This study was conducted in order to evaluate the combined action of chemicals on the growth of the green alga, Selenastrum capricornutum and on the glucose consumption of microorganism populations in medium where many chemicals from among the environmental water quality standard items relating to human health in Japan coexist, Tests were conducted under three conditions： (1) medium containing a mixture of the standard levels of 13 chemicals from among the environmental standard items (26 chemicals); (2) medium containing a mixture of the guideline levels of 18 chemicals frbin among the items requiring close monitoring (22 chemicals)； (3) medium containing a mixture of the standard levels plus the guideline levels of a combination of the 31 chemicals from among the environmental standard items and the items requiring close monitoring (environmental water quality standard items), The three kinds of tests and their respective dispersant controls (A), (B) and (C) were the same as regards the concentrations and kinds of dispersants used, The results are summarized as follows, 1) At the end of the growth inhibition tests, the number of cells of the test alga in the above tests (1), (2) and (3) had decreased to 57,9, 63,3 and 56,6%, respectively, in comparison with the findings for each of the dispersant controls, The growth of the test alga was inhibited under each of the three test conditions, 2) At the end of the glucose consumption inhibition tests, the amdunt of glucose consumption of the test microorganisms in the above tests (1), (2) and (3) had decreased to 60,1, 58,9 and 63,7%, respectively, in comparison with the findings for each of the dispersant controls, The amount of glucose consumption of the test microorganisms was inhibited under each of the three test conditions, 3) ln addition, the mutagenicities under each of the three test conditions・and those of each of the dispersant controls were examined by the Ames test using Salmonella Typhimurium TAIOO, However, mutagenicities were not observed either in the presence or the absence of the microsomal preparation (S9mix), Judging from the results described above, it would seem that the current environmental water quality standards present some problems with regard to the protection of living aquatic organisms in public water areas, such as rivers, lakes, and coastal waters where the standard levels and the guideline levels of many of the chemicals from among the environmental water quality standard items coexist.

本研究では，水質環境基準を構成する化学物質の複合毒性を，緑藻 Selenastrum　capricornutum による増殖阻害試験および水生好気性微生物（水生微生物）による糖消費阻害試験により評価し・次の結果を得た．なお，環境基準項目試験区は13種類の化学物質，要監視項目試験区は18種類の化学物質，環境基準項目と要監視項目を合わせた試験区（水質環境基準項目試験区）は31繍の化学物質が，基準値および指針値の濃度で共存する条件下で試験を行った・分散剤の種類および濃度については試験区と分散剤対照区は同様にした．緑藻の増殖阻害試験の結果，供試藻細胞数の比（％）は，分散剤対照区に対して，環境基準項目試験区は57．9％，要監視項目試験区は63．3％，および水質環境基準項目試験区は56．6％であり，供試藻の増殖が阻害された．水生微生物の糖消費阻害試験の結果，糖消費量の比（％）は，分散剤対照区に対して，環境基準項目試験区は60.1％・要監視項目試験区は58.9％，および水質環境基準項目試験区は63.7％であり，糖消費量が阻害された．水質環境基準の基準値および指針値でも多数の化学物質が共存すれば，緑藻の増殖および水生微生物囎肖費を阻害することは明らかである．ところで，上述した3種類の混合試験液および分散剤対照区の変異原性の評価を行い，サルモネラ菌TA100（Salmonella Typhimurium TA100）を用いたエームス試験では，代謝活性化の有無に関わらず，変異原性は確認されなかった．以上の結果から，水質環境基準を構城する化学物質が基準値および指針値の濃度で共存すると水生生物の生存にとって好ましくない水環境と評価された．