A computer program is developed in order to assist the selection of best SAR (Structure-activity relationships) equation from the chemical structure in question. Four calculating methods of similarity are presented and tested. One calculating method is based on the sum of similarity to each chemical descriptor in a group and the others are on the range of the chemical descriptor in the group. The efficiency is measured by whether the program can show the original SAR group as the first candidate from which the test chemical is pulled out. The methods showed the candidates successfully and two of three methods based on the range of chemical descriptor in a group have selected the original SAR group for all chemicals with plural candidates.

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Changes with time in river water toxicity were monitored by 14-d shrimp test from April to October 1995. Tests were conducted 3 times a week during spring and summer. Water samples were collected from 3 sampling sites on the Koise River system, which flows through a rural district composed mainly of paddy fields. Shrimp mortalities and the concentrations of several pesticides changed in parallel between the middle and lower stations, 8 km apart. This strongly suggests that the shrimp mortality is due mainly to overall pesticide effects in the river water. The mean 14-d shrimp mortalities were 67% and 48% at the 2 stations during the summer. Several organophosphorus insecticides might have caused the shrimp mortality at the middle station in August. However, the cause of mortality from May to July was not clear, even thoughfenobucarb, a carbamate insecticide, was detected continuously from spring to early summer with a peak concentration of 1.6 μg/L. Other possible causes are discussed, Concurrently, macrobenthic fauna at the upper and middle sites was investigated; this is reported in the following paper.

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Macrobenthic fauna at 2 sites on tributaries of the Koise River system was compared to assess the effects of river water toxicity revealed by the shrimp-test on the fauna. Net-stones (4 stones in a net bag) were placed on the riverbed at each sampling site. Macrobenthos collected at the downstream site, where high water toxicity was found, were composed exclusively of several dominant species: 2 species of Trichoptera (both insecticide-resistant), Dipteran Antocha bifida and Chironomidae (several unidentified species), and insecticide-susceptible Baetis thermicus (Ephemeroptera). The continuous existence of B. thermicus in the toxic environment might be due to natural night drift or passive drift independent of the physiological diurnal cycle; the insects were inert and had a slightly opaque body color. At the upstream site, where the shrimp mortality in the river water was comparatively low, the number of macrobenthic taxa was twice that at the downstream site. Sampling using net-stones on the sandy riverbed was efficient for assessing water toxicity to macrobenthos.

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It is well known that Chlamydomonas can regenerate flagella to their original lengths within 2-4 hr after flagellar amputation. However, flagella grow only to 50% their original lengths in the presence of 20 μg/ml cycloheximide, an inhibitor of protein synthesis. Taking advantage of these features of this organism, we can evaluate roughly the influence of pollutants upon protein synthesis or organelle morphogenesis. In this study, we examined the effects of Cu²⁺, Zn²⁺ and Cd²⁺ on flagellar regeneration using samples in culture media supplemented with heavy metals. The results suggested that Cu²⁺ and Zn²⁺ inhibit flagellar morphogenesis (assembly of flagellar components), whereas Cd²⁺ of much lower concentrations inhibits both protein synthesis in an early phase of flagellar regeneration and morphogenesis in later phases. The 4-hr EC_50s for Cd²⁺, Cu²⁺ and Zn²⁺ on flagellar regeneration were 15.8 μM, 1.1 mM and 2.2 mM, respectively. When these assessments were carried out in distilled water, EC_50s decreased 10 to 100-fold, suggesting that the effect of heavy metals depends on the water hardness. We examined effluents from eight factories in Toyama Prefecture using cells in them, and found one sample clearly inhibited flagellar regeneration. The effluent appeared to contain Zn²⁺ in a concentration as high as 200% of the effluent standard. Thus, the Chiamydomonas flagellar regeneration should be useful as an endpoint for assessing environmental water pollution with these heavy metals.

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