RESUMO
In recent years, it has become evident that human activities have significantly disrupted the nitrogen cycle surpassing acceptable environmental thresholds. In this study, chemical and isotopic tracers were combined with a mathematical mass balance model (EMMA), PHREEQC inverse mixing model, and statistical analyses to evaluate groundwater quality, across an area experiencing substantial human activities, with a specific focus on tracing the origin of nitrate (NO3-) with potential water mixing processes. This multi-technique approach was applied to an unconfined aquifer underlying an agricultural area setting in an inter-mountain depression (i.e., the "Pampa de Pocho Plain" in Argentina). Here, the primary identified geochemical processes occurring in the investigated groundwater system include the dissolution of carbonate salts, cation exchange, and hydrolysis of alumino-silicates along with incorporating ions from precipitation. It was observed that the chemistry of groundwater, predominantly of sodium bicarbonate with sulfate water types, is controlled by the area's geology, recharge from precipitation, and stream water infiltration originating from the surrounding hills. Chemical results reveal that 60% of groundwater samples have NO3- concentrations exceeding the regional natural background level, confirming the impact of human activities on groundwater quality. The dual plot of δ15NNO3 versus δ18ONO3 values indicates that groundwater is affected by NO3- sources overlapping manure/sewage with organic-rich soil. The mathematical EMMA model and PHREEQC inverse modeling, suggest organic-rich soil as an important source of nitrogen in the aquifer. Here, 64 % of samples exhibit a main mixture of organic-rich soil with manure, whereas 36 % of samples are affected mainly by a mixture of manure and fertilizer. This study demonstrates the utility of combining isotope tracers with mathematical modeling and statistical analyses for a better understanding of groundwater quality deterioration in situations where isotopic signatures of contamination sources overlap.
Assuntos
Monitoramento Ambiental , Água Subterrânea , Nitratos , Poluentes Químicos da Água , Argentina , Nitratos/análise , Água Subterrânea/química , Água Subterrânea/análise , Poluentes Químicos da Água/análise , Monitoramento Ambiental/métodos , Isótopos de Nitrogênio/análise , Modelos Químicos , Isótopos de Oxigênio/análise , Modelos TeóricosRESUMO
Due to adverse impact of the global warming on hydrological resources, we intended to document the hydrogeochemical evolutions of surface and groundwater at tropical central-south Mexico in terms of seasonality of rock-water interaction, precipitation/evaporation variation and moisture source by evaluating the major ion chemistry in Piper and Gibbs plots, Durov diagram and through estimation of the chloro-alkaline indices as well as assessing the stable isotope compositions (δ18O and δ2H) in samples from different seasons of a year. Surface water of the Lake Coatetelco shifted from mostly Ca-Mg-HCO3 facies in wet summer-autumn to Na-HCO3-Cl facies in the dry spring due to elevated Na, Cl and HCO3. Greater evaporation in spring led to a maximum δ18O enrichment of ca.7 compared to the other seasons, and much depleted deuterium excess (-40.92 to -39.20). Interaction of the lake water with subsurface carbonate lithologies, and comparable isotopic compositions reflected the enhanced interaction between the surface water body and aquifers in the wet autumn. Effect of seasonality, however, was unclear on the groundwater facies, and its heterogenous composition (Ca-Mg-HCO3, Na-HCO3-Cl and Na-HCO3) reflected the interactions with different lithologies. Fractionations in isotope compositions of the groundwater were caused from recharge at different elevations, seasonality of moisture sources and moisture recycling. The water-mineral saturation index was an efficient proxy of seasonality as the lake water and groundwater (avg SIcalcite > 0.5) of the dry autumn were saturated with calcite. This vital information about carbonate precipitation, pCO2 and chemical facies would be useful for the better interpretation of paleoclimate archives in this region.
