Ecotoxicity assessment is usually done by classical tests under controlled conditions. However, field situations may not be accurately predicted by laboratory testing. In situ testing is a pertinent way for assessing the ecological relevance of laboratory bioassays. The objectives of this study were to develop an in situ test chamber and respective test protocols suitable for ecotoxicity testing with zooplankton and to evaluate the use of laboratory protocols (water column and solid phase) by comparing results obtained under controlled conditions with in situ results at an aquatic system receiving acid mine drainage. At the most contaminated stations and at the reference stations, good agreement was found between in situ and classical testing. At intermediate stations, in situ toxicity was generally higher than that in classical tests. Sample collection and preservation probably altered actual toxicity, thus emphasizing the need for caution in estimating or extrapolating field effects from laboratory results. Keywords-Insitu testing Test development Daphnia magna Field validation Acid mine drainage Environ. Toxicol. Chem. 18, 1999 A.M.M. Pereira et al.

In situ bioassays are becoming very popular for laboratory test validation and field extrapolation. Natural conditions, including environmental variables, affect the "behavior" of contaminants and, consequently, their toxicity. This work aimed to develop protocols for in situ chronic bioassays with cladocerans and to assess the ecological relevance of conventional protocols for laboratory testing (water-column and sediment). An aquatic system impacted with acid mine drainage was chosen for the study. At some stations that were contaminated with heavy metals, water-column bioassays did not reveal any toxicity, while sediment and, especially in situ bioassays, revealed a delay in reproduction and a reduction in fertility. Thus, both laboratory bioassays underestimated the actual toxicity of studied sites: sediment, besides being an important contaminant source, became significantly altered with sampling, transport, storage, and manipulation. Therefore, an extra caution is needed when interpreting laboratory results, since the extrapolation to natural systems could be a very problematic step.

No abstract

No abstract