| Mercury is a highly toxic global pollutant,which can exist in a variety of forms in various environmental media,among which methyl mercury(Me Hg)is considered to be the most toxic form of mercury,and the consumption of aquatic products has been proved to be the main way of human methyl mercury exposure.However,recent studies have found that rice fields are hot spots of mercury methylation,and rice has a strong ability to enrich methyl mercury.Therefore,rice consumption is considered to be the main source of methyl mercury exposure among people in mercury polluted areas.Therefore,the methylation of mercury in the paddy system and the migration and accumulation of methylmercury into rice plants are of great concern.The application of organic materials(such as organic fertilizer and straw)is a common agronomic measure in rice cultivation,which can improve the nutritional conditions and physical and chemical properties of the soil,and is conducive to the growth of crops.However,organic matter also affects the environmental behavior of soil mercury to a large extent,and straw returning has been revealed to increase the ecological risk of methyl mercury in mining paddy fields by increasing the bioavailability of mercury and microbial activity.However,organic fertilizer is also a common organic material in the paddy field system,and its organic composition and decomposition degree are significantly different from straw.However,there are few reports on whether the application of organic fertilizer will affect the generation and enrichment of methyl mercury in the paddy field system.Therefore,this research adopts the potted experiment,comprehensive inspection pig manure(PM),chicken manure(CM)and rice straw(ST)after plowing,different rice growth period(green stage,tillering stage and filling stage and mature period)the change of soil mercury forms and the production of methyl mercury,and the different growth period of rice each part(root,stem and leaf,rice husk and rice)methyl mercury accumulation characteristics.The results showed that:1.The different components of soluble organic matter(DOM)of the organic material characteristics have bigger difference,the DOM of chicken manure have higher BIX index and its aromaticity is stronger,therefore has higher biological availability and environmental geochemical activity,while the DOM of pig manure and straw has larger molecular weight and stronger hydrophilicity,which leads to reduced bioavailability of mercury when combined with mercury.2.After organic materials were applied,soil mercury methylation was promoted in the regreening stage,and the promotion effect of CM > PM > ST treatment was in descending order,After that,due to the absorption of rice,the content of Me Hg decreased significantly,and there was no significant difference at the maturity stage.Different from the variation trend of organic materials,the content of methyl mercury in the soil of control treatment(CK)increased gradually from the greening stage to the grain-filling stage,and decreased significantly at the maturity stage.Since the change range of total mercury(THg)content in soil is small,the ratio of methyl mercury to total mercury(Me Hg/THg)is mainly affected by the change of soil methyl mercury content,so the change trend of Me Hg/THg ratio in soil is basically the same as the change trend of methyl mercury content.3.The contents of water-soluble mercury(Hg-wh)and acid-soluble mercury(Hgwh)in soil under CM treatment were the highest and the lowest under ST treatment,which were basically similar to those under CK treatment.The contents of ST treatment increased significantly at tillering stage,and the contents of CK treatment increased gradually during the whole growth cycle of rice.Methyl mercury content in rice roots and panicles was significantly correlated with soil Hg-wh content,and organically bound mercury(Hg-o)content was negatively correlated with soil and rice methyl mercury content.The proportion of strongly complex mercury(Hg-e)in all the treated soils was the highest,ranging from 50% to 75%,and the proportion of Hg-Wh was the lowest,less than 2%.4.The content of methyl mercury in roots was higher than that in stems and leaves at greening stage and tillering stage,and then decreased gradually.At the grain filling stage,the methyl mercury content in panicle of CM>CK>PM>ST treatment,and the methyl mercury content in rice of CM treatment was significantly higher than that of CK treatment(P < 0.05),while the methyl mercury content in PM and ST treatment was significantly lower than that of CK treatment(P < 0.05).5.The highest enrichment coefficient(BCF)was found in roots at the greening stage and tillering stage,and the BCF value > 10 was much higher than that in other parts,indicating that rice roots had a strong ability to enrich methyl mercury in soil at the early and middle stage,and CM treatment was higher than other treatments.After grain filling stage,methyl mercury of rice plant shifted to panicle,and BCF value of other parts began to decrease.BCF value of rice at maturity stage was much higher than that of other parts,BCF value of CM and ST treatment was much higher than that of PM and CK treatment.In conclusion,the selected organic materials(pig manure,chicken manure and rice straw)have great differences in the formation and migration of methyl mercury.Chicken manure can promote the formation of methyl mercury in soil and the absorption of rice plants.Pig manure can promote the formation of methyl mercury in soil to a certain extent,but it can inhibit the absorption of methyl mercury in rice.These two kinds of organic fertilizer is mainly due to the differences between two kinds of organic material DOM composition features and influence on the distribution of soil mercury forms have bigger difference,the straw on the whole,inhibits methylation of mercury from soil,which is different from the results of the study before,may be due to the study of soil mercury for the added exogenous mercury,its activity is higher than other research of mining area soil mercury,it also shows that distribution of soil mercury forms and different causes after the straw returned to soil mercury methylation has differences. |
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