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The (11)B/(10)B ratio exhibits wide variations in nature; thus, boron isotopes have found numerous applications in geochemistry, hydrology, and environmental studies. The main analytical techniques used are as follows: positive thermal ionisation mass spectrometry is the most precise (about 0.2 per thousand of the boron isotope ratio), but requires complex and laborious sample preparation; negative thermal ionisation mass spectrometry is less precise (about 0.5 per thousand), but rapid and suitable for water samples, whereas total evaporation-NTIMS allows for identification of the precise boron isotope composition of marine carbonates. It is expected that multi-collection system inductively coupled plasma mass spectrometry (MC-ICPMS) will eventually combine high precision with simple analytical procedures. Secondary ion mass spectrometry and laser ablation (LA)-MC-ICPMS allow in situ determinations on solid samples, but require the availability of calibration materials which are chemically and mineralogically similar to samples. These features of boron isotope measurement techniques were confirmed by the results of the first inter-laboratory comparison of measurements, organised by the Istituto di Geoscienze e Georisorse in Pisa. Finally, two examples of boron isotope applications in groundwater investigations are reported.

The wide boron isotopic variations occurring in natural waters mainly are derived from the 20‰ fractionation between dissolved boric acid and borate anions, associated with the preferential removal from the system of 11 B depleted borate ions by adsorption and/or minerals formation. Typical adsorbants of boron dissolved in groundwater are clay minerals of the aquifer matrix. Boron (and strontium) isotopes were used in investigating two alluvial aquifers in Tuscany, where boron concentration is often above 1 mg L − 1 and may attain 8 mg L − 1 . The isotopic results indicate that, in the first case (Cecina River basin), the boron contamination is anthropogenic and derives from past discharge into streams of boron-rich industrial wastes. In the second case (Cornia Plain), the dissolved boron is released by boron-rich clayey sediments of the aquifer matrix and has, therefore, a natural origin.

The origin of carbon-bearing compounds (CO 2 , CH 4 , C 2 –C 4 saturated hydrocarbons) and helium in the geothermal fluid of Larderello is investigated by means of the variations in concentration and isotopic composition. The CO 2 ( δ 13 C from −1.4 to −7.1‰ versus V-PDB) is mainly of crustal origin. The carbon isotopes of methane ( δ 13 C from −20.9 to −31.7‰) and other hydrocarbons indicate a complex thermogenic origin. The temperatures obtained with the CH 4 –CO 2 isotope geothermometer are in rough agreement with those observed in deeper geothermal wells. The CH 4 /C 2 H 6 ratios show a tendency towards partial equilibrium with increasing temperature. He isotopes ( R / R A from 0.5 to 3) indicate that although the major part of helium derives from crustal sources, a significant fraction of mantle helium is also present. Helium contamination by air, deducted from He/Ne ratios, is generally negligible.

The kinetics of isotopic exchange between dissolved inorganic carbon (DIC) of groundwater and calcite of the matrix of karst aquifers of Cyrenaica, Libya, can be deduced from 13 C and 14 C data. The aquifers are mostly confined, and the majority of the wells do not show any occurrence of modern recharge: in 1976–1980, in fact, the tritium content was below 1 tritium unit (TU) in most sites. Assuming that the isotopic exchange takes place through a first order reaction such as 14 C radioactive decay, it can be shown that a linear correlation occurs between ln A and ln( δ M − δ − e P ), where A is the 14 C activity, δ M and δ are the 13 C contents of matrix calcite and DIC, respectively, and e P is the 13 C enrichment in CaCO 3 precipitation. The slope of the correlation provides the half-life of the isotopic exchange process. For Cyrenaica karst groundwater, a half-life of about 11,000 years is obtained, i.e. about double that of 14 C radioactive decay. The isotopic exchange kinetics also depends on the ratio between groundwater volume and the calcite surface exposed to the exchange process. Thus, other aquifers will show different exchange half-life values. The Cretaceous chalk aquifers of the Paris Basin, France and Lagerdorf, Germany give a half-life of about 4000 years, much shorter than that of Cyrenaica, which may be due to the high porosity, i.e. to the large surface available for the isotope exchange process. The Berkshire Chalk aquifer, UK, gives a half-life of about 10,000 years. Much higher half-lives, above 20,000 years, are obtained for two sandy aquifers in Flevoland, The Netherlands, and Texas, USA, which could be explained by the low CaCO 3 content of the aquifer matrix. The highest half-life value, about 40,000 years, is obtained in an artesian limestone aquifer in Florida, USA.

