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].


Specifications table
Raw and analysed data Parameters for data collection All the isotopic ratios are reported in delta ( δ) notation relative to Vienna Standard Mean Ocean Water (VSMOW), where δ ( ‰ ) = [(R sample /R standard ) -1] × 10 0 0, and R = 2 H/ 1 H or 18  Gautam, M.K., Song, B.Y., Shin, W.J., Bong, Y.S., Lee, K.S., Spatial variations in oxygen and hydrogen isotopes in waters and human hair across South Korea [1] Value of the data • The data will contribute to better understanding the geospatial variation in isotopes of water and hair on national scale and are an addition to the global isotope database • Data are useful to other researchers who are interested in using water isotope for generating better global isoscapes and for those who use isotopes of drinking water and hair for provenance discrimination and in forensic analyses. • The data will contribute to better understanding the application of oxygen and hydrogen isotopes as geographic tracer for agricultural products. • The data can be used by other researchers who use isotope signatures of drinking water and human hairs for provenance discrimination and forensic analyses.

Study location
Our sampling sites for meteoric waters (groundwater, stream water and tap water) and hair samples were located across the country, encompassing all the eight administrative provinces of South Korea ( Fig. 1 ).

Water samples
In September-October 2010, 56 groundwater, 130 stream water and 91 tap water samples were collected across South Korea, and their GPS coordinates and other metadata were recorded. Sampling emphasized obtaining nation-wide high-resolution datasets for the construction of reliable interpolated isoscapes. For successful sampling that incorporated the maximum variability, the campaign was carried out in urban, suburban and rural areas. Groundwater samples were obtained from local houses in person (offered by residents) and from automated bore wells. Prior to sample collection, water was allowed to flow out for 10 to 15 min to remove factors that might cause fractionation (e.g., water trapped in the pipes since the last use of the well) and to obtain well-mixed groundwater samples. When possible, we collected tap water (municipal water supply) samples from the same locations where groundwater sampling was conducted. Samples were collected only from in-use cold water taps, and the tap was run for one min prior   to sample collection. Where feasible, the surface water and stream water sampling locations were chosen based on proximity to groundwater and tap water sampling locations. To remove the possibility of evaporative enrichment, samples were collected only from the flowing sections of streams. All water samples were filtered after collection through a 0.45-μm PVDP Millipore® syringe filter (Millipore Corporation, Billerica, USA) into 60-mL glass vials. Vials were filled to the neck and closed with rubber-lined caps to avoid exchange with the atmosphere. The vials were immediately stored in portable iceboxes with re-usable ice packs (to reduce photodegradation) after collection and transported to the laboratory. In the laboratory, the vials were stored at 4 °C until isotopic analyses.

Human scalp hair samples
Human scalp hairs were sampled from different locations (barbershops) across South Korea (n = 100). Hair samples discarded at the barbershops were collected. The length was not taken into consideration, but it was usually 4-6 cm long and there is a weak possibility that a hair will mix with various lengths of hair. Only undyed hair samples were collected for the study. To ensure that the isotopic signature of hair samples reflected the geographic location of sampling regions, hair samples were obtained from local residents, when possible, who lived in close proximity to the barbershop. Care was taken to select barbershops near the water sampling sites. With this approach, we can assume that the individuals whose hair was collected had access to local water sources. In addition, three sets of discarded hair clippings were collected in the suburban towns to increase the probability that the hair samples were associated with local residents.  were sent to the USGS to analyze oxygen and hydrogen isotopic compositions. The oxygen and hydrogen isotopic compositions of the hair samples were analyzed at least in duplicate using standard reference materials (USGS42 and 43) at the Stable Isotope Lab of the United States Geological Survey in Reston, Virginia.

Interpolated maps
Based on oxygen and hydrogen isotopic compositions, spatial patterns of water samples and human hair in South Korea were generated using ArcGIS v10.1 (ESRI, Redlands, CA, USA). The inverse distance weighted (IDW) interpolation method was used to analyze spatial patterns because IDW is intuitive and efficient (Azpurua and Ramos, 2010). For IDW, we used the default in the ArcGIS that included the inverse of the distance raised to the 2 nd power. Spatial interpolation was performed using IDW, which assigns values to unknown points based on a weighted average of the values at known points.

Declaration of Competing Interest
The authors declare that they have no conflict of interest.