Studies on the toxicity of coal-tar dyes. III. Reason of acute toxicity to fish caused by coal-tar dyes and their industrial effluents.

Reason of acute toxicity to fish caused by coal-tar dyes and their industrial effluents were studied from the three points of view. 1) Partition coefficient (n-octanol/water) was determined on several coal-tar dyes, and it was found that the larger the ratio was, the stronger was toxicity to fish. 2) As a result of determination about existent form of xanthene dyes under photo-irradiation, it was clarified that dyes in solution were in the form of excited triplet state and halogen in dye molecule was liberated in free form. 3) When coal-tar dyes were treated with sodium hypochlorite, harmful chloroform was detected from dye solution. Chloroform and its homologous compounds showed the low TLm value and had the serious effect on fish.