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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

Isotopes in hydrogeology

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;
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;
  223,224,226,228Ra radiological evaluation;
change of inflow during pumping tests;
  234,235,238U radiological evaluation;
  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;
origin and development of water
  39Ar mean residence time of middle-aged groundwater (some centuries)

Isotopes and food

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
food additives

δ13C origin of food;
verification of illegal additives;
  δ18O, δ2H origin
  δ15N sort of growth of fruit and vegetable - organic or not organic?
  δ34S origin
  δ 87Sr 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
δ 2H, δ 37Cl 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





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