. "Circumstances" . . . "2004-07-08T13:06:56+02:00"^^ . "con" . "A set of circumstances, often the relative amount of the Toxic_substance that is present, under which the Toxic_substance is specified to have or lack a toxic effect. Some metals, such as copper and selenium, are essential to normal metabolic function as trace elements but are toxic at high levels of exposure"@en . . . . "6769"^^ .