Relation Between the Toxicity of Some Toxicants to the Aquatic Animals (Tanichthys albonubes and Neocaridina denticulata) and the Hardness of the Test Solution

The concentration toxicity of a river is detected by the freezing concentration method and the the toxicity test with the aquatic animals. Many inorganic substances such as Ca²⁺, Mg²⁺, Na⁺, and Cl⁻ are soluble in river water are also concentrated with a toxicant by the freezing concentration method. The toxicity of a toxicant would change due to these increasing substances. I studied the relation between the toxicity to the aquatic animals and the hardness of the test water. The fluctuation pattern of the toxicity to the fish and shrimp was the same. The pattern was divided into three types. The first pattern was decreasing toxicity according to increasing hardness of the test water. Zn²⁺, Cu²⁺ and Cd²⁺ belonged to the type. The second pattern was increasing toxicity according to increasing hardness of the water, and these toxicants included anmonia and the surfactants. The last pattern was the type that the hardness of the test water had no effect. Hg²⁺ and the synthetic detergents belonged to this type