Spatial And Temporal Distribution Of Mercury In Soil-vegetable System And Its Biological Availability In The Manasi River Basin

The rapid development of industry and agriculture has caused a variety of pollution in the soil environment.Mercury pollution has attracted much attention due to its hidden nature,irreversibility,and acute toxicity,which have caused serious damage to the environment and humans.Human activities such as coal-fired power generation,chlor-alkali production,and agricultural production are the most important sources of mercury pollution.The Manasi River Basin is not only a base of thermal power generation and chlor-alkali production but also a major grain-producing region in Xinjiang.It is important that ensuring soil quality and safety for agricultural products and human health.This study selected Manasi River Basin,Xinjiang as the study area,studied the spatial and temporal distribution characteristics of mercury pollution in the study soil-vegetable system,assessed the level of environmental ecology and human health risk in the study area,and used pot experiments to study the distribution and migration of soil-vegetable mercury.The main conclusions are as follows:The top soil in the study area is alkaline with low organic matter content.The average mercury content in the surface soil in spring,summer and autumn was 7.47,12.29 and 9.59 times background value in Xinjiang,respectively,but neither exceeded the National standards???.The level of mercury contamination in summer was higher 64.56%and 28.22%than spring and autumn,respectively.In spring,there is a clear trend of proliferation.The spatial distribution of summer and autumn is relatively concentrated in the chemical industry.The main diffusion distance is 1-2 km around the chemical park.Forming the situation where an industry park as the center of the spread around in spring,summer and autumn.The differences of spatial and temporal distribution in spring,summer and autumn are closely related to the basic properties and the mineral composition of the soil.Meteorological factors are the main external factors that cause differences.Wind direction and speed affect the direction and distance of mercury diffusion.Precipitation mainly affects vertical migration of mercury in surface soil.Precipitation and ozone concentration mainly affect the diffusion and sedimentation of atmospheric mercury into surface soil.The content of mercury in vegetables in summer was significantly higher than in winter.The mercury content in the soil and atmospheric deposition were the main reasons for the significant differences.The mercury content of the six green leafy vegetables at different sampling sites showed regularity.The average order of their contents was:Asteraceae>Umbelliferae>Cruciferae>Chenopodiaceae>Convolvulaceae>Liliaceae.Mercury pollution of the surface soil in different seasons did not have a significant impact on the environmental quality of urban areas and agricultural areas overall.The level of soil mercury pollution in spring is from clean to moderate pollution,and it is generally clean to severe pollution in summer and autumn.The three seasons are mainly moderate pollution.Shihezi industrial park,Manasi coal-fired power plant and its surrounding soil mercury show heavy pollution or serious pollution,and the potential ecological risk is high.Urban and farmland areas show moderate to mild severity pollution,and are moderately potential of ecological risk.Southern mountainous and the desert show a clean to light pollution,with low potential ecological risks.Human health risk of mercury in soil and vegetables for children and adults were acceptable,which increase with the increase of mercury content.Overall,children are higher than adults,and in vegetables are higher in summer than winter.The total mercury in soil had no obvious effect on the migration of vegetables,and only had a significant effect on the accumulation of roots in vegetables.Compositae,cruciferous,and umbelliferae vegetables showed preliminary strong accumulation.Speciation of mercury in soil plays an important role in the growth of vegetables.CaCO₃-Hg,Fe₂O₃-Hg and MnO₂-Hg show low potential availability in alkaline soils.Humic acids-Hg contributes to the accumulation of mercury in the roots of vegetables but no significant effect on the migration of vegetables.During the growth of vegetables,the proportion of available mercury and residual mercury significantly changed,as well as the proportion of available mercury decreased from 19.48%to 6.01%and gradually converted to stable residual mercury,but the matrix-bound mercury did not change significantly.The mercury content in the roots and edible parts of vegetables was significantly related to the available mercury,and the soil mercury was Soil properties and vegetable growth are interconverted.Soil in the growing stage of vegetables not only plays a role in the main source of mercury,but also has the effect of fixing and reducing the toxicity of mercury in the soil to vegetables,so that the vegetables can grow normally within a certain range of pollution.