Vol. 59 No. 12

December, 2010

Development of the Multielemental Determination Method for Bioactive Trace Metals in Open Ocean Seawater and Its Application to International Intercalibration
Tomoharu Minami1, Eri Higo1, Seiji Nakatsuka1, Abigail Parcasio Cid1, Thi Dieu Huong Vu1, Kazuhiro Norisuye1 and Yoshiki Sohrin1
1 Institute for Chemical Research, Kyoto University, Gokasho, Uji-shi, Kyoto 611-0011
(Received 30 July 2010, Accepted 21 September 2010)

Bioactive trace metals are essential or highly toxic elements for organisms. The most important bioactive trace elements in the ocean environment are Al, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb, whose concentrations in seawater are generally less than tens of nmol kg−1. In previous methods, there were problems, such as contamination, interferences by major constituents and a non-quantitative recovery of the target metals, especially Al and Mn. We developed a novel method for analyzing the 9 elements based on solid-phase extraction-inductively coupled plasma mass spectrometry (ICP-MS). In this method, a column packed with chelating absorbent, which had ethylenediaminetriacetic and iminodiacetic acid groups, was used in a closed concentration system. The proposed method was able to concentrate all of the 9 elements simultaneously and quantitatively, and to remove the major constituents in seawater. The procedural blanks for Mn, Co, Ni, Cu and Cd were less than the detection limits for ICP-MS (3 times the standard deviations of 1 mol L−1 HNO3), and those for Al, Fe, Zn and Pb were 0.14, 0.03, 0.07 and 0.003 nmol kg−1, respectively. The overall detection limits for Al, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb were 0.24, 0.01, 0.04, 0.002, 0.01, 0.01, 0.06, 0.01 and 0.001 nmol kg−1, respectively. In this paper, we review the development of this method and its application to international intercalibration using open-ocean seawater.

Keywords : ICP-MS ; solid-phase extraction ; bioactive trace metals ; open ocean seawater ; international intercalibration.

Research Papers
Speciation Analysis of Phosphorus in Coastal Seawater near Okinawa Island and Concentration Correlation between Dissolved Phosphate Ions and Trace Metals Classified as Nutrient Type
Akihide Itoh1, Mami Yamaguchi2, Ayako Yamada1, Teruo Arakaki2, Noriko Kabe2 and Shoko Ganaha2
1 Department of Science Education, Faculty of Education, University of the Ryukyus, 1, Azasenbaru, Nishihara-cho, Nakagami-gun, Okinawa 903-0213
2 Subject Education Department of Natural Science, Graguate School of Education, University of the Ryukyus, 1, Azasenbaru, Nishihara-cho, Nakagami-gun, Okinawa 903-0213
(Received 23 July 2010, Accepted 29 September 2010)

A molybdenum-blue method with the preconcentration of ion pairing form on MF was applied for the speciation of phosphorus in coastal seawater at three points in Okinawa island and their monitoring from 2007 to 2008. The features of water quality for coastal seawater near Okinawa island were discussed from four kinds of physicochemical forms of phosphorus, such as dissolved, particle-adsorbed, insoluble particulate, and total. As a result, analytical results for Sesoko island samples in the suburb area showed a significantly different concentration distribution from those for Tomari port samples in the urban area. The total concentrations of P for Sesoko island samples were 14.0 μg L−1 on the average, and 16% and 65% of the total P were dissolved and insoluble particulate forms, respectively. On the contrary, the total concentrations of P for Tomari port samples were 14.0 μg L−1 on the average and 64% of total P was dissolved form. In addition, the concentration correlation between dissolved phosphate ions and trace metals classified as the nutrient type was investigated. The molar ratios of [Cd]/[PO43−] for Sesoko island samples were 1.46-3.7 × 10−3, which were significantly the higher than those for literature values in open surface seawater of the North Pacific Ocean. The cause of higher ratios of [Cd]/[PO43−] can be attributed to the input of Cd to the coastal seawater near Sesoko island or the difference of the intake speed of dissolved phosphate ions by each phytoplankton.

Keywords : phosphorus ; trace metal ; speciation ; coastal seawater ; Okinawa.

