WERF Research Report Series- Silver Biotic Ligand Model (BLM)

The biotic ligand model (BLM) is a computational tool that may be used to predict toxic effect levels of metals, including Ag. The BLM considers the effect of site-specific water quality characteristics on Ag speciation and bioavailability. This provides a basis for extrapolating from laboratory waters, used for most Ag toxicity tests, to natural waters, where the bioavailability and toxicity of Ag may differ. The original version of the BLM for the acute toxicity of Ag was reviewed by the USEPA Science Advisory Board (SAB) in 1999 and they recommended the completion of additional Ag chemistry and toxicity studies to provide data to test and refine the model. This project was completed to satisfy these recommendations. A chemistry component was completed to improve the representation of Ag speciation in natural waters and to characterize the important effect of sulfide on Ag bioavailability. These investigations added to the information that was available to characterize Ag chemistry and provided a basis for updating the earlier version of the Ag BLM. The BLM was also calibrated to laboratory toxicity data that were generated for a Ag-sensitive invertebrate, Ceriodaphnia dubia, a cladoceran that had previously been tested to only a limited degree. The studies were carried out in laboratory waters in which the chemistry was systematically varied to provide a basis for calibration of the BLM to the toxicity data for C. dubia. Toxicity tests were also performed with both Pimephales promelas and C. dubia in natural water samples that were well characterized chemically, with the data then used to test the model. While the C. dubia BLM results were relatively successful at simulating the observed effect levels the P. promelas results highlighted the need for further testing…