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Algal growth inhibition tests for environmental risk assessment require improved efficiency to evaluate large numbers of chemicals. As an endpoint for rapid estimation of the effect concentration of test chemicals, we propose the delayed fluorescence (DF) measurement from an alga 24 h after exposure. Eight chemicals (bifenox, bromoxynil, bensulfuronmethyl, diuron, diflufenican, thiobencarb, m-chlorophenylhydrazone and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) were tested. The EC50 values from the 24 h DF measurement were similar to those from the conventional 72 h growth test for seven tested chemicals excepting thiobencarb. We conclude that 24 h DF measurement is a possible endpoint for rapid estimation of the EC50 values obtained in the 72 h growth test for those seven chemicals.

We propose that rapid algal bioassay using delayed fluorescence (DF) may be useful to apply to the whole effluent toxicity test. In this report, we compared the conventional algal growth inhibition test and the rapid algal bioassay using DF to detect the toxicity of industrial effluents. We used the industrial effluents from eight factories in Toyama Prefecture. Delayed fluorescence is a special type of luminescence; it detects the growth of only those cells that have photosynthetic capability. Therefore, DF can detect algal growth inhibition in a shorter time than the 72 h conventional test, as cells that have lost photosynthetic capability can be detected. The DF test in 6 h and 24 h exposure found algal inhibition from six out of eight effluent samples, and found chronic toxicity unit over 10 from four out of eight effluent samples, the same as the conventional 72 h growth test. These observations suggest that the rapid bioassay using DF is potentially applicable to the selected industrial effluents.