METIER (modular ecotoxicity tests incorporating ecological relevance) for difficult substances .4. Test chamber for cladocerans in flow-through conditions

Continuous-flow systems in toxicity testing an advantageous because they introduce constant toxicant concentrations and constant food to the test organisms and continuously purge wastes. Therefore, continuous-flow systems are particularly useful in hazard assessment of substances that may readily be lost from test chambers (i.e., poorly water soluble, volatile, readily biodegradable or photodegradable, hydrolitically unstable compounds). Within METIER (Modular ecotoxicity tests incorporating ecological relevance, a European Union-funded project, a basic design for a standard flow-through exposure system was developed. This paper addresses the adaptation of the flow-through system for use with cladocerans, which involved designing a suitable test chamber and appropriate operation procedures. The sublethal toxicity of a reference compound (3,4-dichloroaniline) to Daphnia magna Straus was evaluated under both flow-through and semi-static conditions. Tests conducted under flow-through conditions provided a less sensitive measure of toxicity than under semi-static conditions. This result is probably a function of the higher food availability within the flow-through system. The no-observed-effect concentration for reproduction was the most sensitive endpoint and was 5 mu g/L in the flow-through system and 2.5 mu g/L in semi-static conditions.