Suguru Inoue

Global pollution monitoring of butyltin compounds using skipjack tuna as a bioindicator

Butyltin compounds (BTs) including mono- (MBT), di- (DBT), tri-butyltin (TBT) and total tin (sigmaSn), were determined in the liver of skipjack tuna (Katsuwonus pelamis) collected from Asian offshore waters (off-Japan, the Japan Sea, off-Taiwan, the East China Sea, the South China Sea, off-Philippines, off-Indonesia, the Bay of Bengal), off-Seychelles, off-Brazil and open seas (the North Pacific). BTs were detected in all the skipjack tuna collected, suggesting widespread contamination of BTs even in offshore waters and open seas on a global scale. Considering specific accumulation, Sex-, body length- differences and migration of skipjack tuna did not seem to affect BT concentrations, indicating rapid reflection of the pollution levels in seawater where and when they were collected. Skipjack tuna is a suitable bioindicator for monitoring the global distribution of BTs in offshore waters and open seas. High concentrations of BTs were observed in skipjack tuna from offshore waters around Japan, a highly developed and industrialized region (up to 400 ng/g wet weight). Moreover skipjack tuna collected from offshore waters around Asian developing countries also revealed the levels comparable to those in Japan (up to 270 ng/g wet weight) which may be due to the recent improvement in economic status in Asian developing countries. High percentages (almost 90%) of BTs in total tin (sigmaSn: sum of inorganic tin+organic tin) were found in the liver of skipjack tuna from offshore waters around Asian developing countries. This finding suggests that the anthropogenic BTs represent the major source of Sn accumulation in skipjack tuna from these regions.

Convective generation of “giant” undulations on the evening diffuse auroral boundary

Convective generation of “giant” undulations on the equatorward boundary of an evening diffuse aurora is numerically simulated. A giant undulation is defined as a waveform having the crest-to-trough amplitude comparable to the wavelength. The two-dimensional electrostatic particle code is used for studying the motion of magnetospheric plasma perpendicular to the geomagnetic field. According to the simulation results by Yamamoto et al. [1993], the giant undulation is a manifestation of the Kelvin-Helmholtz (K-H) waves arising from the polarization of “an arc sheet” (dense plasma population of ionospheric origin) in the magnetosphere, which is assumed to be located just equatorward of the region of proton diffuse aurora. In this previous simulation, initially, irregularities are given evenly over the entire azimuthal length of the arc sheet so that the resulting undulations are periodic. The present simulation deals with a different situation, that a K-H wave starts growing from local irregularities on the polarized arc sheet. The simulation results show that the disturbance propagates both westward and eastward (relative to the background flow), forming a series of K-H waves along the arc sheet. As a consequence, giant undulations with spatially varying amplitudes are developed on the equatorward boundary of a diffuse aurora, which is located just poleward of the arc sheet. A series of giant undulations convectively produced in the simulation is remarkably similar to some auroral images photographed from the Defense Meteorological Satellite Program (DMSP) satellites. In addition, we show the direct evidence for the presence of an arc sheet, probably associated with the giant undulations, which is provided by the measurements of precipitating particles from the DMSP F7 satellite crossing the equatorward boundary of the diffuse aurora; the high-density (∼10 cm−3) ions with energy of a few hundred electron volts are detected near the edge of the region of energetic (∼10 keV) ion precipitation. The primary cause of the formation of that arc sheet is thought to be escape of the oxygen and hydrogen ions from the topside ionosphere, due to the transverse acceleration by the ion-cyclotron waves.

Specific accumulation of polychlorinated biphenyls and organochlorine pesticides in Japanese common squid as a bioindicator.

Organochlorines (OCs) representing Persistent Organic Pollutants (POPs) such as PCBs (polychlorinated biphenyls), DDTs (DDT and its metabolites), CHLs (chlordane compounds), HCHs (hexachlorocyclohexane isomers) and HCB (hexachlorobenzene) were determined in the liver of Japanese common squid (Todarodes pacificus) collected from the waters around Japan (Japan Sea and western North Pacific Ocean). Among OCs concentrations, PCBs (upto 5600 ng/g lipid wt.) were the highest, and those of other OCs were in the order of DDT> CHLs > HCHs > HCB. Studies on growth trend and seasonal variation of OCs in this species suggest a rapid reflection of the pollution levels in seawater where and when they were collected, regardless of body-length and time of collection. These results indicate that Japanese common squid is a suitable bioindicator for monitoring OCs pollution in waters around Japan. With regard to the geographical distribution of OCs in this species collected from waters around Japan, OCs concentrations in specimens from Japan Sea were higher than those from the Pacific Ocean. This result might reflect some existing of local pollution sources of OCs around Japan Sea, and slower water exchange between Japan Sea and open ocean.

