However , there are no currently valid SGVs for many important and common elements , such as copper , zinc , lead or chromium .
SGVs are derived by the Environment Agency using the ' CLEA ' model ( which can also be customised or used for DQRA ) .
There are no currently valid SGVs for many important and common elements , such as copper , zinc , lead or chromium .
SGVs are derived by the Environment Agency using the ' CLEA ' model ( which can also be customised or used for DQRA ) .