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Predicting sediment metal toxicity using a sediment biotic ligand model: methodology and initial application.
Dominic M Di Toro1, Joy A McGrath, David J Hansen
1Department of Civil and Environmental Engineering, University of Delaware, Newark, Delaware 19716, USA. dditoro@ce.udel.edu
Environmental Toxicology and Chemistry
|November 5, 2005
Summary
A new method using the biotic ligand model (BLM) predicts sediment toxicity from metals without complex pore-water chemistry calculations. This approach simplifies assessing metal effects concentrations in aquatic environments.
Area of Science:
- Environmental Chemistry
- Aquatic Toxicology
- Ecotoxicology
Background:
- The simultaneously extracted metals/acid-volatile sulfide (SEM/AVS) procedure is a standard for assessing sediment metal toxicity.
- Predicting sediment metal effects concentrations often requires complex pore-water chemistry modeling.
- Existing models may not fully capture the bioavailability of metals in diverse sediment matrices.
Purpose of the Study:
- To extend the SEM/AVS procedure to predict acute and chronic sediment metal effects concentrations.
- To integrate a biotic ligand model (BLM) with a pore water-sediment partitioning model.
- To simplify toxicity predictions by bypassing detailed pore-water chemistry analysis.
Main Methods:
- Developed an extended SEM/AVS procedure incorporating a BLM and a pore water-sediment partitioning model.
- Focused on partitioning to sediment organic carbon (OC) to predict metal-ligand equilibrium.
- Validated predictions against acute and chronic toxicity data for cadmium, copper, nickel, lead, and zinc using Daphnia magna BLM.
Main Results:
- The normalized median lethal concentration (SEM*(x,OC)) remained consistent across various pore-water conditions, with pH being the primary factor.
- SEM*(x,OC) values were similar for copper, nickel, zinc, and lead, but distinct for cadmium.
- Established approximate SEM*(x,OC) values at pH 8: Cd ≈ 100, Cu ≈ 900, Ni ≈ 1100, Zn ≈ 1400, Pb ≈ 2700 (micromol/gOC).
Conclusions:
- Biotic ligand models can effectively predict sediment toxicity without detailed pore-water chemistry modeling.
- The findings explain previously observed empirical dose-response relationships between SEM and toxicity.
- The simplified approach offers a more accessible method for assessing sediment metal contamination and ecological risk.