anchor: The concentration of the metals, Al, As, Cr, Co, Cu, Fe, Pb, Ni, Zn, expressed as total metal, should not exceed 1 eg/L each, and Cd, Hg, and Ag, expressed as total metal, should not exceed 100 ng/L each.
positive: Metal is concentrated but should not exceed 100 ng/L.
negative: Metal should not exceed 5 ng/L.