Evaluation of acidity in late Permian outcrop coals and its association with endemic fluorosis in the border area of Yunnan, Guizhou, and Sichuan in China

Abstract

The junction area of Yunnan, Guizhou, and Sichuan provinces is the heaviest coal-burning endemic fluorosis zones in China. To better understand the pathogenicity of endemic fluorosis in this area, 87 coal samples from the late Permian outcrop or semi-outcrop coal seams were collected in eight counties of the junction area of Yunnan, Guizhou, and Sichuan provinces. The total fluorine and sulfate content, etc. in the coal was determined using combustion-hydrolysis/fluoride-ion-selective electrode method and ion chromatography, respectively. The results show that the total fluorine concentrations in the samples ranged from 44 to 382 µg g, with an average of 127 µg g. The average pH of the coals is 5.03 (1.86-8.62), and the sulfate content varied from 249 to 64,706 µg g (average 7127 µg g). In addition, the coals were medium- and high-sulfur coals, with sulfur mass fraction ranging from 0.08 to 13.41%. By heating the outcrop coals, HF release from the coal was verified quantitatively without exception, while simulated combustion directly confirmed the release of sulfuric acid (HSO). The acid in coal may be in the form of acidic sulfate ([Formula: see text]/HSO) because of a positive relationship between pH and [Formula: see text] in the acidic coal. The possible reaction mechanism would be that a chemical reaction between the acid (HSO or [Formula: see text]) and fluorine in the coal occurred, thereby producing hydrogen fluoride (HF), which would be the chemical form of fluorine released from coal under relatively mild conditions. The unique chemical and physical property of HF may bring new insight into the pathogenic mechanism of coal-burning endemic fluorosis. The phenomenon of coal-burning fluorosis is not limited to the study area, but is common in southwest China and elsewhere. Further investigation is needed to determine whether other endemic fluorosis areas are affected by this phenomenon.

Chemical Characteristics and Cytotoxicity to GC-2spd(ts) Cells of PM2.5 in Nanjing Jiangbei New Area from 2015 to 2019

“…In contrast, Na + and Cl - in PM 2.5 mainly came from the ocean in 2017, 2018 and 2019. In addition, F - was emitted from fossil fuel combustion [ 40 ], K + was mainly from biomass combustion [ 41 ], Ca 2+ was mostly influenced by construction dust [ 42 ] and both the latter two sources contributed to Mg 2+ [ 43 ].…”

Weathering of Clay-Pyrite of Coal-Bearing Formation in the Endemic Fluorosis Area of Southwest China

“…The clay sample acidity test method was based on a previous study [30]. The electrometer was calibrated using three types of standard pH buffer solutions (at pH values of 4.01, 7.00, and 9.02; Mettler Toledo) prior to measurement.…”

“…This study had provided new evidence to further explain the cause and mechanism behind the once-endemic fluorosis in the local area, which results from the coupling of natural and human activities. Previous studies showed that heating of outcrop coal also released HF [8], and further studies were conducted to determine the contribution of fluorine released from clay during coal burning and the fluorine species during transfer among the coal, food and the human body. For example, it is unknown if fluoride is the only form of fluorine in smoke dust aerosol, or if the digestive system is the sole pathway for human intake of fluorine in endemic fluorosis.…”

“…Heavy endemic fluorosis affects northeastern Yunnan, northwestern Guizhou, and southern Sichuan provinces, which contain villages covering large areas andaccounting for 73% of all fluorosis villages in the coal-burning fluorosis areas of China. More than 70% of these fluorosis patients live in western Guizhou and eastern Yunnan provinces [8][9][10][11].…”

Spatial distribution and risk assessment of fluorine and cadmium in rice, corn, and wheat grains in most karst regions of Guizhou province, China

“…The F background value (929 mg/kg) of soils in Guizhou is higher than that of other areas in China (478 mg/kg) and other nations (20–700 mg/kg) ( 3 ). Surveys showed that Guizhou is a high geological background area of F, which may lead to excessive F concentration in plants ( 4 ). Furthermore, Guizhou has the phenomenon of coal combustion, which can be hazardous to human health.…”