To avoid contamination, Wells in the Bengal Basin can be drilled into deep layers that were oxidized during the last ice age, in which the water is free of arsenic, Berg says.

为了防止被污染，孟加拉盆地的水井钻入了在上一个冰河时期被氧化的深层地层中，这一层的水是不含砷的，伯格说。

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The standard states that the citric acid-sodium nitrate treatment is the least hazardous for removal of free iron and other metallic contamination and light surface contamination.

该标准声明：柠檬酸-硝酸钠处理在去除游离铁合其他金属污染和轻的表面污染物时，危险性最低。

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The presence of exogenous surface contamination, including dirt, grease, free iron from contact with steel tooling, and so forth, may interfere with the formation of the passive film.

外生的表面污染，包括：尘土、油脂、来自钢铁加工的游离铁等等，可以影响到钝化膜的生成。

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For another guest, even the promise of contamination-free beef wasn't enough.

CNN: Should Americans banish the burger?

But in February this year a Health and Safety Executive report said the site was essentially free of asbestos contamination.

BBC: Cwmcarn High School

The Health and Safety Executive said the site was essentially free of asbestos contamination after a second round of tests, which some campaigners say should be enough to reopen the school, which also commissioned its own report.

BBC: Asbestos: Cwmcarn school repairs could cost up to ?1.5m