# Is tin and tinware toxic?

I tried to find info on tin toxicity but there is not much. Wikipedia here says that it is not very poisonous; but there could be cases.

My question is: is it dangerous to say have a coffee boiled in a tin container? I know that coffee has some acidity, so it can probably react with tin.

• It is known for metals to disassociate and react, for example, the process of rusting. High heats definitely increase reaction rates in alot of chemicals. I wouldn't recommend it for coffee cooking, but for food storage yes, given the proper conditions and lined ofcourse for prevention and reaction reduction. But im only a bio student. Aug 24 '17 at 22:10
• You are right to be suspicious! In fact, the CDC's Public Health Statement for Tin at atsdr.cdc.gov/phs/phs.asp?id=541&tid=98 issued by Agency for Toxic Substances and Disease Registry appears to be a well-kept secret! Feb 17 '20 at 18:08
• It is lucky pewter is not toxic as it has been used to some degree for eating utensils for over a thousand years. And all those who have used pewter beer mugs would likely be dead. Apparently adding a couple percent copper to tin to make pewter , makes it safe. ( Warning : serious level of sarcasm in this comment). Feb 17 '20 at 20:35
• And copper cookware made before about 1960 is tin coated on the inside . And "Gourmet " /expensive copper cookware is still coated with tin today. Feb 18 '20 at 3:37

The Wikipedia article you quoted clearly says:

The low toxicity is relevant to the widespread use of tin in dinnerware and canned food.

Moreover, tin cookware, which used to be very common in earlier centuries, is still sold for outdoor cooking purposes. It is thus without a doubt deemed safe to use under current health regulations.

As a side note, the pH of coffee is around 5, which is only weakly acidic (same as unpolluted rain, and less acidic than tomato juice or beer):

• There are two serious typos in that chart. The two places where it says "hydrofluoric acid" should be replaced with "hydrochloric acid". The stomach secretes HCl, not HF! And HF is not a strong acid, so it seems unlikely it could achieve a pH of 0. From what I've read, the pH of concentrated HF is ~1. Feb 16 '20 at 0:50
• The Wikipedia article (en.wikipedia.org/wiki/Tin_poisoning ) on Tin poisoning seems to be abbreviated and does wonderfully extoll the safety of inorganic tin. The widespread health issue of organic tin compounds is not referenced, or also importantly, the CDC's Public Health Statement for Tin at atsdr.cdc.gov/phs/phs.asp?id=541&tid=98. See my answer below for perhaps a more balanced perspective actually incorporating various sources. Feb 17 '20 at 17:44
• You can not use pewter/tin for outdoor cooking , it melts. Surprising and disappointing to me as a kid; maybe that is part of why I became a metallurgist. Feb 17 '20 at 20:39
• Pewter/tin alloy begins to melt above 471 F , not a good choice for "out door" cooking. Feb 18 '20 at 3:33
• Anything in widespread is safe? Then, why do scientists criticize the widespread use of pesticides (see theguardian.com/environment/2017/sep/21/… ). Feb 20 '20 at 18:28

I don't believe it is the metal itself that should concern you, but when it reacts with something in your food it might lose its metallic bond and therefore allow you to ingest tiny amounts of tin via a molecule that includes tin itself. This is perhaps what can potentially happen when food is cooked inside a tin container.

We had a conversation about this last year in general-chemistry when the OCHEM instructor was talking about using metals as containers for dishes during recitation for our lab on cell potential. She was saying that the acids in food might create undesirable compounds when reacting with the metal containers, but that was probably a guess. She was saying something about how pop cans, for example, are made of aluminum, but the insides are lined with a plastic to prevent any undesired reactions (presumably). But then again she also went on to say that the FDA would not allow plastic containers (2 Litre pop bottles for example) until they finally passed off the plastic as a "food additive." Interesting stuff...

As a rule of thumb, I always say that too much of anything is bad for you, and eating food from tin containers might be one of those ways of getting tin toxicity, but this is all speculation here so take it with a grain of salt, or a grain of tin whichever you prefer.

