Regional Fluorosis caused by coal-burning pollution (“coal-burning fluorosis” for short) is a kind of cumulative chronic poisoning suffered by people who live in the area with high content of coal-burning fluorine pollution for a long period of time and take in excessive fluorine through water, air, food, and some other media. There have been many studies about this in China, however, none of them is comprehensive enough to illustrate this issue. This article hence conducts a systematic and comprehensive investigation on the coal type fluorosis in children’s dental fluorosis, the residents’ usage of stoves, food fluorine, and urinary fluoride in Chongqing, China. In order to evaluate the effect of preventive and curing measures against coal-burning fluorosis in our City, the authors conducted an investigation on the current prevalence conditions of coal-burning fluorosis in our city from June 2013 to June 2015, whose results are analyzed as follows:
2. Research Object and Method
Children aged between 8 and 12 and the households were chosen from May to August 2015 from the 661 villages that are historically prevalent with fluorosis in the 100 townships in 13 districts of Chongqing City.
a) For Children’s dental fluorosis:
The Dean’s Method  was applied to examine the dental fluorosis conditions of all the locally-born children aged between 8 and 12, and calculate the dental fluorosis morbidity rate, dental fluorosis index, fluorotic teeth defect rate.
b) For Investigation in households:
Investigations were carried out on the utilization conditions of modified stoves and the drying conditions of food maize and hot pepper in households in the endemic area; calculations were made on the stoves modified rate, qualified rate of modified stoves, and correct utilization rate of qualified modified stoves, as well as the correctly drying rate of food maize and hot pepper.
c) For children’s urinary fluorosis:
Children aged between 8 and 12 from over 3 endemic villages in every endemic county were sampled for test of their urinary fluorosis conditions, with the children selected from each village divided into 5 age groups and each age group assigned with 5 boys and 5 girls, i.e. 50 samples altogether from each village. And tests were conducted as per the National Standard (WS/T30-1996) to calculate the geometric mean and standard deviation for obtaining the urinary fluorine content of the sampled children.
d) For maize fluorine content:
10 households from over 3 endemic villages of every county were sampled to test the fluorine content in the maize according to the National Standard (GB/T5009-2003) by calculating the median and standard deviation.
e) For Fluorine content in hot pepper:
10 households from over three endemic villages of every endemic county for testing the food pepper in accordance with the National Standard (GB/T5009-2003) by calculating the median and standard deviation.
3) Statistical analysis was conducted adopting SPSS17.0 software to calculate the morbidity rate of fluorotic teeth and other indicators.
This research has been approved by department of health and family planning commission in Chongqing. We conducted this investigation according to the ethic guideline about the medical system study for people.
1) Basic conditions
The investigations covered 661 endemic villages from 100 townships of 13 districts, where there are 399,314 households with a population of 1,425,705, of which children aged between 8 and 12 are numbered to 91,070 and the examined children are amounted to 66,162, making an examination rate of 72.65%.
2) Children’s dental fluorosis conditions
Of the 66,162 examined children, 7464 were diagnosed with dental fluorosis, the detectable rate being 11.28%, the dental fluorosis index being 0.14, and the defect rate being 0.29%. Of the villages surveyed, 426 have a dental fluorosis rate of ≤15%, and 642 have a dental fluorosis rate of ≤15% (as detailed in Table 1).
4. Household Investigation
4.1. Stove Modification
Of the 399,314 households surveyed, 399,314 modified their stoves, reaching a modified rate of 100%; 394,613 modified their stoves up to the qualification level, a qualified modification rate of 98.82%; and 392,441 of the qualified households utilized the modified stoves correctly, representing a correct utilization rate of 99.45%, benefiting a population of 1,425,705 (as detailed in Table 2).
4.2. Drying Conditions of Food Maize and Hot Pepper
Of the 661 villages surveyed from 100 townships of 13 districts, 344 have food
Table 1. Dental fluorosis examination result for children aged between 8 and 12 in the endemic counties of Chongqing City prevalent with coal-burning fluorosis in Chongqing City.
Table 2. Modified stoves’ examination result for endemic counties prevalent with coal-burning fluorosis in Chongqing City.
maize, and 99.88% of them correctly dried up the maize, 342 have a correct drying rate of ≥90%, making up 99.42% of the villages with food maize, and 341 have a drying rate of ≥95%, comprising 99.13% of the villages consuming maize. Of the villages surveyed, 657 consume edible hot pepper and 99.75% of them correctly dried the hot pepper; 655 have a correct drying rate of ≥90%, amounting to 99.70% of the consuming villages, 655 have a correct drying of ≥95%, amounting to 99.70% of all the consuming villages (as detailed in Table 3).
5. Children’s Urinary Fluorine Content
The survey altogether examined 2471 urine samples from children of 52 endemic villages of 38 townships, and the result shows that the urinary fluorine’s geometric mean is 0.42 mg/L, standard deviation is 0.31, the minimum value is 0.02 mg/L, and the maximum value is 2.550.42 mg/L (as detailed in Table 4).
