2002 Progress Report: Bioturbation and Bioavailability of Residual, Desorption-Resistant Contaminants

EPA Grant Number: R828773C001
Subproject: this is subproject number 001 , established and managed by the Center Director under grant R828773
(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: Bioturbation and Bioavailability of Residual, Desorption-Resistant Contaminants
Investigators: Reible, Danny D. , Fleeger, J. W.
Current Investigators: Reible, Danny D. , Fleeger, J. W. , Pardue, J.
Institution: Louisiana State University - Baton Rouge
Current Institution: Louisiana State University - Baton Rouge , Rice University
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 2001 through September 30, 2006 (Extended to September 30, 2007)
Project Period Covered by this Report: October 1, 2001 through September 30, 2002
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (2001) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management


The overall objective of this research project is to evaluate the dynamics of uptake and availability of desorption-resistant contaminants to tubificid oligochaetes. The proposed studies will address two critical aspects of the bioavailability of the desorption-resistant compartment: (1) the availability to sediment-dwelling, deposit-feeding macrofauna; and (2) the effect of macrofaunal sediment processing on subsequent availablity to other organisms or to natural desorption processes. These studies will focus on polynuclear aromatic hydrocarbons (PAHs), which are known to be biodegraded and bioaccumulated and are a primary sediment contamination problem in the Gulf Coast and in other industrialized regions of the United States.

Contaminated sediment quality is determined by the risks of contaminants to human and ecological receptors; in turn, this is controlled by the availability and exposure to those contaminants. Contaminants are generally assumed to be completely available to organisms that might ingest that sediment and to organisms in contact with porewater adjacent to contaminated sediment particles. Recent research, however, has shown that a significant fraction of the organic contaminants in soils and sediments may not be readily available for uptake and organism effects. A desorption-resistant fraction is often observed that is released more slowly and in lesser amounts from contaminated sediments.

The slowed rates of physicochemical release also have been reflected in microbial degradation processes. Physicochemical measures of desorption-resistance as an indication of bioavailability may hold great promise for assessing exposure and setting environmentally acceptable endpoints. In particular, the desorption-resistant contamination may represent the endpoint of natural attenuation processes. Until the present, however, there has been limited assessment of the bioavailability of this fraction beyond microbial assays. Other animals, notably deposit-feeding benthic organisms, may represent a more intense environment for the assessment of availability and are more directly linked to the food chain. Preliminary results with sediments and benthic organisms suggest that the ultimate organism uptake of desorption-resistant contaminants is reduced, compared to reversibly desorbed contaminants, but predictable with a biphasic equilibrium model. The preliminary work also suggests that the rate of uptake by benthic organisms is enhanced relative to that as expected by physicochemical desorption measurements. This work is primarily aimed at confirming the preliminary results and extending the database of compounds and sediments for which availability is understood. The ultimate goal is to develop a predictive model of biological availability based upon physico-chemical availability.

The fundamental approach has been to prepare sediments effectively containing only desorption resistant contaminants and monitoring the accumulation of the contaminants in deposit-feeding oligochaetes, Ilyodrilus templetoni. Deposit-feeding oligochaetes represent an intense processing environment for the sediments and thus the mass-transfer resistances that are inherently part of microbial assays of bioavailability do not complicate bioavailability tests employing these organisms.

A key aspect of the methodology, however, is sediment preparation. Based on preliminary evaluations by Mason Tomson, we identified dilute alcohol washes of inoculated sediment as a means of rapidly removing reversibly sorbed contaminant. Little or no change in total organic carbon results from such washes and the batch desorption isotherms generated by such an approach tracked multiple batch desorptions with water. Recent work has shown that there is some change in particle size distribution associated with this washing, with a depletion of silty size particles in the range of 1-5 µm and an enhancement of submicron size particles, but this difference has not been reflected in desorption isotherms, which are of primary interest here.