Per this source, Chemical Reviews: Transition Metal-Tin Chemistry, I surmise that a potential safety issue with Tin stems from its ability to create complexes, which can act in distinctly catalytic roles in organic-based reactions.

In particular, the author discusses the co-ordination chemistry around stannylenes, $$\ce{R2Sn}$$, to explain a considerable amount of tin transition metal related complex formation (note, technically, Sn is a post-transition metal).

Direct toxicity levels of elemental Sn, itself, is likely just a secondary concern upon ingestion.

[EDIT, CORRECTED MEDICAL REFERENCE] Relating to long term exposure, here are some comments courtesy of the Ecology Center, to quote:

Depending on the form and level of exposure: Exposure to high levels of inorganic tin may cause symptoms including stomach aches, liver and kidney problems, and anemia.

Organic forms, known as organotins, are believed to be toxic at lower levels of exposure. Several tin compounds cause nervous system harm, including tributyl tin, dibutyl tin, trimethyl tin, and dimethyl tin (Cooke 2004, Jenkins 2004, ASTRD).

The developing brain is particularly vulnerable. Dibutyl tin is toxic to nervous system cells at concentrations similar to those found in people today (Jenkins 2004).

My understanding of redox chemistry surrounding corrosion suggests that I should not store opened can foods (as this chemically introduces oxygen) in their container, especially those containing citrus acids (which, together with O2, can cause so-called spot-corrosion of steel). A dented or otherwise damaged container may introduce a galvanic based corrosion as well. Note, cited reactions are not immediate, but require days and could eventually introduce a small amount of potentially problematic Fe(II) (or other anodic alloys) into the food product (but not tin ions as it serves in the role of a cathode, see this).

Interestingly from an electrochemical perspective, boiling acidic coffee in a tin-plated container that has a surface defect (from scratching on cleaning) likely introduces ions not of Sn, but of associated alloyed elements (perhaps copper). However, elemental Sn does react with dilute (especially warmed) HCl albeit slowly. Boiling in air with dilute acid found in coffee for extended periods of time, and left to warm over many hours, suggests a possible path for some tin from organic acids, and much more so, for associated alloyed transition metal ions, to be ingested, in my opinion. Also, why is a fragile glass pot the preferred vessel for preparing coffee? Answer: Perhaps a difference that can be even tasted.

The louder some claim that inorganic Tin is safe, being indeed cathodic, makes me think of what metal is dissolving at the anode, Copper or Iron? And, what about organic bound Sn?

High-temperature chemistry suggests heating a tin cup (without water) to the point that it is red hot, could directly create some SnO2 as a product.

I will leave further comments to our resident contributing bio-chemists.

I just found this Public Health Statement for Tin from the CDC's Agency for Toxic Substances and Disease Registry, providing amazingly confirming comments on my ramblings relating to chemistry suggested above, to quote:

Because tin is naturally found in the environment at low levels, we cannot avoid being exposed to it. The major route of exposure to tin is from eating or drinking canned products. Reducing the amount of canned products you eat or drink may reduce your exposure to tin. Since tin concentrations in food increase if food is stored in opened cans, you can reduce your exposure by storing unused portions of canned foods in a separate container. You may be exposed to organic tin compounds by eating seafood from areas that may be contaminated with organic tin compounds or from contact with household products that contain organotin compounds (polyurethane, plastic polymers, and silicon-coated baking parchment paper). Reducing the amount of seafood that you eat from areas that may be contaminated with organic tin compounds and reducing contact with household products that contain organic tin compounds may reduce your exposure to organic tin compounds. If you are accidentally exposed to large amounts of tin or tin compounds, consult a physician immediately.

And also:

Food from unlacquered tin-lined cans contains up to 100 ppm of tin since the reaction of the food with the can causes some of the tin to dissolve in the contents of the can. Greater than 90% of tin-lined cans used for food today are lacquered. Only light colored fruit and fruit juices are packed in unlacquered tin-lined cans, since tin helps maintain the color of the fruit. Tin concentrations in food also increase if food is stored in opened cans.

