Definition of trace element

The term "trace element" originated in the field of chemistry to describe elements that are needed by living organisms in very small amounts, as these elements are only required in trace quantities. In scientific nomenclature, an element is considered a trace element if it is required by an organism in a concentration of less than 100 parts per million (ppm) in dry weight tissue. This contrasts with major or bulk elements, such as carbon, oxygen, and nitrogen, which are necessary in larger quantities of over 1,000 parts per million. These trace elements, however, still play essential roles in various biological processes in small quantities, such as enzyme activity, DNA synthesis, and protection against oxidative stress. Some well-known trace elements include iron, zinc, copper, iodine, and selenium, each with specific functions in the physiology of living organisms.