On the algicide Delrad 70

The algicidal efficiency of Delrad 70, an algicide prepared at Herculus Powder Co. U.S.A., was tested on some fresh-water algae and a water plant, including Chlorella, Scenedesmus, Oedogonium, Microcystis, Oscillatoria and Hydrilla. The efficiency of the toxicant was determined by mannonmetric method from the rate of photosynthetic activity or by macroscopic observation on change of color and sedimentation of the algal cells. The results obtained were as follows: (1) The valid concentration of the Delrad 70 varied from 0.1 to 1.0 ppm. according to kind of algae or their population dencity. It was also harmful to the gold-fish in almost the same concentration as to the algae. In dense culture of algae, the efficiency decreased probably due to the influence of adsorption to the algal cells. (Fig. 1, 2, 3, and Table I, II) (2) The adsorption degree of the Delrad 70, or the decrease of toxic efficiency was great in the existence of mucous excreta of gold-fish or in dense population of Scenedesmus, but not so great in Kaoline suspension. (Fig. 4, 5)