(1) Discussion on the critical value of human daily fluoride intake.
Fluorine is an indispensable trace element for human growth and development. The average fluorine content in human body is 37 ~ 70 mg/kg, and the total fluorine content in normal adults is about 2.6 g, which is the third trace element in human body, second only to silicon and iron. However, it does not mean that the more fluoride the human body ingests, the more beneficial it is to the human body. On the contrary, long-term excessive intake of fluoride will cause damage to hard tissues such as teeth and bones, causing endemic fluorosis. Therefore, as far as human health is concerned,
There are three ways for human body to ingest fluoride: drinking water, food and air. However, the fluoride content in the air is generally not high, and the existence of fluoride is often not monitored in normal air. Even in areas with serious fluorine pollution, the fluorine content in the air is only 0.0 1 ~ 0.02 mg/m3, but it is in a small range after all, so there are basically no reports of a large number of fluorine accumulation events caused by breathing natural air, which is why this paper only discusses the first two major events.
At present, the World Health Organization (WHO) stipulates that the suitable fluoride intake per capita is 2.5 ~ 4.0 mg/d, and the fluoride content in drinking water is generally 1.0mg/L, while in Europe it is 1.5mg/L (Chen et al.,1990; Sandeng, 1983). However, there is no strict standard for fluorine content in food at present. In some foreign countries, the per capita fluoride intake in the United States is 0.2 ~ 0.3 mg/d (excluding fluoride in drinking water), the fluoride content in drinking water is 0.6 ~ 1.7 mg/L, and the per capita fluoride intake in Russia is 0.6 ~ 1. 12 mg/d, The standard of fluoride content in drinking water is1.5 mg/l ... The per capita fluoride intake in Japan is 0.47 ~ 2.66 mg/d (including the per capita daily intake of green tea is 0.07~0.86mg), and the fluoride content in drinking water is 0.8 mg/L ... "Total fluoride intake" issued by China in 1996 The total fluoride intake per person in the two groups of people aged 8 ~ 15 and over 15 is 2.0 mg/d, the allowable fluoride intake per person aged 8 ~ 15 in coal-burning fluorosis areas is 2.0mg/d, and the allowable fluoride intake per person aged 8 ~ 15 in drinking water fluorosis areas is ... The limit of fluorine in China's Hygienic Standard for Drinking Water (GB 5749-2006) is 1.0mg/L, while the limit of fluorine in rice, flour, beans, vegetables and eggs is1.0×10-.
To sum up, the total fluoride intake of people in different countries and regions is different from the fluoride limit value of drinking water and food, which may be closely related to the natural geographical conditions, food structure and individual physique of each region. However, no matter which region, the per capita daily total fluoride intake is calculated according to the per capita drinking water and standard calorie value, and this value is compared with the per capita daily standard fluoride intake. Determine whether the study area belongs to the endemic fluorosis prone area, and divide the endemic fluorosis into four main types: drinking water type, food type, soot pollution type (caused by ingesting food and air contaminated by soot) and mixed type (drinking water-food type, soot-food type, etc.). ) according to the proportion and influence of fluoride in drinking water and food in the total fluoride intake.
(2) Discussion on various forms of fluorine in soil, water and food chain.
Fluorine is the ninth element in the periodic table of elements, belonging to the nonmetallic element with the strongest electronegativity and the most active chemical properties. Therefore, it can directly react with many chemical elements to form simple compounds, such as acidic salts with al, Fe and Cr, alkaline salts with alkali metals or alkaline earth metals such as Ca, Mg, Na and K, and various complexes or coordination ions with many other elements, such as AlF2+ under acidic conditions. Considering that this paper mainly studies the effects of different forms of fluorine related to bioavailability on human health in the surface environment, the discussion of different forms of fluorine in the surface environment is mainly carried out according to the fluorine migration path of soil-water-food chain.
