Comparison of the relative toxicity relationships based on batch and continuous algal toxicity tests

In this study, we compare individual and combined responses of metal toxicants, on Selenastrum capricornutum, using batch and continuous techniques. The batch test is characterized by its saturated nutrient status for algal growth and, on the other hand, the continuous test is conducted at a nutrient-limiting condition. The two test methods depict completely different relationships in relative toxicity. In addition, the batch tests seriously underestimate the toxicity of metal mixtures containing lead. The above phenomena can be attributed to the surplus amounts of a limiting nutrient (phosphorus) and chelators in the growth medium. Since algae in the field are grown under low concentrations of nutrients and chelators, the results presented herein suggest that the significance and adequacy of current algal toxicity test protocols should be carefully reviewed.