Residues containing arsenic, mercury, thallium, cadmium, or lead at elevated concentrations — particularly those under subheadings 262021, 262029, 262060, and 262091 — are most likely to be characterized as hazardous waste under RCRA. The EPA's Office of Resource Conservation and Recovery administers consent-based import requirements for such materials, and importers must obtain the appropriate notification or consent before shipment.

Hard zinc spelter is a specific by-product of galvanizing operations — a zinc-iron alloy solidified from the galvanizing bath — and is named explicitly in subheading 262011. All other ash and residues whose principal metal content is zinc, such as zinc skimmings, zinc dross from die-casting, or zinc-bearing flue dust, fall under the residual subheading 262019.