This study assessed the radiological hazard associated with sediment and silt samples collected from the Nile River. The results consistently demonstrated low levels of natural radioactivity. Calculated dose parameters were found to be well within international safety limits. The average outdoor annual effective dose equivalent (AEDEout) was 50 µSv/y for sediments and 60 µSv/y for silt. Similarly, the average indoor AEDE (AEDEin) values were 280 and 350 µSv/y, respectively, remaining significantly below the worldwide limit of 450 µSv/y. Long-term risk assessment further supported these findings, with the annual gonadal dose equivalent (AGDE) averaging 0.28 mSv/y for sediments and 0.36 mSv/y for silt. Finally, the calculated excess lifetime cancer risk (ELCR) remained low, at 1.15 × 10-3 for sediments and 1.44 × 10-3 for silt. The average radon concentrations in soil were 7.17 Bq/m3 for sediment and 5.65 Bq/m3 for silt. In conclusion, all measured activity concentrations and derived radiological risk factors confirm that the Nile River sediment and silt samples pose no significant radiological hazard to the public.
On oceanic islands, invasive rats represent a significant threat to native species, especially seabirds. However, we do not yet fully understand the ecological impacts of rats or how their dietary niches are affected when more than one rat species is present. Our aim was to examine kiore (Rattus exulans) and ship rat (R. rattus) isotopic niche overlap on Chatham Island, and to determine the threat they might pose to at-risk or threatened native bird species, including endemic species such as the parea (Hemiphaga chathamensis), and an endangered ground-nesting seabird, the tāiko (Pterodroma magenta), in the island's only large remaining tract of forest. Liver stable isotope analysis (δ13C and δ15N) for kiore and ship rats showed some segregation between species in isotopic niche space. Generally, there was low overlap of hypervolumes defined by diet proportions between species, but some seasonal variation in the degree of overlap, and differences between kiore and ship rat niche size that likely facilitate coexistence. Mixing models indicated that birds, but probably not tāiko, were dominant food sources for both species. Proportions of parea and passerines varied across seasons, while invertebrates and plants were also represented. The occurrence of birds in the diet of both rats may be due to either direct predation or scavenging. The results suggest that, as expected, rat control is a critical element of native species management in this remaining forest, most likely acting to protect small forest birds and endemic species like parea, although it remains unclear whether rats are directly impacting endangered populations of ground-nesting birds.
Commercially valuable fish face intense pressure from capture fisheries with demand for fish protein, whether farmed or wild-caught, growing globally. Consequently, the provenance of fish is increasingly vital to regulatory bodies, market chain actors, and consumers. The limitations of current fish provenance methods can be overcome using complementary techniques. Here, we applied a multi-tracer approach combining stable isotope ratios (δ¹³C and δ¹⁵N) and trace element mass fraction to assess the provenance of the Amazonian pirarucu (Arapaima gigas) in Brazil. Dorsal muscle samples from 79 individuals of known origin and management were analysed, including wild-caught fish from the Amazon and Tocantins-Araguaia river basins and farmed fish from intensive aquaculture systems. To evaluate the method under real market conditions, additional 52 samples obtained from commercial establishments in the Brazilian Federal District were included. Stable isotope analysis effectively differentiated management regimes and river basins, with δ¹³C providing the strongest discrimination. Trace element analysis revealed significant differences in cesium (Cs) and strontium (Sr) mass fractions between wild fish from the two basins, reflecting underlying geological and hydrological contrasts. Linear discrimination analysis (LDA) integrating isotopic and elemental data demonstrated a high discriminatory capacity of both isotopic and elemental tracers for distinguishing pirarucu samples according to origin and management category. Although the reference groups showed complete discrimination under cross-validation, commercial samples displayed broader dispersion within the discriminant space, suggesting heterogeneous sourcing patterns and potentially mixed supply chains. These findings demonstrate that the combined use of isotopic and elemental tracers offers a robust framework for assessing the provenance of freshwater fish and represents a valuable tool for fisheries monitoring and the enforcement of conservation measures.
