Fluoride hydrogeochemistry and associated human health risks implications are investigated in several aquifers along the southern edge of the Chinese Loess Plateau. Locally, 64% shallow groundwater samples in loess aquifer exceed the fluoride limit (1.5 mg/L) with the maximum of 3.8 mg/L. Presently, the shallow groundwater is the main source of private wells for domestic use, and this is clearly a potential risk for human health. Hydrogeochemistry and stable isotopes are used to elucidate the diversity of occurrence mechanisms. Enrichment of fluoride in groundwater is largely controlled by the F-containing minerals dissolution. Furthermore, alkaline condition and calcium-removing processes promote water–rock interactions. Stable isotopes of hydrogen and oxygen (δD and δ18O) in study area waters demonstrate that groundwater in loess aquifer is old, which means groundwater remains in the aquifer for a long time. Long residence time induces sufficient water–rock interactions, which play significant roles in the resolution of fluoride minerals. Samples from the shallow loess aquifer show elevated fluoride levels, which may pose human health risk for both adults (60%) and children (94%) via oral intake. To ensure drinking water safety, management measures such as popularizing fluoride-removing techniques and optimizing water supply strategies need to be implemented.
Spatial distribution and sources of 16 priority polycyclic aromatic hydrocarbons (16 EPA-PAHs) in soils were studied in Shenfu Irrigation Area (SIA) located at northeast of China. SIA (1.3 x 10(4) ha) was an important agricultural farmland irrigated with oil-sewage since the 1960s. Soil profiles at 91 sites controlling all SIA were sampled. The results demonstrated that four- and five-ring PAHs accounted for 71.2% and 73.0% of the total PAHs in surface (0-20 cm) and subsurface (20-30 cm) soil, respectively. Phenanthrene (Phe), Fluoranthene (Fla), Pyrene (Pyr), Benzo(b)fluoranthene (BbF), benzo(a)pyrene (BaP) were identified as five dominant individual PAHs. Generally, there was a decreasing trend in concentrations of 16 EPA-PAHs from upper to lower reaches (by distance away from source) within 0.6-12.36 mg kg(-1) and 0.04-4.99 mg kg(-1) in surface and subsurface soil, respectively. The concentrations of 16 EPA-PAHs in the surface soil were threefold higher than those in the subsurface soil. A combination of grass, wood or coal combustion and petroleum combustion in surface soil and a combination of grass, wood or coal combustion and petroleum sources in subsurface soil might be the most significant contributors of 16 EPA-PAHs in SIA, indicating different pollution periods.
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