The rules should also impose a duty on States to prevent serious transnational environmental harm, as already laid down in principle 2 of the Rio Declaration and principle 21 of the Stockholm Declaration.
这种规则还应根据《里约宣言》的原则2和《斯德哥尔摩宣言》的原则21的规定，规定国家有义务预防严重的跨界环境损害。