Twenty-four-hour IC50 values (50% immobilization concentration) for phenol, o-cresol, m-cresol, p-cresol, six xylenols, and three trimethylphenols were determined for Daphnia magna under static conditions. Our results show that cresols are more toxic than phenol, that xylenols do not exhibit significantly higher toxicity than cresols, and that trimethylphenols are less toxic than cresols. Thus, no direct relationship can be found between the number and position of methyl groups on the phenol nucleus and their acute toxicity to the water flea.
