The worst pollution threat is concentrated in and near large cities.

最严重的污染威胁集中在大城市内或其附近。

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However, substantial amounts of urban garbage are dumped and buried at the surface, which constitutes a serious pollution threat to the groundwater source.

但其地表堆埋了大量的城市垃圾，对地下水源构成严重的污染威胁。

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Supplies are under increasing threat from overuse and pollution.

供应正受到日益增长的过度使用和污染的威胁。

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Yet, while our livelihoods are inseparable from the health of these natural systems, our oceans are under threat from pollution, coastal development, overfishing, and climate change.

WHITEHOUSE: Presidential Proclamation -- National Oceans Month, 2012

Pollution also poses a threat: floating plastic bags look a lot like the jellyfish they rely on as their main food source, and have been found in the digestive systems of about half of the leatherbacks studied in recent times.

CNN: Race to save the leatherback turtle

This does not surprise environmentalists, who have long argued that any policy of pollution-reduction that does not include a threat of punishment for non-compliance is useless.

ECONOMIST: The Lone Smog State