Trace elements and stable isotopes (δ13C and δ15N) in shallow and deep-water organisms from the East China Sea

Trace elements (22) and stable isotope ratios (delta15N and delta13C) were analyzed in marine organisms from shallow (SW) and deep-water (DW) of the East China Sea to understand biomagnification and prey source of trace elements. In the benthic marine organisms from DW, delta15N values were negatively correlated with Ba, Cu, Ag, Mo, Sr, As, and Co concentrations. This may be due to the specific accumulation in lower trophic animals and/or the biodilution through the food web in DW. Relationships between delta15N and concentrations of Co, Cr, Bi, and Tl in fish and Ag, Bi, V, Hg, and Tl in crustaceans showed positive correlations, suggesting that trophic position was affecting the concentrations of those elements in phyla, with higher trophic animals retaining higher concentrations than the lower trophic animals. Positive correlations between delta13C and Rb were observed in marine organisms. Therefore, Rb may be a possible substitute of delta13C as tracer of prey source in the East China Sea although further investigation is required.

Effect of maternal exposure to tributyltin on reproduction of the pearl oyster (Pinctada fucata martensii).

We examined the effect of tributyltin (TBT) on reproduction of the pearl oyster (Pinctada fucata martensii). In a maternal exposure test, five female pearl oysters were exposed to TBT at measured concentrations of 0 (control), 0.092, or 0.191 microg/L at 25 degreesC for one week, and the embryo developmental success (the ratio of normal D-larvae to all larvae) was measured. The embryo developmental success was significantly decreased in the 0.191-microg/L treatment group (65.5%) compared to that in the control group (82.5%; p = 0.031). Concentrations of TBT in the ovary reached 0.088 microg/g in the 0.191-microg/L treatment group. In a waterborne exposure test, inseminated eggs were exposed to TBT at measured concentrations of 0 (control), 0.020, 0.045, 0.091, 0.192, or 0.374 microg/L for 24 h. The embryo developmental success also was significantly decreased in the 0.192-microg/L treatment group (78.3%; p = 0.020) and no development at all was observed in the 0.374-microg/L treatment group compared with that in the control group (95.4%). These results clearly demonstrate that TBT accumulating in the bodies of bivalves has the potential to inhibit reproduction.

Formation of auroral omega bands in the paired region 1 and region 2 field-aligned current system

As an extension of the model for generation of a pair of region 1 and region 2 field-aligned currents (FACs), which has been proposed by Yamamoto and Ozaki [1993], we study the formation of auroral omega bands in the region 1-region 2 FAC system. In their model the hot plasma torus (HPT) is defined as the hot (≥1 keV) plasma population contained in the magnetic shell which is connected to two ovals of diffuse auroras on the northern and southern polar ionospheres. Their numerical simulation has shown that the paired region 1-region 2 FACs can be generated as a result of the distortion of the HPT in the magnetosphere, which occurs under the influence of the solar wind convection. That HPT system is potentially unstable: Under certain conditions the electrostatic interchange instability due to the particle magnetic drifts can be fully developed on the poleward side of the HPT. The two-dimensional particle simulation in the present paper demonstrates that an azimuthal chain of electric dipoles is formed by the interchange instability developing in the paired region 1-region 2 FAC system. This means a drastic modification of the original region 1 and region 2 FACs such that a sequence of east-west oriented pairs of downward and upward field-aligned currents emerges in the region I zone. The pattern of upward FACs thus formed, with tongues extending poleward, can be identified with the omega bands or torch structures. The magnetospheric (or ionospheric) potential distribution obtained in the simulation is consistent with the observed distributions of ionospheric electric field and field-aligned currents in events of torches/omega bands.

Exposure, metabolism, and health effects of arsenic in residents from arsenic-contaminated groundwater areas of Vietnam and Cambodia: a review.

In this review, we summarize the current knowledge on exposure, metabolism, and health effects of arsenic (As) in residents from As-contaminated groundwater areas of Vietnam and Cambodia based on our findings from 2000 and other studies. The health effects of As in humans include severe gastrointestinal disorders, hepatic and renal failure, cardiovascular disturbances, skin pigmentation, hyperkeratosis, and cancers in the lung, bladder, liver, kidney, and skin. Arsenic contamination in groundwater is widely present at Vietnam and Cambodia and the highest As levels are frequently found in groundwater from Cambodia. Sand filter system can reduce As concentration in raw groundwater. The results of hair and urine analyses indicate that residents from these As-contaminated areas are exposed to As. In general, sex, age, body mass index, and As exposure level are significantly associated with As metabolism. Genetic polymorphisms in arsenic (+III) methyltransferase and glutathione-S-transferase isoforms may be influenced As metabolism and accumulation in a Vietnamese population. It is suggested oxidative DNA damage is caused by exposure to As in groundwater from residents in Cambodia. An epidemiologic study on an association of As exposure with human health effects is required in these areas.