The primary advantage of the dilute alcohol washes is that complete removal of the reversibly sorbed contaminants can be achieved in 1-3 batch washes, while 10-100 steps might be required to achieve the same result using only water. This allows the efficient preparation of sediment that is essentially only contaminated with desorption resistant contaminants for inclusion in the bioavailability studies.

Progress Summary:

Preliminary results with phenanthrene indicated that the reduction in porewater concentration associated with the desorption-resistant contaminants was consistent with the reduction in normalized accumulation in the deposit-feeding oligochaetes. Similar work with aged sediments (i.e., sediment inoculated with phenanthrene more than 2 years ago) showed that both the effective partition coefficient and the normalized accumulation was equivalent to that from desorption-resistant phenanthrene in the above experiments.

Phenanthrene, however, is expected to accumulate in benthic organisms predominantly through the porewater pathway (i.e., the more hydrophobic a compound, the more likely that ingestion controls uptake). Thus, a reduction in uptake due to reduced porewater concentration may not be surprising. Evaluation of the kinetics of that uptake, however, showed that the single-gut passage adsorption efficiency of phenanthrene from sediments is essentially identical for reversibly sorbed and desorption-resistant contaminants. Thus, the ingestion of sediments by the worms seems to speed the rate of uptake, but that ultimately the porewater concentrations control the steady state accumulation.

We repeated the work with phenanthrene with benzo[a]pyrene (BAP), a more hydrophobic compound that is expected to be taken up primarily via ingestion. BAP also is interesting in that the model of desorption-resistance by Mason Tomson suggests that there is less of a difference between the partitioning of reversibly sorbed and desorption resistant BAP. This was demonstrated by desorption isotherms, which show almost no difference between reversible and desorption-resistant fraction partitioning. The uptake dynamics were quite slow for BAP, requiring approximately 4 weeks of sediment ingestion before the benthic organisms achieved steady-state accumulation. In addition, unlike phenanthrene, there was no difference in steady-state accumulation of BAP in the benthic organisms, consistent with the identical partitioning from reversible and desorption-resistant fractions.

These results continue to point to the porewater paradigm as a reliable indication of the steady-state accumulation of PAHs in deposit-feeding organisms, regardless if the primary route of exposure is through the porewater or through the sediment. We tested a model originally proposed on the basis of the preliminary phenanthrene data against the new data, and additional data in our laboratory from pyrene partitioning in a three-phase system (sediment, water, and non-aqueous phase), and literature data on sorption of fluoranthene on artificial sorbents. The results indicate again that the aqueous phase porewater concentrations are reliable indicators of steady-state accumulation in the deposit feeding organisms.

Future Activities:

Based on these initial results, work in the coming year will be directed toward improving our ability to predict the physico-chemical partitioning, which seems to provide the upper bound for benthic accumulation. Mason Tomson's work resulted in a model, but it is unclear how robust this model is, and it exhibits some inconsistencies with the work of Luthy, et al., and Weber, et al. The appearance of an essentially compound-independent desorption-resistant fraction partitioning seems that it must be the product of higher partition coefficients and slower mass transfer rates to the soot and hard carbon that Richard Luthy and Walt Weber believe are the primary source of desorption resistance. That is, the apparent equilibrium must be based on a balance of rate (which should be slowed for more hydrophobic compounds) and true equilibrium (which should increase for more hydrophobic compounds). We will conduct modeling and experimental work to confirm this and attempt to connect the competing models of physico-chemical desorption resistance.

The initial results also encourage the questions as to the extent that the availability of hydrophobic organic compounds can be applied to metals or mixtures of metals and hydrophobic organic compounds. We will work with metal mixtures and PAHs to determine synergistic or antagonistic effects on uptake and work with metals alone may be appropriate when reviewing the preliminary results of metals partitioning and release work being conducted by Mason Tomson and Louis Thibodeaux.