Concentration–depth Profiles of Trace Nickel and Vanadium in Lake Mashu and the Possible Input of Anthropogenically Derived Nickel and Vanadium from the Atmosphere
Hirotsugu Minami1, Hirotoshi Sakagami1, Junling Bai1, Kanako Mantoku1, Daisuke Harada1, Nobuo Takahashi1, Ikuo Atsuya1, Tatsuya Fukazawa2, Hiromi Hamada3, Seiki Igarashi4, Shin Fujie5, Hiroshi Kobayashi6, Atsushi Tanaka7 and Kazuo Jin8
1 Department of Materials Science and Engineering, Kitami Institute of Technology, 165, Koen-cho, Kitami-shi, Hokkaido 090-8507
2 Division of Built Environment, Graduate School of Engineering, Hokkaido University, Kita 13, Nishi 8, Sapporo-shi, Hokkaido 060-8628
3 Earth Science Laboratory, Faculty of Education, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba-shi, Chiba 263-8522
4 Institute of Environmental Sciences, Hokkaido Research Organization, Kita 19, Nishi 12, Sapporo-shi, Hokkaido 060-0819
5 Teshikaga Natural History Research Association, 2-2-5, Kawayu Onsen, Teshikaga, Hokkaido 088-3465
6 Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 4-3-11, Takeda, Kofu-shi, Yamanashi 400-8511
7 Environmental Chemistry Division, National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba-shi, Ibaraki 305-8506
8 Hokkaido Institute of Public Health, Kita 19, Nishi 12, Sapporo-shi, Hokkaido 060-0819
(Received 24 August 2010, Accepted 2 October 2010)

The determination of trace nickel in water samples was conducted by isotope dilution–microwave induced plasma mass spectrometry (ID-MIP-MS) to clarify the concentration-depth vertical profiles of nickel in Lake Mashu (maximum water depth : 212 m), Japan. This lake serves as the Baseline Station of the United Nations GEMS/Water (Global Environment Monitoring System/Water) Programme. The concentrations of nickel in the lake water samples decreased with depth from 0.3 m (surface) to 50 m (quarter of the maximum water depth) water depths. The nickel concentrations in rain- and snow-water samples retrieved at the lakefront and the wall of the caldera lake were higher than those in the surface lake water (0.3 m) samples. This phenomenon was also observed for the concentrations of vanadium in those water samples. The concentration ratio of vanadium to nickel of the snow sample is comparable in magnitude to the reported values in the particulate matter samples originating from fossil fuel combustion. Anomalously high concentrations of nickel in lake water at the thermocline depth were observed in September of 2007 and 2009. The sedimentation process was considered to be responsible for these phenomena since the density and the coefficient of viscosity increase drastically at the thermocline depth, and they would cause a decrease of the sedimentation velocity of the particulate matter containing nickel. The concentrations of nickel as well as vanadium in the water samples support the possibility of the input of anthropogenically derived particulate matter containing both nickel and vanadium, presumably originating from fossil-fuel combustion, into Lake Mashu.

Keywords : Lake Mashu ; GEMS/Water Baseline Station ; nickel ; vanadium ; ID-MIP-MS.

Determination of Silver in Environmental Samples by Electrothermal Atomic Absorption Spectrometry after Preconcentration with Protein
Kiyoyuki Egusa1, Satoshi Kaneco1, Yoshimasa Kondou1, Hideyuki Katsumata1, Tohru Suzuki2 and Kiyohisa Ohta1,2
1 Department of Chemistry for Materials, Graduate School of Engineering, Mie University, Tsu-shi, Mie 514-8507
2 Environmental Preservation Center, Mie University, Tsu-shi, Mie 514-8507
(Received 5 July 2010, Accepted 8 October 2010)

A new preconentration with protein biosorption was developed for graphite furnace atomic absorption spectrometry (GFAAS). Nutrose protein was used for the biosorption. The effect of various factors, such as initial pH of sample solution, stirring time, Nutrose amounts, pyrolysis temperature, atomization temperature and matrix elements, on the absorbance of silver was investigated for the optimization of experimetnal conditions. The optimum pyrolysis temperature and atomization temperature were 350°C and 1400°C, respectively. Under optimum conditions, silver in aqueous sample was concentrated approximately 15.5 fold by the present method. The dynamic range for calibration curve was in the range of 0.1 to 3 ng/mL. The detection limit (3S/N) was approximately 9 pg/mL. The reproducibility for GFAAS with the nutrose biosorption was relative standard deviation (RSD) 5.6% with Ag 1.0 ng/mL sample solution for seven measurements. Even through matrix elements existed in 103 fold excess in water, the silver biosorption was not affected by the matrix elements. The present method was applied into the determination of silver in environmenal samples. The recovery of spiked silver was in the satisfiable range.