Stable isotopes of hydrogen (δ2H) have long been used to trace the movement and geographic origins of wildlife. δ2H analysis of individual amino acids (AA) offer a multivariate alternative to bulk tissue analysis, but the geographic resolving power of this approach remains underexplored. Here, we analyzed AA δ2H, along with bulk tissue δ2H, δ13C, and δ15N values of 32 feathers collected from Canada geese (Branta canadensis) with known molting locations along a latitudinal gradient in the Midwestern United States (34-48 °N). We evaluated isotopic variation among three latitudinally defined geographic groups across this gradient. The δ2H values of essential AA showed strong latitudinal separation, with isoleucine, leucine, and valine differing among all pairwise comparisons and exhibiting between-group differences exceeding those observed in bulk feather δ2H. In contrast, δ2H values of non-essential AA were far more variable within groups and, apart from proline and glutamic acid, did not exhibit significant differences among geographic localities. A bootstrapped flexible discriminant analysis (FDA) incorporating δ2H values of five essential AA yielded a mean classification accuracy of 82 %, with misclassification concentrated between adjacent North and Central groups. Including bulk tissue δ13C values marginally improved model accuracy (mean 83 %), likely reflecting geographic variation in native or agricultural C4 plant abundance. An FDA model based only on non-essential AA δ2H values performed poorly (mean 59 % accuracy), which contrasts with recent studies on humans in which non-essential AA δ2H values were better predictors of region of origin. We suggest this discrepancy reflects differences in food sourcing; barring carry-over effects, wildlife primarily incorporate locally derived essential AA whereas human (supermarket) diets often integrate protein sources across continental spatial scales. Our results indicate that essential AA exhibit clear latitudinal structure in δ²H values and hence these analyses offer strong potential for geographic assignment of migratory birds.
Insect migration is a massive and broad phenomenon, yet there are major knowledge gaps regarding the migration properties of this group. Many dragonfly species are considered migrants but only a few have been thoroughly studied, none of which migrate from Europe to other areas. The red-veined darter Sympetrum fonscolombii (Insecta: Odonata) is a common and widespread species which has recently expanded its range northwards in Europe and Asia. Recently, stable hydrogen isotope analysis showed that individuals from the Levant migrate north during spring, but no concrete evidence of a return southward autumn migration exists. To clarify the migratory status of S. fonscolombii in Israel, we collected observations from various sources (experts, citizen science and social media platforms), spanning all seasons and multiple years, and provide a first phenological description for the species in the area. Natal origins of individuals appearing on the Israeli coastline during autumn were inferred using stable hydrogen isotope analysis from wing samples in a spatially explicit probabilistic assignment. We found that the phenological pattern, with a peak in abundance between August and November, fits a migratory influx. The wing stable isotopes analysis resulted in a broad potential natal origin zone, covering a substantial part of the species' Eurasian range. These results provide the first direct evidence for a southward migration out of Europe and West Asia of S. fonscolombii or any other dragonfly species, with some individuals likely originating from the extreme northern parts of the species' known range.
Stable hydrogen isotope analysis (δ²H) of organic compounds requires accurate correction for exchangeable hydrogen, yet this remains a major analytical challenge, particularly for amino acids. In this study, we evaluated the determination of exchangeable hydrogen fractions fex in a suite of amino acids using a multiple equilibration approach, comparing room-temperature liquid-water-phase equilibration with 90 °C online vapor equilibration using the UniPrep2 system. Theoretical fex values for the amino acids were derived from their molecular structure and compared with the experimentally determined values. Liquid equilibration yielded fex values that were generally consistent with theoretical expectations for most amino acids, indicating effective access to the exchangeable organic hydrogen pools. In contrast, online vapor equilibration frequently resulted in near-zero fex for several amino acids, particularly the hydrophobic and crystalline compounds, consistent with limited accessibility of exchangeable sites under heated, low-pressure equilibration conditions. Only a subset of amino acids (e.g. glycine, threonine) showed comparable results between the methods, while others exhibited clear method-dependent discrepancies or analytical artefacts (e.g. persistent water background for proline). A soluble protein (BSA) exhibited low but consistent exchangeability (∼ 4 %) with both approaches, highlighting the role of structural protection and accessibility in governing hydrogen exchange. Our findings demonstrate that experimentally derived fex values are likely to be significantly method- and compound-dependent and should be interpreted as operational parameters rather than intrinsic molecular constants. The observed variability has important implications for interlaboratory comparability and underscores the need for standardised methodologies and improved reference materials for compound-specific δ²H analysis of amino acids.
