Use of Existing Studies

2 Use of Microcosm, Mesocosm, and Field Studies for EQS Setting 4.7.2.1 Use of Existing Studies 

Historically, the United Kingdom and some other regulatory authorities have based EQS values on single-species tests and only used mesocosm data as corroborative evidence. Under the WFD, however, mesocosm no-effect data have recently been used directly to set a freshwater EQS for chlorpyrifos in the European Union, and similar action has been taken for atrazine in the United States (USEPA 2003a). It is clear that such data are more relevant to the natural environment than laboratory-based single-species tests. 

Mesocosm no-effect data on a rapidly dissipating compound such as a pyrethroid insecticide may not be suitable for a chronic EQS applied to a river. Furthermore, most existing micro- and mesocosm studies are inappropriate for EQS derivation if fish are the most sensitive species because fish have generally been excluded from such tests. There is consequently a need for evidence-based decision making for interpretation of nonstandard mesocosm studies. Microcosm and mesocosm tests can, however, be used directly for EQS derivation if algae, macrophytes, and invertebrates are appropriately represented in the test systems and if they concern substances subject to transient exposure. They are then directly applicable for the derivation of M AC-EQSs. For this purpose, the NOEAEC can be used as it represents the highest initial concentration that causes no ecologically relevant effects. 

Microcosms and mesocosms can also directly be used to derive AA-EQSs if the test substance concentration was relatively constant over time (due to stability of the test item or due to experimental manipulation) and the study duration was long enough to detect possible long-term effects (usually at least 8 weeks, but this will depend on the life cycle of sensitive taxa). These test systems are more difficult to 

Environmental and Human Health Standards for Water and Soil 

---