Influences of water chemistry on bioavailability and toxicity of copper to fresh water algae: an implication for the biotic ligand model (BLM)

摘要

The Biotic Ligand Model (BLM) has been previously developed to explain and predict the effects of water chemistry on the toxicity of copper to rainbow trout, fathead minnow and D. magna. In this paper, we describe the development and application of a BLM for copper to freshwater alga. The variations in Cu toxicity to alga over a range of EDTA and the site-specific variables in DOC, alkalinity and chloride were examined. Higher content of variables in EDTA, DOC, alkalinity and chloride linearly increased the 96-h EC50 (as the total Cu), supporting the concept of complexes of these ligands with Cu to reduce the chance of Cu adsorbed on the active sites at the organism-water interface. Based on the BLM concept, we developed a methodology to estimate stability constants and complexation capacity (or BL, which equals to concentration of binding sites on the single cell) for the Cu to bind biotic ligand on the basis of toxicity data. Following values were obtained: log K_(BL)= 5.8, and CCBL=5.74x10~(-8) μmol·cell~(-1). Further, we determined that the critical accumulation of Cu EC50 (or LA50) is 2.5x10~(-8) μmol·cell~(-1) corresponding to the dissolved Cu EC50, and the average 43% of biotic ligand sites need to be occupied by Cu to induce a 50% acute effect for alga after 96-h exposure. Using the estimated constants, we examine the key assumption that underlies the BLM, whose toxicity can be defined as accumulation of copper at the physiological activity sites (or biotic ligand) on the alga cell membrane at or above a critical threshold concentration. The initial BLM was developed that can predict acute Cu toxicity to alga as a function of water characteristics. After validation with reconstituted and natural waters, the developed model will support efforts to predict Cu EC50s for use in WER determinations. The presented methodology can easily be applied for BLM development for prediction of Cu toxicity to other organisms.