Development of a protozoan chemoattraction bioassay for evaluating toxicity of aquatic pollutants.

A microcapillary assay technique was developed to assess effects of pollutants on the chemoattraction of the ciliate, Tetrahymena pyriformis. Parameters in the protocol such as starvation period, exposure period, and trough design were standardized in an effort to obtain consistent results. Cadmium, phenol, and naphthalene were tested for effects on ciliates' chemoattraction to 0.15% yeast extract. All three toxicants inhibited chemoattraction; cadmium had the greatest effect, followed by naphthalene and phenol, respectively. The percent inhibition of chemoattraction for each concentration was used to determine EC50 values for both 1 and 5 h exposures. Results show that the chemoattraction assay may provide a rapid, inexpensive, and sensitive asessment of aquatic toxicity. Inclusion of a protozoan assay fills the existing taxonomic gap in the routine battery of toxicity tests used for many hazard evaluations.