A third concern is that pollutants in soils and ground water,once introduced,remain there for a long time,due both to the chemical stability of many of the compounds involved,and the extremely slow rates at which ground water is circulated or exchanged.

• 第三个涉及的是土壤和地下水污染，由于所含的许多化合物的化学性质稳定及地下水循环或交换速率极低，这种污染一旦发生就会残留很长时间。