Note, a focus on organic tin compounds (which is in accord with my opening paragraph) which appears to be particularly problematic. Also, open fruit cans or fruit juice generally sold in unlacquered tin-lined cans, after opening, can be an increased source of organic transition-metal ions, including those of tin. My thoughts on how this occurs, in the case of electrochemically created copper ions (from a galvanic cell with tin) where cuprous can be further oxidized to cupric by O2 and H+. Instrumentally, in the presence of elemental Tin, the following REDOX reaction can proceed:

$$\ce{Sn(s) + 2 Cu(II) (aq) -> Sn(II) (aq) + 2 Cu(I) (aq)}$$

Source: Page 29 at this reference.

No word from our resident biochemist, so here is a debate on a cookware site. I would believe the comment posted by PaulJoseph (which is actually taken from a prior version of Wikipedia's commentary on the Toxcity of Copper, since edited, which supportingly states the accelerated formation of copper ions and implies with Cu(II) (a 'reactive salt'), a likely attack on Tin as noted above), to quote:

When acidic foods are cooked in unlined copper cookware, or in lined cookware where the lining has worn through, toxic amounts of copper can leech into the foods being cooked.[11]. This effect is exacerbated if the copper has corroded, creating reactive salts.[12] Many countries and states prohibit or restrict the sale of unlined copper cookware. Cited source

which echoes my comments on the electrochemistry presented above. Once the lining on the copper pan with Tin (versus stainless steel) becomes damaged, this could lead to accelerated corrosion of the copper, and possible toxicity issues. A conceivable dangerous scenario is where one cooks food in an acidic sauce (tomato-based) with the pan having a damaged lining. Then, following the consumption of most of the food, a small amount is left open in the pan for days in a refrigerator. This would allow time, based on the REDOX above, for tin ions to problematically accumulate, adding to the copper ions (which can recycle, in the presence of an acid source, oxygen and elemental tin).

• The "dot gov website" article you cite uses TIN as an acronym for a medical condition. It says nothing at all about the element "tin". Feb 17 '20 at 19:00
• Thanks Jeff, I noted the mistake and inserted some comments from the Ecology Center. Feb 17 '20 at 22:41

Pure Tin may be fine as a food container. However, Tin ore is accociated with the ores of Lead and Antimon. Traces of these may find their way into Tinware. I believe there is an metallurgy motive to alloy Tin with Lead as well. Lead tends to react when in contact with acidic food, and it accumulates in the body. This was not taken seriously for a long time.Tinware once thought to be save might better not be used today.

• You can actually get copper pots and cookware retinned at, e.g., East Coast Tinning. URL: www.eastcoasttinning.com . So it is still done.
– Ed V
Feb 20 '20 at 18:53
• @EdV they use pure Tin i hope. Feb 20 '20 at 20:45
• That is what they say! I have no copper cookware, so I have no actual experience with this.
– Ed V
Feb 20 '20 at 20:54

Tin lined cans are commonly used in processing light colored fruit as the tin is preferentially oxidized by residual oxygen left in the product and the headspace of the can, headspace gasses can be reduced by steam flushing immediately before seaming. If the oxygen levels are high enough a black line will be found at the juncture of the product and the headspace indicating loss of tin into the product, exposing the steel can to the acidic contents. When sufficient amounts of tin become incorporated into the product as stannous oxide some consumers will react adversely complain of stomach ache and loose bowels. There is a secondary problem with lead contamination. All tin sources are naturally contaminated with lead especially those originating in Malaysia, lead levels can be reduced if the tin is subjected to a distillation process but this increases the cost of the tin. Lead levels in most tin canned products will not meet the lead tolerances set by California Prop 65. One further observation, I do not consider ANY product packed in a tin lined can to be "organic" as it will certainly have measurable levels of tin and lead within days of being processed.