Spatial variations in oxygen and hydrogen isotopes in waters and human hair across South Korea

Spatio-temporal variation characteristics of stable isotopes of tap water and its potential as a proxy for surface water in Sichuan, China

The stability and safety of tap water are essential for human health and economic and social development. The stable isotopes can be used to reveal characteristics of tap water and link it with its source. In this paper, 1556 tap water samples were collected from Sichuan, China and the stable isotope ratios for these samples were determined. The δ2H ranges from -126.4 ‰ to -26.4 ‰, and the range of δ18O is -17.04 ‰ to -2.08 ‰, reflecting the tap water sources are affected by complex spatial features and changing meteorological elements. Stable isotopes in tap water usually reach the maximum values in summer, indicating that heavy isotope enrichment is easily achievable by the large amount of evaporation from water sources during the summer season. By using spatial interpolation and isoscapes, we can find that there is a strong correlation between both simulated tap water δ2H and river water δ2H, with the maximum difference not exceeding 10.0 ‰, while the overall mean relative error is 6 %. Consequently, it is feasible to use tap water isotopes as a proxy for surface water isotopes in representative watersheds where surface water is the main source of water. The study shows the variation characteristics and influencing factors of tap water isotopes and enriches the isotope database of tap water in China. Meanwhile, the utilize of stable isotopes in tap water as a proxy for surface water expands the application field of tap water stable isotopes and opens new perspectives for indirectly obtaining isotope data of surface water.

BITACORA: An isotopic database of modern human tissues (keratin, teeth) for Argentina

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.

National-scale investigation of dual nitrate isotopes and chloride ion in South Korea: Nitrate source apportionment for stream water

Nitrate sources in surface water have been identified using dual-isotope compositions of nitrate with various tools to efficiently manage the water quality at the local scale. Correlation between Cl and NO₃ has also been used to identify NO₃. In this study, we assess the reliability of the dual-isotope approach and Cl in terms of nitrate source apportionment. To this end, we collected stream water samples throughout South Korea to estimate nitrate sources in streams and determine whether the land-use pattern was closely related to nitrate sources. The δ¹⁵N-NO₃ ranging from -1.3 to 14.8‰ showed a spatial distribution that was lower in mountain ranges (<7‰) than plain areas (>8‰). The Cl concentration in this national-scale distribution was also assessed. The relationship between the proportion of Cl and δ¹⁵N-NO₃ classifies nitrate sources into areas characterized by three land-use patterns: (1) agricultural and business areas, (2) forests in highlands, and (3) lowland forests, of which (1) had proportions of Cl >50%, while (2) and (3) were <50%. The samples in (3) showed δ¹⁵N-NO₃ values > 6‰, similar to those of (1). Deuterium excess of samples was negatively correlated (R² = 0.53) with δ¹⁵N-NO₃, accounting for the fact that δ¹⁵N-NO₃ reflected land-use patterns. Samples were dominantly affected by agriculture-derived sources and domestic sewage showed NO₃/Cl of <0.4 and δ¹⁵N-NO₃ of >6‰. These results suggest that nitrate source apportionment should be comprehensively evaluated considering the dual-isotope approach, land-use patterns, and Cl proportions.

The effects of dyes and bleaches on the sorption and desorption of trace elements in human hair

Trace element concentrations and isotope ratios of hair reflect the blood levels at the time of hair formation, but can be affected by external factors such as dyeing, bleaching, and bathing. To investigate the effect of dyeing, bleaching, and bathing on hair, hair was immersed in tap water, and changes in trace element concentrations and the Sr isotope ratio were observed over time. During soaking, alkaline earth metals (Ca, Mg, and Sr) from tap water were gradually absorbed into the hair over time. After about one day, the adsorption capacity of hair reached a maximum and the reverse reaction started to occur. In contrast, alkaline metals (Na and K) behaved in reverse. In dyed and bleached hair, Na was significantly desorbed from the hair and gradually migrated to the water over time. The adsorption and desorption of trace elements were minimal in untreated original hair, but much higher in dyed and bleached hair. Thus, dyeing and bleaching appear to damage the hair surface structure and greatly promote the exchange of trace elements. The rapid exchange of trace elements, including Sr, between hair and tap water observed in this study indicates that hair samples can be easily contaminated during bathing.

