Lentic mesocosms

A threefold difference in threshold concentrations is reported for long-term exposure to copper (adjusted to 50 mg/L CaC03 hardness) derived from 1 lentic mesocosm and 6 artificial stream studies conducted in the United States and Europe (Versteeg et al. 1999). The NOECecosystem values of these studies with copper were in the range of 2.1 to 6.6 pg/L. 

Predicted no-effect concentrations (PNECs) are traditionally used in risk assessments and form the basis of most EQS values. There are 3 basic approaches to the derivation of PNECs and resultant EQS values. The traditional method uses standard toxicity data and applies an AF to the most sensitive endpoint to derive a protective concentration. The SSD approach utilizes all available toxicity data to derive a value that is protective of a given percentage (e.g., 95%) of the species and is increasingly being used by many countries, often with a small AF placed on, for example, a predicted HC5 (hazardous concentration to 5% of species, i.e., the 5th percentile of the SSD) based on chronic data. Finally, model ecosystems such as lentic mesocosms can be used to derive safe values, again usually with a small AF. 

Microcosm and mesocosm studies can be directly designed for the purpose of EQS derivation (e.g., the exposure scenario, communities to be monitored, etc.). Guidance for design and conduction of microcosm and mesocosm studies can be found in the references given for pesticide risk assessment, but OECD has recently published a guideline for a lentic field test that is not focused on pesticides alone (OECD 2006b). 

OECD] Organization for Economic Cooperation and Development. 2006b. Guidance document on simulated freshwater lentic field tests (outdoor microcosms and mesocosms). Paris (France) Environment Directorate, Organisation for Economic Co-operation and Development. Series on testing and assessment, no. 53, ENV/IM/ MONO(2006)17. 37 p. 

OECD Organisation for Economic Co-operation and Development, Guidance Document on Simulated Freshwater Lentic Field Tests (Outdoor Microcosms and Mesocosms), ENV/JM/MONO, 2006, 17. 

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