Effects Of Straw Addition With Different Humic Degrees On Soil Mercury Methylation And Biological Enrichment

At present,China has entered a critical stage of soil heavy metal pollution control.The soil environmental safety of agricultural land and construction land has been effectively guaranteed,and the comprehensive control of soil environmental risks has become an urgent problem to be solved.In recent years,straw returning to the field has been vigorously promoted by the state as a kind of green utilization.However,recent studies have found that the return of fresh straw from mercury(Hg)mining areas promotes Hg methylation and plant enrichment,and increases the risk of human exposure to Hg.At the same time,although the studied straw modification methods have shown certain positive effects in the remediation of Hg-contaminated soil,there are still few straw modification methods that have been applied in the remediation of Hg-contaminated rice fields,the modification costs are high,the promotion is difficult,and there is still a lack of in-depth understanding of the mechanism and systematic risk assessment.Therefore,it is urgent to screen the straw returning method which is suitable for Hg mining area.This topic purport to straw from different sources and composting process as the breakthrough point,the humification degree changes in system study of different crops and the degree of humification straw returned after the impact on the soil of methyl mercury(Me Hg)and bioaccumulation,after preliminary proven straw as the input of soil organic matter in the regulatory mechanism of Hg methylation,provide scientific basis for the rational utilization of straw.In different crops straw as raw material,this paper first through the composting experiment,preliminary proven in the composting process straw humification degree and its structure change,and then through different kinds of straw DOM solution leaching by indoor simulation experiment,such as Fourier infrared spectrum,isothermal adsorption experiment,etc.,discusses the straw into the soil after the potential impact of the Hg migration transition,Finally,pot experiments were carried out to simulate the effects of straw on soil Me Hg and biological enrichment under the condition of falling dry and flooding,in order to preliminary explore the regulatory mechanism of straw with different humic degrees on soil Hg methylation and biological enrichment.The main results of this paper are as follows:1)In the process of different straw aerobic composting,the values of C/N and T,representing the degree of humification,decreased gradually with the passing of time,indicating that the degree of humification increased gradually and tended to a stable value in the later stage.For the straw with different degrees of humification,the structural composition of the straw is obviously different from that of the straw with different degrees of humification.2)The DOC of all the treatment groups showed a decreasing trend over time.Longitudinal comparison showed that the DOC content of the overlying water in the aerobic compost straw addition group decreased successively with the deepening of straw rot(C/N,T),while the anaerobic compost straw addition group showed no obvious pattern.Similar to the change of DOC content,DHg decreased with time(except for different proportion of rape straw addition group),and DHg of overburden water was significantly correlated with DOC in the early and middle periods(P<0.01).Under the drying condition,compared with other groups with different decaying degree and fresh straw addition,the high decaying degree straw addition group had a significant effect on the accumulation of Hg in soil Me Hg and leaves of Ipomoea aquatica Forssk.Under the condition of flooding,we found that the input of anaerobic fermentation straw could significantly reduce the soil Hg methylation and the accumulation of Hg in Ipomoea aquatica Forssk,but the application of aerobic composting straw to the soil could significantly increase the accumulation of Hg and Me Hg in the leaves of Ipomoea aquatica Forssk.In practical agricultural production,we suggest that straw with high decolorization degree should be returned to the field under the condition of drying to reduce the risk of soil Me Hg exposure.Under the condition of flooding,straw can be used for anaerobic fermentation.But in general,under the condition of flooding,the utilization of straw has a greater risk.