Keywords : GFAAS ; silver ; environmental sample ; preconcentration ; biosorption ; nutrose.

Extraction and Determination of Polycyclic Aromatic Hydrocarbons in the Sediment with Sodium Dodecyl Sulfate
Yoko Tomita1, Yoshihiro Mihara1 and Shunitz Tanaka1
1 Graduate School of Environmental Science, Hokkaido University, Nishi-5, Kita-10, Kita-ku, Sapporo-shi, Hokkaido 060-0810
(Received 13 July 2010, Accepted 5 November 2010)

A determination method for polycyclic aromatic hydrocarbons (PAHs) in sediment samples was investigated on the basis of HPLC with fluolesence detection after the extraction of PAHs from sediment with sodium dodecyl sulfate (SDS), followed by the phase separation of an SDS-rich phase from water with HCl. The concentration of SDS for extraction, the concentration of HCl and the temperature for phase separation were investigated and optimized. The accumulation efficiency of PAHs was estimated by measuring the concentration of Quinizarine Green SS before and after phase separation. In the optimized condition, 0.1 M SDS, 4 M HCl, 60°C and 90 min for phase separation, the recovery ratio of antracene, fluoranthene and pyrene from a model sediment sample was more than 95% and the accumulation times were about 10. The proposed method was applied to sediment sample collected from the Songhua river in China ; the concentrations of antracene, fluoranthene and pyrene in the sediment were 80 μg/kg, 230 μg/kg and 220 μg/kg, respectively.

Keywords : Sounghua river ; Sediment ; PAHs ; HPLC ; Sodium Dodecyl Sulfate.

Elemental Analysis of Leaching Solution from Soils in the Mountain District of Shikoku with a Handy-type Liquid Electrode Plasma Atomic Emission Spectrometer
Takashi Yamamoto1, Isao Kurotani2, Ayumi Yamashita3, Jun Kawai4 and Shoji Imai1
1 Institute of Socio-Arts and Sciences, The University of Tokushima, 1-1, Minamijosanjima-cho, Tokushima-shi, Tokushima 770-8502
2 Department of Regional Sciences, Graduate School of Integrated Arts and Sciences, The University of Tokushima, 1-1, Minamijosanjima-cho, Tokushima-shi, Tokushima 770-8502
3 Department of Mathematical and Natural Sciences, Faculty of Integrated Arts and Sciences, The University of Tokushima, 1-1, Minamijosanjima-cho, Tokushima-shi, Tokushima 770-8502
4 Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto-shi, Kyoto 606-8501
(Received 26 July 2010, Accepted 3 September 2010)

The elemental analysis of a 1M hydrochloric acid leaching solution from soil samples in the mountain district of Shikoku was carried out by a portable liquid electrode plasma (LEP) atomic emission spectrometer. The contents of Na, K, Ca, Mg, Mn, and Fe were determined, and compared with those by flame photometry, flame atomic absorption spectrometry, ICP-MS and ICP-AES. The 600 V of the applied voltage was found to be suitable for the present sample solution at the use of a sample holder made of resin. The precision of the emission intensities for iterative measurements was improved by a normalization procedure with an emission line from the atomic hydrogen, and the relative standard deviations were ca. 20%. Results of quantitative analysis of soil-extracts by LEP atomic emission spectrometry were discussed based on geological data around the sampling area.

Keywords : liquid electrode plasma atomic emission spectrometry ; soil ; hydrochloric acid extraction ; internal standard.

Successive Determination of Chromium(VI) and Total Chromium by FIA Using Photo-oxidation with Vacuum Ultraviolet
Shigeru Taguchi1, Ayako Fujii1, Takashi Okoshi1, Hideki Kuramitz1 and Noriko Hata1
1 Graduate School of Science and Engineering for Research, 3190, Gofuku, Toyama-shi, Toyama 930-8555
(Received 23 July 2010, Accepted 24 September 2010)