Understanding recharge processes and surface-groundwater interactions in rapidly urbanizing coastal regions is essential for sustaining freshwater availability under growing climate and anthropogenic pressures. The objective of this study was to evaluate surface water-groundwater interactions and delineate groundwater potential zones (GWPZ) in coastal regions of Chengalpattu district, Tamil Nadu, using an integrated approach of water stable isotope analysis (δ¹⁸O, δ²H), analytical hierarchy process (AHP) and electrical resistivity survey (ERS). For the isotopic analysis, we collected precipitation, surface water, and groundwater samples for the pre-monsoon, monsoon, and post-monsoon seasons. The ERS was conducted to identify the aquifer geometry, fractures, and lineament for identifying the GWPZ. Seasonal variations in isotopic compositions were observed, with a depletion in isotopic compositions during the monsoon season in wells and lake waters, indicating a surface and groundwater interaction, and an isotopic enrichment during the pre-monsoon and post-monsoon seasons due to evaporation. Based on the δ18O-δ²H plot, two sources of groundwater recharge were discerned, (i) direct recharge from precipitation; (ii) recharge from the lakes. Using a conservative isotope (δ18O) mixing model, the contribution of lake to the groundwater was estimated. The average contribution from lake water to groundwater was found to be nearly 25 %. ERS using vertical electrical sounding identified true resistivity ranging from 13.10 to 59.49 Ω·m with an average resistivity value of 20.68 Ω·m. The integrated isotopic-geophysical approach provides an effective framework for understanding recharge dynamics and managing groundwater in coastal semi-urban environments.
Measurement of radon, thoron, and their progeny was conducted in 49 dwellings in Bangui city, Central African Republic, followed by the annual inhalation dose assessment. The measurements were performed by passive-type radon-thoron discriminative detectors and thoron progeny monitors exposed for a 3-month period. The geometric means of indoor radon, thoron, radon progeny and thoron progeny concentrations (geometric standard deviations, GSDs) were 123 Bq m-3 (1.2), 76 Bq m-3 (3.0), 49 Bq m-3 (1.2), 5.2 Bq m-3 (2.5), respectively. The average value of the equilibrium factor of thoron, the total annual effective dose, excess lifetime cancer risk (ELCR) × 10-3, and lung cancer cases (LCC) × 10-9 measured in 49 dwellings were 0.10 ± 0.07, 4.12 ± 0.93 mSv y-1, 12.28 ± 2.78 and 74.2 ± 16.8, respectively. The contribution of thoron and its progeny to the total inhalation dose varies from 5 to 64 % with an average value of 34 %. Total annual effective doses for indoor radon, thoron and their progeny be much lower than the International Commission of Radiological Protection (ICRP) recommended range of 3-10 mSv y-1 and the World Health Organization's (WHO) limit of 10 mSv y-1. The findings suggest that indoor radon, thoron, and their progeny concentrations in Bangui dwellings are within safe limits, supporting the need for continued monitoring and public awareness programmes to maintain low exposure levels and mitigate potential long-term health risks, particularly lung cancer, in line with global radiation protection guidelines.
