailability of Desorption Resistant Hydrocarbons in Sediment-Water Systems.
    R825513C025 Interactive Roles of Microbial and Spartina Populations in Mercury Methylation Processes in Bioremediation of Contaminated Sediments in Salt-Marsh Systems
    R825513C026 Evaluation of Physical-Chemical Methods for Rapid Assessment of the Bioavailability of Moderately Polar Compounds in Sediments
    R825513C027 Freshwater Bioturbators in Riverine Sediments as Enhancers of Contaminant Release
    R825513C028 Characterization of Laguna Madre Contaminated Sediments.
    R825513C029 The Role of Competitive Adsorption of Suspended Sediments in Determining Partitioning and Colloidal Stability.
    R825513C030 Remediation of TNT-Contaminated Soil by Cyanobacterial Mat.
    R825513C031 Experimental and Detailed Mathematical Modeling of Diffusion of Contaminants in Fluids
    R825513C033 Application of Biotechnology in Bioremediation of Contaminated Sediments
    R825513C034 Characterization of PAH's Degrading Bacteria in Coastal Sediments
    R825513C035 Dynamic Aspects of Metal Speciation in the Miami River Sediments in Relation to Particle Size Distribution of Chemical Heterogeneity