Different partitioning among thorium isotopes in seawater of the Northern North pacific

Each about 400 l of seawater sample was collected in the northern North Pacific and filtered through a membrane filter. Four radioisotopes of thorium,²³²Th,²³⁰Th,²²⁸Th and²³⁴Th, were determined for the two FractionsF (filtrate) andP (particles on the filter). In the percentages of FractionP in the subsurface water,²³⁰Th was significantly larger than other 3 isotopes, and²³²Th was significantly smaller than other 3 isotopes. The former finding can be explained by the slower rates in the reversible change between the FractionsF andP. The latter one, however, cannot be explained if thorium isotopes in the FractionF are truly dissolved with the same chemical form. This suggests that major part of the FractionF of²³²Th is not identical with those of other radiogenic thorium isotopes, and it should not be composed of simple dissolved ions. The removal of radiogenic²³⁴Th was related to the biological activity, but there was a deviation, between the FractionP and radioactivity deficiency of²³⁴Th in their vertical profiles. The deviation was similar to that between the chlorophylla and phaeo-pigments contents including their maximum depths.     

Ba, Si, U, Al, Sc, La, Th, C and C/C in a sediment core in the western subarctic Pacific as proxies of past biological production

A sediment core covering the last 145 kyrs was collected in the western subarctic Pacific (WSAP), and analyzed for Ba, U, Al, Sc, La, Yb, Th, biogenic opal (Opal) and organic carbon (C_org) as well as its isotopic ratio (δ¹³C). This study examined the change of past biological production in WSAP with multiple proxies, together with understanding the relation between Loess from the Asian continent and the biological production. The Loess content was estimated from the metal components, Al, Sc, La, Yb and Th. In this high latitude core (50°N), the Loess content was generally high during the glacial periods, but it was also high even in some interglacial periods. The excess amount of Ba relative to the detrital material composition, Ba_ex, showed the best correlation with the Vostok δD (r = 0.72, p < 0.001), indicating that the biological production was lower in the glacial periods than in the interglacials. This corroborates the pervasive correlation between Ba_ex in the polar region, WSAP and the Antarctic Sea, and Antarctic temperature, combined with previous research. This correlation might be explained by the stratification caused by cooling. In addition, the time variations of Ba_ex in WSAP were similar to those of Ba_ex in the Okhotsk Sea and of other proxies (C_org and Opal) in both the Okhotsk and the Bering Sea, indicating the spatial homogeneity of Ba_ex in WSAP including proximal marginal seas. The Opal content was more weakly correlated with the Vostok δD (r = 0.46, p < 0.001) than Ba_ex, reflecting that Opal in WSAP including proximal marginal seas was spatially heterogeneous compared to Ba_ex. While both the C_org content and U_ex, the excess amount of U relative to the detritus composition, were not positively correlated with the Vostok δD, they behaved similarly in the sediments. The positive correlation between δ¹³C and the Vostok δD (r = 0.42, p < 0.001), between δ¹³C and Ba_ex (r = 0.60, p < 0.001) and between δ¹³C and Opal (r = 0.36, p < 0.01) indicates that δ¹³C in WSAP may give some information on the phytoplankton growth rate. There was not a significant correlation between the spatially homogeneous Ba_ex in WSAP and Loess (r = − 0.16, p > 0.01), suggesting that the increase of biological production with the increase of Loess supply during the glacial periods did not occur.     

A practical method for the simultaneous determination of234Th,226Ra,210Pb and210Po in seawater

A practical method has been developed for the simultaneous determination of²²⁶Ra,²³⁴Th,²¹⁰Pb and²¹⁰Po in seawater. In the method, the samples are spiked with²²⁸Ra,²³⁰Th,²⁰⁸Po and common lead to determine chemical yield. These nuclides are coprecipitated with calcium carbonate and ferric hydroxide from 20 to 50 l of seawater and separated from one another by using coprecipitation and ion exchange techniques. Counting sources of Ra and the other nuclides are prepared by electrodeposition onto silver discs. Their radioactivities are counted with an-spectrometer and a low background-counter. This method gives a standard deviation of about 5% for replicate determination of²²⁶Ra and the other nuclides.     

Continuing observation of disturbed reproductive cycle and ovarian spermatogenesis in the giant abalone, Haliotis madaka from an organotin-contaminated site of Japan

Histological examination of gonads as well as chemical analysis of organotin compounds in tissues of the giant abalone, Haliotis madaka, was conducted to evaluate continuing endocrine disruption in abalone populations in Japan. Abalone specimens were collected from two different areas, Tsushima as a reference site and Jogashima as a site representative of declining abalone populations where serious organotin contamination had been observed, each month from January 1998 to March 1999. Scores were given to the development stages of reproductive cells in the ovary and testis. The degree of sexual maturation was evaluated by calculating the mean value of a histogram of these scores for the reproductive cells of each abalone. The temporal variations in degree of sexual maturation showed that female and male abalone from Tsushima matured synchronously, while those from Jogashima did not, which were similar to results of the previous study during September 1995–November 1996. Approximately 19% of the female abalone from Jogashima were masculinized with an ovo-testis, which was also similar to the result of the previous study. The masculinization of female abalone is reported to be induced by tributyltin (TBT) and triphenyltin (TPhT) from antifouling paints. Concentrations of the sum of butyltins (TBT, dibutyltin (DBT) and monobutyltin (MBT): ΣBTs) and the sum of phenyltins (TPhT, diphenyltin (DPhT) and monophenyltin (MPhT): ΣPhTs) in the muscle of abalone from Jogashima (n = 73) of 7.8 ± 9.0 ng/g wet wt. and 4.5 ± 6.8 ng/g wet wt., respectively, were significantly higher than those from Tsushima (n = 87) of 4.7 ± 4.9 ng/g wet wt. and 0.8 ± 1.7 ng/g wet wt., respectively (p < 0.05 for ΣBTs; p < 0.001 for ΣPhTs), although concentrations of TBT and TPhT in the muscle of abalone from Jogashima (n = 73) of 2.2 ± 2.5 ng/g wet wt. and 5.8 ± 5.1 ng/g wet wt., respectively, were insignificantly and significantly higher than those from Tsushima (n = 87) of 0.4 ± 0.6 ng/g wet wt. and 0.5 ± 0.9 ng/g wet wt., respectively, (p > 0.05 for TBT; p < 0.001 for TPhT). Thus, endocrine disruption as well as contamination by organotins in the giant abalone from Jogashima is still persisting.     

Phosphorus sorption from aqueous solution using natural materials

The sorption of phosphorus by using four different natural materials (marble dust, sawdust, soil, and rice husk) was studied by conducting batch tests and kinetic sorption model. The kinetic sorption model based on a pseudo equation was applied to predict the rate constant of sorption. Thorough investigations to understand the mechanism of phosphorus sorption onto the natural materials using kinetic sorption models, pseudo first- and second-order kinetic sorption model showed that the kinetic sorption is consistent with the second-order model, from which it can be inferred that the mechanism of sorption is chemisorption. Batch tests and kinetic sorption model results showed that by using marble dust as sorbent, among other materials, could remove more than 93 % of phosphorus from aqueous solution.     

Formal education and disaster response of children: evidence from coastal villages in Indonesia

Natural Hazards - Although children are exposed to a high mortality risk during disasters, what determines their disaster response, especially during earthquakes, remains largely unexplored. The...