Study On The Law Of Migration And Transformation Of Soil Fluoride And The Improvement Of Calcium On Soil Fluoride Pollution In Kuitun Area,Xinjiang

Fluoride is widely found in nature,and a small amount of ingestion can help to prevent dental caries and prevent osteoporosis.Excessive intake can cause harm,causing dental fluorosis and skeletal fluorosis.High-fluorine irrigation water in the Kuitun area of Xinjiang has been receiving much attention.Because of the rich fluorine ore in the Kuitun River Basin,it provides a rich source of fluorine for local soil and groundwater.This study will systematically analyze the distribution of fluorine in soil,water and plants in Kuitun area;simulate high fluoride water irrigation in Xinjiang,and study the law of migration and transformation of fluorine in water-soil-plant system;The saline-alkali soil in Xinjiang was simulated to study the adsorption and desorption of soil fluoride under salt stress.The effects of calcium on soil fluoride pollution improvement were studied by pot experiment.Combined with mathematical model,soil fluoride pollution and health risk assessment were carried out.The main findings are as follows:（1）Collect soil,water and plant samples from Kuitun area to study the distribution of fluorine pollution in Kuitun area.The southwestern part of Kuitun city belongs to the industrial and commercial area,the total fluorine content is high,the northwestern part and the southeast part belong to the agricultural area,the total fluorine content is lower than the national standard value,and the soil water soluble fluorine content in urban and mission areas is higher than the national standard;The fluorine content of tap water is within the normal drinking range;the average fluorine content of surface water is 0.618 mg/L,which is lower than the standard of irrigation water in GB 5084-2005（F^-≤2.0 mg/L）,and the pH is alkaline;the average fluoride content in well water is 3.977 mg/L.,exceeding the quality standard of groundwater in GB/T 14848-93（F^-≤1.0 mg/L）,the pH is alkaline.The variation of fluoride content in plants in the mission area is 4.37-25.00 mg/kg,which is higher than the standard of environmental vegetable pollution（GB18406.1-2001,F^-≤1.0 mg/kg）.（2）Simulate the local high-fluorine water irrigation,and choose the green vegetables with strong metabolism:pakchoi,leaf lettuce,and water spinach for pot experiment.Before and after planting,total fluorine（TF）and residual fluorine（Res-F）in soil decreased,while water-soluble fluorine（Ws-F）,exchangeable fluorine（Ex-F）,and organic bound fluorine（Or-F）in soil increased,In the different systems,the soil fluoride was redistributed in order to achieve equilibrium;the Ws-F and Ex-F in the soil increased with the increaseing of fluoride content in the irrigation water;The change of the biomass showed that the low fluoride concentration promoted the growth of plants,and the high fluoride concentration inhibited the growth of plants;the fluorine content in different parts of the plant showed the following trend:root>stem>leaf;the enrichment factor（BCF）of the three plants was investigated,the ability to enrich fluorine from large to small is:pakchoi,spinach,and leaf lettuce;the transfer coefficient（TF）of plants to fluorine is less than 1,and the transfer ability from root to stem and leaf is:leaf lettuce>water spinach>pakchoi.Fluorine-contaminated irrigation water can significantly increase the total fluorine and available fluorine content in the soil,under low fluoride concentration,plants can quickly absorb the available fluorine from the soil and transfer to stems and leaves,with the increase of fluorine concentration in irrigation water,fluorine will gradually deposit on the roots.The fluoride content of irrigation water in local residential areas is 2.7-6.2 mg/L.If long-term irrigation,plant growth will be affected.（3）Study the effect of calcium on soil fluorine pollution improvement.After treatment with three kinds of fluoride-reducing agents CaO,Ca（NO₃）2 and CaSO₃,the pH of CaO soil increased,and the pH of CaSO₃group increased slightly,The pH of Ca（NO₃）₂ group soil decreased gradually;the change of Ws-F in the soil was compared with that before the defluoridation,the Ws-F in the soil showed a downward trend;after two months of equilibrium,two kinds of fluorine-rich ability plants were selected,alfalfa and ryegrass were harvested for two months,all plants showed no signs of toxicity in appearance.The biomass changes were evaluated.The plant biomass of the calcium oxide group decreased,and the biomass of calcium nitrate and calcium sulfite group did not change much;The soils in the roots of the plants were collected,and the total fluoride and other state of fluoride contents in the soil and the fluoride content in the plants were analyzed.The contents of TF and Ws-F in the soil decreased,and the fluoride content in the edible parts of the plants decreased.Soil fluorine pollution and food-borne fluorine pollution have been improved.（4）Studying the static adsorption and desorption characteristics of fluoride in salinized soil,the results show that the adsorption capacity of salinized soil for fluorine is greater than that of non-salted soil,but the degree of salinization has little effect on the adsorption of fluorine;The desorption of fluorine in salinized soils is different,and the desorption of salinized soil is greater than that of non-salted soil.Using the Freundlich equation,Langmuir equation and isothermal linear adsorption equation to fit the soil fluorine adsorption characteristics,it is found that the Freundlich equation has the better fitting effect,while the Langmuir equation and the isothermal linear adsorption equation have the second fitting effect.（5）The soil fluorine pollution was evaluated by the single factor pollution index method,the Nemero pollution index method and the ground accumulation pollution index method.It was found that Ws-F was used to evaluate the soil as moderate pollution;and T-F was used to evaluate the soil as mildly contaminated.The magnitude of the hazard quotient average found under three different exposure pathways is:the oral intake of soil pathway hazard quotient（HQois）>inhaled air soil particulate pathway hazard quotient（HQpis）>skin contact soil pathway hazard quotient（HQdcs）.It is indicated that oral intake is the most important route of exposure.