Identification of nitrate sources in tap water sources across South Korea using multiple stable isotopes: Implications for land use and water management

Stable nitrate isotopes (δ¹⁵N-NO₃ and δ¹⁸O-NO₃) in conjunction with stable water isotopes (δ¹⁸O-H₂O and δD-H₂O) were used to identify nitrogen (N) sources and N-biogeochemical transformation in tap water sources sampled from 11 water purification plants across South Korea. The raw water sources are taken from rivers within the water supply basins, which indicates the quality of tap water is highly dependent on surrounding the land use type. We estimated the proportional contribution of the various N sources (AD: atmospheric deposition; SN: soil nitrogen; CF: chemical fertilizer; M&S: manure/sewage) using Bayesian Mixing Model. As a result, the contribution of N sources exhibited large seasonal and spatial differences, which were related to the type of land use in the water supply basins. Commonly, the M&S and SN were the dominant N source during the dry and wet seasons in almost regions, respectively. However, in the regions with high N loading ratios from urban and industrial sources, the M&S was the dominant N source during both the wet and dry seasons. In addition, the regions were characterized by high NO₃^- concentrations due to the decreased dilution effect of precipitation during the dry seasons. In contrast, the SN was the dominant N source in the regions with high N loading ratios from agricultural areas during both the wet and dry seasons. The NO₃^--N concentration during the wet season was significantly higher than those during the dry season in these regions due to the input of non-point sources with high concentrations. Meanwhile, denitrification and nitrification were observed in the watersheds. It is important to understand the isotope fractionation due to N-biogeochemical transformation for considering the potential misinterpretations of the origin and fate NO₃^-. Collectively, our findings provide a basis on N source control strategies to ensure tap water quality in complex land use areas.

Paired stable carbon and oxygen isotope analyses of human enamel for forensic human geolocation: An exploratory study

Stable carbon isotope analysis has proven utility for reconstructing dietary information in humans in past populations. The usefulness of stable carbon for forensic geolocation has been little investigated, largely because of the globalization of the human diet seemingly rendering it inconsequential. This study queried this assumption at a country-wide level on a known sample group. Stable carbon isotope values were obtained from human enamel with known biographical and geographical information to determine whether stable carbon, when paired with stable oxygen isotope values, could differentiate Canadians from non-Canadians. Samples originating outside of Canada were separated into three regions, and a linear discriminant analysis was used to generate discriminant functions that best separate the regions according to the stable carbon and oxygen isotope values. The results revealed two functions, where the first function explained 92.1% and the second 7.9% of the variance. Although some overlap in stable carbon and oxygen values was observed for individuals from both the United States and Canada, differences were observed between those from Canada and other geographical regions. This study demonstrated that pairing the dietary isotope carbon with the geolocator stable oxygen isotope, produced an interesting separation geographically, one that might well be helpful when attempting a geolocation query on unknown human remains.

Examination of amino acid hydrogen isotope measurements of scalp hair for region-of-origin studies

RATIONALE

Hydrogen isotope (δ2 H) analysis of keratinaceous bulk tissues has been used in forensic science to reconstruct an individual's travel history or determine their region-of-origin. Here, we use a compound-specific approach to examine patterns of individual amino acid δ2 H values in relation to those of local tap water, bulk scalp hair tissues, and region-of-origin.

METHODS

We measured δ2 H values of amino acids in anonymously collected scalp hair (n = 67) and tap water from 28 locations in the United States. Samples were hydrolyzed into their constituent amino acids, derivatized alongside in-house reference materials, and analyzed in triplicate using a GC-C-IRMS system.

RESULTS

Non-essential amino acid (AANESS ) δ2 H values and their corresponding tap water samples varied systematically across continental regions. Hydrogen isotope values of alanine, glutamic acid, and glycine were significantly correlated with tap water and an estimated 42%-51% of the hydrogen atoms in these AANESS were derived from tap water. We used linear discriminate analysis (LDA) to explore regional patterns in scalp hair bulk tissue and amino acid δ2 H values. For the model that included AANESS data, 87% of the variance was explained by the first linear discriminant axis (LD1), and was driven by bulk hair tissue, alanine, and proline. This model had an overall 72% successful reclassification with samples from the south and northwest regions reclassifying correctly 92% and 78% of the time, respectively. For the model that included AAESS data, LD1 explained 81% of the variation and was driven bulk hair, threonine, valine, phenylalanine, and isoleucine. The overall reclassification rate for the model that included AAESS was 70%.

CONCLUSIONS

Our findings suggest that δ2 H analyses of AANESS and AAESS could help improve geolocation models for human and wildlife forensics by simultaneously providing information about both dietary and tap water inputs of hydrogen to tissue synthesis.

