Thorium(²³²Th), an actinoide element, is among the most common naturally-occurring radioactive materials found in the environment. Thorium was used as a radiographic contrast agent(thorotrast) from 1930 to 1955, and many studies on its effects on the human body have been reported. Once thorium is absorbed, the risk of cancer increases due to direct bombardment from alpha-particles with high linear energy transfer during thorium decay. Most of these reports focused on irradiation damage caused by long-term thorium exposure. In contrast, acute thorium toxicity derives more from thorium's chemical reactivity than its radioactive decay. Here, we report the chemical toxicity of thorium using yeast DNA microarray analysis. Thorium treatment of yeast was found to induce 136 genes. Genes involved in “C-compound and carbohydrate metabolism“,“energy”,“cell rescue, defense and virulence” and “biogenesis of cellular component” were induced significantly by thorium treatment. These genes were further classified into the following processes: oxidative stress(7 genes), glycogen and trehalose metabolism (6 genes), and cell wall damage(10 genes). However, only one gene related to DNA damage was induced. These results indicate that thorium causes cell wall damage and induces oxidative stress, and suggest that in order to overcome oxidative stress, cells promote metabolism of energy reserves in the form of glycogen and trehalose.

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A growth inhibition test method using fresh water attached diatoms was developed by improving microplate algal assay technique for planktonic green algae. Applying the solid culture technique for the pre-culture, using the flat bottom microplate for the test vessel and shaking the microplate at least twice a day were necessary procedures for ensuring the reproducibility of the test using attached diatoms.
Reproducible result was obtained from seven repetitions of growth inhibition tests using dimethametryn, a triazine herbicide on Achnanthidium minutissimum of attached diatom. The average ErC₅₀ values calculated from these tests was 7.9μg/l (n=7, SE=1.3).
The optimum culture condition and the adaptability as test organism were evaluated in ten kind of attached diatoms (A. minutissimum, Craticula molestiformis, Eolimna minima, Eolimna subminuscula, Fistulifera saprophila, Mayamaea atomus, Nitzschia palea, Planothidium frequentissimum, Planothidium lanceolatum, Sellaphora seminulum).
The optimum culture temperature was 15-30°C. The difference of illumination intensity (c.a.2,000lux or c.a.5,000lux) did not influence the growth rate of every diatom at the optimum culture temperature. It is concluded that C. molestiformis, E. minima, E. subminuscula, F. saprophila, M. atomus and N. palea are suitable test species in these diatoms in terms of high growth potential and that M. atomus and N. palea are valuable test species in terms of habitat diversity and easiness of isolation.

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We present the results of a test run done for protocols drafted to evaluate the toxicity of different bioremediation agents against spilled-oil using marine organisms and crude oil. The aim of the study was to evaluate experimentally the change in toxicity of oil when mixed with bioremediation agents and fertilizers used on oiled shores to enhance oil biodegradation under actual environmental conditions prevailing at the oiled site before considering any large-scale application. The protocols were designed to use three marine species at different trophic levels, i.e. diatoms Skeletonema costatum, rotifers Brachionus plicatilis, and red sea bream Pagrus major, and to carry out algal growth inhibition, zooplankton acute immobilization, and fish acute toxicity tests. The agents tested are: Inipol EAP22™, oleophilic fertilizer; Terrazyme™, bioaugmentation agent; and Super IB™/Linstar™, slow-release fertilizer.
While Super IB™/Linstar™ did not enhance the toxicity of oil, clear suppression of diatom cell growth was observed when 100 ppm of Inipol EAP22™ was added to oil. The concentration is estimated to be of the same range as that of the interstitial water at the Exxon Valdez remediation site after the spraying of Inipol EAP22™. This suggests that the toxic effect of the agent on some marine microalgae could be greater than the harm done by the oil itself.
Effective test methods for evaluating the ecotoxicity of bioremediation agents, therefore, need to allow comparison of the toxicity of the agent with the coexistence of contaminants and their biodegraded products, reproducing the actual conditions at oiled seashores.

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We conducted acute toxicity tests using a calanoid species (Eodiaptomus japonicus) and two cyclopoid species(Mesocyclops pehpeiensis, Thermocyclops taihokuensis)of different life stages(nauplius and adult)and assessed their sensitivities to the insecticide diazinon and carbaryl.
The EC₅₀ values of nauplii of the three species ranged between 2.8 and 4.1 ppb for diazinon and between 9.9 and 19.7 ppb for carbaryl, which were in the similar range of the EC₅₀ values of neonates of the cladoceran Daphnia for the same insecticides. In contrast, adults of the copepod species showed much higher tolerance to the chemicals; their EC₅₀ values were in a range between 30.6-46.8 ppb for diazinon and between 785.7-1190.0 ppb for carbaryl, which were 10-70 times higher than the values of nauplii. The difference in the sensitivity to the chemicals between neonates and adults was much larger in the copepods than in Daphnia. This suggests that the copepod populations are controlled mostly by the mortality of nauplii if they are exposed to insecticides.

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Estrogens (17β-estradiol and estrone) concentrations in river and estuarine waters around Kuala Lumpur, Malaysia were determined by enzyme-linked immunosorbent assay while estrogenic potential of the waters were ascertained by three in vitro bioassays, namely E-screen, Ishikawa cell-alkaline phosphatase and yeast estrogen screen. Moreover, hepatic vitellogenin, a precursor of yolk protein that is specific to females, were examined in male and female Java-medaka collected in the same area.
17β-estradiol and estrone concentrations were less than 6.1 ng/L and 127 ng/L, respectively. The highest 17β-estradiol equivalent activity, 284 ng/L, was detected by in vitro assay in Sungai Kuyoh, which was adjacent to a sewage plant. 17β-estradiol and estrone concentrations were not equal to their estrogenic potentials determined by in vitro assay implying the presence of other estrogenic chemicals in these waters. Hepatic vitellogenin concentrations of both male and female java-medaka were the same to laboratory-cultured individuals.
Although relatively high estrogen concentrations were detected in some waters of Malaysia, these were not high enough to induce hepatic vitellogenin in male fishes. Further research, however, is necessary to cover more number of sampling sites.

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Bioavailability of heavy metals in soil is to be considered in order to examine toxic effects on soil organisms. Particularly, metal speciation in soil pore water must be taken into account in order to examine the bioavailability to soil organisms. In the Center for the Study of Metals in the Environment, Department of Civil and Environmental Engineering, University of Delaware, some practical studies have been conducted to examine the bioavailability of metals in soil. In this manuscript, some of the promising studies including Terrestrial Biotic Ligand Model (TBLM) are introduced.

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