Assessment of drift as a recovery endpoint in aquatic snails exposed to ammonia.

Pollutants are an important factor that causes among others drift (i.e. downstream transport of aquatic organisms in the current) in aquatic invertebrates. However, drift response is taxon-specific, which necessitates the investigation of a wide variety of taxa. Additionally, no information on the effects of the common toxicant ammonia on this endpoint is available. Our study focuses on the effects of exposure and post-exposure to ammonia on the drift of the common aquatic mollusc: Potamopyrgus antipodarum (Hydrobiidae, Mollusca). The effects of ammonia were tested using percentage of drift and stay time (i.e. time that animals stay without dislodging), which were monitored during 2 days of exposure and 2 days of post-exposure in a laboratory stream microcosm. Drift was observed at concentration 4.3 times lower than the LC50 48 h to this species. Our results show that ammonia increases the percentage of drift and caused a reduction in stay time of the exposed animals, both endpoints recover to their normal values after 24 h of post-exposure to ammonia.