Assuntos
Deutério , Água Subterrânea , Isótopos de Oxigênio , Estações do Ano , México , Água Subterrânea/química , Água Subterrânea/análise , Isótopos de Oxigênio/análise , Deutério/análise , Monitoramento Ambiental/métodos , Lagos/químicaRESUMO
Soils in hyper-arid climates, such as the Chilean Atacama Desert, show indications of past and present forms of life despite extreme water limitations. We hypothesize that fog plays a key role in sustaining life. In particular, we assume that fog water is incorporated into soil nutrient cycles, with the inland limit of fog penetration corresponding to the threshold for biological cycling of soil phosphorus (P). We collected topsoil samples (0-10 cm) from each of 54 subsites, including sites in direct adjacency (<10 cm) and in 1 m distance to plants, along an aridity gradient across the Coastal Cordillera. Satellite-based fog detection revealed that Pacific fog penetrates up to 10 km inland, while inland sites at 10-23 km from the coast rely solely on sporadic rainfall for water supply. To assess biological P cycling we performed sequential P fractionation and determined oxygen isotope of HCl-extractable inorganic P δ 18 O HCl - P i $$ \mathrm{P}\ \left({\updelta}^{18}{\mathrm{O}}_{\mathrm{HCl}-{\mathrm{P}}_{\mathrm{i}}}\right) $$ . Total P (Pt ) concentration exponentially increased from 336 mg kg-1 to a maximum of 1021 mg kg-1 in inland areas ≥10 km. With increasing distance from the coast, soil δ 18 O HCl - P i $$ {\updelta}^{18}{\mathrm{O}}_{\mathrm{HCl}-{\mathrm{P}}_{\mathrm{i}}} $$ values declined exponentially from 16.6 to a constant 9.9 for locations ≥10 km inland. Biological cycling of HCl-Pi near the coast reached a maximum of 76%-100%, which could only be explained by the fact that fog water predominately drives biological P cycling. In inland regions, with minimal rainfall (<5 mm) as single water source, only 24 ± 14% of HCl-Pi was biologically cycled. We conclude that biological P cycling in the hyper-arid Atacama Desert is not exclusively but mainly mediated by fog, which thus controls apatite dissolution rates and related occurrence and spread of microbial life in this extreme environment.
Assuntos
Fósforo , Solo , Isótopos de Oxigênio , Água , Chile , Clima DesérticoRESUMO
A 22.48 m long ice core (BR-IC-4) was collected in the West Antarctic Ice Sheet (at 83°58'59.4" S, 80°07'01.4" W, 1,295 m above the sea level) during the Austral summer of 2004-2005, as a contribution to the International Trans-Antarctic Expedition program. The isotopic composition (δD and δ18O) of 599 samples, corresponding to the upper 12.98 m of the ice core, was determined by gas source mass spectrometry and cavity ring-down spectroscopy. Relative dating was based on the isotopic ratios and major ions (MS-, Na+, nssSO4 2-) and trace elements (Na, S, Sr) concentrations. The record covers approximately 13 years - from 1990 to 2003. The mean accumulation rate of 0.48 ± 0.09 m water equivalent per year (m eq H2O a1) is relatively high for the geographical area and possibly results from snowdrifting from near areas, as attested by ice glaze surfaces in other sites in the region. The stable isotope δD content varies between -367.90 and 256.30 (mean -314.42 ± 19.01); and δ18O ranges from -44.96 to 35.08 (mean -39.95 ± 2.05). Deuterium excess values (mean 3.70 ± 1.54) indicate episodic intense oceanic evaporation and high relative humidity in the moisture sources.
