DEVELOPING SITE-SPECIFIC WATER QUALITY CRITERIA FOR METALS USING THE BIOTIC LIGAND MODEL
Abstract:The Biotic Ligand Model (BLM) is a relatively new tool for explaining and predicting the effects of water quality on the bioavailability and toxicity of metals to aquatic organisms. While it is well known that metal toxicity can be affected by water quality, the existing metals criteria ignore water quality factors other than hardness. As a result, a water quality criterion for metals may be overprotective for many receiving water bodies. Sitespecific criteria can be developed from bioassay information, such as in a water effect ratio (WER) study. The BLM was developed as a regulatory tool to provide an expedient and cost-effect alternative to bioassay testing in the establishment of sitespecific metals criteria.
The BLM has been successfully applied and tested in a wide variety of settings, in waters from geographically diverse areas in North America, South America, and Europe. The Water Environment Research Federation (WERF) has funded studies for the development and testing of the model for copper, silver, and nickel. As a result of the success of these programs, the U.S. EPA is considering the use of the BLM in the upcoming revision of the ambient water quality criteria for copper. Development is ongoing for a number of metals including copper, silver, zinc, nickel, lead, and cadmium.
The BLM uses easily obtained water chemistry for input data, including pH, DOC, cation and anion concentrations. The model has been extensively tested in settings where traditional bioassay-based methods have been used to develop site-specific criteria in freshwater and marine settings. WER datasets using fish or daphnia in freshwaters, or Mytilus edulis in marine waters have been compared with model predictions and typically shows excellent agreement. As a result of the relative ease of obtaining input parameters for the model, it is often possible to investigate temporal and spatial variability at a site in much greater detail than would be possible with bioassay-based methods. For example, a WER study was conducted for San Francisco Bay in support of a TMDL for copper. The model was used to predict WER results prior to conducting the bioassay tests. After confirmation that the model was in good agreement with the test results, the model was used to predict spatial variation in the site-specific copper criterion throughout the bay.
Document Type: Research Article
Publication date: January 1, 2003
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