The photo-oxidation of Cr(III) to Cr(VI) with OH radicals formed under the irradiation of vacuum ultraviolet (VUV) was applied to the successive determination of Cr(VI) and total chromium by FIA. A sample solution containing Cr(III) was introduced into a quartz tube contacted to a VUV lamp radiating the light of 185 nm and 254 nm. Chromium(III) was oxidized to Cr(VI) quantitatively while passing through the quartz tube. The Cr(VI) was converted into a colored species with diphenylcalbazide in a reaction coil and the colored species was detected with an UV detector. For a sample solution containing Cr(III) and Cr(VI), without VUV irradiation, only Cr(VI) was determined. On the other hand, under VUV irradiation the total concentration of chromium, that is Cr(III) plus Cr(VI), was determined. The speciation of Cr(III) and Cr(VI) was easily performed by on/off switching the VUV lamp. Linear calibration was obtained at 0.05 – 1.0 mg dm−3 for both Cr(III) and Cr(VI). More than four samples were analyzed in one hour. This technique was successfully applied to synthesized plating wastewater.

Keywords : chromium(VI); total chromium ; vacuum ultraviolet ; photo-oxidation ; FIA.

Speciation of Aluminum in Lake Kasumigaura, Japan
Masami Kanao Koshikawa1, Mirai Watanabe1, Hiroshi Koshikawa2, Kazuhiro Komatsu1, Akio Imai1, Kazuho Inaba1 and Takejiro Takamatsu1,3
1 Water and Soil Environment Division, National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba-shi, Ibaraki 305-8506
2 Asian Environment Research Group, National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba-shi, Ibaraki 305-8506
3 Center for Water Environment Studies, Ibaraki University, 1375, Ohu, Itako-shi, Ibaraki 311-2402
(Received 21 July 2010, Accepted 7 October 2010)

Speciation of aluminum (Al), including inorganic monomeric Al (Ali, the sum of aquo, hydroxy, and inorganically complexed forms), organic monomeric Al (Alo, the organically complexed form), and colloidal mineral Al (Alc, the fine particulate form that passes through a 0.4-μm pore size membrane filter), was investigated in circumneutral (pH 7–9) eutrophic Lake Kasumigaura, Japan. The mean concentrations calculated from the result of monthly observations during the period from January to December 2003 were compared among ten stations. Ali decreased downstream from the mouth of the influent rivers (0.07–0.10 μM) to the mouth of the effluent river (0.03 μM). Alc, which also decreased downstream (from 0.11 to 0.06 μM), was the major fraction (>50%) of total dissolved Al at all stations. Alo remained around 0.02 μM at all stations. In Lake Kasumigaura, a high concentration of Si (average 0.23 mM) seems to be involved in the removal of Ali and formation of Alc. Also, a high concentration of Ca (ave. 0.43 mM) seems to be acting as a competitive cation for complexation with a high concentration of dissolved organic carbon (ave. 0.26 mM), and inhibit the formation of Alo.

Keywords : circumneutral water ; aluminum ; silicon ; calcium ; dissolved organic carbon.

Reexamination of Optimum pH Condition for the Determination of Dissolved Iron(II) in Aquatic Environments Using Colorimetric Reagents
Masahiro Maruo1, Kazuki Nagaoka1, Issei Kobayashi1, Kanako Kozawa1 and Hajime Obata2
1 School of Environmental Science, The University of Shiga Prefecture, 2500, Hassaka, Hikone-shi, Shiga 522-8533
2 Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa-shi, Chiba 277-8564
(Received 26 August 2010, Accepted 8 October 2010)

The pH conditions for the colorimetric determination of Fe(II) in oxic natural water samples were reexamined for analyses using PDTS (ferrozine) or bathophenanthroline disulfonic acid salt for the fixation of Fe(II) onboard a boat without an electricity supply. Bathophenanthroline disulfonic acid salt enhanced the reduction of Fe(III) to Fe(II), and produced an overestimation of the Fe(II) concentration in the water of a natural lake. PDTS enhanced the reduction of Fe(III) at pH 4.0, but showed almost no reduction of Fe(III) at pH 6.8. Oxidation of Fe(II) was observed at pH 9.0. PDTS at pH 6.8 showed no variation in Fe redox speciation in water within 30 h. As analyzed in the field onboard a boat, the Fe(II) concentration of a Japanese lake was measured by using the latter conditions with a solid-phase Fe(II)-ferrozine complex. Under irradiation with sunlight, the formation of Fe(II) on the lake surface was observed during the daytime. In contrast, the Fe(II) concentration in another lake that received no sunlight did not show a significant change within 6 h of sampling. This finding suggests that a portion of Fe(II) is stabilized by complexation with ligands present in the water. This estimate is supported by the difference between the Fe(II) concentration of identical river water samples measured using this method (26 nmol L−1) and chemiluminescence (0.8 nmol L−1).

