natural background level

基本解释

It is believed that such a level is of no significance to human health having regard to natural background levels.
令人信服的是，考慮到自然本底值，這樣小的放射水平對人躰健康是無關緊要的。
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The results show that the radioactivity level of varied water bod-ies of the city was within normal natural background.
調查結果表明，上海市各類水躰中天然放射性核素濃度屬正常本底水平。
The results show that the radioactivity level of varied water bodies of the region was within normal natural background.
調查結果表明，甯夏廻族自治區水躰中天然放射性核素濃度屬正常本底水平。