The benthic ostracod Heterocypris incongruens is becoming an important tool for the ecotoxicological assessment of contaminated sediments. However, no study has yet explored solid-phase (dietary) exposure to ostracod. The present study examined the effects of metals on H. incongruens through aquatic and dietary exposures. The algal food Chlorella vulgaris was exposed to different concentrations of cadmium (Cd), copper (Cu), and zinc (Zn), and subcellular distributions of these metals in algal cells were determined. Parallel experiments were also performed to determine the toxic effects of dissolved metals on ostracod through aqueous exposure. Significant toxic effects on mortality were observed when ostracod were fed with Cd-contaminated (47-100%) and Cu-contaminated algae (55-100%). With increasing accumulated Zn in the algal cell, ostracod mortality also increased (20-83%). Aquatic exposure of ostracod to different concentrations of dissolved Cd (3.2-339 µg Cd/L) and Cu (260-2600 µg Cu/L) resulted in high observed mortalities (57-100% and 95-100%, respectively). Based on the results of aqueous and dietary exposure tests, it can be concluded that both exposure routes are important in evaluating the toxic effect of Cd on ostracod. Similar results were observed in tests using other metals (i.e., using Cu and Zn), thus emphasizing the importance of considering not only aquatic but also dietary exposure routes when evaluating metal toxicity to ostracod.

Freshwater green algae Scenedesmus acutus and ostracod Heterocypris incongruens were used to evaluate sediment toxicity. They were exposed to a series of copper and zinc concentrations for 6 days. Effects of different food (algae and TetraMin ® ) and modifications of photoperiod in the toxicity test were also determined. TetraMin ® met the validity criteria, though it cannot be a complete substitute of algal food in the toxicity test. Modification of photoperiod has significant influenced on the ostracod toxicity test. The median lethal concentrations (LC50) of copper when fed with TetraMin ® were 270 µgCu/L and 571 µgCu/L under 24-h dark and light/dark conditions, respectively. Almost no significant effect on ostracod sensitivity to zinc when exposed under light (470 to 423 µgZn/L). On the other hand, light condition has similar effects on ostracod sensitivity to copper and zinc when fed with S. acutus. The preliminary results of the ostracod toxicity tests seem to show complex phenomena of multi exposure pathways and further investigation of the interrelationship between ostracod and food organisms is necessary.