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Soil pollution of fluorine is a serious environmental problem in the world, and the fluorine pollution evaluation of spatial and vertical distribution study in the Karst region is quite limited. In this study, the farmland around lead-zinc mine in the Karst region was chosen as the study area. Ninety-one upper layer soil samples and two soil profiles (one in paddy field, the other one in aerated field) samples were taken. The average concentration of total fluorine of topsoil in the paddy fields is 378 mg/kg, whereas in the aerated field it is 508 mg/kg. The concentrations of total fluorine in all paddy soil samples and 97.87% aerated field soils are higher than that of the background value of Guangxi. The total fluorine contaminations in all aerated field soils are much higher than in paddy soil samples, so the aerated field is contaminated severely. The vertical distribution of fluorine is different in paddy field and aerated field. In paddy field, the content of fluorine increases from 20 to 40 cm, then it decreases rapidly from 40 to 60 cm in depth, and then increases gradually. However, in the aerated field, the content of fluorine rises gradually with the depth of the sampling point. The results of relative analysis and regression analysis between fluorine in soil and soil properties show that the spatial distribution and vertical variation of fluorine in this region are mainly affected by parent rock.

Summary Accurate evaluation of metal bioavailability to hyperaccumulators is necessary for prediction of metal uptake and estimation of phytoextraction potential. Sedum plumbizincicola X.H. Guo et S.B. Zhou ex L.H. Wu (Crassulaceae), a hyperaccumulator of cadmium (Cd) and zinc (Zn), was grown in a pot experiment in 108 agricultural soils representing a wide range of typical Chinese soil types. The contribution of soil properties to Zn uptake was assessed quantitatively. Soil total Zn, soluble Zn, CaCl2‐extractable Zn and (DGT)‐extractable Zn concentrations (Zntotal, Znsoln, ZnCaCl2 and ZnDGT, respectively) were compared to predict shoot Zn concentration (Znshoot) using a piecewise equation. This showed a logarithmic increase with increasing Zntotal from 100–1000 mg kg−1 but plateaued outside this range. The optimum soil pH for Zn removal was ~ 5.5 and further acidification was unnecessary because Znshoot increased significantly with a decrease in pH from 7.5 to 5.5 and rarely changed at pH < 5.5. Sedum plumbizincicola grown in loamy or clay loam soils had larger Znshoot than in sandy or clay soils. The ZnCaCl2 was superior to other methods in estimating Zn bioavailability across all the data. At pH < 5.5, ZnCaCl2 showed much stronger correlation with Znshoot than Zntotal, Znsoln or ZnDGT. Piecewise equations (single linear regression equations at different intervals of soil properties) versus Zntotal and ZnCaCl2 at different pH ranges considerably increased the accuracy of prediction of Znshoot compared with the global equations derived from all data. Estimation of the potential of S. plumbizincicola for Zn phytoextraction in the field indicated that it is feasible to decontaminate acid‐polluted soils with Zntotal ≤ 500 mg kg−1 with S. plumbizincicola. Highlights Zn bioavailability to hyperaccumulators needs to be estimated over a wide range of soil types. Piecewise equations considerably improved the prediction of shoot Zn concentration. CaCl2 extraction was more suitable than DGT for the estimation of Zn bioavailability. Decontamination with S. plumbizincicola is feasible for acid soils with Zntotal ≤ 500 mg kg−1.