safe concentration of pollutant

例句：

1. 1. The factory has to ensurethat the air pollution is kept within safeconcentrations.
   工厂必须确保空气污染保持在安全浓度以下。
2. 2.The government has set strict limits on thesafe concentrations of chemicals in the environment.
   政府对环境中化学物质的安全浓度设定了严格的限制。
3. 3.The study found that the safe concentrations ofcertain chemicals could be reduced by using moreefficient technologies.
   研究发现，通过使用更高效的技术，某些化学物质的安全浓度可以降低。