Tracing the geographical origin of bottled water collected in South Korea via isotopic and elemental analyses

RATIONALE

The production of bottled water requires a forensic discriminant technique that enables the identification of the brands or accidents caused by intended contaminants. The bottled water poisoning crimes have drawn much attention, and such crimes may recur in the future. The water is colorless and odorless, and thus it is difficult to detect contaminated water through visual observation. Thus, bottled water can be easily exploited for poisoning, and a method for tracing their origin is currently required.

METHODS

In this study, a total of 27 brands of bottled water samples were analyzed to determine stable oxygen isotopes, strontium isotopes, major and trace elements. The geographical origin of the water was traced based on the climatic and geographical characteristics of the location from where water was sourced, which was assumed to be reflected in the bottled water. Furthermore, we investigated whether this method can be applied to identify bottled water products.

RESULTS

The results demonstrated that the characteristics of the bottled water, including the oxygen stable isotope ratios, reflect the latitude and altitude of bottled water source in South Korea, from the high-latitude region to the coastal regions. In addition, the results indicated that excellent discrimination was achieved using strontium isotopes to identify source areas with different types of bedrock, complex underlying lithologies, and ocean areas in South Korea. A statistical method based on discriminant analysis was applied to measure trace elements, and the results effectively reflected the characteristics of water-rock interactions (cross-validated classification probability: ≥92%).

CONCLUSIONS

These data suggest that the geographical characteristics of the source area are well reflected in commercial bottled water in South Korea. The proposed analytical methods can be utilized to trace the geographical origin of different bottled water samples and identify bottled water products used in poisoning crimes.

Multi-isotopes in human hair: A tool to initiate cross-border collaboration in international cold-cases

Unidentified human remains have historically been investigated nationally by law enforcement authorities. However, this approach is outdated in a globalized world with rapid transportation means, where humans easily move long distances across borders. Cross-border cooperation in solving cold-cases is rare due to political, administrative or technical challenges. It is fundamental to develop new tools to provide rapid and cost-effective leads for international cooperation. In this work, we demonstrate that isotopic measurements are effective screening tools to help identify cold-cases with potential international ramifications. We first complete existing databases of hydrogen and sulfur isotopes in human hair from residents across North America by compiling or analyzing hair from Canada, the United States (US) and Mexico. Using these databases, we develop maps predicting isotope variations in human hair across North America. We demonstrate that both δ2H and δ34S values of human hair are highly predictable and display strong spatial patterns. Multi-isotope analysis combined with dual δ2H and δ34S geographic probability maps provide evidence for international travel in two case studies. In the first, we demonstrate that multi-isotope analysis in bulk hair of deceased border crossers found in the US, close to the Mexico-US border, help trace their last place of residence or travel back to specific regions of Mexico. These findings were validated by the subsequent identification of these individuals through the Pima County Office of the Medical Examiner in Tucson, Arizona. In the second case study, we demonstrate that sequential multi-isotope analysis along the hair strands of an unidentified individual found in Canada provides detailed insights into the international mobility of this individual during the last year of life. In both cases, isotope data provide strong leads towards international travel.

Spatial distributions of oxygen and hydrogen isotopes in multi-level groundwater across South Korea: A case study of mountainous regions

This study presents the spatial distributions of stable isotopes for groundwater according to well depth and spring water across South Korea, using an interpolation model to provide baseline information for hydrological studies. In total, 888 groundwater and 108 spring water samples were collected across South Korea; their oxygen and hydrogen isotopic compositions (δ¹⁸O and δ²H) were analyzed. δ¹⁸O and δ²H values biased toward the summer local meteoric water line and low d-excess values indicate that summer precipitation is important for groundwater recharge. The δ¹⁸O and δ²H values for groundwater and spring water decrease progressively from the southwest to the northeast on the Korean Peninsula. Based on eight hydrological regions, the average δ¹⁸O values of groundwater and spring water are negatively correlated with latitude, but they are positively correlated with temperature. This result indicates that the spatial distributions of groundwater isotopic values in South Korea are significantly influenced by latitude and altitude effects associated with the movement of the North Pacific air mass in summer. Spring waters showed a negative correlation between δ¹⁸O and d-excess, with more depleted ¹⁸O values than groundwater, indicating that local recharge and flow within mountainous areas is dominant. Considering that the correlation in multi-level groundwater located in northern regions is similar to that of spring water, the contribution of regional groundwater flow, which is recharged in mountainous areas, is considered to be higher in the northern regions. The spatial distribution of δ¹⁸O in groundwater gradually approached the spatial distribution of spring water with increasing well depth, indicating that the contribution of regional groundwater flow may be greater in deep groundwater. Our results provide estimates for data-poor regions, supporting the investigation of links between groundwater and other hydrological factors.

