Ecological effects of p-octylphenol a kind of environmental estrogen to Culex pipien molestus were assessed in order to develop the use of Culex pipiens molestus as model organism. The immature stages (from egg to pupa) of Culex pipiens molestus were exposed to p-octylphenol and monitored for alterations in molting, development time, mortality and fecundity. The emergence of female adults was delayed by exposure. p-octylphenol also reduced reproduction capacity (numbers of eggs produced per larvae), which showed the ups and downs depending on the size of population, at concentrations ranging from 10 to 100 μg/L. The weight of adult female decreased at same concentrations. These results indicate that p-octylphenol interfered in the growth of Culex pipiens molestus, and thereby decreased the weight of adult female. Further, this inhibition led to decrease reproduction capacity which included development and fecundity parameter. But these effects were not observed at 125 μg/L. Reproduction capacity may be used for endocrine-sensitive endpoint in the Culex pipiens molestus reproduction test. These endpoints and some knowledge of endocrine systems suggest that Culex pipiens molestus may have potential as model organism of endocrine disrupters.

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In order to make an ecological risk assessment of formaldehyde in aquatic environment, acute toxicities of formaldehyde to marine diatom Skeletonema costatum, marine zooplankton Tigriopus japonicus and marine fish Sillago japonica have been determined. Among them, S. costatum was the most sensitive organism, i.e. the 96hEC₅₀ was 0.49 mg/L. T. japonicus was the next, i.e. the 24hEC₅₀ and 24hLC₅₀ were 10 mg/L and 11 mg/L, respectively. S. japonica was the least sensitive organism, i.e. the 96hEC₅₀ was 50 mg/L. Further, the no observed effect concentration (NOEC) for S. costatum was calculated to be 0.32 mg/L. Based on the this data set, the predicted no effect concentration (PNEC) of formaldehyde was estimated to be between 10^-3 and 10^-2 mg/L.

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The effects of river water discharged from agricultural region around Lake Biwa on Daphnia magna mortality were investigated in this study. Water samples were collected from six sites periodically for one year, starting in April 1997 and continuing until April 1998. The toxicities of water samples are observed in all sites. The samples collected from June to August are more toxic than those taken at the other seasons. Four kinds of pesticides were detected from the river water by chemical analysis, and the relevance to toxicity and agricultural activity was indicated. In single toxicity tests, the toxicities are not observed for all pesticides except diazinon. Detected toxicity depends mainly on diazinon. It was guessed that the unknown water quality component was concerned in the toxicity by contrast between single and compound toxicity of the standard pesticides and the toxicity of the environmental sample.

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The activities of acetylcholinesterase (AChE) and butyrylcholinesterase (BtChE) were examined in various tissue homogenates of Koi carp (Cyprinus carpio). The AChE activity was highest in brain followed by body muscle, kidney, liver and spleen, and the BtChE activity was also highest in the brain. On the other hand, the activity ratio of AChE to BtChE was high (11 - 17) in the body muscle and plasma (or serum), and lower in the brain, kidney, liver and spleen (1 - 4). The AChE activity in the body muscle was mostly localized in the insoluble fraction when the homogenate was prepared with a buffer of low salt concentration, but more than 85 % of the activity in the fraction was extracted with another buffer containing 1 M NaCl. This suggests that most of AChE in the muscle is in the membrane-bound, collagen-tailed asymmetric forms. We purified AChE 79700-fold from the muscle homogenates and the final preparation had a specific activity of 14900 μmol?min^-1?mg^-1 protein. Analysis of the purified AChE by SDS-polyacrylamide slab gel electrophoresis under the reducing condition also suggests that the AChE is in the collagen-tailed asymmetric forms and the molecular mass of the catalytic subunit was 76.8 kDa. The enzyme is subject to substrate inhibition, at high substrate concentrations, and showed a markedly higher V_max/K_m and a lower K_i with acetylthiocholine as a substrate than those with propionyl- and butyrylthiocholine as substrates. The enzyme is highly sensitive to the known inhibitors for AChE and far less sensitive to those for BtChE. Those results confirm that the enzyme thus purified from Koi carp muscle is certainly an AChE.

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