trac·er / ˈtrāsər/ • n. a person or thing that traces something or by which something may be traced, in particular: ∎  a bullet or shell whose course is made visible in flight by a trail of flames or smoke, used to assist in aiming. ∎  a substance introduced into a biological organism or other system so that its subsequent distribution can be readily followed from its color, fluorescence, radioactivity, or other distinctive property. ∎  a device that transmits a signal and so can be located when attached to a moving vehicle or other object.

tracer A substance that is used to follow the passage of groundwater in places where it cannot be observed directly. Typical tracers include fluorescent dyes and salt. The presence of radioactive isotopes, e.g. tritium and carbon-14, may also be used as tracers in that they allow the age of groundwater to be determined. The presence of small amounts of other substances may also be used to make deductions about the origin and flow path of groundwaters.

tracer A substance that is used to follow the passage of groundwater in places where it cannot be observed directly. Typical tracers include fluorescent dyes and salt. The presence of radioactive isotopes (e.g. tritium and carbon-14) may also be used as tracers in that they allow the age of groundwater to be determined. The presence of small amounts of other substances may also be used to make deductions about the origin and flow path of groundwater.

tracer (tray-ser) n. a substance that is introduced into the body and whose progress can subsequently be followed so that information is gained about metabolic processes. Radioactive tracers, which are substances labelled with radionuclides, are used for a variety of purposes in nuclear medicine.