## 3 Results and Discussion  
Table 2 shows the descriptive statistics for all study participants (for each study participant's data, see Appendix A), group of smokers and non-smokers including measured data of air samples and urinary fluoride samples. Among the monitored work positions in Table 1 there were no statistically significant differences (\(p>0.05\)) for measured fluoride concentrations (particulate and gas-phase fluoride) in the occupational air. Within the total fluoride exposure, workers are the most exposed to the particulate fluoride emissions. The highest total (particulate + gas phase) fluoride concentration (12.120 mg/m\({}^{3}\)) was registered in anode replacement work position. 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. By contrast, the lowest concentration (0.018 mg/m\({}^{3}\)) was found for the crane operator who is relatively isolated from direct exposure in the crane cabin. A similar conclusion was reached by [PERSON] and [PERSON] [22] who investigated 41 workers in an aluminum plant in Sweden during an eight-hour work shift; the mean total fluoride exposure in this study was 0.91 mg/m\({}^{3}\), of which 34% was HF. For comparison, [PERSON] et al. [9] found mean particulate fluoride and gas-phase fluoride (HF) concentrations were 4.1 and 0.7 mg/m\({}^{3}\) when they evaluated the relationship between particulate fluoride exposure and urinary excretion in an aluminum smelter. Contrary to determined distribution of particulate and gas-phase fluoride in the occupational environment of investigated potroom, the Risk assessment report [4] concluded that the average fluoride emission of a primary aluminum smelter within the EU consists of 53% HF and 47% particulate fluoride. This may be explained due to the composition of study participants. The majority of workers were exposed to emissions during anode replacement in cells, including the particulates during crust cleaning of the anode cavity before installing new anodes. Gas-phase fluoride is formed in electrolysis process directly in the cell and it is emitted especially during anode replacement process; however, particulates are formed from handling by application of cryolite powder in the molten bath mixture and when crust is disrupted. Crust is a solid matter transformed from anode covering material by heat [23]. The Kruskal-Wallis test (K-W test) showed that there was no statistically significant difference (\(p=0.57\)) in particulate fluoride concentrations in the monitored years of the research. However, gas-phase concentrations were statistically significantly different (\(p=0.003\)). As can be seen in Figure 1, this was due to increased gas-phase fluoride concentrations in 2014 (an approximately five times higher mean value compared to other years). Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of fluorides (as F) at a value of 2.5 mg/m\({}^{3}\) (as time-weighted average) was exceeded (2.67-10.29) in 10 workers (see Appendix A) [24]. Compared to the general population, inhalation of fluoride present in ambient air does not contribute more than 0.01 mg per day to the total fluoride intake [25]. Since 1996, long-term average annual concentrations of fluorides in ambient air are <1 ug/m\({}^{3}\) in the district of Ziar had Hronom [12, 26]. Figure 2 shows a comparison of mean \(\pm\) SE urinary fluoride concentrations during the research period. No statistically significant difference (\(p>0.05\)) was found for either pre- or post-shift urinary fluoride over the monitored years. The most effective way to examine fluoride exposure provides the relation between the concentration in the air and the quantities excreted in the urine at the end of the shift [27].