HCB most frequently appears as a trace impurity in chlorinated solvent streams, certain pesticide formulations, or industrial chemical by-products rather than as an intentionally manufactured ingredient. Importers of chlorinated chemical mixtures should test for HCB content, as its presence — even at low levels — can trigger classification under this heading and require EPA disclosure.

Yes. Because both substances are Stockholm Convention POPs, importers may need to provide documentation demonstrating the purpose of the import (e.g., research, reference standard, or unavoidable by-product) and comply with EPA TSCA import certification requirements. A licensed customs broker familiar with POPs regulations should be consulted prior to shipment.