Objectives/Hypothesis:
The overall objective of the proposed research is to evaluate the dynamics of uptake and availability of desorption-resistant contaminants to tubificid oligochaetes and the corresponding consequences to control and regulation of contaminated sediments. Physicochemical measurements suggest that some contaminants are slow or limited in their release from the sorbed state. Evaluation of the influence of these physicochemical limitations to biological availability, however, has generally been limited to microbial degradation processes which often display an asymptotic approach to a persistent residual level. A much more intense biological challenge is presented by tubificid oligochaetes that often dominate disturbed, polluted environments and which feed and burrow in the sediments and which serve as food to higher organisms. Work to-date both in our laboratories and elsewhere has demonstrated that these organisms process sediments in large quantities, enhance contaminant release from bed sediments, and can absorb and metabolize polynuclear aromatic hydrocarbons (PAH) by digestive processes from ingested sediment. These organisms can access and assimilate desorption-resistant contaminants but the rate and extent is uncertain as is the relationship to physicochemical measurements. Preliminary measurements suggest that the rate of uptake is enhanced by the metabolic processes of tubificid oligochaetes but that the ultimate extent of uptake is determined solely by equilibrium factors. It is this hypothesis that will be tested in the proposed research.
Approach:
The focus will be on polynuclear aromatic hydrocarbons, nonpolar hydrophobic organic compounds that are important contaminants in the sediment environment and for which the most is known as to desorption-resistance. The dynamics of uptake and fate of desorption-resistant contaminants in tubificid oligochaetes will be measured and compared to the rates and extent of contaminant release by strictly physicochemical processes. Small microcosms that have been used extensively in our laboratories will be employed. The microcosms allow a complete contaminant material balance to be collected, including assessment of organism ingestion, uptake and egestion. Both cumulative measurements and single gut passage measurements will be used to indicate contaminant fate. In addition, fecal material will be evaluated by both physicochemical means and by microbial challenges to assess the influence of digestive processing on contaminant availability.
Expected Results:
The research is expected to relate physicochemical desorption resistance to biological availability in a class of organisms important to contaminated sediments. It is expected that the results will allow improved models of uptake to these organisms to be developed, ultimately improving the ability to predict food web uptake since these organisms reside at the base of benthic food webs. Ultimately, the research is expected to assist in answering questions as to required cleanup levels and the persistence of desorption resistant contaminants.
Supplemental Keywords: Bioturbation, sequestration, natural recovery
Relevant Web Sites:
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Last Updated: May 22, 2002