環境指標としての降水中の微量元素

Abstract

降水中に含まれる微量元素を分析し, 環境指標としての有効性を調べた。降水は環境条件を考慮しネパールヒマラヤのヤルンカン氷河, 滋賀県桐生および京都市将軍塚で採取した。降水中に含まれるAl, Ca, Fe, Mg, Mnなど16種の微量元素を非破壊のまま熱中性子放射化分析法で定量した。降水中の微量元素濃度の季節的な変動は数倍から100倍程度であった。海から調査地までの距離が遠くなると降水中のNa濃度は減少し, Naが海洋起源の指標元素であることを確認した。また, 降水中のMn, VおよびSb濃度は将軍塚, 桐生, ヤルンカンの順に減少しており, 人為的な環境汚染レベルとよく一致していた。さらに, Al, CaおよびMgの濃度には大気中の浮遊粉塵が明らかに関与していると考えられる。

The trace elements in precipitation were investigated from the view point of utility as an environmental indicator. Precipitations were collected in Yalung Kang glacier (non-polluted, Himalaya, Nepal), Kiryu (meso-polluted, Shiga prefecture), and Shogun-zuka (highly polluted, Kyoto city). The trace elements, such as Al, Ca, Fe, Mg, Mn, Na, Ce, Co, Cr, Cs, La, Sb, Sc, Sm, Th, and V, in water samples were determined by means of non-destructive thermal neutron activation analysis. The concentration level of trace elements varied seasonally in the range from several to about one hundred times. Since the concentrations of Na in precipitation samples decreased with the distance from sea to sampling sites, it is plausible to say that they reflect the maritime effect. The concentrations of Mn, V, and Sb were higher at Kiryu and Shogun-zuka than at Yalung Kang. This can be attributed to the environmental pollution resulting from various industrial activities and automobiles. Airborne dust particles seem to influence on the concentrations of Al, Ca, and Mg in rain waters.