The Istituto di Geoscienze e Georisorse (IGG), on behalf and with the support of the International Atomic Energy Agency (IAEA), prepared eight geological materials (three natural waters and five rocks and minerals), intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials were distributed to twenty seven laboratories - virtually all those performing geochemical boron isotope analyses in the world -which agreed to participate in the intercomparison exercise. Only fifteen laboratories, however, ultimately submitted the isotopic and/or concentration results they obtained on the intercomparison materials. The results demonstrate that interlaboratory reproducibility is not well reflected by the precision values reported by the individual laboratories and this observation holds true for both boron concentration and isotopic composition. The reasons for the discrepancies include fractionations due to the chemical matrix of materials, relative shift of the zero position on the δ11B scale and a lack of well characterized materials for calibrating absolute boron content measurements. The intercomparison materials are now available at the IAEA (solid materials) and IGG (waters) for future distribution. L'Istituto di Geoscienze e Georisorse (IGG), pour le compte et avec le soutien de l'Agence Internationale de l'Energie Atomique (AIEA), a prepare huit materiaux geologiques (trois eaux naturelles et cinq roches et mineraux) destines a la conduite d'une comparaison en aveugle des mesures de composition isotopique et de concentration du bore entre differents laboratoires. Vingt-sept laboratoires -pratiquement tous ceux qui travaillent sur les isotopes du bore en geochimie - ont accepte de participer a cette intercomparaison, mais quinze seulement ont finalement envoye leurs donnees de composition isotopique et/ou de concentration du bore. Les resultats demontrent que la precision des valeurs indiquee par les laboratoires reflete mal la reproductibilite entre laboratoires des mesures de composition isotopique comme de concentration du bore. Les raisons de ces discordances peuvent comprendre l'existence de fractionnements isotopiques dus aux matrices chimiques des materiaux, un deplacement relatif du zero de l'echelle de δ11B, ainsi que le manque de materiaux bien caracterises pour calibrer les mesures de concentration du bore. Les materiaux utilises pour l'intercomparaison des mesures sont maintenant a disposition a l'AIEA (materiaux solides) et l'IGG (eaux) pour etre distribues.

The vacuum distillation method of extracting soil water for stable isotope analysis was tested for three different types of soil characterized by high water content: (1) pure sand, (2) cambisol with high organic matter content, developed on calcareous sandstone under temperate climatic conditions (Austria), and (3) tropical latosol poor in organic matter, developed on sandy clay sediment (Brazil). The method yields accurate and reproducible results for sand, provided that more than 98% of the original soil water is extracted. The time required for complete extraction is a function of sample size and the applied extraction temperature. Column experiments with the clayey soils revealed existence of a weakly bound, easily exchangeable pool of water which is isotopically different from the mobile water. The experiments showed that the extracted soil water is depleted in both deuterium and oxygen-18 by 5–10% and 0.3–0.5%, respectively, when compared with the percolate (mobile water). This depletion depends strongly on the soil type. The reproducibility for replicate extractions of soil water from clayey soils is around ±3% and 0.3% for δD and δ 18 O, respectively.

The 11B/10B ratio exhibits wide variations in nature; thus, boron isotopes have found numerous applications in geochemistry, hydrology, and environmental studies. The main analytical techniques used are as follows: positive thermal ionisation mass spectrometry is the most precise (about 0.2‰ of the boron isotope ratio), but requires complex and laborious sample preparation; negative thermal ionisation mass spectrometry is less precise (about 0.5‰), but rapid and suitable for water samples, whereas total evaporation-NTIMS allows for identification of the precise boron isotope composition of marine carbonates. It is expected that multi-collection system inductively coupled plasma mass spectrometry (MC-ICPMS) will eventually combine high precision with simple analytical procedures. Secondary ion mass spectrometry and laser ablation (LA)-MC-ICPMS allow in situ determinations on solid samples, but require the availability of calibration materials which are chemically and mineralogically similar to samples. The...

We briefly present here the environmental isotope intercalibration programs of the International Atomic Energy Agency (IAEA). In fact, the IAEA has implemented two parallel programs during the last 20 years: for stable isotopes of light elements and for a radioactive isotope of hydrogen, tritium. This IAEA activity resulted in the preparation of a number of reference and intercomparison materials of various types, now stored in the Agency and available upon request.

