On Grain Gradation Distribution & Availability Features Of The Soil Lead Of Anxi Tea Garden In Fujian Province

Tea serves as an important beverage in China and beyond, but the excess lead in tea leaves had been a hotspot issue for society once. A large number of studies show that the main source of lead in tea leaves is soil, whose lead content will dominate that in tea leaves; and the existing form of heavy metal elements in soil determines the bio-availability and ecological effect therein. Therefore, the relationship between the existing form and availability of soil lead and the lead content in tea leaves has become a research focus within the circles.Taking the main production area for Tieguanyin Tea in Anxi of Fujian Province as the research area, this thesis has measured the content of elements like lead in the surface soil, sub-surface soil and tea leaves of 56 tea gardens, and divided 27 samples of selected surface soil and sub-surface soil into 5 grain gradations with the use of ultrasonic vibrating screen, with a view to further studying the distribution rule of soil lead grain gradation and the content of 4 extractions.Studies demonstrate that the average content of soil lead in Anxi is approximately two times higher than the background value of soil lead in China, and that the soil content in the surface and sub-surface varies little. The grain gradations of soil lead are distributed unevenly, with a tendency of accumulation in the soil of fine gradations. The results of four extraction methods show that the quantity order of soil lead extracted from the surface soil is complexant extraction>acid extraction>salt extraction > water extraction; meanwhile, the size order of soil lead extracted from the sub-surface soil is acid extraction>complexant extraction>salt extraction>water extraction, with the available lead contents extracted by complexant and acid close to and exceeding those extracted by salt and water. Except for the lead extracted by water, the quantities of lead extracted by salt, acid and complaxant increase as the grain gradation of soil decreases. The total amount of lead in soil is positively correlated with the lead content in soil, based on which a relational model of tealeave—soil lead content can be established. The lead content in tea leaves is more relevant to the available lead content in soil than the total amount of lead in soil.Therefore, the available lead content in soil can better reflect the ecological risks in soil lead. Through comparisons, 0.1mol/L diluted hydrochloric acid combined with mixed complexant solution(0.02mol/L EDTA + 0.5mol/L HOAc + 0.5mol/L NH4OAc) can offer the best extraction effects. A multiple linear regression equation of the lead content in tea leaves and the soil physiochemical properties is set up.Results show that soil physiochemical properties like p H value, cosmid composition,Corg and CEC exert certain but limited influence upon the lead content in tea leaves,and that the soil lead content plays a decisive role in determining the lead content in tea leaves. This research result provides the foundation for setting up the methods of assessing the soil availability of Anxi Tea Garden and predicting the impact of soil lead pollution upon the safety as well as quality of tea leaves.