Using Isotopes in the environment

Isotopes are forms of the same chemical element that vary in their atomic mass. They may be stable or unstable, decaying radioactively over time and emitting characteristic particles or radiations. These unstable isotopes are commonly called radioisotopes (more properly radionuclides).

Isotopes can be used to study biological, agricultural and industrial processes, in archaeology, fisheries, ocean and atmospheric research, and in geological and environmental studies. Information can be gained from the relative amounts of stable isotopes, from the tracing of radioactive isotopes from the radiation emitted, and from the extent that a radioactive isotope has decayed into a more stable product. For example, the short-lived radioisotopes carbon-11 and nitrogen-13 can be produced in the laboratory to investigate soil nitrogen processes and plant photosynthesis.

Certain radioisotopes mimic the behaviour of components in industrial and natural processes, and tracing them benefits geothermal system development, environmental management, and the petrochemical industry. Leaks and blockages, flow rates and flow paths, and residence times in pipes can be discovered. Hydrogen, oxygen, carbon, sulphur and tritium studies of groundwater give information on aquifer storage capacity, aquifer recharge, and flow directions and velocities. The sources and age of groundwater can also be determined.

Tracing the fluid flow in geothermal systems is important to reservoir management in developed geothermal fields. Isotope techniques using carbon, oxygen, hydrogen, sulphur and boron are used in field development to show flow direction and rate. Temperatures at depth can be predicted from isotopic measurements of geothermal gases and waters, as can their origin. The economic resources of gas fields may be shown by carbon dioxide variations in reservoirs, and sulphur, carbon and hydrogen isotope measurements help oil-to-oil and oil-to-source rock correlations. They also determine the origin of natural gases.

Beryllium isotopes are good indicators of environmental change and have been used to investigate climatic warming and river down-cutting from marine sediments in the Wanganui Basin. Beryllium isotopes in rainwater also have relevance to investigating the global movement of air masses.

Stable and radiogenic isotopes are commonly used in the study of rocks and fluids from the earth's crust. Measurements of sulphur, oxygen, carbon and hydrogen help solve geological questions such as the origin of lavas, periods of polar climates, the association of gold-scheelite mineralisation with local shear zones, temperatures of mineral formation, and origins of ore components .