Also consistent with equilibrium solubility predictions, a fraction of aluminum in 0.45 µm filtrate was colloidal (Figure ). This fraction was sized nominally between 17 nm-the hydrodynamic diameter of thyroglobulin (19.6 min. retention time)-and 450 nm-the pore size at which samples were filtered. Colloids in this size range may have served as a mobile sink for lead, promoting release from corrosion scale.