1. biological effects of fluorine in soil
Soil is a kind of weathered rock, because many forms of fluoride are often adsorbed on the surface during weathering and migration, which may be simple anionic fluoride (such as NaF and CaF2) or complex fluoride (such as Na3AlF6 and Na2SiF6). Therefore, Dai and others believe that the total fluorine in soil should include soluble fluorine, colloid-adsorbed fluorine, insoluble fluorine salt and mineral residue, among which water-soluble fluorine (a kind of soluble fluorine) is of great significance for studying the relationship between human health, because only water-soluble fluorine can be absorbed by human body through drinking or first absorbed by plants and then transferred to human body to play its biological role. Chen et al. (1990) thought that fluorine with biological effects in soil basically exists in the form of colloid adsorbed ions (simple anions and complex complex ions) and molecules (mainly fluoride), that is, soluble fluorine, including water-soluble fluorine, acid-soluble fluorine and hydrochloric acid-soluble fluorine. Because fluorine is easy to form complexes with aluminum, silicon, iron, calcium, magnesium, boron and other elements, and some complexes are soluble, fluorine can migrate in the form of complexes, for example, it can form soluble compounds with Ca2+, and a considerable part of fluorine absorbed by plants in soil exists in the form of complex ions of al F2+(mccaffreytal). , 1993). Xie et al. (1999) classified the forms of fluorine in soil into five types: water soluble, exchangeable, iron-manganese oxide, organic bound and residual fixed, among which the first two types have higher biological effects on animals, plants and humans. Water-soluble fluorine mainly exists in the form of ions or complexes, such as F-,,,, and so on. The higher the content of water-soluble fluorine and fluorine in shallow groundwater, the higher the incidence of endemic fluorosis in this area. Exchangeable fluorine refers to fluoride anions adsorbed on exchangeable positive charges such as clay particles, organic particles and hydrated oxides by electrostatic attraction. Yang Junyao and others (2000) thought that fluorine in unsaturated soil can be roughly divided into three forms: soluble fluorine, adsorbed fluorine and fixed fluorine, of which the first two have activity and migration and transformation ability. Soluble fluoride refers to fluoride existing in unsaturated soil in the form of soluble salt (such as NaF). When dissolved in water, fluoride exists in the form of monovalent anion (F-), which is the most active form. Adsorption fluorine refers to fluorine ions or ion pairs existing on the surface of solid particles in vadose zone by ligand exchange adsorption and physical adsorption, and its activity is dual, which can be converted into free fluorine by desorption or into fixed fluorine by decomposition of old minerals and formation of new minerals, but the fixed fluorine has basically lost its activity. Abroad, Japanese scholar Hideyoshi Yamada et al. (1979) put forward a hypothesis of the existing state and behavior of soil soluble fluorine, that is, the pH value of soil and the amount of Ca2+ and Al3+ have the greatest influence on the existing form of soil soluble fluorine.
To sum up, studies at home and abroad show that the forms of fluorine with biological effects in soil are mainly divided into soluble forms and colloidal adsorption forms, while it is generally believed that insoluble fluorine in the form of minerals and amorphous deposits can not be absorbed by drinking water or plants, but can be transformed into different forms of fluorine under specific chemical conditions, and there is no absolutely untransferable fluorine form.
2. Discussion on biological effects of fluorine in groundwater.
No matter where and how fluorine enters the water body and becomes a hydrochemical component, it exists in water in the form of simple anion (F-), fluoride molecules and complex ions (such as complex cation MgF+ and complex anion), in which fluoride is divided into organic fluoride and inorganic fluoride, the former is absorbed by organisms in molecular form, and the latter includes soluble and insoluble. Soluble fluoride molecules such as NaF, HF, H2SiF6, Na2SiF6 and Na2PO3F can be absorbed rapidly and completely by the organism, while insoluble fluoride molecules such as CaF2, apatite and cryolite can not be absorbed completely. The coordination ions preferentially generated with fluoride ions in water are metal cations with inert gas electronic configuration, such as Li+, Na+, K+, Be2+, Mg2+, Ca2+, Sr2+, Al3+, Sc3+, La3+, Si4+, Ti4+, Zr4+, Th4+ and so on. Their coordination trend must have a certain pH value. Only in water with strong acidity (pH < 2) and fluorine concentration greater than 1mg/L can a stable complex be formed. The common stable complexes are F- complexes with Ca2+ and Mg2+, but at low fluorine concentration, pH