Study On The Heavy Metal Forms And Its Bioaccumulation In Nanjing Suburb Soils

Base on the analysis of the content and distribution of heavy metals and its forms in soil in Nanjing suburb, this paper compared the different accumulation proportions of heavy metal in vegetables, and then discussed the relationship between the heavy metal forms and the different parts of vegetables by the correlative and regression analysis. Simultaneously, the relationship between the heavy metal forms and pH and TOM were analyzed.The contents of different fractions (dissolved, exchangeable and bound to carbonate, bound to iron and manganese oxides, bound to organic and sulphidic matter, residue form) of heavy metals showed the residue form predominated for Pb, Cu, Zn, Cd, Cr. The sequence of different fractions of Pb was residue form (B4) >bound to iron and manganese oxides (B2) >bound to organic and sulphidic matter (B3) >dissolved, exchangeable and bound to carbonate (B1) . The sequence of different forms of Cu, Zn was B4>B3 >B2>B1．The sequence of different forms of Cd was B4>B2>B1>B3．The sequence of different forms of Cr was B4>B3>B1>B2．At the same time, the proportion of activity form (B1+B2+B3) in total content of five elements was quite different. The proportion of active Cd in total content was highes, and active Cr was lowest. As far as the correlative coefficients between the heavy metal forms were concerned, the B2 and B3 of Cd were belonged to intension variation. The variation coefficients of the rest heavy metal forms was 25%～75%, which accorded with moderate variance.The analysis of heavy metals in different parts of vegetables indicated that the nutritive element Zn and Cu which are necessary for vegetables accumulated in higher proportions, the cumulative percentages were more than 20%. But for Cd, the cumulative percentage in the leaf part has exceeded Zn and Cu. The cumulative percentages were lowest to Pb and Cr, all less than 4%. Pb was without exception comparatively low in two kind vegetables, a part of Pb in stem and leaf mainly originated from atmosphere, it is displayed that the Pb is comparatively difficult from other four metals. The accumulation sequence of Cd was eggplant-fruit vegetables> stem-leaf vegetables, and the absorbed Cd in vegetable were both high, which testified that Cd had high movement and activity. The accumulation sequence of Cr was stem-leaf vegetables>eggplant-fruit vegetables, and it was low in vegetable, which was explained that Cr is very difficult to move. The accumulation sequence of Cu and Zn was stem-leaf vegetables>eggplant-fruit vegetables, and they were both belong to medium level in vegetable. Simultaneously, the distribution of heavy metal in vegetables was different between different elements. As far as accumulative rate was concerned, the accumulative sequence of stem-leaf vegetables to Pb was leaf>stem>root, Cu was root>leaf>stem, Zn was root>leaf>stem, and Cd was leaf>stem>root, Cr was root>leaf>stem, the accumulative sequence of fruit vegetables to Pb was leaf>stem>root>fruit, Cu was root>fruit>leaf>stem, Zn was root>fruit>leaf>stem, and Cd was leaf>stem>root>fruit, Cr root>leaf>fruit>stem. For the accumulative rate, the sequence of the different heavy metals contents in two kind vegetables was totally Cd>Zn>Cu>Pb>Cr.The relationship between the content of heavy metal in each parts of vegetables and the content of the heavy metal forms in soil indicated that the content of Pb in root was significant positive correlative relation to its organic and sulphidic bound form in soil.The content of Cu in root and stem had no significant correlative relation to metal forms. The content of Zn in root had no significant correlative relation to metal forms. The content of Zn in stem was significant correlative relation to dissolved, exchangeable and bound to carbonate. The content of Cd in root was significant negative correlative relation to its organic and sulphidic bound form. The content of Cr in each part had no significant correlative relation to its forms. Anyway,the bioavailability of heavy metals in dissolved, exchangeable, bound to carbonate and organic and sulphidic forms were the most effective for vegetables in Nanjing suburb, and the pH and organic materials take a important role on bioaccumulation.