An understanding of carry-over effects in oviparous wildlife - and thus effective conservation - requires knowledge of how nutrients are allocated during egg production. Stable isotope analysis is commonly used to estimate the contribution of nutrients from body reserves (endogenous) versus those from diet (exogenous) to eggs. However, reliable inference about oviparous nutrient allocation strategies is dependent on isotopic discrimination factors, which are highly variable, species specific, and often based on data for a limited number of species. To determine carbon (δ13C) and nitrogen (δ15N) discrimination factors for birds' eggs, we conducted a feeding trial with captive killdeer (Charadrius vociferus) and measured δ13C and δ15N values in whole food, food constituents (protein and lipid-based), egg components (albumen, whole yolk, lipid-free yolk, and yolk lipid), and somatic tissues (pectoral muscle, subcutaneous fat) in females. We calculated diet and component specific discrimination factors and used Bayesian stable isotope mixing models to evaluate changes in nutrient allocation over the course of the egg-laying period. Our results show that discrimination factors in killdeer are distinct from those reported for other species and suggest seasonally variable endogenous nutrient inputs to protein-based egg components in this system. The first study to report these types of data for a shorebird, our findings provide new insights about the relationships between avian nutrition, reproduction, and potential carry-over effects.
Documenting lifetime diet preference and habitat use is critical for understanding how long-lived, mobile species respond to ecological change, yet such data remain sparse - particularly for comparisons within and among individuals, species, and populations. Eye lens layers (laminae) provide a biochemical archive that records these ecological signals sequentially through time, creating a unique opportunity to reconstruct entire life histories. This approach is especially valuable for elusive chondrichthyans (sharks, skates, rays, and chimeras), whose ecological importance as meso- to apex predators contrasts with the logistical challenges of tracking their movements and resource use. Stable isotope analysis (SIA) of vertebral growth bands is the established method for aging and reconstructing isotopic life histories in chondrichthyans, but eye lens laminae represent a promising yet under-verified alternative. We compared δ13C and δ15N values derived from eye lens laminae and vertebral bands of wild leopard sharks (Triakis semifasciata) to evaluate the ecological utility of eye lenses. Eye lens diameter increased linearly with total length (R2 = 0.95); however, because older laminar cells become progressively compacted, we incorporated a compaction index derived from attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy into aging models. This integration yielded age-specific δ13C and δ15N patterns that closely mirrored those observed in vertebral centra. Across ages, δ13C offsets between eye lens laminae and vertebrae were inconsistent, whereas δ15N values were largely concordant, with only modest increases in the outer laminae. To further verify eye lens isotopic records, we compared δ13C and δ15N values from the terminal eye lens lamina and muscle tissue, enabling estimation of age-specific tissue discrimination factors for both isotopes. Finally, eye lens isotope profiles revealed shared and divergent life history patterns across four Central California estuaries. Collectively, our results highlight eye lens laminae as a robust isotopic substrate for reconstructing lifetime ecological context in chondrichthyans.
Understanding the spatial linkages between breeding and non-breeding grounds of migratory species is important for assessing factors influencing population-specific trends and to guide regional conservation actions. In Canada, the Least Bittern (Botaurus exilis) is considered threatened under the Species at Risk Act. Due to the secretive behaviour of this small heron, information regarding migratory pathways and wintering locations is limited. To estimate the geographic locations of potential wintering grounds, we collected body contour feathers from museum specimens of Least Bittern sampled from across their breeding range in Canada. We measured the hydrogen, carbon, and nitrogen isotopic compositions of feathers to estimate the locations of Least Bittern wintering grounds using assignment-to-origin algorithms. The regions of the highest likelihood of origin of sampled Least Bittern were wintering sites in Mexico, central America along the Gulf Coast, and possibly coastal and Amazonian South America. Habitat loss is acknowledged as the main contributor to the population decline of Least Bittern, and these results may help understand potential factors driving their populations and support conservation and management efforts across their wintering range.
Stable isotope-labelled reagents, as internal standards (IS), are critical for ensuring the accuracy of mass spectrometry-based quantitative analysis, and their quality directly affects the reliability of detection results. 13C-labelled and deuterium (D)-labelled isotopic reagents are the most commonly used, but systematic evaluation of these reagents is still lacking. In this study, four clinically representative steroids were selected to systematically compare the performance of 13C-labelled and D-labelled internal standard reagents. Key parameters including isotope abundance, isotopic distribution, stability, and specificity were investigated, followed by validation in real serum samples. Results showed that both 13C-labelled and D-labelled reagents exhibited good stability. However, 13C-labelled reagents outperformed D-labelled ones in isotopic distribution and specificity. With the extension of analysis time, D-labelled reagents showed a significant separation trend from their corresponding unlabelled compounds, while the retention time difference between 13C-labelled IS and unlabelled analyses was ≤ 0.02 min, ensuring excellent co-elution. Serum spiking recovery experiments further demonstrated that 13C-labelled reagents (such as 13C-progesterone) with superior performance in this evaluation system, especially in methods involving large panels or long analysis times, achieved higher quantitative accuracy and precision.
