Studies Of Transformation And Distribution Of Mercury In Soil- B. Chinensis Var. Oleifera System With Acid Rain

In order to find the distribution of total mercury (T-Hg) in soil-vegetable (B. chinensis var. oleifera) system in Guilin, the mercury content of soil and vegetable in the nine vegetable fields in Guilin city and outskirts was analyzed. The influence of soil T-Hg content and acidity and Hg content of acid rain on the distribution and migration of Hg in soil-vegetable (B. chinensis var. oleifera) system was studied by pot experiment. The conclusions were showed as follow:1. The mean value of T-Hg in soil in the nine vegetable fields was 0.099-0.546 mg/kg. The mean values of soil T-Hg in some vegetable fields were found higher than the value of Environmental Quality Standard for Soils-GB15618-1995 (Hg≤0.3 mg/kg). The closer the distance to the city center is, the higher the content of soil T-Hg in the nine vegetable fields was.2. The forms of mercury in the vegetable soil from high content to low content were the crystal lattice (residue) form(X7), the combined humic acid form(X4), the bio-refractory organic form(X6), the easily biodegradable organic form (X5), the carbonate and Fe/Mn oxide form (X3), the soluble form (X1), the exchangeable form (X2).3. The mean value of T-Hg in B. chinensis var. oleifera in the vegetable fields was 0.046-0.132 mg/kg (dry sample). The T-Hg distributing rule of B. chinensis var. oleifera is similar to that of soil in the vegetable fields. The closer the distance to the city center is, the higher the content of T-Hg in B. chinensis var. oleifera was.4. After harvest, the contents of soil mercury in the soluble form (X1), the exchangeable form (X2) and the carbonate and Fe/Mn oxide form (X3) in the potting soil were lower than that before planting, and the contents of soil mercury in the combined humic acid form(X4), the easily biodegradable organic form (X5) and the crystal lattice (residue) form(X7) in the potting soil were higher than that before planting.5. The mercury contents in different organs of B. chinensis var. oleifera increased with the increase of T-Hg in potting soil. The order of biological concentration factor (BCF) is root > leaf > stem. The mercury in soil mainly accumulate in root of B. chinensis var. oleifera.6. Under the treatment with acid rain with 50ng/L T-Hg, the distributing rule of mercury in different parts of B. chinensis var. oleifera is that: leaf > root > stem. The decrease of acid rain pH restrained mercury accumulation in leaf and stem of B. chinensis var. oleifera.7. Under the treatment with pH3.5 acid rain, the distributing rule of mercury in different parts of B. chinensis var. oleifera is that: leaf > root > stem. The contents of T-Hg in steam and leaf increased with the increase of mercury content in acid rain.8. The methyl mercury (Me-Hg) in soil increased with the increase of T-Hg in soil, and the percentage of Me-Hg to T-Hg was 0.0035% - 0.0095% in potting soil. The Me-Hg in root and leaf of B. chinensis var. oleifera increased with the increase of T-Hg in soil, and the percentage of Me-Hg to T-Hg was 0.0079% - 1.61% in B. chinensis var. oleifera.9. The distributing rule of mercury in subcellular structure of field B. chinensis var. oleifera is that: cell wall > organelle > vacuole. In pot experiment, the mercury in different parts of B. chinensis var. oleifera mainly accumulated in cell wall. In different treatment, the distributing rule of mercury in organelle and vacuole is different in different parts of B. chinensis var. oleifera.