Reclamation Feasibility Of High Mercury-contaminated Soil Repaired By Low-temperature Pyrolysis Technology

Many studies has demonstrated that the soil mercury can enter into the food chain through terrestrial plants,particularly in high levels of mercury-contaminated soil.In order to control mercury into the food chain and ensure the safety of basic farmland planting,low-temperature pyrolysis technology was selected to repair of high levels of mercury-contaminated soil(?100 mg·kg-1)after comparing various soil remediation technologies.So far,this technology is an innovation methods which not only guaranteed the basic physical and chemical properties of soil unchanged,but also more than 70% of the mercury was removed.And the technology was recommended by Environmental Industry Association from Ministry of Environmental Protection;However,it still remained 20%~30% of the soil mercury.It was still unknown whether the residual mercury was a threat to crop safety.In this study,the field planting experiment was conducted to investigate the feasibility about reclamation of high mercury-contaminated soil after repair by low-temperature pyrolysis technology.The results showed that:(1)After the treatment,the organic-bound and residual fractions of Hg were reduced by 73.17% and 57.80% respectively,and the low-temperature pyrolysis technology had less effect on soil fertility.Besides,there was a significant improvement in plant height,and economic yield was increased 2~3 times.The leaf chlorophyll content of crops were increased significantly by 87.66% and 87.66% in celery cabbage and wheat,respectively.At the same time,the leaf proline,POD and CAT of crops had responded on the improvement of mercury environment in soil,including that the leaf proline content and CAT activity were respectively reduced by53.29% and 42.90% in celery cabbage,and the leaf POD activity reduced by 47.73%in radish.(2)In the soil before or after repair,mercury content in the edible parts of potato and corn were lower than the Hg tolerance limit for food in China(GB 2762-2012),while mercury content in the edible parts of leaf vegetables weren't significantly difference and were not up to standard.Besides,mercury content in the edible parts of other crops were significantly decreased after the remediation treatment,including mercury content of wheat and rice were still not up to standard after reduced by42.91% and 53.79%,and mercury content of radish was close to the standard after reduced by 84.05%.It is the most serious to accumulation of MeHg in rice,the MeHg content of rice was 14.521 ?g·kg-1 before repair and 6.478 ?g·kg-1 after repair.At the same time,the MeHg contents in cabbage,corn,rice and wheat were significantly reduced by 38.34%,52.29%,36.31% and 52.29% respectively after the remediation treatment.(3)The root of radish was regarded as its main edible part,which its mercury content was about 5%~40% of other crop roots.Mercury distribution in the radish plant were in the following order: leaf > stem > root,and mercury content of leaf and stem were significantly decreased after the remediation treatment.Besides,mercury distribution in other crops were mainly in the following order: root > leaf > stem,and the roots were suffered serious persecution from soil Hg.Furthermore,after the remediation treatment,mercury content of all roots were significantly decreased 2~5times and other organs weren't significantly difference.(4)The study about the influence of reclamation on the stability of mercury in soil after repair had found that there weren't significantly difference among the total content of all forms of mercury in soil after adding exogenous organic matter to the soil.However,the residual fraction mercury was constantly transformed to other forms of mercury,especially to the the organic-bound,thus the potential available Hg content in soil increased significantly.The activity of Hg was markedly improved in the soil(experimental ratio 4:1:4)including the content of effective Hg increased about 5 times in soil before repair and increased by 34.76% in soil after repair.However,under the condition of other experimental ratio,the content of Hg wasn't significantly difference in soil before repair,while the content of Hg in soil afterrepair significantly decreased from 51.56% to 70.70%.In conclusion,crops growth status was markedly improved,economic yields of crops were significantly increased and mercury contents in edible parts of crops were significantly decreased after reclamation of the repair soil.Also,the repair soil was suggested to cultivate tuber,high strain and root vegetable crops.However,the residual fraction mercury in soil will potentially threaten the food chain and the ecological environment when external conditions change.