6. Food Maize’s Fluorine Content
The investigation surveyed 679 food maize samples from 67 endemic villages of 46 townships, and obtained a median of 0.64 mg/kg, standard deviation of 1.73 mg/kg, minimum value of 0.02 mg/kg, and maximum value of 28.09 mg/kg (as detailed in Table 5).
7. Hot Pepper’s Fluorine Content
The investigation surveyed totally 679 samples of food hot pepper from 67 en-
Table 3. Drying conditions self-inspection result for maize and hot pepper consumed by people in the endemic counties prevalent with coal-burning fluorosis in Chongqing City.
Table 4. Children’s urinary fluorine inspection result for the coal-burning endemic counties of Chongqing City.
Table 5. Maize fluorine content inspection result for the households in endemic counties prevalent with coal-burning fluorosis in Chongqing City.
Table 6. Hot pepper fluorine inspection result for households in the endemic counties prevalent with coal-burning fluorosis in Chongqing City.
demic villages of 46 townships, and obtained a median of 1.60 mg/kg, standard deviation of 61.82 mg/kg, minimum value of 0.11 mg/kg, and maximum value of 1292.20 mg/kg (as detailed in Table 6).
Coal-burning type fluorosis is an endemic disease severely impacting the people’s health in China, and it is a geochemical disease prevalent in China only. In addition to intake amount of pathogenic factors, the prevalence condition of a disease is also closely related with the natural environment, economic conditions, productivity and life habit   . The pathogen of coal-burning type fluorosis in Chongqing City was brought in mainly by intake of food fluorine such as maize and hot pepper, etc.  in the 80s of the last century, and gradually by intake of air fluorine  , and the total intake of fluorine through such way has seen a distinct drop  .
This survey shows that the dental fluorosis prevalence rate for children aged between 8% and 12% is 11.28%, dental fluorosis index is 0.14, and dental defect rate is 0.29, meaning that such prevalence belongs to a kind of negative prevalence. There are 19 villages whose dental prevalence rate is higher than 30%, taking up 2.87%, respectively distributing in Wushan (14), Wuxi (3), and Qianjiang (1), indicating an obvious decrease of children’s dental fluorosis prevalence in our City. The investigations in the households on how they modified their stoves and how they dried up the food maize and hot pepper show that, from 2004 to 2012, with the payment transferred by central government from to local governments for prevention and treatment of endemic fluorosis for the good of public health, 282,755 households completed modifying stoves as required; and up to the end of 2015, 390,000 households of our City had completed modifying their stoves, with stoves modified rate, qualified rate of modified stoves, and correct rate for utilizing qualifiedly modified stoves respectively were 100%, 99.82%, and 99.45%. The survey also found that drying rate of food maize and hot pepper were respectively 99.88% and 99.75%. Such results showed that the prevention and curing measures have been effectively implemented and achieved sound effect. The results are consistent with other similar research results in China   .
Children’s urinary fluorine is one of the important indicators for assessing fluorine content level in the human body, and in this survey, the geometric mean for children’s urinary fluorine is 0.42 ± 0.31 mg/L. Of the 661 villages surveyed, 344 villages consume maize for food, accounting for 52.04% of the total villages surveyed, and maize fluorine content median is 0.64 ± 1.73 mg/kg; and 657 villages consume hot pepper for food, holding 99.39%, and the median for hot pepper fluorine content is 1.60 ± 61.82 mg/kg. From these three key indicators for fluorine intake, it can be perceived that maize consuming villages are decreasing in number, and drying up maize correctly, and hot pepper consuming villages are large in number, and can basically dry up hot pepper in the correct way, which further verifies an evident drop of coal-burning type fluorosis prevalence in our City.
Investigation results demonstrate that there is clear drop of coal-burning type fluorosis prevalence in Chongqing City. the prevention and curing measures, such as adopting biomass gasifiers and fluorine-reducing smoke-recycling stoves, etc. have been effectively implemented and have produced distinct effects, certain achievements have been gained in terms of management of modified stoves in the post-modification period, and that a preliminary mechanism for a long-term prevention and curing of fluorosis has been established. In the future, measures will be taken in the light of the conditions of our City, and instructions will be given according to the types and categories of different endemic areas, i.e. in the endemic villages where prevention measures haven’t been taken, efforts should be strengthened to implement the stove-modification measures, enhance health education, and improve hygiene behaviors; in the endemic villages where prevention measures have been adopted, work should be done for maintenance and management of modified stoves, and for reinforcing health education and intensifying good hygiene behaviors, so that the standards for eliminating fluorosis can be met; and in the endemic villages where fluorosis prevalence has been controlled, people’s awareness in utilizing and purchasing modified stoves should be improved, and efforts should be made to establish such a long-term mechanism “to work on the basis of marketization, under government instruction and departmental cooperation, and with people’s voluntary and positive involvement” for prevention of fluorosis prevalence, and thus maintain the status of elimination in the prevalence of fluorosis    .