水田土壌と米のストロンチウム同位体比の関係  [in Japanese] Relationship between the Strontium Isotope Ratio of Paddy Soil and of Rice Grains  [in Japanese]

ストロンチウム同位体比(^<87>Sr/^<86>Sr)を指標にした米の産地判別手法を確立するため,土壌の^<87>Sr/^<86>Srを測定し,米の^<87>Sr/^<86>Srとの関係を調べ,以下の結果を得た。1)水田土壌11点の水溶性と交換性の^<87>Sr/^<86>Srは,それぞれ0.7066〜0.7099と0.7065〜0.7099の範囲にあり,両者の値は一致した。このことから,水溶性Srと交換性Srの起源は同一であると考えられた。全Srの^<87>Sr/^<86>Srは0.7058〜0.7118の範囲にあり,水溶性および交換性の^<87>Sr/^<86>Srよりも概して高い値を示した。土壌の^<87>Sr/^<86>Srの地域別の違いをみると,米の場合と同様に,東日本側で低く,西日本側で高い傾向にあった。2)米の^<87>Sr/^<86>Srは,土壌の水溶性および交換性の^<87>Sr/^<86>Srと一致した。すなわち,米の^<87>Sr/^<86>Srは土壌の^<87>Sr/^<86>Srによって決まる特性値であり,土壌の^<87>Sr/^<86>Sr情報は,米の産地表示を確認する上で強力な検証データになると考えられた。3)マルチコレクタ型誘導結合プラズマ質量分析計による^<87>Sr/^<86>Sr測定において,時間分割測定(TRA)モードの適用により,試料導入量が従来法の10分の1までに縮減でき,マトリックスの影響に起因する感度低下が抑止された。本法によるSr同位体標準試料(NIST SRM 987, 0.2mgL^<-1>溶液)の測定結果は,認証値とほぼ4桁の範囲で一致し,産地判別分析に必要な精度を有することが確認された。

The strontium isotope ratio (^<87>Sr/^<86>Sr) of paddy soil was determined by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Then the relationship of the ^<87>Sr/^<86>Sr ratios of rice grains to those of the soils was investigated in order to establish a determination method for rice provenance by means of the ^<87>Sr/^<86>Sr ratio of rice grains. The ^<87>Sr/^<86>Sr ratios of the water soluble Sr and the ammonium acetate extractable Sr (exchangeable Sr) in the 11 soil samples ranged from 0.7066 to 0.7099 and from 0.7065 to 0.7099, respectively. A close agreement between the ^<87>Sr/^<86>Sr ratios of the water soluble Sr and those of the exchangeable Sr was obtained, indicating that water soluble Sr and exchangeable Sr in soil were derived from the same origin. The ^<87>Sr/^<86>Sr ratios of the total Sr in the soil, ranging from 0.7058 to 0.7118, were higher than those of the water soluble Sr or the exchangeable Sr. Generally, the lower ^<87>Sr/^<86>Sr regions were mainly present in Northeast Japan, whereas higher ^<87>Sr/^<86>Sr regions were present in Southwest Japan. The ^<87>Sr/^<86>Sr ratios of rice grains had the same ^<87>Sr/^<86>Sr ratios as the water soluble Sr or the exchangeable Sr in soils. This result suggests that the ^<87>Sr/^<86>Sr ratio of rice is constrained by the ^<87>Sr/^<86>Sr ratio of soil, and that information about the ^<87>Sr/^<86>Sr ratio of paddy soil is important basic data for verifying rice provenance. A time resolved analysis (TRA) technique was effective for the minimization of the sample size that was used for MC-ICP-MS measurement. The analytical result of the isotopic reference material (NIST SRM 987) and the accepted value coincided with each other to 4 significant digits, and this analytical precision was enough to detect the regional differences.