“…For heavy metals, the maximum contaminant limit for Pb, Cu, Hg, Cd, Se, Cr, and As in drinking water is 15, 1300, 2, 5, 50, 100, and 100 μg/L, respectively . The permissible level of benzo[a]pyrene, one of the most carcinogenic polycyclic aromatic hydrocarbons (PAHs), in drinking water and various type of foods is <0.2 and 1–10 μg/L, respectively . Due to matrix effects, it is of utmost importance to analyze unknown or known species at these trace levels.…”