The worst pollutionthreat 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。
2
However, substantial amounts of urban garbage are dumped and buried at the surface, which constitutes a serious pollutionthreat 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。
3
Supplies are under increasing threat from overuse and pollution.