Effect of dissolved organic matter source on phytotoxicity to Lemna aequinoctialis.

The effect of dissolved organic matter (DOM) on metal toxicity to aquatic organisms has been reported. Biotic ligand model (BLM) can account for this factor to predict metal toxicity. However, few attempts have been made to assess the effect of the DOM on metal phytotoxicity to duckweeds. The objectives of this study were to examine the effect of DOM on copper toxicity to the duckweed Lemna aequinoctialis, and to determine if DOM concentration alone, regardless of DOM source, is an acceptable input parameter for the BLM for copper. Nine different DOM isolates from nine different sites in Japan were used in this study. A significant difference was observed between the lowest and the highest copper binding capacity. Phytotoxicity for copper decreased with increasing DOM concentration. These observations support use of the copper biotic ligand model (BLM) with AFA% (active fulvic acid percent) as a regulatory tool to predict copper phytotoxicity on duckweeds.