Both litharge (orthorhombic crystal form) and massicot (tetragonal crystal form) are lead monoxide (PbO) and classify together under 282410. The crystal-form difference is a manufacturing and performance distinction, not a tariff-line distinction. Red lead (Pb₃O₄) and other non-monoxide lead oxides classify under 282490.

Lead oxides are subject to TSCA compliance requirements, and importers must certify that the substance is on the TSCA Chemical Substance Inventory or qualifies for an exemption. Shipments must also comply with DOT hazardous-materials transport regulations. Given lead's status as a regulated toxic substance, consulting a licensed customs broker and reviewing EPA guidance before the first shipment is strongly advisable.