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

The spatial distribution of isotopic signatures in the form of isoscape is a valuable tool to map their spatial heterogeneity in various environmental settings. However, only limited information about δ¹⁸O and δ²H in water across South Korea is available and to our knowledge no study so far has tried to examine the isotopic heterogeneity of tap water and human scalp hair in South Korea. Here, we present the first national scale analyses of stream water, groundwater, tap water, and human scalp hair isoscapes for South Korea. Stream water, groundwater, tap water, and human scalp hair samples were collected from across South Korea. These samples were analyzed for δ¹⁸O and δ²H, and the isotopic data were then used to generate interpolated δ¹⁸O and δ²H isoscapes for South Korea. The results of linear regression analyses showed strong and significant relationships between δ¹⁸O_hair and δ¹⁸O_water (R² = 0.83, P < 0.002) and between δ²H_hair and δ²H_water (R² = 0.74, P < 0.006), primarily reflecting a close co-relationship between water and hair. The slopes of linear regressions for δ¹⁸O (Δδ¹⁸O_hair/Δδ¹⁸O_water) and δ²H (Δδ²H_hair/Δδ²H_water) suggested that approximately 27% of hydrogen and 36% of oxygen in hair keratin were derived from the local drinking water. Interpolated δ¹⁸O and δ²H isotope maps of stream water, groundwater, and tap water samples collected from across South Korea showed similar spatial patterns of isotope variability. These samples showed a clear latitudinal gradient with high isotopic values in the south which progressively decrease toward the north. The same trends were observed in hair isoscapes as well, and had gradients matching the isotopic pattern of water samples. The strong relationship between water and human hair, and the consistent spatial pattern between them suggest that hair isotope signatures in South Korea can be used in provenance- and forensic-related activities.