| Studies have shown that mercury in soil enters the food chain under the action of plant enrichment and migration,and the mercury concentration keeps accumulating with the increase of trophic level in the food chain.The higher the mercury pollution concentration in soil,the higher the mercury content in the food chain,thus the higher the possibility of mercury methylation,which magnifies the harm of mercury to soil and plants to some extent.In order to reduce the possibility of mercury entering the food chain and ensure the safety of basic agricultural food crops,low-temperature pyrolysis remediation technology was selected to study the biological changes of residual mercury and selenium on residual mercury.Although low-temperature pyrolysis remediation technology has removed more than 88% of mercury in the soil,there are still residues of total mercury and methylmercury in the soil.The average value of total mercury and methylmercury in the soil is 56.34 mg/kg and 7.53 μg/kg,and the risk of mercury methylation still exists.In this paper,selenium was applied to the soil to study the changes of mercury and methylmercury content in reclaimed soil crops before and after remediation of high-concentration mercury contaminated soil by selenium,and the distribution and accumulation of mercury and methylmercury in different organs of different crops were studied.The changes of mercury and methylmercury content in crops after low-temperature pyrolysis remediation were analyzed,which provided some technical support for agricultural planting in high-concentration mercury contaminated soil and reduced the food safety risk of mercury contaminated agricultural products.The results show that:（1）The soil fertility after low-temperature pyrolysis can still meet the needs of agricultural planting.Soil total nitrogen decreased by 31%,alkali-hydrolyzable nitrogen decreased by 56.4%,available phosphorus content increased,available potassium decreased significantly,organic matter decreased from 23.13 g/kg to 13.78 g/kg,soil p H before and after remediation was 8.27 and 8.06,although the physical and chemical properties of soil changed,it could meet the needs of farmland cultivation,and the soil after low-temperature pyrolysis could still be reclaimed.（2）The remediation effect of low-temperature pyrolysis technology is remarkable,and mercury in soil can be separated and removed.The average concentration of mercury in the soil before remediation was488.74 mg / kg,and the average concentration of mercury in the soil after remediation was 56.34 mg / kg,and the mercury removal rate was88.47%.Although it is still higher than the control value of soil pollution risk of agricultural land（p H > 7.5,6.0 mg / kg）specified in the standard for pollution risk control of soil environmental quality of agricultural land（GB 15618-2018）,it reduces the harm of mercury to the food chain and the environment to a certain extent;The average contents of methylmercury in soil before and after pyrolysis were 25.36 μg/kg and7.53 μg/kg,respectively,and the methylmercury decreased by 70.30%.（3）The distribution of total mercury in various organs of rice was studied by low-temperature pyrolysis-selenium-added composite remediation technology.It was found that the antagonistic effects of different doses of selenium on selenium and mercury in different organs of rice were different: The mercury content of rice roots in pot experiment and experimental field before pyrolysis was the lowest when selenium concentration was 10 mg/kg,and the lowest mercury content was 36.43mg/kg and 28.45mg/kg respectively.In the experimental field experiment,before pyrolysis,when the concentration of selenium was 5 mg/kg,the content of mercury in rice grains was the lowest（0.037 mg/kg）,while that of methylmercury was the lowest（24.6 μg/kg）when the concentration of selenium was 10 mg/kg.The mercury content in rice grains after adding exogenous selenium with appropriate concentration basically meets the national safety value of rice（0.02 mg/kg）.（4）Selenium with appropriate concentration can reduce the residual mercury in the soil after engineering pyrolysis remediation and the mercury and methylmercury content in the edible parts of reclaimed crops;Pot experiment: When the selenium concentration is 1 mg/kg,the total mercury concentration in the edible leaves of Chinese cabbage after pyrolysis is the lowest（0.15 mg/kg）,and the total mercury content is reduced by 72.73%.After pyrolysis,the lowest concentration of methylmercury in Chinese cabbage leaves was 1.67 μg/kg,and the highest decreased by 1.06 μg/kg.In the experimental field experiment,when selenium concentration is 5 mg/kg after pyrolysis,the total mercury concentration in pakchoi leaves is the lowest of 0.22mg/kg.After pyrolysis,the content of methylmercury in Chinese cabbage leaves was the lowest 1.30μ g/kg.After pyrolysis,when the selenium concentration is 10 mg/kg,the total mercury content in rice grains is the lowest（0.022mg/kg）,which basically meets the national food standard of rice.（5）Through the detailed analysis of rice stems,it was found that mercury and methylmercury showed a vertical morphological migration and accumulation rule from the bottom to the top of the plant: near the rhizome > on the stem.It is proved that mercury in soil will migrate to fruits through the growth of plants,and the migration of mercury is in the process of transmission and attenuation in plants. |
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