Many chemicals released from human activity finally flow into rivers, lakes and sea. It is important to assess their toxicity to aquatic organisms. Many species inhabiting freshwater are recommended as test organisms in most toxicity tests such as OECD, ASTM and/or JIS K0102 test guidelines. However,　susceptibilities of freshwater organisms to chemicals often greatly differs from that of marine organisms. In this review, marine organisms for toxicity tests are introduced base on mainly our investigation results. In marine fish, red sea bream, Japanese whiting and Japanese file-fish seem to be suitable for toxicity test. On the other hand, the susceptibilities of marine invertebrates for chemicals, which seem to be suitable for toxicity test are being studied. Those are also introduced here.

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In the process of risk assessment of chemicals in aquatic environment, data on aquatic toxicity and bioconcentration are required. In laboratory testing, single-species tests are usually used rather than multi-species, microcosm or mesocosm tests. The LC₅₀, EC₅₀ and/or BCF of a particular chemical determined through studies of exposure of single species tend to be modified by biotic and/or abiotic factors. Among numerous factors, biotic factors, such as species and development stage of organisms, acclimation, feeding and loading and abiotic factors, such as temperature, pH, hardness, salinity, carrier solvent are important. In this report, certain major factors are discussed in more detail.

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There were many predictive methods for estimating the ecological consequences of toxic chemicals. The predictive methods (statistical extrapolation models) for estimating the ecotoxicological protection levels from NOEC toxicity data, and the microcosm tests to screening toxic chemicals for possible effects at levels of organization above the populations were described. The evolutionary process in ecotoxicological methods is not complete, but much has been accomplished.

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Marine rotifer Brachionus plicatilis exposed to 2-ppm of fenitrothion, a representative organophosphorus insecticide, was cultivated on a minute alga Tetraselimis tetrathele by a water-flow continuous cultivation system constructed in a laboratory for 1037 days. The fenitrothion-exposed B. plicatilis was used to examine the influences on tolerance to fenitrothion and other organophosphorus insecticides, such as salithion, phenthoate, dichlofenthion, cyanophos, diazinon and malathion. Tolerance was estimated at the 50 % lethal concentration (LC50 value) of an insecticide for B. plicatilis. The LC₅₀ value of fenitrothion for B. plicatilis exposed for 1,037 days was 9.2 ppm and that for non-exposed B. plicatilis was 5.4 ppm. The tolerance to fenitrothion by B. plicatilis was certainly increased. The exposed B. plicatilis showed an increased tolerance to salithion, dichlofenthion, cyanophos and diazin on, but a decreased tolerance to phenihnate. The influence on tolerance to malathion could not be estimated in tested concentrations. lt was made clear that B. plicatilis exposed to fenitrothion increased tolerance to fenitrothion, moreover it changed the resistance activity to other organophosphorus insecticides.

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Effects of fenobucarb, a methylcarbarnatc insecticide, on several species of aquatic insects were investigated using indoor model streams. Concentrations of fenobucarb residues in the water of the model streams were 78-85 % of its nominal level until 24 h, except at low concentrations (less than 20 μg1^-1) in the water. The LC₅₀ values of fenobucarb for the larvae of Ephemeroptera, Epeorus latifolium, Ecdyonurus yoshidae and Baetis thermicus were low (2-17 μg1^-1). Their predators, the larvae of Oyamia gibba and Protohermes grandis, were less sensitive (48-h LC₅₀ values,42 and >160 μg1^-1, respectively)than the Ephemeroptera to fenobucarb.　LC₅₀ values among the Ephemeroptera larvae were considered to be significantly different since their 95% confidence limits did not overlap. The larvae of Isonychia japonica and E.yoshidae were more sensitive to fertobucarb in their earlier stages (at head capsule widths of <1.0 mm and <1.6 mm, respectively). On the other hand, the larvae of E. lattfolium seemed to differ considerably in their sensitivity to a low concentration (10 μg1^-1) of fenobucarb.

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Contamination of the aquatic environment by widely used chemicals that can mimic the effects of estrogen is of increasing concern due to the potential for large-scale ecosystem disturbance. Many experiments have characterized the estrogenic activity of these chemicals, but reliable field data on wildlife effects are scarce. We used the detection of serum vitellogenin (VTG) in wild male flounder, as a sensitive biomarker for environmental estrogen in the marine field. An enzyme immune assay (ETA) with use of fluorophore was developed using antiserum for lipovitellin (major component of VTG) in rabbits, along with VTG isolated from wild flounder, Pleuronectes yokohamae. High concentration of VTG was detected (maximum: 670 ng/m1) in 20 of 51 wild male flounder collected in Tokyo Bay. This is the first report of elevated VTG in wild male marine fish in Japan. These biornarker data in dicate that weak estrogenic effects on wild male flounder may he widespread in Tokyo Bay.

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Effects of insecticides on the biodiversity in paddy fields were investigated in Tohoku district. Test paddy field (10a) was divided into four areas, i.e., (A) control area; (B) imidacloprid applied area; (C) imidacloprid and cycloprothrin applied area; (D) imidacloprid, cycroprothrin, and ethofenprox applied are Imidacloprid, cycloprothrin and ethofenprox were applied on 26 May, 25 June and 29 July in 1998, respectively. Population density of aquatic organisms and natural enemies decreased by the insecticide applications. Particularly, that of C and D areas was affected significantly. On the contrary, the density of pests was siginificantly decreased even in B area. The results suggested that single insecticide application such as imidacloprid is preferable for protecting the biodiversity (natural enemies and aquatic organisms) in paddy fields. if we are forced to control pests by insecticides.

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