Isotopic investigation of surface water, groundwater, and precipitation in mine areas, including abandoned mines, is essential for sustainable water management. This study, investigated tritium, stable isotopes, major ions, mercury (Hg) and other potentially toxic elements (Pb, Cu, Fe, Mn, Ba) in precipitation, groundwater and surface water surrounding an abandoned Hg mine in Puerto Princesa City, Palawan Island, Philippines. Samples were collected during dry and wet seasons to determine the origin of groundwater and evaluate surface waters-groundwaters interactions. Groundwater in the mine area was characterized by magnesium-bicarbonate type, mixed magnesium-bicarbonate, and calcium chloride water types, reflecting the local geology. Average Hg concentrations in the groundwater during the dry (0.081 µg/L) and wet (0.024 µg/L) seasons were slightly higher than global background level but remained within WHO and Philippines drinking water standards. Stable isotope results showed that both groundwater and river water originated and recharged through meteoric water. Tritium concentrations in shallow and deep groundwater wells ranged from <0.40 to 0.51 TU, indicating sub-modern water. Distinct isotopic signature of lake water in the δ18O and δ2H plot suggests minimal lake water infiltration into aquifer and limited groundwater discharge into the lake system. It was further confirmed by negative mixing ratio in lake-groundwater interactions using δ18O and δ2H values in both riparian and alluvial aquifer. Isotope mixing ratio analysis revealed low river-groundwater interactions in riparian zones(16.67 and 24.24 %) but high interactions in permeable aquifers in alluvial zone (63.33 and 75.76 %), based on δ18O and δ2H values, respectively. The results suggest that contaminant transfer from river to groundwater may occur in permeable alluvial areas. Therefore, proper mine waste management, mine rehabilitation, and preservation of riparian buffer zones are necessary to minimize contaminant transport. This study demonstrates the value of isotope hydrology tools for water resource assessment and environmental management in mining areas.
Age-related differences in migratory behaviour and non-breeding habitat use are central to the serial residency hypothesis. This hypothesis predicts that young birds disperse more broadly during their first migration, using of a wider range of non-breeding locations and associated resources than older individuals. We tested this prediction by measuring stable carbon (δ13C) and nitrogen (δ15N) isotopes in feathers of young and adult Eurasian reed warblers (Acrocephalus scirpaceus) grown during their first and subsequent non-breeding periods to compare age-related differences in non-breeding resource use. To this end, we quantified isotopic niche breadth and overlap between age classes using kernel utilisation density methods and analyses of standard ellipses in bivariate isotopic space. Isotopic niche breadths were similar for young and adult birds and largely overlapped. In a subset of individuals sampled in two consecutive years, isotopic values indicated no systematic changes between years. Our results do not support a key prediction of the serial residency hypothesis and instead suggest that high inter-individual variability and survivorship bias may obscure age-related differences in realised isotopic niches early in life, thereby limiting the extent to which juvenile exploratory behaviour contributes to population-level niche structure. Our study illustrates the potential and the limitations of δ13C and δ15N for testing age-dependent variation in realised niches and points to the value of integrating additional intrinsic tracers, such as stable hydrogen (δ2H) and sulfur (δ34S) isotopes, to link niche dynamics with large-scale non-breeding distributions and their implications for population resilience under environmental change.
