Shoichi Aizawa

Seasonal change in the level and the chemical forms of aluminum in soil solution under a Japanese cedar forest

The level of dissolved aluminum and its chemical forms in soil solutions consecutively collected by a porous cup vacuum sampler were monitored over a period from January 2001 to December 2001 at a Japanese cedar (Cryptomeria japonica) forestry area susceptible to acid deposition to characterize current soil dynamics and to evaluate potential tree damages. Distinction and characterization of Al species with differential toxicities were performed by two complementary speciation techniques; cation-exchange HPLC with fluorometric detection using 8-hydroxyquinoline-5-sulfonic acid (HQS) and size-fractionation/inductively coupled plasma atomic emission spectrometry (ICP-AES). The concentrations of free Al (mainly Al3+ and Al(OH)2+) and inert Al (existing as the complexed and/or colloidal forms) ranged between 0-150 microM and 10-50 microM, respectively. The concentrations of inert Al were mostly below 40 microM during an annual cycle and showed no marked seasonal variation, while free Al concentrations showed a clear tendency to increase in the spring and summer seasons (in the period from April to August) probably due to the enhanced activity of microbial nitrification and the resultant soil acidification. Major cations and anions were also regularly determined and their seasonal changes were correlated with that of the dissolved Al concentration. Correlations between total Al (mainly existing as free Al) and the related species (and environmental conditions) were as follows: Al and Mg (R=0.96, P<0.01), Al and Ca (R=0.97, P<0.01), Al and NO3- (R=0.68, P<0.01), Al and temperature (R=0.68, P<0.01), Al and solution pH (R=-0.61, P<0.01), solution pH and NO3- (R=-0.65, P<0.01).

Fluorine contents of Permian carbonate rocks in central Japan

Abstract The content of fluorine in Permian carbonate rocks from three localities in central Japan is investigated, and the mode of occurrence of the element discussed in relation to the constituent minerals. The F contents of various rock species indicate that the element tends to concentrate in dolostones rather than in limestones. The result suggests that F occurs as fluorite and/or apatite even in the F-poor carbonate rocks.

Fractionation of radiocesium in soil, sediments, and aquatic organisms in Lake Onuma of Mt. Akagi, Gunma Prefecture using sequential extraction.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has resulted in the contamination of the environment in Gunma Prefecture with radioisotope cesium (radio-Cs, 134Cs and 137Cs). Concentrations of radio-Cs >500Bqkg-1 were found in wakasagi (Hypomesus nipponensis) in Lake Onuma at the top of Mount (Mt.) Akagi in August 2011. To explain the mechanism of this contamination, monitoring studies have been conducted around Lake Onuma by measuring radio-Cs concentrations in samples of fish, aquatic plants, plankton, lake water, lake sediments, and surrounding soil. The leachability of radio-Cs was evaluated using sequential extraction by Tessier et al. The total concentration of radio-Cs in Lake Onuma ecosystems decreased gradually with time. In the brown forest soil, radio-Cs concentrations of 2000 to 6000Bqkg-1 were detected. The abundance ratio of the easy-elution form (exchangeable and carbonate forms) in the samples was <10%. The concentrations in phytoplankton samples were 3-6 times higher than those in wakasagi samples. The ratios of easy-elution forms increased by the rank in the food chain; 37% in phytoplankton, 78% in zooplankton, and 97% in wakasagi. It is likely that the lower ratio of the easy-elution form in phytoplankton is related to the adsorption of radio-Cs on suspended substances in the lake, as suggested by the analyses of aluminum and titanium in the phytoplankton, zooplankton, and wakasagi samples. The high concentrations of radio-Cs in wakasagi would be related also to the characteristics of closed mountain lakes.

Geochemical behavior of transition metals during the formation of protodolomite in Minamidaitojima Island, Japan

Abstract The average transition-metal contents of twenty-nine “pure” carbonate rocks composed of protodolomite, low-Mg calcite, and mixtures of both minerals from Minamidaitojima Island are: Mn, 6.1; Fe(II), 12.8; Ni, 0.71; Cu, 0.59; Zn, 0.39; and Cd, 0.10 ppm. These extremely low contents probably correspond to the background concentrations of these metals in Quaternary carbonate rocks with little or no silicates and oxides. The positive correlations of the concentration of transition metals except for Cu with that of Fe(II) suggest that these metals might have acted together with Fe during the formation of protodolomite and low-Mg calcite in this island. The reduced form of Fe in the protodolomite means that the dolomitization of carbonates in this island had been taken place under reducing environments. This circumstance supports the idea that the protodolomite might have been formed by the action of concentrated seawaters of lagoon origin.

Cadmium contents of Triassic and Permian limestones in central Japan

Abstract Cadmium contents are high in Japanese Palaeozoic limestones in central Japan, the values ranging from 0.17 to 2.41 ppm. The average Cd content of Japanese Palaeozoic limestones is estimated to be ∼ 0.5 ppm, which is significantly greater than those of Japanese limestones of other ages as well as those from other regions. Cd appears to be present in calcite because: (a) most of this element is contained in the 1 M acetic acid-soluble fraction of impure limestones; and (b) even pure limestones show relatively high Cd contents. The enrichment of Cd may be related to the volcanic activity which occurred in Japan during the Palaeozoic.

Abundance of Cadmiun in Permian Dolostones in Japan.

本邦各地区から採取した二畳紀ドロマイト岩試料中のCdを他の重金属元素とともに定量した.ドロマイト岩中のCd含量はSiO2やAl2O3,Fe含量とは正の相関関係を示さず,ZnをはじめMn,Ni,Cuなどの含量と正の相関関係を示した.ドロマイト岩の生成過程でCdはそれらの二価重金属元素とともにドロマイトの結晶格子中に取り込まれたと考えられる.ドロマイト岩試料(n=81)の幾何平均Cd含量はO.43PPmであり,同一一地区の二畳紀石灰岩試料(n=56)の幾何平均Cd含量0.47PPmとほとんど同じであった.これらの値は本邦第四紀石灰岩中のCd含量やMasonとMooreによってまとめられた炭酸塩岩のCd存在度(いずれも約 0.1ppm)に比較して高く,本邦二畳紀炭酸塩岩中のCd含量の特異性を示しているのかも知れない.