Hayao Sakamoto

Mercury contamination in the Yatsushiro Sea, south-western Japan: spatial variations of mercury in sediment

Mercury-contaminated effluent was discharged into Minamata Bay from a chemical plant over a 20-year period until 1965 (from 1958 to 1959, effluent was discharged into Minamata River), causing Minamata disease. In an effort to characterize the extent of the contamination in the Yatsushiro Sea, the vertical and horizontal distributions of mercury in sediment were investigated. Sediment was sampled at 62 locations in the southern part of the sea from 4 to 6 March 1996. In the lower layers of the long cores of sediment, the total amount of mercury was at a relatively uniform low concentration. We interpret these low values to represent the background concentration absent of anthropogenic influence. The background value thus estimated for the Yatsushiro Sea was 0.059 +/- 0.013 mg kg(-1) (mean +/- S.D., n = 51). The highest concentration in each sample ranged from 0.086 to 3.46 mg kg(-1) (mean, 0.57 mg kg(-1)). The higher values were obtained at stations near Minamata Bay and the Minamata River (the sources of the pollution). Concentrations decreased with distance from the source. An inspection of the vertical profiles of mercury concentration in cores suggested that the deposited mercury had not been fixed in sediment but had been transported, despite 30 years having past since the last discharge of contaminated effluent. At nine stations, extractable inorganic and organic mercury concentrations were determined differentially. Inorganic mercury is the predominant species in sediment and organic mercury comprising approximately 1% of the total.

Vertical variations in the concentration of mercury in soils around Sakurajima Volcano, Southern Kyushu, Japan

In an effort to estimate the influence of mercury emitted from Sakurajima Volcano, Southern Kyushu, Japan, on the accumulation of mercury in soil, the vertical distribution of total mercury in soils was investigated together with organic matter content and grain size. The soils were sampled at a thickness of 1 cm from the surface to depth of 1 m at five locations on Sakurajima and two control locations, i.e. Takatoge approximately 11 km southeast and Suzuyama 22 km southwest of the volcano. The concentration in soils increased with the distance from the volcano and was 6.5+/-1.9 ngg(-1) (n=335), 29.0+/-15.6 ngg(-1) (n=100) and 229+/-105 ngg(-1) (n=103) for Sakurajima, Takatoge and Suzuyama, respectively. The concentration of mercury correlated with the amount of organic matter, but not with grain size distribution. The sedimentation rate for Sakurajima, Takatoge and Suzuyama was estimated from geological data to be approximately 1.3, 0.083 and 0.0048 cmyear(-1), respectively. The relatively fast sedimentation of Sakurajima soil was caused by the frequent precipitation of volcanic ash. The annual deposition of mercury estimated for Sakurajima, Takatoge and Suzuyama from the mercury concentration, sedimentation rate and soil density was 9 x 10(4), 3 x 10(4) and 2 x 10(4) ngm(-2)year(-1), respectively. Although the soil of Sakurajima had the lowest concentration among the three sites, it received the largest amount of mercury.

Spectrophotometric determination of traces of bromide based on its catalysis of the pyrocatechol violet/hydrogen peroxide reaction

A kinetic-spectrophotometric method for the determination of bromide (0.004–0.3 mg l−1) based on its catalysis of the oxidation of pyrocatechol violet by hydrogen peroxide in HCl/H2SO4 is described. The effect of bromide is greatly increased in the presence of large amounts of chloride. The relative standard deviations are 6.4 and 13% for 0.034 and 0.010 mg l−1 bromide, respectively (n = 10). Most ions commonly occurring in natural waters do not interfere except for iodide.

