Mechanism of fluorine releasing in coal and clay and its effects on environment in Zhaotong, Yunnan Province.

Objective To study the real releasing of fluorine (F) and its effects on environmen in coalburning-borne fluorosis areas. Methods The coal, clay, briquette, cinder, fresh corn and roasted corn samples from 24 households were collected systematically in Zhaotong of City, Yunnan Province, and the F concentration in all samples was measured using the combustion hydrolysis/fluoride- ion selective electrode method, and the released amount and rate of F in briquette was calculated, and the relation between the released amount of F from briquette and the increase of F in roasted corn was analyzed. Results The F concentration of clay ranged from 266.4 to 2 536.7 mg/kg with a median of 1 087.1 mg/kg; the F concentration of briquette ranged from 115.9 to 635.0 mg/kg with a median of 308.8 mg/kg. The released amount of F in briquette ranged from 63.5 to 432.2 mg/kg with a median of 248.2 mg/kg. The releasing rate of F in briquette ranged from 30.3% to 91.5% with a average of 73.8%. The F concentration in fresh corn ranged from 0.43 to 2.00 mg/kg with a median of 1.31 mg/kg; the F concentration in roasted corn ranged from 2.21 to 44.88 mg/kg with a median of 10.49 mg/kg. The increased amount of roasted corn ranged 0.90 to 44.46 mg/kg. There was a significant correlation between the emission amounts of F from briquette and the F concentration in binder clay (r = 0.714, P 0.05). Conclusion The clay is an important source of F pollution, and the F increase in roasted corn is not only determined by the released amount of F in briquette, but also by several factors. Key words: Coal; Fluorine; Fluorosis, dental