Acartia tonsa eggs as a biomonitor to evaluate bioavailability/toxicity of persistent contaminants in anoxic/sulfidic conditions: The case of cadmium and nickel

Abstract The evaluation of toxicity due to persistent pollutants in anoxic aquatic environments has met with various problems, as most test organisms can not withstand oxygen lack and exposure to free sulfide. We evaluated the suitability of the eggs of the brackish copepod Acartia tonsa for bioassays in anoxic/sulfidic conditions: when exposed to deep hypoxia and free sulfide, the eggs become quiescent and are able to resume hatching after restoring normoxic conditions. Tests with cadmium and nickel were performed in normoxic and deeply hypoxic conditions and in anoxic water containing H 2 S or H 2 S+FeSO 4 on an equimolar basis. Active and quiescent eggs showed equivalent sensitivity to the metals, both suffering significant reductions in hatching success at 89 μM Cd and 17 μM Ni. As expected on the basis of the SEM/AVS model, Cd toxicity was almost completely suppressed in presence of sulfides. Dissolved Cd concentration drastically dropped and hatching success was generally >80%, as against values A. tonsa eggs could be a useful biomonitor to evaluate toxicity due persistent contaminants in anoxic conditions and the role of sulfides in reducing metal bioavailability/toxicity.