Development of a model to predict the effect of water chemistry on the acute toxicity of cadmium to Photobacterium phosphoreum.

Cadmium (Cd) compounds are widely distributed toxic environmental and industrial pollutants, and they may bring danger to growth and development of aquatic organisms. The effects of Ca(2+) (as CaCl2), Mg(2+) (as MgSO4), K(+) (as KCl), pH and complexants (EDTA, the commercial DOM, and three homemade DOMs) on Cd toxicity to Photobacterium phosphoreum were evaluated in standardized 15 min acute toxicity tests. Increases in Ca(2+) concentration resulted in higher EC50 values, indicating the competition between the two ions for uptake sites at the biotic ligand. Increased waterborne Mg(2+) also reduced Cd toxicity, but to a slightly lesser degree compared with Ca(2+). The overall decline in EC50 data with increasing K(+) in test solutions suggested that Cd toxicity was enhanced at larger K(+) concentration. The toxicity alleviation by H(+) was observed over the tested pH range of 5.0-9.0. Additions of complexing agents into the exposure water reduced Cd bioavailability via complexation of Cd(2+), and complexants from different sources displayed different protective effect. The influence of these toxicity modifying factors was finally incorporated into a model that can predict acute cadmidum toxicity for Photobacterium phosphoreum. After validation with laboratory and natural waters, the developed model could support efforts to improve the ecological relevance of presently applied risk assessment procedures.