Spatial distributions of strontium isotope ratios in human hair and tap water from South Korea

Natural variations of ⁸⁷Sr/⁸⁶Sr ratios in biological samples, such as human hair, provide a biological record of provenance. Spatial distribution maps reflecting heterogeneity in isotopic signatures across large geographical regions are helpful for discerning the provenance and mobility of organisms. In this national-scale study conducted across South Korea, we investigated the spatial distribution patterns of ⁸⁷Sr/⁸⁶Sr ratios in human hair and tap water samples to determine their spatial variabilities and the relationships of isotopic signatures between hair and tap water. The strontium isoscapes of tap water and hair showed similar spatial distribution patterns. Non-parametric comparison indicated no significant differences in isotopic ratios between the two sample types. The ⁸⁷Sr/⁸⁶Sr ratios in human hair showed a significant and strong correlation with the ratios in tap water in eastern Korea, suggesting potential use of ⁸⁷Sr/⁸⁶Sr ratios in provenance studies. However, tap water and hair samples from western Korea did not show significant correlation between them, overall reducing the predictive power of the hair ⁸⁷Sr/⁸⁶Sr ratios for provenance studies. The deviation between ⁸⁷Sr/⁸⁶Sr_{tap water} and ⁸⁷Sr/⁸⁶Sr_hair was much larger in western coastal areas than in eastern Korea. Relatively high utilization of groundwater or exogenous materials, such as Asian dust, may have been responsible for this pattern. To fully utilize the potential of the strontium isotope signature as a biorecorder in provenance studies, it is essential to evaluate the effects of groundwater and other exogenous materials on the isotope signatures of hair and other biological samples. In this study, only hair samples from males were used to develop ⁸⁷Sr/⁸⁶Sr isoscapes. Therefore, further studies are required to examine the applicability of ⁸⁷Sr/⁸⁶Sr hair isoscapes based solely on human hair samples from males to forensic and provenance studies of human hair samples from females.

Dietary homogenization and spatial distributions of carbon, nitrogen, and sulfur isotope ratios in human hair in South Korea

Dietary homogenization has progressed worldwide due to westernization and the globalization of food production systems. We investigated dietary heterogeneity in South Korea by examining the spatial distribution of carbon (C), nitrogen (N), and sulfur (S) isotope ratios using 264 human hair samples. Overall, variation in isotope values was small, indicating low dietary heterogeneity. We detected differences in δ¹³C, δ¹⁵N, and δ³⁴S values between administrative provinces and metropolitan cities; inter-regional differences were typically < 1 ‰. Values of δ³⁴S were significantly lower in hair samples from inland regions relative to those from coastal locations, and a similar pattern was observed in δ¹⁵N values. Understanding geographic variation in δ³⁴S and δ¹⁵N values in human hair is useful for provenancing humans in South Korea.

Assessing the predictability of existing water-to-enamel geolocation models against known human teeth

Stable isotope analysis of human tissues has become a valuable tool for mapping human geolocation. This study adds to the existing knowledge of the relationship between oxygen stable isotopes in human enamel and drinking water by presenting enamel oxygen values in clinic-extracted human dental enamel with known provenance. The results from this study indicate that the theoretical isotopic relationship between enamel and drinking water oxygen is weak at the city and country-level. Differences of up to 15‰ were observed between predicted drinking water oxygen values using existing models and observed values, highlighting the complexity of using water/enamel conversion equations. The lower isotopic boundary of enamel oxygen values is now understood for Metro Vancouver at δ¹⁸O_c(VPDB) = - 11.0‰ and presents the possibility of using stable isotope analysis as an exclusionary tool where individuals falling below threshold value can be identified as non-local. Overall, this study's results support the development of geographical reference maps for human enamel oxygen.

Datasets for spatial variation of O and H isotopes in waters and hair across South Korea

The data presented here include the results of oxygen (δ¹⁸O) and hydrogen (δ²H) isotope analyses of water and human scalp hair samples collected from throughout the South Korea. The purpose of data collection was to generate isoscapes of oxygen and hydrogen isotopes for South Korea. To achieve the objective, we collected human scalp hair and three different types of water samples: groundwater, stream water and tap water. The data presented in the article are raw isotope data of water and hair samples in tabulated manner and interpolated isoscapes generated using those data. Further information related to the datasets and discussion about them can be found in the related research article entitled "Spatial variations in oxygen and hydrogen isotopes in waters and human hair across South Korea" [1].