MERCURY, FLUORIDE AND ACID RELEASE FROM UNDERGROUND COAL FIRES IN WUDA, INNER MONGOLIA OF CHINA

The Hetao Plain in Inner Mongolia is a traditional agricultural and densely populated area bordered by the Yellow River in the center of north of China. Since 1980s, endemic fluorosis and arseniasis along with environment deterioration started to emerge in this area, which has never been linked to coal. However, with evidence of temporal and spatial coupling between the endemics and coal, this study focuses on the toxic species released from typical underground coal fire in Wuda, as a preliminary work for the better understanding of the cause of chronic endemic diseases in the Hetao Plain.

108 days of field work and 2 years of lab work were implemented. The Field study mainly focused on in-situ gas analysis, while lab tests measured field samples including coal, gangue, topsoil and plants for mercury, fluoride, sulfate, and acid. The conclusions are: 1.The coal fire releases not only greenhouse gas but also toxic species such as mercury, fluoride and acids; 2.The total amount released may be underestimated, for the releases could come from smoldering or pre-smoldering seams; 3.Contamination of toxic elements from coal fire to the local atmosphere and topsoil were observed; 4.Bioaccumulation of toxic elements was detected in plants in urban and agriculture areas in the vicinity.

A type of acidic upheaved spongy lump of topsoil with mercury >20,000 ng/g, fluoride >5,000 μg/g and sulfate > 200 mg/g was found in Wuda, the toxic elements in this material can easily migrate into shallow groundwater downstream through natural precipitation and surface runoff. Since underground coal fires have lasted over 50 years in the Wuda area, this rises a question then: would continuous underground coal fire activity in high altitude (>1,000 m) be responsible for the high fluorine and arsenic content in shallow groundwater of the downstream plain and subsequent prevalence of endemic fluorosis and arseniasis? Our preliminary study has not yet answered this question, which still calls for further investigations.