Studies on the Toxicity of Rivers―II Inference of Toxicants under Lethal Concentration of the Urakami River in Nagasaki City

Water samples collected from the Urakami River on October 1978 were concentrated with the freezing concentration method in order to detect the toxicity which is under lethal level to the test fish (Tanichthys albonubes). To find the causative toxicants by the toxicity test at 25℃, the concentrated samples were treated with the following three methods. One is pH adjustment test of the water samples at three different values 6.0, 7.0 or 9.0 and other two methods are the extracting tests with n-hexane and with dithizone-carbone tetrachloride. The results of the toxicity test were as follows. The toxicities of samples adjusted to higher pH became higher. The toxicities of samples extracted with n-hexane and with dithizone-carbone tetrachloride were not decreased. These results indicate that one of the causative toxicants is ammonia. However, comparison of the toxicity of water sample adjusted to pH 6.0 with the value of 48-hr. TLm of ammonia at pH 6.0 reveals that the water of Urakami River must include another causative toxicant besides ammonia, which is to exhibit toxicity even at low pH, and to be not extractive with n-hexane and with dithizone-carbone tetrachloride. Because the pollution of Urakami River was caused by household sewage and contents of anion surfactant (MBAS) in the 1000% concentrated water sample is higher than lethal limit. The detergents is estimated as this causative toxicant