The high median F− concentration (supplementary material
Table S2) was observed in NFecas (2069.89 mg/kg), which may be
due to aluminum casting units sampled under this category. To
remove magnesium, molten aluminum is treated with fluoride in
aluminum casting units [34]. Fecas showed the very high concentration
of CN− (median value of 430.38 mg/kg) due to the usage of
CN− bath for case hardening [33].