Spatial variations in soil selenium and residential dietary selenium intake in a selenium-rich county, Shitai, Anhui, China

Shitai, a selenium (Se)-rich county in Anhui, China, has been reported for its resident longevity in the last 20 years. A recent survey by the Anhui Bureau of Geological Survey showed that soil Se contents in the Shitai area ranged from 0.05 to 51.20 mg/kg, with an average of 0.56 mg/kg. To explore the potential relationship between longevity and natural-occurring Se contents in Shitai county, Se concentrations were determined in Shitai's food chain (including soils and foods) and the daily Se intakes and hair Se contents were calculated for the residents. In the present study, 33 soil samples, 66 food samples and 82 hair samples were randomly collected from field sites, local food markets and male and female residents in downtown Shitai and in four nearby villages (Dashan, Xianyu, Yongfu and Yuantou). The total Se contents in all samples and the levels of water soluble, exchangeable, acid soluble, organic bound and residual Se in soil samples were determined with hydride generation - atomic fluorescence spectrometry. The total Se contents in soils ranged from 227 to 2603 μg/kg, with the averages of 1607 ± 242 μg/kg in Dashan, 1149 ± 118 μg/kg in Xianyu, 521 ± 157 μg/kg in Yongfu, and 363 ± 140 μg/kg in Yuantou. The soil bioavailable Se content (soluble and exchangeable Se) in Dashan was highest (14.98%), followed by Xianyu (13.69%), Yongfu (13.18%) and Yuantou (9.38%). For food samples, the highest Se concentration of grains was 468.5 μg/kg in Dashan, while lowest was observed in downtown (41.7 μg/kg). The estimated daily Se intake of residents in Dashan reached 298.4 μg/d/adult, which is about 5 times higher than the recommend nutrient intake in China (60 μg/d/adult), and 6–10 times higher than the levels observed in Xianyu (47.6 μg/d/adult), Yuantou (46.1 μg/d/adult), Yongfu (40.0 μg/d/adult), and downtown (30.0 μg/d/adult). Although hair Se contents in Dashan (male: 709.2 μg/kg; female: 589.2 μg/kg) were significantly higher than those at the other study sites, no significant relationships between daily Se intakes and hair Se contents were observed. The present study demonstrated that Se levels in soils, foods, resident dietary intake and human hairs in Shitai County varied significantly; therefore, the region could be a unique field site to study the direct relationship between Se and human health.