Dietary variation at the individual level plays a fundamental role in carotenoid-based ornamental plumage coloration, which often influences sexual and social signaling. This study investigated how dietary differences shape the coloration of two ornamental feather types (breast and forehead) in males of the saffron finch. This small neotropical bird is considered granivorous, although it frequently incorporates arthropods into its diet. We used reflectance-based color measurements and carbon and nitrogen stable isotopes (δ¹³C, δ¹⁵N) to infer dietary patterns and their association with color variation. A total of 29 males were sampled across seven field campaigns conducted between January 2017 and March 2018 in a farm located in the Central Brazilian savannas. δ¹³C values showed no association with breast or forehead coloration, indicating that variation in carbon sources was not a major driver of color expression. In contrast, δ¹⁵N values were significantly associated with hue variation in both feather types. Higher δ¹⁵N values corresponded to a yellower-shifted hue in breast feathers and red-shifted hues in forehead feathers. Taken together, these findings suggest that saffron finches may selectively forage on high-trophic level prey that are relatively rich in carotenoids and associated with improved nutritional conditions. This dietary variation may be linked to differences in carotenoid processing and allocation across feather patches, contributing to different color phenotypes. In addition, such diets are associated with the production of high-quality feathers and promote more elaborate ornamental coloration. Although δ¹⁵N values may also be influenced by baseline variation in nitrogen sources, the observed patterns are consistent with trophic differences and highlight the role of diet in shaping plumage coloration. Our results highlight the importance of individual dietary strategies in shaping carotenoid-based color phenotypes through both direct (carotenoid acquisition) and indirect (nutritional condition) pathways, with distinct effects across different ornamental feather regions.
Mechanical grinding is increasingly used in samples preparation for stable isotope analysis. However, plastic abrasion could contaminate samples and bias the isotopic analysis. Previous studies on plant material and large quantity of marine animal samples showed that this bias is limited. However, there is no evaluation of this potential contamination on smaller animal samples. We evaluate potential plastic contamination by analysing the C and N elemental composition and stable isotope values of ∼50 mg (dry weight) of samples of a freshwater crustacean hand-ground versus mill-ground for durations of 1, 2 and 5 min. We found no differences in %N among treatment groups, but an increase in the %C with ball milling time, with significant differences between samples hand ground and mill-ground for 2 min, hand ground and mill-ground for 5 min, and mill-ground for 1 min and mill-ground for 5 min. No significant differences in neither the δ15N nor δ13C were found among the four grinding methods. We estimated plastic abrasion to be 1.65 mg. Our results show that the use of ball milling for homogenising samples for C and N stable isotope analysis does not affect animal muscle samples with a commonly used amount of material (∼50 mg). Finally, we provided a graphical recommendation on the minimum amount of sample to be ground by milling without incurring in plastic contamination bias.
This paper describes a simple method for the simultaneous determination of the isotopic composition (δ13CCO2) and concentration of CO2 in volcanic and geothermal gases using a continuous flow mass spectrometry system (CF-IRMS). The instrumental configuration includes a Thermo Fisher Scientific Delta Q mass spectrometer, connected through a Conflo IV to a Thermo Trace 1610 gas chromatograph (GC) physically connected at the module Isolink II. The performance of the developed GC-IRMS method was evaluated through a comprehensive series of tests assessing the precision and accuracy of the δ13C values and the simultaneous determination of CO2 concentrations. Specifically, we evaluated instrumental precision and isotopic data reproducibility (δ13CCO2) under various gas chromatographic operating conditions (split ratio) using gas mixture and certified isotopic standards; concentration calibration curves were specifically developed at different split ratios (3, 20, 35, and 45) using certified gas mixtures to quantitative CO2 determination with a wide concentration range (from 0.06-100 % vol.). The concentration data were compared with those obtained with traditional analytical techniques (GC and IR). Subsequently, the entire system performance, for both isotopic composition and CO2 concentration, was validated on volcanic and geothermal gases. These samples, including fumaroles, bubbling pools, and soil gas emissions, were selected to test the simultaneous determination capability under real-world conditions. The results confirm that the achieved operating configuration ensures optimal performance for the simultaneous determination of δ13CCO2 and CO2 concentrations, guaranteeing a precision of ± 0.08 ‰ and an accuracy within ± 0.1 ‰ for isotopic data and a quantitative accuracy typically within ± 5 % for concentration data.