A theory for generation of the paired region 1 and region 2 field‐aligned currents

We present a new theoretical model for generation of a pair of region 1 and region 2 field-aligned currents (FACs) under the condition of a southward interplanetary magnetic field. On the basis of the satellite observations it is assumed that the hot (≳1 keV) plasma particles are distributed in a magnetic shell connected to two ovals of diffuse auroras on the northern and southern polar ionospheres. The hot plasma population contained in this magnetic shell having several degrees of latitude in width is called the hot plasma torus (HPT). It is proposed that the region 1/region 2 FACs can be generated as a result of natural distortion of the HPT due to the solar wind convection. When the interplanetary magnetic field has a southward component, i.e., the IMF Bz is negative, the solar wind flow across open geomagnetic field lines gives rise to electric field convection patterns over the polar caps, which are modeled as twin vortex cells with antisunward flows in the center of the polar caps. The convection thus driven by the solar wind is referred to as the solar wind convection. If it were not for an E × B convection flow, the HPT would be shaped such that the HPT particles are contained in the “magnetic drift shells,” which are tangent to the averaged total magnetic drift velocity. In the presence of the solar wind convection, the configuration of the HPT will be deformed from the magnetic drift shells. Because of the distortion of the HPT, the pressure gradient in the HPT gains a component parallel to the magnetic drift. Therefore the HPT can be polarized because of oppositely directed magnetic drifts of the HPT electrons and protons: the high-latitude and low-latitude sides of the HPT on the eveningside are negative and positive, respectively, and the polarity is reversed on the morningside. The resulting pattern of large-scale field-aligned currents due to the polarization of the HPT is consistent with the observations of region 1 and region 2 FACs. Moreover, provided that the solar wind acts as a voltage generator in the interaction with the open field lines, as a long-term characteristic of the paired region 1 and region 2 FACs we can obtain the relationship between the FAC intensity and the ionospheric conductivity: both the region 1 and region 2 intensities increase linearly with the Pedersen conductivity, while the proportionality constant for the region 2 FAC is smaller than that for the region 1 FAC. Our predicted relation for geomagnetic quiet conditions quantitatively agrees with the regression lines between the current intensities and the Pedersen conductivities obtained on the basis of Magsat satellite observations by Fujii and Iijima [1987].

Human exposure to arsenic from groundwater in the Red River and Mekong River Deltas in Vietnam

Groundwater contamination by arsenic is a serious environmental problem in the world. Yet there have been few studies conducted in Southeast Asian countries. This article surveys arsenic contamination in groundwater and residents from Vietnam, and is based on our previous studies. Samples of groundwater (n = 118), human hair (n = 59), and urine (n = 100) were collected in the Red River and Mekong River Deltas during 2001–2004. Arsenic was detected in most of the groundwater samples, and its level ranged from <0.1 to 486 µg/l. Elevated concentrations of arsenic were observed in groundwater at some locations in Ha Nam (up to 486 µg/l) in the Red River Delta and Dong Thap (up to 411 µg/l) in the Mekong River Delta. Remarkably, about 33% of these groundwater samples exceeded the WHO drinking water guideline of 10 µg/l. These results suggest that arsenic contamination in groundwater may be widely present in both the Red River and Mekong River Deltas, Vietnam. A significant positive correlation was observed between arsenic concentrations in groundwater and human hair. Arsenic speciation of human urine revealed the presence of inorganic arsenic, and these concentrations positively correlated with arsenic levels in groundwater. Thus, it is likely that residents in our study areas are chronically exposed to arsenic through drinking groundwater, suggesting that there is a health risk from arsenic in Vietnam.

On the limitation of the current sheet approximation in estimation of the northward B z associated field-aligned currents

This paper calls attention to the limitation of the current sheet approximation, which has commonly been used in deducing the field-aligned currents (FACs) from the field-perpendicular components of magnetic field disturbances detected from low-altitude/midaltitude (below a few Earth radii) satellites. We focus our study on the current system involved in the northward interplanetary magnetic field associated FAC (so-called northward Bz (NBZ)). Assuming a numerical model for the total system of the region 1, region 2, and NBZ FACs, plus the associated ionospheric currents, the dusk-to-dawn and sunward components of the resulting magnetic disturbance δBx and δBy are calculated. In contrast to the commonly adopted hypothesis that the field-perpendicular magnetic disturbances as observed from the low-altitude (a few hundred kilometers) satellites are attributed primarily to the FACs, it is found that the ionospheric currents can make a significant contribution to those disturbances. Particularly, in the central part of the region of NBZ FACs, δBx from the ionospheric currents dominates δBx from the FACs. Next, for a simple discussion on the limit of the current sheet approximation we consider the magnetic disturbances at altitudes higher than several hundred kilometers where the contribution (to δBy) from the ionospheric currents can be neglected. It is found that in general, the FAC intensities based on the current sheet model are significantly different from those actually given in the FAC distribution. Specific points to be noted are as follows: (1) On the dusk-dawn lines passing the central part of the NBZ region the intensity of NBZ under the current sheet approximation is considerably smaller than the actual value, and the intensity ratio between region 1 and NBZ can be overestimated, by >50%, under that approximation. (2) On the dusk-dawn lines near the edges (but just inside) of the NBZ region, the current sheet model breaks down even qualitatively; the current sheet model cannot infer the right locations of region 1 and NBZ FACs. (3) On the dusk-dawn lines just outside of the NBZ region the so-called “W”-shaped profile in δBy, which can commonly be interpreted as a signature of the presence of NBZ FACs, emerges in the region where actually no NBZ FAC exists.