COMPARISON OF DAPHNIA-MAGNA, RAINBOW-TROUT AND BACTERIAL-BASED TOXICITY TESTS OF ONTARIO-HYDRO AQUATIC EFFLUENTS

Over a one year program of intensive monitoring of effluents from Onta rio Hydro's nuclear, fossil and hydroelectric generating facilities, t he Daphnia magna and rainbow trout, Oncorhynchus mykiss, acute toxicit y tests correlated well, with 61% of the toxic effluents toxic to both species. If the effluent was toxic to only one of the test species it was generally toxic to D. magna, with from 23 to 57% of the toxic eff luents toxic to D. magna only. The greater sensitivity of D. magna to boiler blowdown effluent likely resulted from a combination of the low conductivity of boiler blowdown effluent and the smaller size and gre ater surface to volume ratio of D. magna relative to rainbow trout D. magna were also particularly susceptible to oil/water separator sample s, with the daphnids frequently observed to be caught at the surface/w ater interface. These observations suggest that an accumulation of org anic material at the air/water interface was responsible for the morta lity of D. magna. In subsequent tests, we also examined the relationsh ip between the D, magna acute toxicity test and a bacterial-based assa y (Toxi-Chromotest(.)) for several toxic effluents from Ontario Hydro stations to determine if bacterial-based tests could provide similar i nformation in less time with smaller sample volumes. The D. magna acut e toxicity test did not correlate well with the bacterial-based Toxi-c hromotest(.). In particular, many of the samples which were toxic to D . magna were not toxic to the Toxi-chromotest(.) assay. The poor corre lation between the D. magna and Toxi-chromotest(.) likely relates to b oth the relatively low toxicity of many of the effluent samples, and t he fact that in many cases toxicity likely resulted from relatively si mple combinations of inorganic toxicants. Accordingly, the Toxi-Chromo test(.) assay would not seen suitable as a surrogate for the D. magna acute toxicity test for our effluents.