Keywords : Fe(II); redox speciation ; PDTS ; solid phase extraction ; freshwater.

Simultaneous Determination of Volatile Halogenated Organic Compounds in Brackish Water and Seawater by Purge and Trap–Gas Chromatography/Mass Spectrometry
Hiroki Karasawa1, Masae Kimura2, Chiharu Wakuda2, Michiko K. Kurihara1, Kanenori Tsujino3, Yukinori Tani2 and Shinya Hashimoto1
1 Department of Chemistry, College of Humanities & Sciences, Nihon University, 3-25-40, Sakurajosui, Setagaya-ku, Tokyo 156-8550
2 Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, 52-1, Yada, Suruga-ku, Shizuoka-shi, Shizuoka 422-8526
3 Hamamatsu North High-School, 1-30-1, Hirosawa, Naka-ku, Hamamatsu-shi, Shizuoka 432-8013
(Received 5 August 2010, Accepted 14 October 2010)

Simultaneous determination method for 12 volatile halogenated organic compounds (VHOCs) in brackish water and seawater has been developed, based on purge and trap-gas chromatography/mass spectrometry. The limits of detection for VHOCs were <0.04 pmol L−1 for bromomethane, iodoethane and tribromomethane, <0.13 pmol L−1 for bromochloromethane, chloroiodomethane, chlorodibromomethane and bromoiodomethane, <0.21 pmol L−1 for chloromethane, dibromomethane, bromodichloromethane, and diiodomethane and 0.67 pmol L−1 for iodomethane. Good linearities of the calibration curves for 12 VHOCs were obtained in the concentration range up to100 pmol L−1. The correlation coefficients were >0.997 for bromochloromethane, chlorodibromomethane, bromodichloromethane, bromoiodomethane and tribromomethane, >0.981 for chloromethane, iodomethane, iodoethane, chloroiodomethane and diiodomethane, 0.967 for dibromomethane and 0.923 for bromomethane. Using this developed method, the concentrations of VHOCs in brackish water, coastal seawater and open ocean seawater were measured. The coefficients of variation were approximately <20% in all samples. Thus, this simultaneous highly sensitive analysis method was valuable for determination of trace levels of VHOCs concentrations in natural water.

Keywords : volatile halogenated organic compounds ; purge and trap ; gas chromatography/mass spectrometry ; brackish water ; seawater.

A Simple in situ Extraction Method for Dissolved Sulfide in Sandy Mud Sediments Followed by Spectrophotometric Determination and Its Application to the Bottom Sediment at the Northeast of Ariake Bay
Shogo Sugahara1, Tatsuya Yurimoto2, Kazuhiro Ayukawa1, Katsunori Kimoto2, Yukiko Senga3, Minoru Okumura1 and Yasushi Seike1
1 Faculty of Science and Engineering, Shimane University, 1060, Nishikawatsu-cho, Matsue-shi, Shimane 690-8504
2 Seikai National Fisheries Research Institute, 1551-8, Taira-machi, Nagasaki-shi, Nagasaki 851-2213
3 Faculty of Geo-Environmental Science, Rissho University, 1700, Magechi, Kumagaya-shi, Saitama 360-0194
(Received 24 July 2010, Accepted 5 November 2010)

We developed a simple in situ extraction method for dissolved sulfide (H2S, HS, S2−) in sandy mud sediments. All analytical procedures were performed in a sealed system of glass syringes to prevent the volatilization of hydrogen sulfide and the oxidation of sulfide by air. An adequate amount of sandy mud sediment was put in a graduated glass syringe on site immediately after sampling. This procedure was performed using a unique and useful tool ; a plastic syringe had its front portion cut, so as to avoid the attachment of sediment to the inside wall of the syringe. To the sediment sample in the syringe, distilled water, deoxygenated by babbling with nitrogen gas, was injected via a three-way stopcock with another syringe. After mixing well, the sample was filtrated into the other syringe through a filter (0.45 μm). In addition, zinc acetate solution was added to the filtrate in the syringe, and was then spectrophotometrically determined by the methyleneblue method after being brought back to laboratory. The proposed method was successfully applied to bottom sediment samples taken from northeast of Ariake Bay. A high concentration of dissolved sulfide was detected in a warmer season. This method should be useful to evaluate sediment quality and to assess the influence of dissolved sulfide on benthos such as bivalves.