Assuntos
Água , Regiões Antárticas , Isótopos de Oxigênio , Espectrometria de Massas , Estações do Ano , Água/análiseRESUMO
Vanillin is the main component of vanilla flavor and is naturally produced from an orchid. However, due to the high cost and time-intensive nature of cultivating natural vanilla pods, most of the vanillin is mainly artificially manufactured. Existing methodologies, such as isotope ratio mass spectrometry (IRMS) and site-specific natural isotopic fractionation by nuclear magnetic resonance (SNIF-NMR), are employed to differentiate natural vanillin from other sources based on carbon and hydrogen isotope measurements. Nevertheless, these methods have limitations, as the carbon isotopic ratio can be counterfeited by adding commercially available enriched vanillin. For this research, we purified 1 mg of vanillin from pods from various geographical and botanical sources. We developed a novel method for analyzing 13C/12C and 18O/16O isotopic ratios of vanillin using direct injection analysis coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). This innovative approach enables the examination of bulk vanillin carbon and oxygen isotopic ratios, as well as specific molecular fragments. By analyzing a characteristic vanillin fragment that provides site-specific 18O/16O isotopic ratio data, we achieved superior clustering and discrimination of samples based on their botanical source and geographical origin. Our proposed method holds significant potential for vanillin authentication and can be performed using a mere 20 µg of pure vanillin in just 10 min of analysis time. Subsequent research should focus on acquiring additional vanillin samples from diverse botanical, geographical, and biosynthetic origins while exploring various isotopic ratios to further enhance the reproducibility and reliability of this methodology.
Assuntos
Carbono , Isótopos de Oxigênio , Reprodutibilidade dos Testes , Isótopos de Carbono/químicaRESUMO
As a consequence of the recent history of Argentina related to crimes against humanity, the country has positioned itself as a leader on Forensic Anthropology in human rights contexts. To some extent it can even be argued that Forensic Genetics for human identification had its origins in human rights work in the early 1980s in Argentina. However, there are still hundreds of unidentified human remains recovered from the dictatorial regimes' crimes. Additionally, every year there are dozens of unidentified deceased buried in public cemeteries. Thus, there is an urgent need to adopt new techniques that could increase the biological profile of a person, and therefore increase the chances of positive identifications. One of such initiatives is the development of isotopic databases and models that can provide information on the population and region of origin of unidentified victims. We present the development of an isotopic database of modern human tissues named BITACORA (from its name in Spanish: Base de Información Isotópica de Tejidos Actuales Como Referencia Argentina). BITACORA holds isotopic data (δ18O, δ2H, δ13C, δ15N and δ34S values) from teeth (enamel and dentine) and keratin tissues (scalp hair, beard and fingernails) obtained from volunteers of known origin, as well as individual information of the donors (age, gender, biometrics, dietary preferences, and relocation history). BITACORA is associated with a tap water isotope database. Currently, we have 345 keratin, 273 teeth and 287 tap water samples gathered from across the country. We present preliminary analyses on the geographic distribution of these isotopic markers, and provide an overall discussion of the current status and future development of the databases.
Assuntos
Antropologia Forense , Queratinas , Humanos , Isótopos de Oxigênio/análise , Argentina , Água/análiseRESUMO
Forensic anthropologists have used oxygen isotopic analyses (δ18O) in recent decades because of its ability to help estimate probable regions of origin of unidentified individuals based on isotopic composition of bodily tissues. Prior research has found that drinking water is geographically patterned and that tap water is often representative of drinking water in assessing these links between human tissues and geography. Researchers have begun applying the method in a variety of global contexts. This research critically assesses the assumption that tap water is isotopically representative of drinking water in Oaxaca, Mexico. Drinking water samples from Oaxaca were analyzed and compared with predicted δ18O values from a previously constructed tap water isoscape of Mexico. Hair samples from Oaxaca were also analyzed to compare against various water sources. Tap water δ18O values do not reliably reflect drinking water δ18O in sampled regions of Oaxaca, Mexico. Further, the models relating hair keratin to drinking water, built on this assumption, fail to hold predictive power. With an incomplete understanding of tap water's ability to represent drinking water isotopically, researchers need to study the role of other key factors in δ18O values. If the individual's being identified with δ18O are from non-Western communities, forensic practitioners run the risk of incorrectly predicting region of origin because of the method's assumptions. Recognizing the varying sociocultural realities of the communities forensic practitioners seek to aid is paramount as we grow and develop our methods moving forward.
