Drinking Container Safety: Metals

Last week I covered plastics for food and drink use; this week I'll cover the common metals you might find or buy for the same purposes. Metal containers have been in use for thousands of years, but the recent crazes of “detox diets” and natural-everything have made it hard to find useful information on the Internet. If a website has “natural” or “health” in the name and doesn't end in .gov or .edu, take the information found there with a healthy helping of skepticism.

Metal cans and cups have been around since humans learned how to work metal. Some metals are safe, some are safe with most liquids, and some should be avoided at all costs. Starting with the lowest atomic number and working up to end with the common alloys, here are the more common metals with their pros and cons:

12 Mg- Magnesium

Known for being light-weight and strong, Mg isn't used for food or water containers very often. Very reactive and hard to work with due to its low ignition temperature, Mg is rare in cookware but may be used in a make-shift water container. Excess Mg is readily excreted from the body, so only those with certain medical conditions need to worry about consuming too much.

13 Al- Aluminum

Once a standard for light-weight cookware and dishes, Al has been linked to several health issues and is falling out of favor. Al is a very reactive metal and is always found in combination with another element. Simple Al oxidizes almost immediately when exposed to air, forming a protective coating of aluminum oxide, but acidic foods and drinks will eat through that layer and leach Al into the food/drink. Heat will also speed up leaching, so cooking in Al will expose you to more.

22 Ti- Titanium

Light, strong, and expensive, Ti is safe for food use. There is slight chance of being allergic to Ti, but it is considered non-toxic. I've got a few pieces of Ti holding bones together, so it's safe to say that it is safe to eat or drink from containers made of it.

24 Cr- Chromium

A component of most stainless steels, Cr is also used to plate or cover cheaper metals to give them a shiny, corrosion resistant covering. Most of the reports of Crpoisoning are related to ions of Cr used in the plating process and not the finished product, so using that old chromed hubcap in your water collection system shouldn't be a problem.

26 Fe- Iron

Required by your body to function, Fe is non-toxic at all but very high doses. You might have to filter flakes of rust out of your water, but iron and steel containers are safe to drink from. Watch for bacteria and other microbes growing in rust and the pores of iron containers.

28 Ni- Nickel

Like Cr, Ni is used in stainless steel alloys and as a plating for other metals. Allergic reactions to Ni are fairly common, so if you can't wear cheap jewelry without breaking out in a rash you should avoid Ni plated drinking containers.

29 Cu- Copper

Being easy to work, fairly cheap, and a good conductor of heat all make Cu a good choice for cookware. It is soft and scratches easily, so it requires some care. Commonly found in distilleries and water pipes in old houses, Cu has become more expensive lately. See Pb, below, for information on solder joints. Cu is another trace element that your body needs, but high doses should be avoided.

30 Zn- Zinc

Commonly used to galvanize steel to give it a rust-proof finish, Zn is a trace mineral needed for proper bodily functions. Fairly non-toxic, but high doses can interfere with Fe and Cu metabolism. Avoid heating galvanized steel since doing so will release toxic fumes. If you are going to use a plated piece of metal as a grill or pan, make sure you safely burn off the plating first.

47 Ag- Silver

Solid silver and silver-plated dinnerware has been around for a long time because not only is it safe to use with food, but it may also have minor antibacterial properties. I'm not going to get into the colloidal silver debate, but silver ions have been shown to kill microbes in many lab tests. Too much in your diet will turn your skin permanently blue-gray (Argyria), but it takes more than that to be toxic.

50 Sn- Tin

Most of us have heard of tin cans, which are actually steel cans with a thin lining of Tin on the inside. Tin is a stable metal and not very reactive, so it is less likely to corrode and contaminate stored food or water than the steel shell which provides strength. Tin by itself is non-toxic and safe to use with food and drinks.

79 Au- Gold

Expensive but one of the best for food contact, gold doesn't tarnish and is almost inert in most environments, making it very unlikely to contaminate food or water.

82 Pb- Lead

One of the well-known heavy metals that is hazardous with long-term exposure. Its low melting point makes it a good solder for joining metals, so it is common in old water supplies and copper radiators. New potable water supply lines need to be soldered together with lead-free solder to avoid ingesting Pb with every cup of water, but such solder is easy to find.

Pb does accumulate in the body, so the longer you're exposed the more damage it will do to the central nervous system (CNS), peripheral nerves, kidneys, and circulatory system. Removing Pb from the body is a delicate procedure requiring hospital care and chelation therapy. Definitely one to avoid at all costs!

Alloys

Brass

And alloy of Cu and Zn, brass is a common decorative metal. It does corrode, as anyone who has ever had to polish brass buttons on a uniform will attest. Some blends of brass can contain Pb and there is concern over the possible leaching of the Pb into water from brass plumbing fixtures. California has greatly reduced the allowable amount of Pb in all consumer goods, so newer fixtures should be safer than old ones.

Often used to make musical instruments, brass has some anti-microbial properties that are being researched. History shows that brass fittings on ships resist biological fouling, but until that can be quantified in a lab it is just “anecdotal evidence”.

Bronze

One part tin and seven parts copper, bronze is one of the oldest alloys used by man, dating back at least 5000 years and is still in production today. Large bells and statues are often made of bronze due to its strength and ease of casting. Like brass, it can contain trace amounts of Pb as well as other metals.

Pewter

A blend of Tin, Lead, Copper, and possibly other metals, pewter is of questionable safety to use with food. Pewter is used when the maker wants a darker alloy than either brass or bronze; it is normally gray or brown in color instead of the reddish-yellow of the other Cu alloys. The presence of any significant amount of lead would put it far down the list of potential materials for me.

Stainless Steel

Stainless steel (SS) is a generic name for a wide variety of alloys of steel and Ni, Mo, Mn, Cr, and a few other metals. Most common SS alloys are well-suited for use with food and water, with the only caveat to avoid storing chlorine-based solutions in SS containers. Chlorine pulls the Chromium out of the alloy, contaminating the stored liquid and weakening the SS.

As long as you avoid Pb, most metals are safer to use with food and drink than plastics. They are also easier to recycle and have a longer usable life than plastics. They may be heavier, but I prefer metal flasks and cups over plastic.

A side-note on metals and water:
If you're using a good reverse osmosis (RO) system or a hearty de-ionization setup, the water coming out may be so clean that it can actually eat away at metal piping and containers. I've seen this on an industrial scale and it is possible on smaller sets; copper contamination in lab-grade pure water that was traced to a repair made with copper piping on a RO system.