Water-column, sediment, and in situ chronic bioassays with cladocerans

In situ bioassays are becoming very popular for laboratory test validation and field extrapolation. Natural conditions, including environmental variab les, affect the "behavior" of contaminants and, consequently, their toxicit y. This work aimed to develop protocols for in situ chronic bioassays with cladocerans and to assess the ecological relevance of conventional protocol s for laboratory testing (water-column and sediment). An aquatic system imp acted with acid mine drainage was chosen for the study. At some stations th at were contaminated with heavy metals, water-column bioassays did not reve al any toxicity, while sediment and, especially in situ bioassays, revealed a delay in reproduction and a reduction in fertility. Thus, both laborator y 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 c aution is needed when interpreting laboratory results, since the extrapolat ion to natural systems could be a very problematic step. (C) 2000 Academic Press.