Sulfites used as food preservatives or antioxidants are regulated by FDA as food additives under GRAS (Generally Recognized as Safe) provisions, with specific labeling requirements when present above threshold levels in finished foods. Importers of food-grade sulfite products should ensure the product meets FDA purity specifications and that any food-contact application complies with 21 CFR labeling rules. Consulting a licensed customs broker and a food regulatory specialist is advisable given the complexity of admissibility review for food-ingredient chemicals.

Sodium thiosulfate is used in municipal water dechlorination (neutralizing residual chlorine after treatment), as a medical antidote for cyanide and cisplatin toxicity, and in gold leaching processes. Its classification under this heading does not change with end-use, but the grade and purity specified on the invoice (technical vs. pharmaceutical vs. photographic) are important for verifying the correct tariff line and for meeting any applicable FDA or EPA import requirements.