Aquatic ecosystems are receiving various harmful effects due to anthropogenic chemical pollutions. To protect wildlife, risk assessments of the chemicals are conducted using reference indexes of toxicity estimated by species-level laboratory tests and/or micro-/mesocosm community-level studies. However, the existing micro-/mesocosm communities are structurally too complicated, and it is also difficult to compare the experimental results directly with those from species-level tests. Here, we developed a procedure of a simple bi-trophic microcosm experiment which contains the common species (a green algae, Pseudokirchneriella subcapitata and a cladoceran, Daphnia magna) for testing chemical toxicities. For the proper operation of bitrophic microcosm experiment, the minimum required concentration of primary producer (P. subcapitata) is 5×105 cells mL-1. The microcosm system showed higher stability when the initially introduced D. magna population was composed of neonates (<24-h old) than adults and those mixture. This simple microcosm system would be an applicable tool to estimate the disturbing impacts of pollutants on plant-herbivore interactions, and linking the species- and population-/community level risk assessments in the future studies.

The mixotrophic marine ciliate Mesodinium rubrum possesses a highly modified algal endosymbiont as a nutrition source for the species. Accordingly, we assumed that the species can reflect the ecotoxicity on marine producer (as phytoplankton) and consumer (as zooplankton) both. A series of experiments were conducted to identify the potential of the species as a standard test species for marine ecotoxicological study. The comparison of species sensitivity on reference toxic materials was made using potassium dichromate for phytoplankton and copper chloride for zooplankton. The ciliate revealed the highest sensitivity on both reference materials among the seven test species including phytoplankton, benthic copepod and rotifer species. The toxicity end point of the species was 72hr-EC50=1.52 mg/L (as potassium dichromate) estimated by population growth inhibition (PGI), which is more sensitive than the most sensitive phytoplankton Skeletonema costatum (72hr-EC50=3.05 mg/L). As comparison to rotifer, it also revealed higher sensitivity on copper chloride; 72hr-EC50=0.38 mg/L for ciliate and 48hr-EC50=0.48 mg/L for rotifer. Also, the elutriate toxicity test of various ocean disposal wastes were conducted to identify the potential of ciliate toxicity test application using industrial waste sludges. The toxicity of leather processing waste sludge was highest on the ciliate, followed by dyeing waste sludge and dye production waste sludge as an increasing order of toxicity. 72h-EC50 of ciliate PGI test was 1.83% and that of S. costatum 3.84% for leather waste sludge which showed highest toxicity. The toxicity test results also revealed that the highest sensitivity was observed on ciliate species on ocean disposed sludge wastes. Also, ciliate toxicity test well discriminated the degree of toxicity between sludge sources; 72h-EC50 values were 1.83% for leather processing waste sludge, 16.75% for dye production waste sludge and 27.75% for textile production waste sludge. Even the laboratory culture methods of the species were not generally established yet, the species has high potential as the standard test species for marine toxicity test in terms of the dual reflection of phyto- and zooplankton toxicity from single test, sensitivity and test replicability.

A series of experiments was conducted to identify the potential of five phytoplankton species as standard test species for marine ecotoxicological tests. The candidate phytoplankton species are Skeletonema costatum, Heterosigma akashiwo, Prorocentrum micans, Isochrysis galbana, and Tetraselmis suecica. Salinity tolerance and sensitivity on potassium dichromate as a reference material were identified. Toxicity of eleven ocean-dumped sewage sludges and four red tide expellent extracts were estimated by the inhibition of population growth rates (PGR) of marine diatom S. costatum. While most species revealed relatively weak tolerance on salinity, T. suecica demonstrated the highest salinity tolerance ranged from 5～35 psu and the others 15～35 psu. H. akashiwo revealed the highest sensitivity as 72h IC50=0.76mg/L and T. suecica the lowest as 72h IC50=8.89mg/L on potassium dichromate. Sludge extracts from industrial waste, domestic sewage and livestock farm waste sludge showed high toxicity as 72h IC50<2% and lowest toxicity from filtration bed sludge as 72h IC50=30.50%. NOEC (No Observed Effective Concentration) of sludge extract ranged from <0.4% to 1.6% and this indicated high phytotoxicity of ocean dumped sewage sludge. The test sensitivity of phytoplankton PGR inhibition was much higher than those of marine rotifer Brachionus plicatilis mortality test and bioluminescent inhibition test by marine bacteria Vibrio fischeri, and comparable with the sea urchin (Strongylocentrotus intermedius) fertilization test. As a result the phytotoxicity test using phytoplankton PGR inhibition (IC50) must be a useful tool for marine phyto-toxicological evaluation of ocean dumped materials.