Tea Plantation–Induced Activation of Soil Heavy Metals

Abstract

The accumulation of heavy metals in tea leaves is of concern because of its impact on tea quality. This study characterized long‐term changes of soil properties and heavy‐metal fractions in tea gardens and their effect on the uptake of metals from soils by the plants. Soil and tea leaf samples were collected from five plantations with a history of 2–70 years in Jinghua, Zhejiang Province, southeast China. The six chemical fractions (water‐soluble, exchangeable, carbonate‐bound, organic‐matterbound, oxide‐bound, and residual forms) of cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), manganese (Mn), lead (Pb), and zinc (Zn) in the soils were characterized. Dissolved organic‐matter accumulation in the soils and effects of low‐molecular‐weight organic acids on solubility of soil heavy metals were also tested. Long‐term tea plantation use resulted in accumulation of dissolved organic matter, decrease of soil pH, and elevation of water‐soluble and exchangeable metal fractions, thereby increasing metal contents in leaves. The influence was more significant when soil pH was less than 4.4. The results indicated that both acidification and accumulation of dissolved organic matter induced by tea plantations were also important causes of increased accumulation of the metals in the tea leaves. This was particularly true for the soils polluted with low concentration of heavy metals, because availability of the metals in these soils was mainly controlled by pH and dissolved organic matter.