Question: What is stainless steel?
Answer: There are actually multiple answers to that question — as there are a lot of different grades of stainless steel.
One of the most common grades of stainless steel (for household uses including cookware/ kitchen items) is “304”. When something reads as “304 Stainless” (with the XRF), I generally consider that a very good thing, because 99.9% of the time it means I am testing an item that does not have any neurotoxic heavy metals (no lead, no cadmium, no arsenic and no mercury – either as constituent ingredients or contaminants) in the product! [This baby bottle is an example of a rare exception, a stainless steel bottle with a solid lead sealing dot.]
As an example, the elemental (metals) make up of 304 (Grade 304 Stainless Steel) can look like this when an item is tested with an XRF instrument (with a one minute test):
- Chromium (Cr): 150,100 +/- 1,100 ppm
- Copper (Cu): 5,593 +/- 568 ppm
- Nickel (Ni): 92,100 +/- 1,700 ppm
- Iron (Fe): 728,100 +/- 2,500 ppm
- Vanadium (V): 950 +/- 191 ppm
- Molybdenum (Mo): 1,959 +/- 146 ppm
- Manganese (Mn): 18,100 +/- 1,300 ppm
This particular reading set is for the male end of a lead-free hose by Water Right, Inc. (pictured here) made of 304 stainless.
The most important characteristics for identifying whether or not something is a certain grade of stainless steel is the ratio of chromium to nickel to iron, as those are the main components of most stainless steel alloys.
As an example to show the range of readings for the same grade of stainless steel (304), below is another set of readings (for the other end – the female end – of the same hose).
Note that while some ingredients are intentional components of the grade of stainless steel, other metals (seen at very low levels) are more like to be coincidental contaminants from the manufacturing process. Not all “contaminants” are considered toxic.
In general, to my knowledge, most grades of stainless steel are considered non-toxic, with many designated safe for food use – and some even considered safe for medical use applications (such as surgical implants).
Female hose end, as tested with an XRF instrument.
- Chromium (Cr): 160,100 +/- 1,100 ppm
- Tin (Sn): 113 +/- 54 ppm
- Copper (Cu): 6,042 +/- 584 ppm
- Nickel (Ni): 88,100 +/- 1,700 ppm
- Iron (Fe): 717,000 +/- 2,500 ppm
- Vanadium (V): 1,035 +/- 207 ppm
- Cobalt (Co): 4,328 +/- 1,467 ppm
- Magnesium (Mn): 21,300 +/- 1,300 ppm
So for 304 stainless steel, we have the following three characteristics that are expected:
- Nickel in the 82,000 to 95,000 ppm range
- Iron in the 700,000 to 750,000 ppm range
- Chromium in the 150,000 to 160,000 ppm range
While I do not currently have any concerns for toxicity in food-safe stainless steel, some people do. I have heard of folks voicing concerns primarily about a specific nickel allergy, or possible leaching of stainless steel elements – like nickel or chromium – into food or beverages contained within stainless cups, water bottles or other vessels or food cooked in stainless pans.
My only real piece of advice when it comes to stainless used for food applications is not to use stainless steel beverage containers with highly acidic beverages (like orange juice or lemonade), and when using a stainless water bottle, be sure to rinse well before each use and replace the contents daily if they are not fully consumed.
Here is a link to the Stainless Steel category of items on my website. As these items are generally (as a category) lead-free (with exceptions being – for example – stainless steel baby bottles with a solid lead sealing dot), I don’t always list the full elemental/metals breakdown for the stainless components of the items I test. However I will work towards creating a blog post for each type of stainless steel to help folks evaluate the potential implications of the use of stainless in their lives.
As always, please let me know if you have any questions!
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