## 3 Results and Discussion
The results of correlation analysis between fluoride exposure in the occupational environment (i.e., by inhalation) and corresponding urinary fluoride levels in monitored participants are presented in Table 3 and Figure 3. \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Group**} & \multirow{2}{*}{**Statistical** **Indicator**} & **Particulate Fluoride** & **Gas-Phase Fluoride** & **Pre-Shift Urinary** & **Post-Shift Urinary** \\  & & **Concentration** **(HF) Concentration** & **Fluoride [mg/g** & **Fluoride [mg/g** \\  & & **[mg/m\({}^{3}\)]** & **[mg/m\({}^{3}\)]** & **Creatinine]** & **Creatinine]** \\ \hline \multirow{3}{*}{All participants} & Mean \(\pm\) SD & 0.966 \(\pm\) 1.658 & 0.327 \(\pm\) 0.809 & 0.455 \(\pm\) 0.353 & 0.957 \(\pm\) 0.686 \\  & Median & 0.285 & 0.112 & 0.385 & 0.880 \\  & Range & 0.009–10.290 & 0–6.210 & 0.100–2.420 & 0.180–3.730 \\ \hline \multirow{3}{*}{Smokers} & \multicolumn{4}{c}{\(n=74\)1} & \(n=74\)1  & \(n=76\) & \(n=76\) \\  & Mean \(\pm\) SD & 0.992 \(\pm\) 1.427 & 0.438 \(\pm\) 1.143 & 0.441 \(\pm\) 0.338 & 1.050 \(\pm\) 0.708 \\  & Median & 0.370 & 0.104 & 0.360 & 0.890 \\  & Range & 0.009–5.910 & 0.009–6.210 & 0.120–2.090 & 0.280–3.730 \\ \hline \multirow{3}{*}{Non-smokers} & \multicolumn{4}{c}{\(n=33\)} & \(n=33\) & \(n=35\) & \(n=35\) \\  & Mean \(\pm\) SD & 0.985 \(\pm\) 1.879 & 0.245 \(\pm\) 0.368 & 0.469 \(\pm\) 0.379 & 0.859 \(\pm\) 0.677 \\ \cline{1-1}  & Median & 0.240 & 0.140 & 0.430 & 0.770 \\ \cline{1-1}  & Range & 0.009–10.290 & 0–1.720 & 0.100–2.420 & 0.180–3.370 \\ \hline \end{tabular}
\end{table} 
Table 2: Mean fluoride concentration, standard deviation, and maximum and minimum values in occupational air and in urine samples. Figure 1: Comparison of the determined concentrations of fluoride in the occupational environment during the research period. Figure 2: Comparison of urinary fluoride concentrations during the research period. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Parameter** \\ \hline \multicolumn{2}{c}{**Post-Shift Urinary Fluoride [mg/g creatinine]**} \\ \hline Particulate fluoride concentration [mg/m\({}^{3}\)] & 0.039 (\(p=0.74\)) \\ Gas-phase fluoride concentration [mg/m\({}^{3}\)] & 0.005 (\(p=0.96\)) \\ Total fluoride concentration [mg/m\({}^{3}\)] & 0.029 (\(p=0.81\)) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Relationship between fluoride concentrations in the occupational environment and post-shift urinary levels (Pearson correlation test result coefficient R, and \(p\) value). No significant correlation between fluoride concentrations in the occupational environment and in urine corrected to creatinine was found in the present study. [PERSON] et al. [PERSON] et al. (2018) reported an association between fluoride concentration of 2.5 mg/m\({}^{3}\) (OSHA PEL) in an occupational environment and post-shift urinary fluoride concentration of 6.4 mg/g creatinine, and a peak value of 7.4 mg/g creatinine, respectively. As mentioned above, our results showed OSHA PEL exceeded in 10 workers. In contrast with [PERSON] et al. [PERSON] et al. (2018), post-shift urinary fluoride levels in this workers reached only 0.2-1.2 mg/g creatinine and peak post-shift urinary fluoride 3.73 mg/g creatinine corresponds to 0.16 mg/m\({}^{3}\) of total fluoride concentration in the occupational environment. More than 50% exceeded samples above OSHA PEL were associated with anode handling working position (i.e., anode replacement, cell operator). Post-shift urinary fluoride levels in these workers proved that personal respiratory protection used during high exposure periods while working over open cells was effective. A similar conclusion was reached by [PERSON] et al. [PERSON] et al. (2018) who ascribed the lack of relationship between particulate fluoride exposure and the post-shift urinary fluoride by the effective use of respiratory protection in carbon setters (anode replacement). [PERSON] et al.