Background levels of atmospheric mercury in Kagoshima City, and influence of mercury emission from Sakurajima Volcano, Southern Kyushu, Japan

Vapor phase mercury concentration was determined daily for 1 year (Jan. 1996-Jan. 1997) in order to present the levels of atmospheric mercury in Kagoshima City and to estimate the influence of mercury emission from Sakurajima Volcano, southern Kyushu, Japan. The atmospheric mercury was collected on a porous gold collector at Kagoshima University and was determined by cold vapor atomic absorption spectrometry; Kagoshima University of Kagoshima City is located approximately 11 km west of Sakurajima Volcano. The mercury concentration obtained was in the range 1.2-52.5 ng m(-3) (mean 10.8 ng m(-3), n = 169). The atmospheric concentration varied from season to season; the concentration was high in summer and lower in winter. A linear relation was obtained by plotting ln[Hg/ng m(-3)] vs. 1/T for the north, south and west winds with correlation coefficients of -0.76, -0.79 and -0.83, respectively, but no such dependency was found for the east wind (r = -0.035). When the wind is blowing from the east, Kagoshima City is on the leeward side of the volcano. The impact of the fumarolic activity of the volcano on ambient air in the city was evident in the disappearance of temperature dependency with the appearance of the east wind. Atmospheric mercury concentration except for the east wind was considered to be background levels of Kagoshima City. As background levels, 8.1 +/- 5.3 ng m(-3), 14.8 +/- 7.9 ng m(-3), 13.9 +/- 11.7 ng m(-3) and 4.4 +/- 1.6 ng m(-3) (mean +/- S.D.) were obtained for spring, summer, autumn and winter, respectively.

Spectrophotometric determination of trace bromide by its catalytic effect on the tetrabase-chloramine T reaction

Abstract A catalytic Spectrophotometric method for the determination of trace amounts of bromide is proposed. In acidic solution 4,4′-bis(dimethylamino)diphenylmethane (tetrabase) is oxidized by chloramine T to form a blue compound, which is further oxidized to a greenish-yellow compound. The reaction is accelerated by trace amounts of bromide and can be followed by measuring the increase in the absorbance at 600 nm; the maximum absorbance is obtained on an absorbance-time curve at a given reaction time. Since the maximum value increases with increase in bromide concentration, this value is used as the measured parameter for the bromide determination. Under the optimum experimental conditions (4.1 × 10−6 M tetrabase, 3.8 × 10−4 M chloramine T, pH 3.8, 20 °C), bromide can be determined in the range 2–100 μg l−1. The relative standard deviations (n = 10) are 0.9, 1.7, 3.7% for 60, 20 and 10 μg l−1 bromide, respectively. This method was successfully applied to a determination of bromide in natural water samples.

Kinetic and mechanistic study of the chlorpromazine-hydrogen peroxide reaction for the catalytic spectrophotometric determination of iodide

Extensive kinetic studies were performed to investigate the mechanism of the chlorpromazine (CP)-hydrogen peroxide reaction utilized in the catalytic determination of iodide. This reaction proceeds by two independent, parallel reactions, one through the formation of a red free radical, another directly to form the colorless product. The red color formation is catalyzed by traces of iodide. The color formation reaction was followed by measuring the increase in absorbance at 525 nm and its kinetic investigations were carried out by the initial rate method. The reaction rate curves for colorless sulfoxide formation were obtained by following the increase in absorbance at 335 nm, and the analysis was carried out by the integration method. The disappearance rate of CP is given by -d[CP]dt = k3[I−[H2O2][H+] + k6[CP][H2O2][H+] + k9[CP][H2O2][H+] + k10[CP][H2O2], where the first and second terms correspond to the chromogenic reaction and the third and fourth to colorless sulfoxide formation. Mechanisms consistent with each term were proposed and analytical implications of the kinetic studies are discussed.

Differential determination of antimony(III) and antimony(V) by indirect spectrophotometry with chromium(VI) and diphenylcarbazide, after reduction of antimony(V)

Abstract Antimony(III) is determined indirectly through its reaction with excess of chromium(VI), the excess being quantified with diphenylcarbazide and measurement at 540 nm. Antimony(V) is reduced to antimony(III) with sodium sulfite in hydrochloric acid solution; excess of sulfite is eliminated by boiling. The subsequent determination of antimony(III) gives the concentration of total antimony, and antimony(V) is found from the difference between the results before and after reduction. Antimony in its different oxidation states can be determined in the range 0.04–0.7 mg l−1 within an error of about 10%.