The final area of effort over the next year is to connect this body of knowledge to the biotechnology initiative efforts of the Hazardous Substance Research Center (HSRC). Specifically, we will assess the interaction of the benthic community with the surrounding microbial community through molecular biology techniques. This work is an attempt to repeat for benthic organisms the work that has proven to be beneficial to the development of phytoremediation, the assessment of the interaction of the plants, and the associated microbial community. In addition, we will direct preliminary work toward identifying genetic markers in benthic organisms that might make them effective or ineffective candidates for metabolic degradation of PAHs in sediments. The latter work will largely be supported by the funds available from the State of Louisiana through the Biotechnology Initiative, but we will maintain a synergistic connection to the current project.

Journal Articles on this Report : 4 Displayed | Download in RIS Format

Other subproject views: All 36 publications 13 publications in selected types All 9 journal articles
Other center views: All 279 publications 92 publications in selected types All 63 journal articles
Type Citation Sub Project Document Sources
Journal Article Lu X, Reible DD, Fleeger JW, Chai Y. Bioavailability of desorption-resistant phenanthrene to the oligochaete Ilyodrilus templetoni. Environmental Toxicology and Chemistry 2003;22(1):153-160. R828773 (2004)
R828773 (Final)
R828773C001 (2002)
R828773C001 (2003)
R828773C001 (2004)
  • Abstract from PubMed
  • Abstract: Wiley-Abstract
  • Journal Article Reible DD, Garcia M. Contaminant processes in sediment. American Society of Civil Engineers (ASCE) Sedimentation Manual. R828773C001 (2002)
    R828773C001 (2003)
    not available
    Journal Article Reible D, Mohanty S. A levy flight-random walk model for bioturbation. Environmental Toxicology and Chemistry 2002;21(4):875-881. R828773 (2004)
    R828773 (Final)
    R828773C001 (2002)
    R828773C001 (2003)
    R828773C001 (2004)
  • Abstract from PubMed
  • Abstract: Wiley-Abstract
  • Journal Article Thibodeaux LJ, Valsaraj KT, Reible DD. Bioturbation-driven transport of hydrophobic organic contaminants from bed sediment. Environmental Engineering Science 2001;18(4):215-223. R828773 (2004)
    R828773 (Final)
    R828773C001 (2002)
    R828773C001 (2003)
    R828773C001 (2004)
    R825513C011 (Final)
  • Abstract: Liebert-Abstract
  • Supplemental Keywords:

    bioturbation, sequestration, natural recovery, polynuclear aromatic hydrocarbon, PAH, bioavailability, biochemistry, biodegradation, bioremediation of soils, contaminants in soil, contaminated sediment, contaminated soil, degradation, desorption-resistant contamination, microbial degradation, natural recovery, phytoremediation, BASF., RFA, Scientific Discipline, Waste, Water, Contaminated Sediments, Environmental Chemistry, Microbiology, Environmental Microbiology, Hazardous Waste, Bioremediation, Hazardous, degradation, microbial degradation, bioavailability, biodegradation, contaminated sediment, turbificid oligochaetes, PAH, contaminated soil, contaminants in soil, bioremediation of soils, desorption-resistant contamination, natural recovery, biochemistry, phytoremediation, bioturbation

    Relevant Websites:

    http://www.hsrc.org/hsrc/html/ssw/ Exit

    Progress and Final Reports:

    Original Abstract
  • 2003 Progress Report
  • 2004 Progress Report
  • 2005
  • 2006
  • Final

  • Main Center Abstract and Reports:

    R828773    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).
    R828773C001 Bioturbation and Bioavailability of Residual, Desorption-Resistant Contaminants
    R828773C002 In-Situ Containment and Treatment of Contaminated Sediments: Engineering Cap Integrity and Reactivity
    R828773C003 Phytoremediation in Wetlands and CDFs
    R828773C004 Contaminant Release During Removal and Resuspension
    R828773C005 HSRC Technology Transfer, Training, and Outreach