Toxic effects, at three pH levels, of two reference molecules on common carp embryo.

Early life-stage survival, motility, and growth toxicity tests were carried out on common carp (Cyprinus carpio L.) endotrophic embryo, with two reference molecules (captafol and DNOC), from fertilization to the end of the first two-thirds period of mortalities by starvation. Thirteen days duration exposure was performed in daily renewed medium, at 24.5 degrees C, in standard synthetic water, at three pHs (6.9, 7.8, 9.0), in the presence of 10 mM/liter nontoxic pH buffer. Nominal concentrations of toxicants were 0.0, 0.25, 0.5, 1.0, and 2.0 mg/liter. Toxic effects on survival, motility, and growth decreased with increasing pH. From pH 6.9 to 9.0, the "no-observed-effect concentrations" differed by a factor greater than 8. Motility and growth cannot be considered, at population level, as true sublethal embryo-larval toxicity criteria. The toxicological interpretation of these results is discussed. They confirm the need of multifactorial methods for toxic risks and effects assessment on fish early life stages in the environment.