Fish early-life stage toxicity and environmental relevance: what does high-dose toxicity testing tell us?

The early-life stage (ELS) toxicity syndrome for fish is well described and has been reported in hundreds of toxicity studies. It is generally characterized by a reduced heart rate, yolk sac and pericardial edemas, and various morphological abnormalities, the most common being spinal curvature. For many of those studies, it appears that the ELS toxicity syndrome is the result of nonspecific (baseline) toxicity that occurs at aqueous and whole-body concentrations that are just below lethal concentrations. Baseline toxicity is essentially a nonspecific response that results from chemicals accumulating in and disturbing the function of biological membranes that leads to lethality and sublethal effects at relatively high doses. The commonality of this acute ELS toxicity syndrome among highly diverse organic and inorganic chemicals is remarkable. It is important to identify baseline toxicity because it is considered minimal toxicity that acts in all tissues and cells, and it has the potential to impair all cellular functions. This means if an effect is observed around baseline-toxic concentrations, it is likely that other cellular functions are also affected (i.e., the effect is not specific). The fish ELS toxicity syndrome can also be the result of specific effects involving receptor interactions; therefore, we emphasize the importance of distinguishing between specific and nonspecific toxicity responses to provide the most relevant data for environmental risk assessment.