Guilin Soil - Crop System Characteristics And Influencing Factors Of Mercury Speciation Studies

Mercury pollution is one of the serious environment issues in the world. It is endangering soil-crop systems and harms health of human being through food chains. Investigations on mercury pollution in soil is up to now focused on estimation about it and on mercury speciation, however, less has been done on biological availability of mercury and on factors influencing transference and transformation of mercury in soil-crop systems. Reports on factors influencing mercury speciation in soil-rhizosphere systems and on systematically similar studies mentioned above for Guilin area have not been found in the literature.With field survey, pot experiment and rhizo-box experiment, investigation was made mainly on speciation of mercury in soil-crop and its influencing factors in Guilin. The investigating scope includes five main city zones and one suburb-county area about 100 km~2. Eight vegetable bases were selected as main investigating regions. Conclusions can be drawn as follows.(1) The results of spot investigation show that the concentration of mercury in soil of Guilin distributes as follows in sequence: the southeast of Yushan Bridge > the northeast of Qixing Park > the northwest of Xishan Park > Zhimapu > the north of Chuanshan >Pengjialing > the northeast of Yushan Bridge >the south of Chuanshan, and the concentration of mercury in soil is related to different regions, decreasing gradually away from the urban district. In relevant kailyard soil, the mercury concentration in vegetables is similar to that in soil.The concentration of mercury in vegetables of Guilin is as follows in sequence: medlar >Chinese cabbage > cabbage> celery >laocai > lettuce, while leaf-vegetable > melon and fruit. Having large biomass, the leaf vegetables over-ground absorb mercury mostly from soil and atmosphere; while having long growth circle, the plants of melon and fruit present high concentration in their under-ground parts. Therefore, concentration of mercury in leaf vegetables is as follows in sequence: leaf > root > stem; but concentration in melon and fruit: root >stem and leaf > fruit.(2) Based on analysis of mercury speciation in soil of the eight main vegetable bases, concentration of different mercury species in Guilin soil is as follows in sequence: residue-bound>humic acids-bound (HAs-Hg) > organic substance-bound which is hard to be oxidized and degraded>organic substance-bound which is easy to be oxidized and degraded > carbonate-bound and Fe-Mn oxide-bound > water soluble > exchangeable Hg species.