Trace elements (Oligoelements) is a mineral salt necessary for the life of an organism, but in a very low quantity, less than 1 ppm (1 mg per kg of body weight).
Trace elements are toxic to the body when they are present at too high levels. The effect of a trace element depends on the intake dose.
When the trace element is said to be essential, a deficiency or on the contrary an excessive intake can lead to serious disorders.