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The chemical fraction of elements has been widely employed in the study of soil chemistry, plant nutrition, and environmental science. For this study we conducted a comprehensive survey on trace elements (Hg, As, Cd, Cr, Pb, Cu, Zn, Mn, Se, Mo, Co, etc.) from the rock tea gardens in Wuyishan, southeastern China. Our results demonstrate that: 1) The contents of heavy metals such as Hg, Pb, As, and Cd in the soil meet the environmental requirements for the growing area of tea (NY/T 853-2004), and the soil in the studied area contains sufficient Mn, Mo, and Se for tea plant growth, with a slight lack of Co. 2) The exchangeable fraction is determined to be the dominant fraction of Cd, which originates from an anthropogenic source and possesses high bioavailability from elemental speciation analysis. 3) The heavy metal contents in all the tea leaf samples are within the safe range, and the average values of the element enrichment coefficients of the tea leaves decrease in the order: Mn > Cu > Hg > Zn > Se > Cd > Mo > Co > As > Pb > Cr.
The Changjiang Delta Region is a rapidly urbanizing area in China. But this area still reveals different anthropogenic activities and urbanization levels. River sediments from urban, suburban, and rural areas were studied to characterize potentially harmful elements (PHEs) and their ecological risks. Chemical compositions of sediments were analyzed, which revealed pronounced differences in three areas. Al₂O₃, Fe₂O₃, CaO, and MgO were elevated in the urban sediments. Sediments from the rural area showed high organic matter. CaO and TOC of sediments fluctuated significantly in the suburban area. They are associated with the local geological provenance and sediment circumstance. The enrichments of PHEs in sediments of urban rivers were prevalent, among which Cd and As were prominent. Concentrations of PHEs in the suburban area fluctuated significantly. Lead and Cu were obviously enriched in this area. Rural sediments had relatively low concentrations of PHEs, which were also stable in the regional distribution, although As showed a slight enrichment. Based on RI values from Hakanson, the urban sediments showed moderate to considerable ecological risk. And the suburban sediments were in moderate ecological risk, except some high-risk samples. The majority of rural sediments revealed low ecological risk. Of these hazardous elements, Cd, Hg, and Pb contribute the largest proportion of the total ecological risk. It is evident that the urbanization level influences the distributions and contamination grades of PHEs for river sediments of the Changjiang Delta Region.
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