Shin'ichiro Kawai

Development of the digestive organ system in Japanese flounder in relation to metamorphosis and settlement

During metamorphosis and settlement the digestive system of Japanese flounder (Paralichthys olivaceus) exhibits various morphological features that include: differentiation and development of gastric glands and pyloric caeca coupled with partial degradation of the pancreas; involution of the liver; inflation of the gall bladder; and shortening of gut epithelium height. Pepsin‐like enzyme activity increases markedly as metamorphosis proceeds, while trypsin‐like enzyme and amylase activities drop significantly. High percentage of newly settled wild flounder at the climax phase of metamorphosis have empty stomachs, indicating that feeding ceases while the gut is undergoing reorganization. These findings suggest that the morphological and functional changes of the digestive system that occur during metamorphosis of Japanese flounder relate to the drastic diet shift at settlement from zooplanktonic to benthic prey.

Contamination of butyltin and phenyltin compounds in the marine environment of Otsuchi Bay, Japan

Butyltin (BT) and phenyltin (PT) compounds were measured in seawater, sediment, and biological samples collected from coastal areas of Otsuchi Bay, Japan. Tributyltin (TBT) compounds in seawater, sediment, plankton, mussels, scallops and fish were in the range of 0.008-0.074 microg liter(-1), 0.01-0.64 mg (kg dry wt)(-1), 0.24-9.8 mg (kg dry wt)(-1), 0.04-0.18 mg (kg wet wt)(-1), 0.10-0.13 mg (kg wet wt)(-1) and 0.01-0.02 mg (kg wet wt)(-1), respectively. Trace amount of PTs were found in seawater. The highest concentrations of TBT and triphenyltin (TPT) were found near a shipyard. Triorganotin compounds were more dominant than their metabolites. A positive correlation was observed between the concentrations of TBT and TPT in the mussels. Concentrations of TBT and TPT in mussels were high in the upper intertidal zone, and decreased toward the water.

Temporal trends of organotin compounds in the aquatic environment of the Port of Osaka, Japan

Abstract Between 1989–1996, butyltin (Bt) and phenyltin (Pt) compounds were monitored in water, sediment, plankton and mussels from the Port of Osaka. Tributyltin (TBT) compounds concentration in water and mussels decreased remarkably in a marina and the mooring places in a zone of poor flushing during 1989–1996. With regard to the composition of Bts in water, the dominant compounds changed from TBT to monobutyltin (MBT). The ratio of TBT in mussels was high throughout the study period. Drastic changes of TBT concentrations in sediment and plankton were not observed. High levels of triphenyltin (TPT) were detected in water between 1989 and 1991, but TPT have not been detected since 1992. Detection frequencies of TPT in sediment and plankton were also very low. TPT levels in mussels were high in 1989 but decreased dramatically thereafter.

Degradation of tributyltin by a bacterial strain isolated from polluted river water

Abstract Organotins loaded into the aquatic environment are generally degraded by bacteria in water and sediment. Though the aspects of microbial degradation have been studied under a mixed culture condition, little is known about the degradation in a pure culture condition, and there is no report on the isolation of organotin-degrading bacteria. In this paper, tributyltin (TBT)-degrading bacteria (no. 4 strain) were isolated from polluted river water in Osaka City. This bacterial strain degraded TBT within 24 h when the initial water concentration was 4–20 μg Sn/liter, and the addition of organic nutrient broth promoted the degradative ability. Following TBT degradation, dibutyltin (DBT) and monobutyltin (MBT) were produced, and finally MBT transformed into inorganic tin. The growth of the no. 4 strain was inhibited by the addition of TBT of more than 20 μg Sn/liter in the medium and, consequently, TBT degradation might have been suppressed with the elapse of time.

Evaluation of the ishikawa cell line bioassay for the detection of estrogenic substances from sediment extracts

This study examines the application of Ishikawa human endometrial adenocarcinoma cells to measure the estrogenic activity of fractionated extracts of sediments from Tokyo Bay, Japan. Estrogen stimulates alkaline phosphatase activity in this cell line. The results of these assays were compared with those of a yeast estrogen screen (YES) assay. The Ishikawa cell line bioassay showed higher sensitivity to 17beta-estradiol (median effective concentration [EC50], 10.7 pM) than did the YES assay (EC50, 480 pM). Fractionation of sediment extracts (all samples collected from 5 sites) showed that the nonpolar fraction was poisonous to yeast cells; the estrogenic activity of this fraction, therefore, could not be measured by YES. However, the nonpolar fraction did not kill the Ishikawa cells. The 17beta-estradiol-equivalent values of 15 extracts (3 fractions from each of 5 sediment samples) ranged from 5.7 to 697 pg/g dry weight according to the Ishikawa cell line bioassay. Chemical analysis using gas chromatography-mass spectrometry revealed that the highest concentrations of endocrine-disrupting chemicals were observed at the sampling station near the sewage treatment plant. The results support that the Ishikawa cell line bioassay is suitable for measuring the estrogenic activity of sediment samples.

Empirical model for disappearance of free oxidants in natural water with wide salinity and ammonia ranges

Abstract An empirical model for the disappearance rates of chlorine-induced free oxidants was developed. Both in seawater and river water, the disappearance of free oxidants occurred in two stages (stage I and II). The disappearance of free oxidants in stage II was considered to be the consumption by organic substances in natural water. The disappearance rate could be empirically explained by a second-order reaction of oxidants. The observed rate constant was decreased with the increase of the oxidant concentration after subtracting the decrease in stage I from the chlorine dose in natural water. Especially in seawater, the maximum persistence of oxidants could be estimated by the self-decomposition rate of hypobromite which was the disappearance rate in artificial seawater, and the rate constant was obtained as a function of bromide concentration. The disappearance in stage I, which was very rapid, was considered to be the reactions with reactive inorganic and organic substances in natural water. The minimum decrease, which was led to the maximum persistence in stage II, could be approximately expressed as the consumption by ammonia. Using our proposed model, the maximum persistence of free oxidants in natural water with wide salinity and ammonia ranges could be estimated.