ACUTE TOXICITY ASSESSMENT OF INDUSTRIAL EFFLUENTS WITH A MICROPLATE-BASED HYDRA-ATTENUATA ASSAY

The acute toxicity potential of ten industrial plants located in Toyam a Prefecture (Japan) was appraised with a microplate-based assay devel oped with the freshwater cnidarian Hydra attenuata. Three measurement end points (LC(50), EC(50), and TC or ''threshold concentration'') wer e determined based on specific morphological changes displayed by Hydr a under conditions of progressive intoxication. Four effluents were sh own to be lethal toward Hydra while eight induced sublethal toxicity r esponses, LC(50)s varied from 18.8 to > 100% v/v, while EC(50)s ranged from 15 to > 100% v/v. Similarly, lethal and sublethal TCs ranged fro m 17.7 to > 100% v/v and from 8.8 to > 100% v/v, respectively. Statist ical analyses performed on all toxicity data for the ten effluents con firmed that the sublethal end points (EC(50)s and sublethal TCs), prev iously unreported to assess complex wastewaters, proved to be more sen sitive than the lethal end points (LC(50)s and lethal TCs). This was a lso reflected by lethality to sublethality ratios, which ranged from 1 to 2.6 (LC(50)/EC(50) comparisons) and from 1.1 to 5.4 (LC(50)/TC com parisons) within a 96 h exposure period. Similar statistical analyses undertaken on 24, 48, 72, and 96 h toxicity data failed to show any si gnificant time-related differences, thereby suggesting that an exposur e time as short as 24 h would not diminish test sensitivity. Since Hyd ra displayed an apparent increase in sensitivity toward a few effluent s with time of exposure, however, we would nevertheless recommend a 96 h time frame for this microtest. A correlation was also observed betw een conductivity and Hydra responses, highlighting a possible link to the presence of toxic metal ions. Based on our study, this simple and cost-effective microassay appears valuable as a (sub)lethal toxicity s creening tool for effluents. Additional studies are planned with chemi cals and other environmental matrices to better circumscribe its scope of usefulness. (C) 1997 by John Wiley & Sons, Inc.