ISOTOPES - Valuable Carriers of Information
Fig. 1-3: Nomenclature of elements, the periodic table of elements, stable and radioactive isotopes.
What are isotopes?
Isotopes are atoms of one element (X) with the same number of protons (Z), but with a different number of neutrons (N). The sum of protons and neutrons presents the atom mass (A).
The 92 elements of the periodic table of the elements create more than 1000 isotopes. Isotopes are differentiated by 2 groups, stable and radioactive isotopes.
Isotopes as carrier of information
Isotopes are valuable and important for the determination
- of age (dating)
- of origin, genesis and development of rock, water, gases, and organic material or elements and compounds, respectively
Modern hydrogeology can not be imagined without isotope methods anymore. They provide a very detailed insight into the hydrological cycle. They are also an important tool for the optimisation of water management of aquifers and wells.
Measurements of the contents of environmental isotopes permit the study of hydrological systems in large regional and temporal scales. In particular isotope analyses allow the characterisation and quantification of groundwater components under difficult groundwater flow conditions.
Applied isotope systems in the hydrogeology are:
| Medium | Isotope system | Information |
| Water | 18O/16O (δ18O) and 2H/1H (δ2H) of H2O |
Climatic conditions of groundwater recharge (altitude of catchment area, pleistocene recharge); Amount and flow time of bank infiltrates and precipitation discharge; evaporation processes; Identification of formation waters; water-rock-interaction; interaction with dissolved gases (e.g. CO2, VOCs) |
| 3H of H2O |
mean residence time of young groundwaters (< 55 a); amount of young groundwater components; evaluation of natural guardedness; identification of landfill leachate |
|
| Dissolved substances |
34S/32S (δ34S) of SO4, H2S and 18O/16O (δ18O) of SO4 |
genesis and origin of dissolved sulphate and sulphur hydrogen; reduction and oxidation processes |
| 13C/12C (δ13C) of DIC, CO2, DOC, CH4 |
evaluation of carbon system, genesis, evolution and interaction of inorganic und organic carbon components |
|
| 14C of DIC, CO2, DOC, CH4 |
dating of old groundwater; evaluation of natural guardedness; origin and genesis of gases |
|
| 15N/14N (δ15N) of NO3, NO2, NH4, N2 |
evalution of the nitrogen system; origin and degradation processes of dissolved nitrogen components (denitrification) |
|
| 37Cl/35Cl (δ37Cl) of Cl- |
genesis and origin of dissolved chloride; development of saline waters |
|
| 87Sr/86Sr |
origin of groundwater; water-rock-interaction |
|
| 223,224,226,228Ra |
radiological evaluation; change of inflow during pumping tests; water-rock-interaction |
|
| 234,235,238U |
radiological evaluation; water-rock-interaction |
|
| 134,137Cs, 90Sr, 239Pt, 131I, 129I | influence of anthropogenic radionuclides (Tschernobyl, Fukushima, nuclear research center, medicine) | |
| 85Kr |
mean residence time of young groundwater (< 55 a); amount of young groundwater component |
|
| 3He/4He, 36Ar/40Ar, 20,21,22Ne |
relative age of groundwater; water-rock-interaction; origin and development of water |
|
| 39Ar | mean residence time of middle-aged groundwater (some centuries) |
Origin and authenticitiy of our food determine the quality and price. To verify the authenticity of food and food additives isotope analysis is widely used. Isotope methods are often the only possibility to prove cases of food fraud. They can provide the following information:
- Geographical origin of products
- Verification of illegal or non-declared additives (e.g. water, sugar, acids) or parental material
- Differentiation of naturally or synthetically produced commodity
- Control of organic or conventional growth
| Medium | Isotope system | Information |
|
food and |
δ13C |
origin of food; verification of illegal additives; authenticity |
| δ18O, δ2H | origin | |
| δ15N | sort of growth of fruit and vegetable - organic or not organic? | |
| δ34S | origin | |
| δ87Sr | origin | |
| δ11B | sort of growth - organic or conventional? | |
| 134/137Cs, 90Sr, 239Pt, 131I | radiological evaluation (e.g. influence of nuclear accident) |
Isotope and organic pollutants
Organic pollutants such as HCH and BTEX have a strong impact on groundwater. It is often difficult to find the person or company responsible for the contamination. The determination of the carbon isotope ratios of the organic pollutants allows the assignment of the contamination to the originator as well as a qualitative and quantitative estimation of the biological degradation (natural attenuation).
| Medium | Isotope system | Information |
| organic pollutants |
δ13C of HCH, BTEX, PAH δ2H, δ37Cl of HCH |
Person or company responsible for the contamination; natural attenuation; age of contamination |
Isotope and resources
Isotope methods are important tools to evaluate the genesis of crude gas and oil. They allow the exploration of possible reservoirs near to the surface. The investigation of isotopes from hydrocarbons gains information about the genetic mechanisms of e.g. methane and the maturity of higher hydrocarbons.
In the course of the energy turnaround and the climate protection sustainable resources should replace fossil energy sources. The determination of the radioactive 14C verifies the amount of the renewable part in a product (e.g. synthetics, biogenic lubricants, oils, etc.). It is also possible to analyse the exhaust fumes from e.g. a biomass heating power plant for its fraction of renewable resources which are used in the combustion.
| Medium | Isotope system | Information |
| crude gas | δ13C and δ2H of CH4 and higher carbon |
origin and genesis of hydrocarbons; maturity of reservoirs; possible crude gas and oil reservoirs |
| crude oil | δ13C and δ2H of oil components and single coal compounds |
maturity of oil reservoirs; genesis of reservoirs |
| renewable resources | δ13C, 14C of organic material | origin and composition of secondary combustible materials |
