Study On Fluorine Accumulation And Defluoridation Measures Of Tea

Tea plant (Camellia sinensis L.) is known as a fluorine (F) accumulator. The F concentration of tea leaves is 100-1000 times higher than that of general plants. A continuous intake of brick tea containing extremely high F might result in serious toxicosis, termed fluorosis. In this study, the effect of tea cultivar and maturity, plucking season, pH value and metal concentration in'culture medium on the F accumulation was investigated, and the F concentration in samples prepared from hot water treatment and different blending formula was also assayed. The results show that:1. Significant difference in F accumulation was observed in different tea cultivars, indicating the genetic background is one of the most important factors for F accumulation of tea and popularization of low-F accumulation cultivars can be used as a good defluoridation measure. Positive correlation was found between F accumulation and growth duration (maturity), and the rate of F accumulation was around 17.9-25.0 mg/kg·d. The concentration of F in different mature samples from same cultivar was significantly correlated with the concentration of aluminium (r>0.98**) and calcium (r>0.86*), i.e., the concentration of F, aluminium and calcium accumulated synchronously with an increase in maturity. The F concentration in tea was also influenced by the year, plucking season and growth region, suggesting ecological factors, such as temperature, rainfall and F in soil and atmosphere, would also affect the F accumulation.2. Under solution culture condition, the F accumulation reached to the highest level when pH value was 5.5. This might be related to the growth effect of pH because the best growth was found around pH=5.5. The F concentration in leaves decreased with the increase of aluminium and calcium in solution medium when pH value of the medium was set to 5.0, indicating that aluminum and calcium would inhibite the F accumulation in tea. Magnesium would accelerate the F accumulation when its level was low than 50μmol/L, and inhibit the F accumulation when its level increased furthermore. It implied that effect of magnesium on the F accumulation might relate to the growth adjustment of this element.3. Under potting culture condition, F concentration in tea increased significantly when exogenous F was applied, suggesting the F level in soil might influence its accumulation in tea plant. The soil pH increased and F concentration in tea decreased after the soils were treated with sodium hydroxide, suggesting the high pH might inhibit the F accumulation in tea. F concentration in tea shoots increased when aluminium sulfate or calcium sulfate was applied. This might be explained as the acidification of these compounds.4. Measures, including using the leaves plucked from low-F accumulation cultivars, timely plucking and inhibiting the acidification of soils would result in decrease of F level in tea products. Although hot water treatment could decrease the F level of tea products, it was not a good defluoridation measure because of its low efficiency and an unavoidable loss of quality components. Blending could efficiently control the F level in final tea products, and it should be popularized in practice.