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，考虑到自然本底值，这样小的放射水平对人体健康是无关紧要的。
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The results show that the radioactivity level of varied water bod-ies of the city was within normal natural background.
调查结果表明，上海市各类水体中天然放射性核素浓度属正常本底水平。
The results show that the radioactivity level of varied water bodies of the region was within normal natural background.
调查结果表明，宁夏回族自治区水体中天然放射性核素浓度属正常本底水平。