Masumi Ishizaka

National Institute for Agro-Environmental Sciences in Japan, Tsukuba, Ibaraki, Japan

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Publications (9)24.71 Total impact

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    ABSTRACT: Arsenic species, including arsenous acid, arsenic acid, methylarsonic acid, and dimethylarsinic acid, were determined using HPLC-ICPMS. The species were separated with a Discovery HS F5 column and a simple, volatile, and isocratic mobile phase of 0.1% (v/v) formic acid and 1% (v/v) methanol. The Discovery HS F5 column with a pentafluorophenyl (PFP) stationary phase gave sharp peaks and full separation of the arsenic species in 5min, and other PFP columns showed lower performance. This separation method was applied to arsenic species analysis in rice. The extraction of arsenic from rice samples was performed using 0.15M nitric acid. The methodology was validated by use of certified reference materials, NMIJ CRM 7503-a and NIST SRM 1568a, and extremely low arsenic rice samples as blank samples.
    Journal of chromatography. A. 06/2014;
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    ABSTRACT: Diphenylarsinic acid, phenylarsonic acid, methylphenylarsinic acid (MPAA), dimethylphenylarsine oxide (DMPAO), and methyldiphenylarsine oxide (MDPAO) in soil and rice were extracted, separated by reversed-phase chromatography, and quantified by ICPMS with a membrane desolvating system. For the extraction of arsenicals from rice grain and straw, 68% HNO3 provided better extraction efficiency than water, 50% methanol, or 2.0 mol L(-1) trifluoroacetic acid. For the extraction from soil, 68% HNO3 provided better extraction efficiency than H2O, 1 mol L(-1) H3PO4, or 1 mol L(-1) NaOH. The contaminated soil contained all five aromatic arsenicals along with inorganic arsenicals as main species (5.86 +/- 0.19 microg of As kg(-1): 60.8 +/- 2.0% of total extracted As). After pot experiments, rice straw contained mainly DMPAO (7.71 +/- 0.48 microg of As kg(-1): 60.5 +/- 3.7%), MDPAO (0.91 +/- 0.07 microg of As kg(-1): 7.2 +/- 0.5%), and inorganic As (2.85 +/- 0.20 microg of As kg(-1): 22.3 +/- 1.6%). On the other hand, rice grain contained mainly MPAA (1.17 +/- 0.04 microg of As kg(-1): 86.7 +/- 2.7%). The root uptake of each species from the soil and transport from straw to grains were significantly related to the calculated log K(ow) values.
    Analytical Chemistry 07/2008; 80(15):5768-75. · 5.82 Impact Factor
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    ABSTRACT: The cholinesterase (ChE)-inhibiting activity of water and the concentrations of representative inhibitors were monitored in the Tone canal, Japan, during April to December 2006. The ChE-inhibiting activity, measured by using horse serum as enzyme source, increased from late April to early June, and from September to October. Although the trends in the ChE-inhibiting activity of the samples were consistent with concentration changes of organophosphorus pesticides, ChE-inhibiting activity was not observed in samples replicated on the basis of the chemical concentrations detected. The water samples were treated with chlorine to enhance the ChE-inhibiting activity by conversion of thiophosphate pesticides to phosphate pesticides. The ChE-inhibiting activity increased in almost all the chlorine-treated samples, although organophosphorus pesticides were either not detected or detected in traces in the samples by gas chromatographic-mass spectrometric analysis. These results suggested that assay of ChE-inhibiting activity is important for evaluating the ecotoxicity of environmental water, because toxicological investigations based solely on inhibitor concentrations may underestimate the contamination. Furthermore, the combined method of oxidation by chlorination and the ChE assay is very effective for screening and monitoring of organophosphorus pesticides in environmental water.
    Ecotoxicology 06/2008; 17(4):221-8. · 2.77 Impact Factor
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    ABSTRACT: We found that aquatic crustaceans, decapoda; atyidae (Caridina multidentata, Neocaridina denticulate, and Paratya compressa), metabolize pyrene to a new conjugation product. The results of deconjugation treatments indicated that glucose and sulfate combined with 1-hydroxypyrene. Further analysis by LC/ESI-MS/MS showed that the molecular weight of the product was 460 (m/z 459; deprotonated ion), and that it has a glucose-sulfate moiety (m/z 241; fragment ion). These results indicated that the new metabolite was the glucose-sulfate conjugate of 1-hydroxypyrene. The glucose-sulfate conjugate is a phase II product that has not been reported previously from any organism. Several studies have demonstrated that sulfation is an important pathway for metabolism of xenobiotics in aquatic invertebrates. Thus, glucose-sulfate conjugates may add an important signal for excretion or sequestration of xenobiotics for aquatic invertebrates.
    Biochemical and Biophysical Research Communications 09/2007; 360(2):490-5. · 2.28 Impact Factor