In 1999 the Istituto di Geoscienze e Georisorse (IGG), with the support of the International Atomic Energy Agency (IAEA), undertook the collection, preparation and distribution of eight geological materials intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials came from Italian sources and consist of three natural waters (Mediterranean seawater and two groundwaters) and five rocks and minerals (tourmaline, basalt, obsidian, limestone and clay). The solid materials were crushed, milled and mixed, in preparation for distribution. Extensive assays performed at the IGG on these materials demonstrated that their boron isotopic and chemical compositions are homogeneous. Additional homogeneity tests were carried out on solid material fragments at the GeoForschungsZentrum Potsdam, with the specific objective of investigating the suitability of some of them for the calibration in situ of micro-analytical techniques. Two materials, B4 (tourmaline) and B6 (obsidian), proved to be isotopically homogeneous and may become excellent references for in situ microanalyses of boron isotopes. The materials described here were used as the basis of a major laboratory intercomparison study and are now available for further distribution from either the IAEA (solid materials) or the IGG (waters). L'Istituto di Geoscienze e Georisorse (IGG), avec le soutien de l'Agence Internationale de l'Energie Atomique (AIEA), a entrepris en 1999 la recolte, la preparation et la distribution de huit materiaux geologiques dans le but de conduire une comparaison en aveugle des mesures de composition isotopique et de concentration du bore entre differents laboratoires. Les materiaux, qui derivent tous de sites italiens, comprennent trois eaux naturelles (une eau de la Mer Mediterranee et deux eaux souterraines) et cinq roches et mineraux (tourmaline, basalte, obsidienne, calcaire et argile). Pour la distribution, les materiaux solides ont ete reduits en fragments, broyes et melanges et leur homogeneite de composition isotopique et chimique du bore a ete verifiee par des essais exhaustifs. D'autres essais d'homogeneite ont ete effectues au GeoForschungsZentrum Potsdam sur des fragments des materiaux solides avec le but particulier d'etudier la possibilite d'utilisation de ces materiaux pour la calibration in situ des techniques microanalytiques. Deux materiaux, le B4 (tourmaline) et le B6 (obsidienne), se sont reveles isotopiquement homogenes et donc peuvent devenir d'excellents materiaux de reference pour les microanalyses isotopiques in situ du bore. Les materiaux, qui sont decrits dans cette note, ont ete utilises pour une etude d'intercomparaison des mesures isotopiques et chimiques du bore entre differents laboratoire. Ils sont maintenant a disposition a l'AIEA (materiaux solides) et a l'IGG (eaux) pour leur distribution ulterieure.

The isotopic compositions of the waters discharged from Parbati Valley geothermal areas indicate a higher altitude meteoric origin, with discharge temperatures reflecting variations in the depth of penetration of the waters to levels heated by the existence of a ‘normal’ geothermal gradient. On the basis of mixing models involving silica, tritium, discharge temperatures and chloride contents, deep equilibration temperatures of 120–140°C were obtained for Manikaran, possibly reaching 160°C at even greater depth. Geothermometers based on sulfate-water 18O exchange and gas reactions point to similar temperatures. Exceptionally high helium contents of the discharges correspond to apparent crustal residence times of the waters in the order of 10–100 Ma; relative nitrogen-argon contents support a largely meteoric origin of the waters with a possible fossil brine, but no detectable magmatic component.

Some of the trends and characteristics of the isotopic composition oh precipitation in tropical stations are discussed. Stations in small Pacific islands show a variation with latitude, with lower 8-values between 15°N and 1S°S and higher values at higher. Inland stations are depleted in heavy isotopes with respect to coastal stations but sometimes this continental effect is rather complex, as f,or instance in África. Mean monthly 8-values show a remarkable correlation with the amount of precipitation, but the slope variations do not show a clear dependence on the mean long term 8-value,as should be expected theoretically. In Southern American stations the seasonal variations of the meanmonthly 5-values are correlated and they are greater in inland stations due to con-tinentaly. The possible effects of recycling of water vapour by evapotranspiration are also discussed. São discutidas algumas tendências e características da composição isotópica das precipitações nas estações tropicais. Em ilhas pequenas do Pacífico, as estações apresentam variação de acordo com a latitude, com valores-8 menores entre 15°N e 15°S e variações maiores a latitudes mais elevadas. Os isótopos pesados, nas estações interioranas tias, apresentam-se empobrecidos com relação às estações costeiras, porém algumas vezes esse efeito continental é bastante complexo, como por exemplo na África. A média mensal de valores -8 indica uma sensível correlação com a quantidade de precipitação, porém as variações em declive não indicam uma dependência clara da média a longo prazo do valor-8 como era de se esperar teoricamente. Nas estações da América do Sul, de acordo com as estações do ano, há uma correlação entre as variações das médias mensais dos valores-8 os quais são maiores nas estações mais para o interior devido a continentalidade. São também discutidos os possíveis efeitos da reciclagem do vapor dágua proveniente da evapotranspiração.

About a hundred gas samples were collected and studied from different wells in a multilayer gas field of Southern Italy. The reservoir is constituted by alternating sand an clay layers of Pliocene age. The total volume of gas accumulated in the sand traps is on the order of several billions cubic meters.

SINCE the fundamental paper by Craig1 on the geochemistry of the stable carbon isotopes, much work has been done on the determination of carbon isotope distribution in different materials.