Testing for the toxicity of chemicals with Tetrahymena pyriformis.

A test was developed using Tetrahymena pyriformis in order to determine the toxicity of various chemicals. Pre-cultured T. pyriformis was exposed for 24 h at 30 degrees C to various concentrations of chemicals, and the number of T. pyriformis surviving were then counted. The concentration of the chemical, at which the proliferation of T. pyriformis was restricted to one-half of the blank test (EC50), was determined. The method, applied to 57 chemicals, demonstrated that it could be used to detect the chemicals at low concentrations rapidly and with ease. The EC50 values showed a good relationship with 48 h LC50 values for Himedaka (Orizias latipes), and could be explained on the basis of the partition coefficient between water and n-octanol.