Keywords : in situ extraction method of dissolved sulfide ; sandy mud sediment ; methyleneblue method ; interstitial water.

Solid-Phase Extraction of Chromium(VI) by Polyurethane Foam Treated with Hydrochloric Acid
Hiroaki Minamisawa1, Kento Mizushima2, Hiromichi Asamoto1, Mayumi Minamisawa3, Kazunori Saitoh4 and Tatsuro Nakagama4
1 Department of Basic Science, College of Industrial Technology, Nihon University, 2-11-1, Shin-ei, Narashino-shi, Chiba 275-8576
2 Graduate School of Industrial Technology, Nihon University, Izumi-cho, 1-2-1, Narashino-shi, Chiba 275-8575
3 Department of Bio Technology, Tokyo College of Medico-Phamaco Technology, 6-5-12, Higashikasai, Edogawa-ku, Tokyo 134-8530
4 Department of Applied Molecular Chemistry, College of Industrial Technology, Nihon University, 1-2-1, Izumi-cho, Narashino-shi, Chiba 275-8575
(Received 24 July 2010, Accepted 5 November 2010)

Chromium exists widely in nature as both trivalent and hexavalent forms. Although, Cr(III) is an essential element for humans at trace levels, Cr(VI) has great toxicity and carcinogenicity at low concentrations. Cr(VI) is typically present in aqueous solutions, such as CrO42− anion. Polyurethane foam (PUF) was impregnated with hydrochroric acid (HCl-PUF) and then used to remove Cr(VI) from environmental water samples. However, Cr(VI) was not adsorbed on PUF, Cr(VI) was adsorbed on HCl-PUF. In this study, the adsorption conditions of Cr(VI) on HCl-PUF were investigated, such as the adsorption time and the solution pH. Further, the deadsorption conditions of Cr(VI) from HCl-PUF were investigated, such as the kind of eluents and their concentrations. Cr(VI) was quantitatively adsorbed on HCl-PUF at a pH range 3.0-8.0 from aqueous solutions and their adsorption isotherms were fitted by the Freundlich equation. The Cr(VI) adsorbed on HCl-PUF as eluted with 3.0 mol dm−3 nitric acid. The property of HCl-PUF was extended to the preconcentration and determination of trace amounts of Cr(VI) in water samples by Inductively Coupled Plasma Emission Spectrometry (ICP-AES).

Keywords : inductively coupled plasma emission spectrometry (ICP-AES); solid phase extraction ; polyurethane foam (PUF); chromium.

Analytical Reports
Long-Term Monitoring of Copper and Iron in the Surface Water of Lake Kasumigaura, Japan
Noriko Tomioka1, Kazuhiro Komatsu1, Masami Kanao Koshikawa1, Akio Imai1, Kazuo Matsushige1 and Kazuho Inaba1
1 Water and Soil Environment Division, National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba-shi, Ibaraki 305-8506
(Received 21 July 2010, Accepted 22 September 2010)

In order to learn about the environmental conditions of Lake Kasumigaura, National Institute for Environmental Studies has been pursued in a limnological survey of the Lake monthly from 1977. The concentrations of copper and iron in surface water of Lake Kasumigaura were monitored at five sites from 1989. The concentrations of copper were about 0.6-1 μg L−1 for St. 1, 3, 9 and 12, whereas they were 0.8-1.4 μg L−1 for St. 7. This similarity may be due to the formation of a stable soluble complex species, and also small variations of the copper concentrations in inflowed rivers. The seasonal changes in the copper concentrations became unclear in the middle 1990s. The iron concentrations in the Lake were lower than 10 μg L−1, except those at St. 1. It seems that most of the iron is supplied from rivers, and it precipitates at the river-mouth region. The concentrations of iron at St. 1 were 50 μg L−1 before the early 1990s, whereas they became 20 μg L−1 after the late 1990s. Although the reasons for the changes in the late 1990s are very complicated, the change in the surface level of the lake water, by controlling the Hitachi River Watergate, which started in 1996, may be one of the reasons. The surface level of the lake water became 30 cm higher after control of the Watergate ; this may have moved the sedimentation-active river-mouth area to the upper side of the lake.

Keywords : limnological survey ; trend monitoring ; copper ; iron.