Formation Mechanism And Human Health Influence Of Fluorine And Iodine Of Groundwater In Wei River Basin

Wei River is a tributary of the Yellow River, and the economic conditions of Wei Riverbasin are relatively developed in northwest of China, which have an important strategicposition in the national economy. However, with the rapid economic development in recentyears, urban population growth and water demand increasing, the contradiction of watersupply and demand is exacerbated. Due to the impact of natural and human activities, thereare some high fluoride, low fluoride, high iodine, low iodine and other poor quality water.Drinking these kinds of poor quality water have caused the majority local people sufferingfrom fluorosis, goiter and other endemic diseases in different degrees, which seriouslyendangers the health of local people and restricts the development of the national economy.Therefore, studying on the formation mechanism of fluorine and iodine in Wei Riverwatershed groundwater and the health effects has great practical significance to theimprovement of water quality for prevention and control of endemic diseases.This article relies on―The research on the ecological geochemical environment mapcompilation and drinking water safety of typical local ward in Wei River basin‖, which is thesurvey project of China Geological Survey Bureau. This paper takes Wei River watershed asstudy area, groundwater as study object and hydrogeochemistry as theoretical guidance inorder to reveal the source, distribution and differentiation mechanism of fluorine and iodine ingroundwater, and it also analyzes the fluorine and iodine existing ecological geochemicalenvironment and its effect of human health. The main results are summarized as following:(1) According to the division principle of groundwater system, the Wei River basin isdivided into the following five secondary groundwater systems. Namely, Longxi loess plateausubsystem, Longdong loess plateau subsystem, Shanbei loess plateau subsystem, GuanzhongBasin subsystem and Qinling Mountains subsystem. Overall, the Longxi loess plateau andQinling Mountains subsystems belong to recharge area of groundwater and Longdong andShanbei loess plateau subsystems are runoff area. Nevertheless, Guanzhong Basin subsystembelongs to discharge area of groundwater in Wei River basin.(2) Chemical types of groundwater in the study area mainly are HCO3-Ca and HCO3-Na,but there are also distributed HCO3·SO4-Na, HCO3·SO4·Cl-Na, SO4·Cl-Na, SO4·Cl·HCO3-Naand Cl·SO4-Na types water at the northern and central parts of the study area. The fresh water,which TDS is less than1g/L, is mainly distribute in most parts of the Wei River watershedin study area. The weak salt water, which TDS is between1g/L and3g/L, is mainly distributein the upper reaches of Malian River and Luo River, the Loess Tableland at the north of Wei River and east of Jing River in Guanzhong Basin and most areas of the alluvial plain. The saltwater is mainly distribute in the upper reaches of Huanjiang and Pucheng city of GuanzhongBasin, which TDS is between3g/L and10g/L. Whereas, TDS is bigger than10g/L, the strongsalt water, is mainly distribute in Dangmu town of Pucheng city.(3) The formation of the groundwater chemical composition in study area is mainlyaffected by dissolution of fluorite, gypsum and aluminum silicates, precipitation ofcarbonates(including calcite and dolomite) and cation exchange. As well as, small part of thechemical composition of groundwater is affected by evaporation.(4) According to the relationship between rF-/rCa2+ratio and the incidence of fluorosis,combined with fluorine content of groundwater, the morbidity of fluorosis is researched instudy area. When ratio is less than0.25, there is no fluorine poisoning disease occurrence, andthese areas mainly distribute in Shanbei loess plateau and Qinling Mountains. When ratio isbetween0.25to1.25and the concentration of fluoride ion is greater than1.5mg/L, theincidence of fluorosis is generally less than5%, mainly in Gangu and Qin’an of Tianshui cityin Longxi loess plateau, Pengyang of Ningxia city in Longdong loess plateau, Qianxian andLiquan of Xianyang and Fuping and Heyang of Weinan in Guanzhong Basin. When ratio isbetween1.25to2.0and the concentration of fluoride ion is greater than3.6mg/L, theincidence of fluorosis is from50%to70%, mainly in Chaoyi of Dali. When ratio is greaterthan2.0, the incidence of fluorosis is as high as70%, mainly in Anren and Liangyi of Dali.According to theoretical study above, when the concentration of fluoride ion is greater than1.5mg/L, there is fluorine poisoning disease occurrence and the incidence is generally lessthan5%. The threshold of the fluoride ion concentration(1.5mg/L) is different from thenational drinking water standards(1.0mg/L), but this threshold is the same as drinking waterstandards of the World Health Organization(1.5mg/L).(5) It is observed the occurrence of thyroid disorders substantially follow the distributionof the iodine content of water with parabolic relations. Iodine in water also has two sides onhuman health. Iodine deficiency conducts lots of diseases as well as the high iodine does inthe study site.WeiHe river basin upstream, near LiuPan mountain watershed and QinLingmountain front range is the groundwater recharge area which Iodine deficiency goiter’spotential incidence is5%to50%. While high iodine goiter occurs mainly in the dischargearea of groundwater it is about5%to100%of fluctuating potential incidence in PuCheng,DaLi and GuanZhong basin area.(6) High fluoride groundwater in the study area has two different formation mechanism.The first reason is the relationship between fluoride concentration and water-rock interaction in various aquifers with different geologic settings. Fluorite (CaF2) has generally beenconsidered a dominant source of groundwater fluoride, especially in Gansu,Huanjiang-MaLianhe upstream and Liquan of Guanzhong Basin, Xianyang area, respectively41.5%and62.5%. The discharge area of groundwater near Guanzhong Basin, Pucheng, andDali area of low-lying land show high fluorine values, it is evident that the evaporation is themajor contribution with57%.(7) Weathering of heavy minerals and active water circulation condition control the levelof iodine in the iodine deficiency area. Iodine suitable areas I-content is controlled by watercirculation condition compared with the positive control of groundwater. As far as iodineaccumulation area, the dominant factors are the evaporation of shallow groundwater, thebiodegradation of organic matter and the HCO3-and I-competitive adsorption.(8) This paper, based on the study area’s hydrogeochemical action, Chemicalcomposition of water, migration, differentiation and water chemical partitioning and guidedby niche theory and Bertrand Law, selects5typical profiles for structuring multipleecological geochemical coupling model selection of geology, hydrogeology,hydrogeochemical and ecological environment conditions. The low level of fluorine andiodine may be a reflection of the short time of the mineral dissolution reactions. Thedecreased fluorine and iodine could also be contributed from the high hydraulic gradient andfast groundwater velocity. Generally, these areas are located in groundwater recharge andrunoff region which belongs to the leaching and migration hydrogeochemical zone with easilyleading to the occurrence of Iodine deficiency disorders and dental caries. Fluorine and iodinesuitable areas are located in the groundwater runoff zone where the time of the mineraldissolution reactions is enough and the type belongs to the hydrogeochemical zone. Theconcentration of fluorine and iodine in the water are not beyond the human tolerance. Theredoes not have endemic diseases caused by abundance or deficiency of element. The high levelof fluorine and iodine may be a reflection of the strong mineral dissolution reactions and poorwater cycle. Fluorine disease and high iodine goiter could also be contributed from theexceeded fluorine and iodine.