Abstract
Workers in primary aluminum smelter are exposed to fluoride from cryolite (Na3AlF6) used in the electrolysis process. Post-shift urinary fluoride is considered as an appropriate index for examination of fluoride exposure. The objective of the study was to investigate the exposure to fluoride in primary aluminum smelter in Žiar nad Hronom (Slovakia) during three consecutive two-year periods between 2012 and 2018. The relationship between fluoride exposure in the occupational environment, tobacco smoking, and pre- and post-shift urinary fluoride concentration was investigated in 76 male workers in the ages from 21 to 60 years. Workers were monitored by personal fluoride sampling equipment. Their urinary samples were collected prior to the start and at the end of an eight-hour shift. Fluoride content in urine samples was analyzed by potentiometric ion-selective electrode and expressed as weight ratio of fluoride content to creatinine. The Mean ± SD particulate fluoride concentration in occupational air was 0.966 ± 1.658 mg/m3 and gas-phase fluoride concentration was 0.327 ± 0.809 mg/m3. Mean urinary fluoride concentration of all workers was significantly higher (p < 0.001) after the eight-hour shift. Smokers tended to have a higher post-shift mean urinary fluoride concentration than non-smokers, but this difference was not statistically significant (p = 0.11). The difference between these two groups of workers was also not statistically significant (p = 0.62) before the shift. Therefore, according to results, smoking caused no statistically significant difference in urinary fluoride levels between the group of smokers and group of non-smokers in primary aluminum workers.
Highlights
Primary aluminum production is one of the most important industries in the world with a total global production of 5438 thousand metric tonnes [1]
Our findings are consistent with the assumption that during anode replacement the worker is temporarily exposed to the open environment of the steel container and despite the increased efficiency of the air conditioning, the highest rate of fluoride exposure occurs in this operation
The degree ofalthough correlation between occupational exposure to in groups of smokers and non-smokers, non-smokers had slightly higher levels fluoride and urinary fluoride levels was ascribed to person respiratory protection
Summary
Primary aluminum production is one of the most important industries in the world with a total global production of 5438 thousand metric tonnes [1]. The mechanism of the primary aluminum production is electrolytic reduction (Hall–Héroult process) of aluminum oxide–alumina (Al2 O3 ) dissolved in a molten fluoride electrolyte consisting of cryolite (Na3 AlF6 ) at a temperature of about 960 ◦ C. Electrolytic reduction is a continuous process inside steel container cells coated with carbon. It gives pure liquid aluminum metal at the negative carbon electrode (cathode) and carbon dioxide (CO2 ) at the positive carbon electrode (anode) [2]. The anode slowly reacts under intense heat, carbon dioxide, and other gaseous emissions such as polycyclic aromatic hydrocarbons (PAH) and hydrogen fluoride (HF). Most current aluminum smelters use pre-bake anode technologies and the older plants use the Søderberg process [2,3]
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