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    ABSTRACT: The objective of this study was to clarify the adsorption and desorption characteristics of several herbicides in sediment. Five herbicides, esprocarb, thiobencarb, dimethametryn, pretilachlor, and simetryn were examined in this study. The adsorption ratio on the sediment increased in the following order: pretilachlor < dimethametryn < simetryn < thiobencarb < esprocarb. On the other hand, the adsorption ratio on the sediment without organic matter increased in the following order: thiobencarb < esprocarb < pretilachlor < dimethametryn < simetryn. Furthermore, the amounts of simetryn, dimethametryn, and pretilachlor adsorbed on the sediment without organic matter increased, while those of esprocarb and thiobencarb decreased in comparison to the original sediment. These results strongly suggested that the mineral surface in the sediment was very important as the adsorption site for the herbicide, especially in the case of simetryn, dimethametryn, and pretilachlor. All the adsorption and desorption data fitted well with the Freundlich equation. The hysteresis in the adsorption-desorption phenomena in the sediment was observed for all the herbicides, and it was affected by the organic matter in sediment, especially in the case of dimethametryn and pretilachlor.
    Journal of Environmental Science and Health Part B 02/2007; 42(1):1-8. · 1.21 Impact Factor
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    ABSTRACT: The aquatic crustacean Daphnia magna is an important species for ecotoxicological study, and is often used as a test organism for environmental risk assessment. However, the mechanism of xenobiotic metabolism by this species has not been studied in detail. In the present study, pyrene was used as model substance to investigate the mechanism of xenobiotic metabolism in D. magna. The results of 24-h exposure experiments showed that D. magna could metabolize pyrene and biotransform it into water-soluble metabolites. On the other hand, the metabolism of pyrene was significantly inhibited by SKF-525A as the cytochrome P450 (CYP) inhibitor. These observations indicated that oxidation by CYP participated in the biotransformation of pyrene by D. magna. We also identified the pyrene metabolites formed by D. magna by HPLC with an electrospray ionization triple quadrupole mass spectrometry detector (LC/ESIMS/MS) and de-conjugation by sulfatase, beta-glucuronidase, and beta-glucosidase. One of the metabolites was ionized in ESI negative mode and formed a dominant mass of m/z 297 (MS) with the product ion of m/z 217 (MS2). Furthermore, this metabolite formed 1-hydroxypyrene on treatment with sulfatase. This metabolite was considered to be a sulfate conjugate of oxidized pyrene (1-hydroxypyrenesulfate). Furthermore, we quantified the deconjugated 1-hydroxypyrene formed by the above enzyme treatment. It showed that 52% of the total metabolized pyrene was biotransformed into 1-hydroxypyrene-sulfate, and more than 73% was biotransformed into oxidized pyrene conjugate. These results indicated that CYP and several conjugation enzymes participate in its biotransformation, and sulfation is important in D. magna for metabolism and elimination of xenobiotics.
    Aquatic Toxicology 12/2006; 80(2):158-65. · 3.51 Impact Factor
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    ABSTRACT: This work describes the analytical performance of the enzyme-linked immunosorbent assay (ELISA) for the fungicide chlorothalonil to effectively exploit as a simple and rapid detection system for pesticide residue on the scenes of the agricultural production and distribution. This ELISA represents the satisfactory analytical characteristics (I50 value, 0.34 ng/g; limit of detection, 0.052 ng/g) to detect chlorothalonil at the regulatory values or thereabout in a sample. Noticeable cross-reactivities were shown with two fungicides, fthalide (58.8%) and pentachloronitrobenzene (quintozene) (20.0%), and some non-agrochemicals such as tetrachloroterephthalonitrile (96.8%) and tetrachlorophthalonitrile (68.3%). The influence of three organic solvents (methanol, acetone, and acetonitrile) used as extractants for chlorothalonil residue was evaluated, with the result that methanol was the most suitable solvent for the ELISA, and the final concentration in the well could be up to 5% (v/v) without any negative influence on the ELISA. It has been possible to directly analyze chlorothalonil residue only by giving dilution of each sample extract with water prior to the ELISA analysis. The average recovery values from the spiked samples by the ELISA were between 101.7 and 113.6% with the average coefficients of variation between 2.6 and 5.9%. Although the results obtained from the ELISA correlated well with those from the reference GC/MS methods for all agricultural samples (r>0.98), the linear function inclined to the ELISA results because of loss during complex sample preparations for GC/MS analysis. Nevertheless, the results demonstrated that the proposed ELISA is a reliable, cost-effective, and rapid quantitative method for chlorothalonil residue.
    Journal of Chromatography A 10/2006; 1129(2):273-82. · 4.61 Impact Factor
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    ABSTRACT: No abstract available.
    Bulletin of Environmental Contamination and Toxicology 06/2005; 74(5):954-61. · 1.11 Impact Factor
  • Koji Baba, Eiki Watanabe, Heesoo Eun, Masumi Ishizaka
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    ABSTRACT: Direct determination of cadmium in rice flour by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is described. This superior quantitative method needs no conventional laborious sample pretreatment such as decomposition and extraction. To construct the calibration line and estimate the detection limit, three certified reference materials for rice flour, NIES nos. 10a, 10b and 10c, were used and contaminated with three different concentrations of cadmium (0.023, 0.32 and 1.82 mg kg−1, respectively). These three kinds of rice flour were finely ground and pressed into disks for analysis. The calibration line showed good linearity in the range 0.023–1.82 mg kg−1. The determination did not require internal standardization and no significant interference was observed.
    Journal of Analytical Atomic Spectrometry 12/2003; 18(12):1485-1488. · 3.40 Impact Factor