Draft Guidance Document on Simulated Freshwater Lentic Field Tests (Outdoor Microcosms and Mesocosms)

1. Outdoor microcosms and mesocosms are useful in risk assessment when lower-tier and higher-tier laboratory studies (single-species and multi-species) indicate potential risks. They can be an important tool in bridging the gap between these studies and in attempting to understand and predict what may occur in the natural environment subjected to these risks. Every microcosm or mesocosm study should be designed to test a specific hypothesis using information gained in previous steps of the risk assessment. This makes every microcosm or mesocosm study unique in at least some aspects of its design. Guidance for conducting microcosm or mesocosm studies is therefore necessarily generic and flexible (Campbell et al. 1999).