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topic 3757

Phosphating coating - Harmful to Humans?


Dear Sir / Madam,

I would like to know if the Zinc phosphating on steel is harmful to human beings. If one puts a zinc-phosphated component in the mouth and tastes, will he or she be poisoned?

Is is allowed by Law (USDA or FDA) in the States that zinc-phosphated parts can be used in Food Industry?

Many thanks.

Kwok-wai CHOOK
- Hong Kong, China


Hello Kwok-wai,

First off, you're NOT going to find many experts on the USDA or FDA on these pages. So I am no help there. A well rinsed zinc-phosphated component will not poison you if licked once. But, the zinc-phosphate coating is too porous to prevent the food's acids or bases from reaching and leaching the base metal. This causes a spoiling of the taste and/or presentation (odor) of the food in this manner. Sorry, but you still need to find out more about this application. Have you tried any of the USDA sites?


Fred Mueller, CEF
- Royersford, Pennsylvania


Hi Kwok-wai,

The main purpose for phosphating steel is to enhance the adhesion of substrate material to subsequent paints. Of course, phosphate coating itself provides a little bit of corrosion protection. It usually stands salt spray less than one week. Therefore, post treatment is often involved in the phosphating process, such as immersion in a corrosion inhibitor solution, chromate solution rinse, and the like. Although zinc phosphate coating is not toxic, the post treatment usually contains poisonous chemicals that are certainly harmful to human being. In practice, no one would use zinc phosphate coating as a final finish. A top coating must be followed for both decoration and corrosion protection. It is not clear to me why you choose zinc phosphated steel material as food containers that are mostly tin-plated steel.

Anyway I would certainly refuse to eat any food that directly contacted zinc phosphate coating, even if there is no law to regulate this issue because no one would use it in this way before. Would you?


Ling Hao
- Grand Rapids, Michigan

March 27, 2011

Zinc is used to galvanize some iron containers such as wash tubs and trash cans which apparently have been used for bulk cooking for canning purposes, and will cause food poisoning if the foods are acidic such as tomatoes, and fruits, also includes steak marinade that contains these sort of acids for tenderizers or flavoring.

Pretty dangerous, you would experience severe food poisoning symptoms within 3 to 12 hours after exposure.

Hope this helps.

Da Magouirk

Da Magouirk
- Wedowee, Alabama USA

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