Effects Of Exogenous Sulfur And Iron Addition On Soil Mercury Absorption By Rice

Mercury is a non-essential and globally toxic pollutant.As mercury mining and industrial development,mercury pollution has become an important environmental issue today.Most of Chinese mercury mining areas are located in the southwestern karst area.The ecological environment of the karst area is fragile.Once it is contaminated by mercury,it will have a serious impact on the health of the ecosystem.The Wanshan mercury mining area in Guizhou is extremely representative.Due to mercury mining and smelting activities,it has caused serious mercury pollution to local ecosystems,especially in rice fields.Studies have shown that rice consumption is the main methylmercury exposure pathway for the local populations in the Wanshan mercury mining area.Therefore,it is extremely urgent to carry out the mercury pollution restoration of paddy soil in the Wanshan mercury mining area.In this paper,sulfur and iron were separately added to the soils of two different mercury sources（Gouxi soil and Wukeng soil）to study the different concentrations of sulfur,iron and both.The effects of mercury accumulation in stems and leaves,as well as changes in mercury in root soils,determine the appropriate sulfur and iron concentrations that hinder rice from absorbing soil mercury,and initially explore its mechanism of influence.Concluded as follow:（1）The addition of sulfur at a certain concentration can reduce the total mercury content in the rice grown in the Gouxi soil and the Wukeng soil;among them,the sulfur addition has the most obvious effect on the reduction of total mercury content in the soil of the Gouxi soil,and the reduction effect can reach 63%.The addition of sulfur can significantly reduce the content of methylmercury in paddy rice grown in two soils,and the maximum decrease in methylmercury content in both soil groups is in the S4gradient（S concentration is 500 mg/kg）,which is 97%and 78%,respectively.In addition,the addition of sulfur can significantly reduce the ratio of methylmercury to total mercury in rice.Combined with the economic factors for the application of sulfur to rice production,the S3 gradient（S concentration of 300 mg/kg）is a suitable sulfur addition concentration.The addition of sulfur also reduced the total mercury content in the roots of the two soil groups,with the maximum reductions of 64%and 63%,respectively.It also reduced the total mercury content in the stems and leaves of the Gouxi soil,but increased total mercury content in stems and leaves of rice in the Wukeng groups.The addition of sulfur can also significantly reduce the methylmercury content in the roots and stems of rice both in the two soil groups and the methylmercury content in the rice leaves of the Gouxi soil groups,but increase the methylmercury content in the leaves of the Wukeng soil group.The addition of sulfur had no effect on the total mercury content of rice roots.The addition of sulfur increased the available mercury content in the roots of the Gouxi group（R=0.82,P<0.05）.The addition of sulfur reduced the root soil of the two soil groups.The methyl mercury content was reduced by a maximum of 63%and 52%,respectively.（2）Adding a certain concentration of iron can reduce the total mercury content of rice grown in the soil of the Gouxi soil.In addition to the Fe2 gradient,the total mercury content of the rice decreased with the increase of iron addition,the maximum decline was 45%;The methylmercury content was lower than that of the blank group（CK group）,and the Fe6 gradient had the largest reduction of 59%.In the Wukeng soil group,except for the Fe5 group,the total mercury content in the iron-added group was higher than that in the blank group（CK group）;except for the Fe4 gradient,which the methylmercury content in the rice was lower than that in the blank group,and the maximum reduction was 45%.The ratio of methylmercury to total mercury in the two soils was lower than that in the blank group,and it showed a trend of decreasing with the increase of the concentration of iron added and then decreasing.Combined with the economic factors of iron addition for rice production,the Fe2 gradient（Fe concentration of 250 mg/kg）is a suitable iron addition concentration.The total mercury content in the roots of the two soils grown in the iron-added group was lower than that in the corresponding roots of the CK group;the total mercury content in the stems of the iron-added soil was lower than that in the stems of the CK group;The total mercury content in the stems of rice grown in Wukeng soil was higher than that in the CK group.In addition,for the Wukeng soil group,the addition of iron increased the total mercury content of rice leaves.The content of methylmercury in the roots and stems of rice planted with iron added to the soil was lower than that of the roots and stems of the CK group,and the degree of reduction was large,with the maximum reductions of 86%,85%and 95%,respectively.After iron addition,there was no effect on the total mercury content of rice root soils in the two soil groups,and the available mercury content was higher than that in the CK group,and the soil available mercury content was positively correlated with the iron addition concentration.（Gouxi groups:R²=0.6,P<0.05;Wukeng groups:R²=0.82,P<0.01）.In addition,the content of methylmercury in the roots of rice in the iron-added group was lower than that in the CK group.（3）When the sulfur and iron was added at the same time,the total mercury content of the B treatment（300 mg/kg FeSO₄?7H₂O）group of the Gouxi soil group was lower than that of the CK group,which was 11%;and the total mercury content of the A（250mg/kg FeSO₄?7H₂O）and B groups was high.In the CK group.When the sulfur and iron was added at the same time,the total mercury content of the rice in the A,B and C（250mg/kg Na₂SO₄+300mg/kg Fe（OH）₃）groups was lower than that in the CK group,and the maximum reduction was 27%.And the methyl mercury content of rice in CK,A and B groups showed a decreasing trend with the increase of ferrous sulfate.The methylmercury content of rice in the A,B and C treatment groups of the two soil groups was also significantly lower than that of the CK group,and the maximum reduction was 72%（Gouxi soil）69%（Wukeng soil）.The ratio of methylmercury to total mercury in the three groups of A,B and C in the two soil groups was also lower than that in the CK group.The content of total mercury and methylmercury in rice roots of A,B and C treatment groups were lower than that of CK group when fertilized iron was added simultaneously.The total mercury content of rice stems in A,B and C groups is higher than the CK group,and the total mercury content in the stems of CK,A and B groups tends to increase with the increase of ferrous sulfate content;however,the methyl mercury content in the stems of the three groups is lower than that of the CK group.The content of methylmercury in the stems of CK,A and B groups showed a tendency to decrease with the increase of ferrous sulfate content.When sulfur and iron was added at the same time,it had no effect on the total mercury content of rice root soil,while the effective mercury content in root CK group soil was higher than that of CK group.The content of methylmercury in the roots of A,B and C soils in the soil was higher than that in the CK group.The methyl mercury content in the A and C groups of the Wukeng soil was lower than that in the corresponding CK group,only the B group.The base mercury content is higher than that of the CK group.