Assuntos
Água Potável , Humanos , Isótopos de Oxigênio/análise , Água Potável/análise , México , Medicina Legal , GeografiaRESUMO
PET cyclotrons are widely used for producing medical diagnostic radionuclides. The main radionuclide produced in these facilities is the 18F, which is obtained from the [18O (p,n)18F] reaction when 18O-enriched water is bombarded with the proton beams. This work aimed to estimate the radiation source term from the bombardment of an 18O-enriched water target with protons of 16.5 MeV to determine the radiation neutron field around the accelerator.
Assuntos
Ciclotrons , Prótons , Isótopos de Oxigênio , Método de Monte Carlo , ÁguaRESUMO
Stable isotope ratios of nitrogen and oxygen (15N/14N and 18O/16O) of nitrate (NO3-) are excellent tracers for developing systematic understanding of sources, conversions, and deposition of reactive atmospheric nitrogen (Nr) in the environment. Despite recent analytical advances, standardized sampling of NO3-) isotopes in precipitation is still lacking. To advance atmospheric studies on Nr species, we propose best-practice guidelines for accurate and precise sampling and analysis of NO3- isotopes in precipitation based on the experience obtained from an international research project coordinated by the International Atomic Energy Agency (IAEA). The precipitation sampling and preservation strategies yielded a good agreement between the NO3- concentrations measured at the laboratories of 16 countries and at the IAEA. Compared to conventional methods (e.g., bacterial denitrification), we confirmed the accurate performance of the lower cost Ti(III) reduction method for isotope analyses (15N and 18O) of NO3- in precipitation samples. These isotopic data depict different origins and oxidation pathways of inorganic nitrogen. This work emphasized the capability of NO3- isotopes to assess the origin and atmospheric oxidation of Nr and outlined a pathway to improve laboratory capability and expertise at a global scale. The incorporation of other isotopes like 17O in Nr is recommended in future studies.
Assuntos
Nitratos , Poluentes Químicos da Água , Nitratos/análise , Isótopos de Nitrogênio/análise , Monitoramento Ambiental/métodos , Poluentes Químicos da Água/análise , Nitrogênio/análise , China , Isótopos de Oxigênio/análiseRESUMO
OBJECTIVE: To evaluate, in-vitro, the change in crown inclination that occurs during orthodontic leveling and alignment using different archwire-bracket-ligation combinations. MATERIALS AND METHODS: Four archwire types were tested: (1) 0.012-in stainless steel and (2) 0.0155-in stainless steel multi-stranded, (3) 0.012-in nitinol Orthonol® and (4) 0.012-in nitinol Thermalloy®. Combinations with five types of 0.022-in slot orthodontic brackets were tested: SmartClipTM and Time3® self-ligating brackets, Mini-Taurus® and Victory SeriesTM conventional brackets, and Synergy® conventional-low friction bracket. Conventional brackets were ligated with both stainless steel and elastomeric ligatures. The simulated malocclusion comprised 2.0mm gingival and 2.0mm labial displacements of a maxillary right central incisor. Rotation around the Y-axis (representing labio-palatal inclination) was measured for the different archwire-bracket-ligation combinations. RESULTS: The largest rotation was measured whith Orthonol® and Thermalloy® wires when combined with SmartClipTM brackets (8.07±0.24º and 8.06±0.26º, respectively) and with Synergy® brackets ligated with stainless steel ligatures (8.03±0.49º and 8.0±0.37º, respectively). The lower rotation was recorded when Thermalloy®, multi-stranded, and Orthonol® wires were ligated with elastomeric rings to Mini-Taurus® brackets (1.53±0.18º, 1.65± 0.23º and 1.70±0.28º, respectively) and to Victory SeriesTM brackets (1.68± 0.78º, 2.92± 1.40º and 1.74±0.46º, respectively). CONCLUSIONS: All archwire-bracket-ligation combinations produced lingual crown inclination; however, lower changes were observed when the conventional brackets were ligated with elastomeric rings. The multi-stranded archwire produced less rotation with nearly every bracket-ligation combination, compared to the other archwires. The effect of the archwire-bracket-ligation combination on tooth inclination during leveling and alignment should be considered during planning treatment mechanics.