Formaldehyde is listed in 40 CFR 68.130 with the qualifier "solution." Does the qualifier refer only to mixtures of formaldehyde and water, or does it apply to any liquid mixture containing formaldehyde?

Formaldehyde (CAS No. 50-0-0) is listed with the qualifier "solution" because pure formaldehyde has a tendency to polymerize and it is usually handled as an aqueous solution (commercially, 40% formaldehyde, 15% methanol, water). Although the listing refers to aqueous solutions of formaldehyde, other solutions or mixtures may be covered, just as any solution or mixture of any other listed substance. In these cases, the mixture provisions apply; the concentration must be greater than 10 mm Hg to include the amount of listed substance in a threshold quantity determination. Urea-formaldehyde (CAS No. 9011-05-6) is not a formaldehyde solution but a complex polymer molecule. Urea-formaldehyde usually is combined in a reactor to form UF resin. It is shipped to customers as a colloidal aqueous solution with a solid content of about 65%. This liquid is odorless and slightly opaque. When shipped, the UF resin already is polymerized and cross-linked to a certain degree.