| Fluoride (F) is an essential element to mammals, a small amount helping bone development. For humans, one of the important dietary sources of F is tea, which contains relatively high concentrations that are released during infusion. Ingestion of F from drinking teas containing normal F concentrations has been considered safe and was seen as a way of protecting against tooth decay. However, some special teas (e.g. brick tea) containing extremely high F concentrations or excessive daily consumption of other teas have resulted in the over-intake of F in severe cases. Therefore, reducing F uptake by tea plants and consequently its levels in tea products has become important when high F concentrations in tea constitute a hazard to human health. We studied the Accumulation and Distribution of Fluoride in Tea Plants (Camellia sinensis L.) and measure of reducing Fluoride uptake by the soil experiments, solution culture experiments and field investigations. The following is the summary of the results .1. The soil experiments have shown that F uptake by tea plants was usually linearly correlated with F concentrations in soils. A major proportion of F taken up by tea plants was distributed to leaves, approximately accounted for 90%, whereas much lower concentrations of F were found in stem and root. The distribution of F in tea plants was that leaves>> the absorption roots> main roots> stems. Solution culture experiments have also shown that F uptake was strongly influenced by F concentrations in thesolution. We have got same results by field investigation.2. Leaf F(x) concentration in tea plants is usually linearly correlated with the water-soluble F(y) in 0-20cm soil depth, expressed as: y=3862.9x+746.8 (n=55, r=0.369**) , and y=2576.1x+904.29 (n=55, r=0.302* ) in 20-40 cm soil depth. Leaf F concentrations from tea gardens nearby the fluorite mine, the brickkiln and the concrete factory were obviously higher than those from ordinary tea gardens, e.g. water-soluble F concentrations in soil were increased by 1400%, and leaf F concentrations were increased by 200%. Whereas the properties of soils can affect the water-soluble F concentrations, such as pH value and organic matter contents. Linear regression analysis revealed a high positive correlation between pH value and water-soluble F concentration (r=0.588, p<0.01), and a high negative correlation between the organic matter concentration and water-soluble F concentration (r=-0.397, p<0.05). In addition, the high negative correlation between the water-soluble F concentration and exchangeable Al, Mn concentrations. The high positive correlation between water-soluble F concentration and exchangeable K, Ca, Mg concentrations.3. The application of Ca at 100 mg/kg didn't affect the new shoot F, but young shoot F concentrations were significantly decreased by the addition of Ca at 500 mg/kg. Leaf and young shoot F concentrations were significantly decreased by the addition of Ca at 500 mg/kg. Leaf F concentrations linearly and negatively correlated with the amounts of Ca(NO3)2 applied[y=1567.4-72.179x (R2=0.73, P<0.01); where y is the leaf concentration (mg/kg) and x is the amount of Ca(NO3)2 applied (mg/kg)]. The addition of Ca to the uptake solution significantly decreased leaf F concentrations, leaf F concentration was decreased by 10.5% (P<0.05) compared with the control without Ca when 0.5mg/L Ca was applied. Leaf F concentration were further decreased with increasing Ca concentrations in the uptake solution. Leaf F concentrations were dramatically reduced by liming, being reduced by 37.2% and 88.7% following CaO application at 2.1g and 5.1g per pot, respectively, compared with the unlimed control.4. Enhancing Al concentrations in the nutrient solution or adding Al to the soil significantly increased the uptake of F. In soil experiment, F concentrations in the mature leaves and new shoots were increased by 30% or 63% respectively when 100mg/kg Al application, compared without Al application. Leaf F concen...
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