Fluorosilicic acid contains
Metal content of fluorosilicic acid and sodium fluoride “varies with batch, and all HFS samples contained arsenic (4.9–56.0 ppm) or arsenic in addition to lead (10.3 ppm). Two NaF samples contained barium (13.3–18.0 ppm) instead. All HFS (212–415 ppm) and NaF (3312–3630 ppm) additives contained a surprising amount of aluminum.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4090869/
