[The effect of pesticides on the protozoan Tetrahymena pyriformis].

The toxic effect of the following pesticides was examined: metathion (doses from 1.49 micrograms to 100.0 g per litre of medium), phenmedipham (doses from 24.42 micrograms to 400.0 mg per litre of medium), gamma-hexachlorocyclohexane (doses from 122.07 micrograms to 250.0 mg per litre of medium), and chlormequat (doses from 305.16 micrograms to 20.0 g per litre of medium). The tests were performed on the protozoan Tetrahymena pyriformis. The LD50 of metathion was found to be 8.94 micrograms per litre and the LD100 ranged from 23.84 to 47.68 micrograms per litre. In phenmedipham the LD50 ranged from 12.5 to 25.0 mg per litre and its LD100 was above 400.0 mg per litre. The LD50 of gamma-hexachlorocyclohexane is 976.56 micrograms per litre and LD100 about 7.91 mg per litre. The LD50 of chlormequat ranged from 312.5 to 625.0 mg per litre and LD100 was about 20.0 g per litre of medium.