pH dependent toxicity of five metals to three marine organisms

The pH of natural marine systems is relatively stable; this may explain why metal toxicity changes with pH have not been well documented. However, changes in metal toxicity with pH in marine waters are of concern in toxicity testing. During porewater toxicity testing pH can change 1–2 units as porewater is transferred from in situ to a test container. These changes in pH may alter metal toxicity. Also, deliberately altering the sample pH is an important toxicity identification and evaluations (TIE) manipulation designed to detect changes in ammonia toxicity. If altering pH also changes metal toxicity, this may confound interpretation of TIE manipulation results. This study demonstrates that alteration of pH can also change the toxicity of Cu, Cd, Ni, Pb, and Zn to Mysidopsis bahia (mysid), Ampelisca abdita (amphipod) and Vibrio fischerii [Microtox solid phase test (MSP)]. Changes in toxicity with respect to pH were metal and organism specific with the following trends. For the MSP assay, as pH decreased there was a decrease in toxicity for Pb, Ni, Cd, and Zn and an increase in toxicity for Cu. For mysids, as pH decreased, there was a decrease in toxicity for Pb and an increase in toxicity for Cu and Ni. For amphipods, Cu was the only metal that showed decreased toxicity with decreasing pH; the toxicity of all other metals for amphipods remained constant. Results of this study indicate changes in metal toxicity with respect to pH must be considered for porewater testing and TIE interpretation. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 235–240, 1999