Heavy metal contamination of soils and tea plants in the eastern Black Sea region, NE Turkey

Abstract

The study area covers two geologically different regions which have intensively been carpeted by tea plants in the eastern Black Sea. The rocks exposed in the region contain considerable amount of trace metals due to Upper Cretaceous massive sulfide formations and tertiary epithermal mineralizations. Tea plants that grow in soils derived from such mineralized rocks contain different concentrations of Cu, Pb, Zn, Fe, Cd, P, Al, Na, K, and S. The content ratios of most of the analyzed elements except Al are higher in basaltic and sedimentary rocks. To describe the transfer of metals from soil to tea leaf, the Freundlich-type model (log c plant = ac soil + log b) is used. The metal concentrations in leaves of tea plant in the studied soils are ranked as Zn > Cu > Pb > Al > Cd > Fe. The capacity of the plant to affect the metal accumulation decreased as follows: Fe > Cd > Pb > Cu > Zn > Al. Negative correlations were found between pH and availability of Cu, Pb, Zn, Mn, and Al elements by the tea plant. Experimental applications indicated that tea plant leaves growing on soils with high metal contents show some signs of toxicity. In soils where, particularly, ammonium sulfate fertilizer is used, metal uptake by the tea plant was found to be significantly higher as a result of extremely acidic character of the soil.