M7 AM Metals in the Environment: Chemistry and Fate Issues
Monday, 14 November 2005: 8:00 AM - 11:40 AM in 327-329

(BHA-1117-863731) Estimating Critical Loads of metals to surface aquatic systems using a coupled metal TRANsport-SPECiation-TOXicity (TRANSPEC-TOX) model.

Bhavsar, S¹, Gandhi, N^{1, 2}, Diamond, M¹, ¹ University of Toronto, Toronto, ON, Canada² Current address: Gartner Lee Ltd, Markham, ON, Canada

ABSTRACT- Environmental regulators and water resources managers seek science-based critical loads (CL) for compounds discharged into aquatic ecosystems. Estimating CL for metals is challenging because metal bioavailability and toxicity depend on water chemistry and fate and transport processes. To address this need, we developed a generic model termed as TRANSPEC-TOX by integrating the coupled metal fate/TRANsport and SPECiation/complexation (TRANSPEC) model of Bhavsar et al. (2004a,b) with a TOXicity module. The TRANSPEC-TOX uses (1) the multi-species fugacity/aquivalence concept (Diamond et al. 1992) for the fate calculations, (2) incorporates the effects of chemistry parameters (e.g., pH, metal and ligand concentrations) on metal partitioning/distribution and speciation by means of a chemical equilibrium speciation module (e.g., WHAM, MINEQL+), and (3) assesses toxicity to aquatic receptors (e.g., fish) using the toxicity module. TRANSPEC-TOX calculates critical loads of the metals using a toxicity reference value such as an LC50. We illustrate utility of the model through application to several lakes with characteristics varying in trophic status and we use use the Biotic Ligand Model (BLM) as the toxicity module. We focus on Zn in Rainbow trout. Results suggest that for the systems where sediments are acting as a source of the metal in water column, critical load may not be linearly related to LC50 water concentrations. However, effects of chemistry parameters (e.g., pH) with constant fate/transport parameters (e.g., particle movement rates) on LC50 and CL can be possibly explained by linear relations between LC50 and CL.

Key words: metal fate and transport, metal chemistry, critical load, BLM