Grantee Research Project Results
2000 Progress Report: Biogeochemical Control of Heavy Metal Speciation and Bioavailability in Contaminated Marine Sediments
EPA Grant Number: R825220Title: Biogeochemical Control of Heavy Metal Speciation and Bioavailability in Contaminated Marine Sediments
Investigators: Shine, James P.
Institution: Harvard University
EPA Project Officer: Hahn, Intaek
Project Period: December 2, 1996 through December 1, 2001
Project Period Covered by this Report: December 2, 1999 through December 1, 2000
Project Amount: $453,630
RFA: Exploratory Research - Early Career Awards (1996) RFA Text | Recipients Lists
Research Category: Early Career Awards
Objective:
The total concentrations of contaminants in an environmental sample are not indicative of the potential for adverse ecological effects. Contaminant speciation and its effect on bioavailability are critical to understanding ecotoxicology. This information also is crucial for development of policies concerning the use and disposal of toxic material in the environment.In contaminated marine sediments, the presence of sulfides has been appropriately identified as a factor altering the availability of heavy metals to benthic organisms. However, at high metal concentrations, when the ability of sulfides to buffer the toxicity of metals is exhausted, toxicity is not always observed. This implies other binding phases which also may contribute to reduction of metal availability in sediments. These other binding phases may include dissolved and particulate organic matter which can form stable complexes with heavy metals, thus reducing their bioavailability.
This project is examining the role of dissolved and particulate organic matter on metal speciation and bioavailability in marine sediments. Methods to determine speciation parameters have been developed and applied at contaminated locations in New Bedford Harbor, USA. Observations will be made over multiple seasons to observe the temporal and spatial variability of these ligands on metal speciation and bioavailability.
The specific objectives of this project are to: (1) develop methods to determine the role of dissolved and particulate organic ligands on the partitioning of metals in marine sediments and observe how partitioning varies in space and time; (2) determine, in conjunction with acid volatile sulfides, how adsorbed (particle bound) and porewater ligands control the availability of heavy metals to transplanted and native benthic organisms; (3) develop methods to quantify the thermodynamic characteristics of adsorbed and porewater metal binding ligands; and (4) develop the study findings in a framework that assists development of criteria for protection of aquatic ecosystems.
Progress Summary:
Sediments and sediment porewater have been collected from three locations: New Bedford Harbor (contaminated); Boy's Creek, Fairhaven, MA (contaminated); and Buzzards Bay (uncontaminated). Porewater samples have been collected using passive samplers (peepers), with the concentration and thermodynamic stability constants of the dissolved metal binding ligands estimated using an acetylacetonate competitive ligand technique. The thermodynamic characteristics of the particulate organic carbon ligands are estimated using an anaerobic titration technique in the presence of EDTA. Results indicate that the concentration of dissolved metal binding ligands in the porewater is in the micro-equivalent per liter range with conditional stability constants similar to those observed in overlying seawater. Further, the concentration of particulate organic carbon ligands is on the order of micro-equivalents per gram of particulate organic carbon, with similar conditional stability constants as observed for the dissolved ligands. Given that coastal sediments will typically have 1-10 percent organic carbon (on a dry weight basis) with a porosity of 0.7?0.8, most of the metal binding carbon ligands in sediments are in the particulate phase. Based on measurements of simultaneously-extracted metals (SEM) and acid volatile sulfide (AVS) in these sediments, overall speciation calculations indicate that the binding capacity of sulfides in sediments is approximately equal to binding capacity of organic carbon. Thus, the overall binding capacities of these sediments are approximately twice that which would be predicted from AVS concentrations alone due to complexation with organic carbon ligands. Modeling efforts of metal mixtures show that the equilibrium distribution of a given metal is not only a function of that metal's concentration and the concentration of the reactants (sulfides and organic carbon), but also the concentrations and reactivities of the other metals competing for complexation to those same reactants. Depending on the routes and mode of exposure of benthic organisms to sedimentary contaminants, regulatory criteria may have to consider both organic carbon and sulfides, as well as the effects of complex mixtures, in order to determine site-specific standards truly protective of human and ecosystem health.Future Activities:
Experiments currently are underway to relate the geochemical speciation measurements with uptake into biological organisms. By altering the distribution of metals between sulfides, organic carbon, and freely dissolved in porewater, the uptake rate constants for each metal species can be determined. This can be used to model the fate and effects of metal mixtures in marine sediments.Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 6 publications | 2 publications in selected types | All 1 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
Shine J, Vinturella A, Connolly J. Speciation of metals in anaerobic marine sediments. Eos 2000;80(49):OS292. |
R825220 (2000) |
not available |
Supplemental Keywords:
sediments, marine, estuary, bioavailability, heavy metals., RFA, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Hydrology, Contaminated Sediments, exploratory research environmental biology, Environmental Chemistry, Ecosystem/Assessment/Indicators, Chemical Mixtures - Environmental Exposure & Risk, Ecosystem Protection, Geochemistry, Ecological Effects - Environmental Exposure & Risk, Ecological Effects - Human Health, Biochemistry, Ecological Indicators, biogeochemical partitioning, particulate organic carbon, ecological exposure, marine ecosystem, colloidal particles, contaminant transport, benthic biota, contaminated sediment, adverse human health affects, chemical contaminants, chemical transport, ecological impacts, marine sediments, aquatic ecosystems, heavy metal contamination, ecotoxicologyProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.