Keizo Hiraki

Species and Concentrations of Selenium and Nutrients in Tanabe Bay during Red Tide due to Gymnodinium nagasakiense

A red tide due toGymnodinium nagasakiense was observed in August 1988 in Tanabe Bay, Wakayama Prefecture, Japan. The maximum cell concentration ofG. nagasakiense reached 1×105 cells ml−1 at the surface water. From May to September 1988, the following were monitored: water temperature, salinity, chlorophylla, D.O., dissolved nutrients (NO2−N, NO3−N, NH4−N, PO4−P DON, DOP), particulate nutrients (PON, POP) and three dissolved selenium species [Se(IV), Se(VI), Organic Se]. Dissolved inorganic nitrogen (NO3−N, NH4−N) decreased but PON, POP, DON, DOP and inorganic phosphate increased at the peak of the bloom. The concentration of organic selenium increased up to the bloom initiation period which started on 5 July, and then the concentration of Se(IV) increased as the concentration of organic selenium decreased at the peak of the bloom (3 August). The strong relationship was found between the concentration of Se(IV) and the cell concentration ofG. nagasakiense (r2=0.98). The Se(IV) requirement ofG. nagasakiense was 2.89×10−17 moles cell−1, which was agreed well with 4.4×10−17 moles cell−1 found in a laboratory experiment onG. nagasakiense using selenium spiked artificial sea water medium. The average ratio of Se(IV) to dissolved inorganic nitrogen (DIN) during the red tide bloom was 1∶1441, the ratio of Se(IV) to DIN at the surface with the maximum cell concentration ofG. nagasakiense of 1×105 cells ml−1 was 1∶137. These results suggested that selenium may play an important role in red tide outbreak ofG. nagasakiense.

Determination of thorium in phosphate minerals by solvent extraction-ICP atomic emission spectrometry.

リン酸塩鉱石中のトリウムのICP発光分光分析法における基礎的検討を行なった。ゼノタイムでは共存希土類元素により, また, アパタイトでは高濃度のリン酸カルシウムにより, それぞれ分光干渉や負の干渉を受けた。本研究ではトリウムをこれらの共存元素から選択的に分離する方法として溶媒抽出法を検討したところ, キレート剤としてはトリウムと安定な錯体を形成する 1-フェニル-3-メチル-4-トリフルオロアセチル-5-ピラゾロンを, また, 抽出溶媒には有機溶媒のプラズマ炎への導入効率と抽出挙動などの点からジプチルエーテルが非常に有効であることが明らかになった。本溶媒抽出により実試料中トリウムの分析を行った結果, ゼノタイムやモナズ石中でそれぞれ0.43および6.79%, アパタイトでは(0.4～1.5)×10-3%であり, とくにゼノタイムやモナズ石では分光干渉を補正した(直接法) ものとよく一致し, 本法が ICP 発光分析の前処理法として, きわめて信頼性のある方法であることが認められた。