VARIABILITY OF SPECIES SENSITIVITY TO COMPLEX-MIXTURES

In Denmark, as well as in a few other countries, the regulatory practi ce for granting permits for discharge of industrial waste water is bas ed on evaluation of the potential effects of both the individual chemi cal substances in the waste water and the complex waste water itself b y establishing ''predicted-no-effect-concentrations'' (PNECs). The pre sent study was initiated in order to establish an extrapolation method for deriving PNECs for complex mixtures. The toxicity of 5 complex mi xtures comprising from 5 to 20 different substances was tested with 5 different species/test systems: the green alga Rhaphidocellis subcapit ata, daphnia (Daphnia magna), zebra fish (Brachydanio rerio), duckweed (Lemna minor) and Microtox (Vibrio fischeri). The results of the test s showed that the differences in sensitivity of the test species were considerably lower (5-12 times) than was the case for the individual s ubstances present in the complex mixtures. Thus, based on the differen ces in sensitivity of the species, application factors for complex mix tures are proposed. Moreover, the results showed that the joint toxici ty of the complex mixtures could be described by assuming that the tox icity of the individual substances in the mixtures was more or less ad ditive. Copyright (C) 1996 IAWQ.