Stainless steel has been around since the early 20th century and is now used in a myriad of applications around the world ranging from cutlery to the kitchen sink, cookware to cars, scalpels to prosthetic implants, planes, trains, automobiles, and even teeth. And of course, water bottles and food storage containers -- tiffins too!
What is stainless steel?
Technically, stainless steel is defined as a steel alloy with a minimum of 10.5 % chromium content by mass. As the name suggests, stainless steel is steel that should stain 'less' and not corrode (i.e., not rust). It should stain less, but it is not stain-proof. It is normally thought of as being corrosion-resistant, but given the wide range of grades of stainless steel, that is actually not a very useful defining characteristic, because it is the quality and grade of the stainless steel which determine its strength and corrosion resistance.
The base element in stainless steel is iron (Fe), and to this chromium (Cr) is added, which makes it into a corrosion-resistant alloy, an alloy being a mixture of metals. A small amount of carbon (C) is often included to increase hardness and strength. Nickel (Ni) may be added to stabilize the crystalline structure of the iron, and thus increase the integrity at all temperature extremes and to assist with corrosion-resistance. The crystal structure of iron makes the stainless steel non-magnetic and less brittle at low temperatures. Other alloying elements such as molybdenum (Mo) or titanium (Ti) may be added to improve heat- and corrosion-resistance properties.
One of the wonderful qualities of stainless steel is that it is self-repairing. The chromium, through a process called passivation, forms an invisible layer over the iron to protect it from air and water. If the surface is scratched, the layer quickly rebuilds itself in the presence of oxygen. This is why high quality stainless steel will not rust, even if it becomes scratched.
There are literally hundreds of types of stainless steel. For comprehensive overviews of the numerous types of stainless steel, and explanations of the classification systems, you may wish to visit these links:
Stainless Steel Grades
The stainless steel used to make the products Life Without Plastic offers - including the Sanctus Mundo brand - is called grade 304, which is a high quality, sanitary, food grade stainless steel used in numerous food, dairy, brewing, hospital and sanitation applications all over the world. The grade 304 products we carry are designated as either 18/8 or 18/10. The '18' refers to the percentage of chromium in the stainless steel, and the '8' or '10' the percentage of nickel. Both are high quality stainless steels. The chromium and nickel are what make stainless steel corrosion-resistant, and increase its strength, durability, and, in the case of nickel, also its temperature resistance.
There is no major difference in the mechanical properties – the strength – of 18/8 and 18/10 stainless steels. The 18/10 'may' be very slightly more ductile (i.e., slightly more able to bend without fracturing) than 18/8, but the difference is so minute as to be completely inconsequential for the purposes of food and drink containers. And we say 'may' because the overall quality of the stainless steel could also affect the ductility. So for our purposes, the 18/8 and 18/10 designations are practically irrelevant, though they are still widely used. One possible advantage of the 18/8 is that the lower nickel content could be an advantage to anyone who has a nickel allergy (see the section below on possible releases from stainless steel) - but here again, quality is an issue because a higher quality stainless steel with more nickel in it, may release less nickel, or none at all, compared to a lower quality stainless steel with less nickel in it.
Stainless steel grades with very little nickel do exist (e.g., grade 430) and cost less, but they are considered lower quality because of their decreased corrosion- and temperature-resistance. Similarly, there are other grades with low nickel content (e.g., grades 201 & 202), in which the nickel is replaced by more manganese. Manganese (Mn) is significantly less expensive than nickel, but the resulting stainless steel may be slightly more susceptible to corrosion in certain circumstances and may have a slightly inferior surface appearance. The nickel content also may be increased, creating a slightly higher grade stainless steel. For example, grades 316 and 317 may have 10-15% nickel content and include molybdenum, the combination of which increases resistance to specific forms of corrosion in extreme environments, such as chloride corrosion.
The standard composition of grade 304 stainless steel is as follows:
The health issue - does stainless steel release anything, and if so, what?
Regarding the release of elements from stainless steel, it may occur in trace amounts with any standard food/medical-grade stainless steel (18/8 or 18/10, grade 304) – but the higher the quality of the stainless steel, the less - if any - the release. There are four key possibilities for release from grade 304 stainless steel: iron (Fe), chromium (Cr), manganese (Mn) and nickel (Ni).
Iron is the base material from which steel is made. The nickel and chromium are what make stainless steel stainless, corrosion-resistant and durable. The '18' refers to the percentage of chromium in the stainless steel, and the '8' or '10' the percentage of nickel.
Our bodies need iron to produce red blood cells. While large amounts can be poisonous, in North America the chances are much greater that we lack iron. In general, iron cookware and dishes provide less than 20% of the total daily iron intake, which is well within safe levels.
As with iron, small doses of chromium are also positive for human health. The safe intake range is around 50 to 200 micrograms per day and one meal prepared with stainless steel products might release around 45 micrograms of chromium, which is well within safe levels. Even eating with stainless steel dishes several times a day is fine, as less chromium is released from just eating off the dishes compared with cooking in them using heat. Keep in mind that if the stainless steel is of high quality it will be stable and should not be releasing anything. And any releases through normal wear and tear of high quality stainless steel should be miniscule at most.
Manganese is an essential trace nutrient in all forms of life. The form of manganese used in industrial applications is considered toxic at levels above 500 micrograms. The US Environmental Protection Agency has determined that exposure to manganese in drinking water at concentrations of the equivalent of 1 milligram/litre for up to 10 days is not expected to cause any adverse effects in a child. The uptake of manganese by humans mainly takes place through food, such as spinach, tea and herbs. Other foods containing high concentrations of manganese are grains and rice, soya beans, eggs, nuts, olive oil, green beans and oysters. For more information on manganese, take a look at this US Department of Health and Human Services Manganese Fact Sheet.
Nickel is not toxic in small amounts, but it can provoke a reaction in people allergic to nickel. An allergic reaction may consist of a metallic taste in the mouth or a skin rash on the hands (eczema) or elsewhere on the body. Small amounts of nickel can be transferred from stainless steel containers or cookware to foods – especially when the food in question is acidic (e.g., tomatoes, rhubarb). However, the amounts of nickel that may be released from non-corrosive stainless steel products - which all our stainless steel products are - are generally smaller than the amounts one would ingest by eating certain food items such as beef, chocolate, soya beans, oatmeal, nuts & almonds, and fresh & dried legumes, all of which have a relatively high nickel content. That said, if someone suspects s/he may have an allergy to nickel, we always suggest avoiding all stainless steel completely. If you suspect you may have an allergy to nickel - or anything, for that matter - the best way to know for sure is to have an allergy test with a health specialist.
For detailed scientific information on nickel, take a look at this comprehensive Environment Canada/Health Canada Asessment Report of Nickel and its Compounds. If you take a look at pages 22 and 24 of this document, it will give you an idea of the amounts of nickel released from different foods, and from stainless steel (last sentence in second paragraph on p. 24). As well, this US Department of Health and Human Services Nickel Fact Sheet. Included in the 'References' section of this Fact Sheet is a link to a detailed toxicological profile of nickel (397 pages). The upshot is that using corrosion-resistant stainless steel will not add a significant amount of nickel to your diet (the average person ingests about 150-200 micrograms of nickel daily) - you'll get much more from nickel-rich foods. However, as mentioned above, if you suspect you are sensitive to nickel, the best route would be to avoid any contact with nickel, including via stainless steel products.
In summary, there may be minute amounts of the above elements coming out of stainless steel as it goes through normal wear and tear – but such releases are also highly dependent on the quality of the stainless steel. Our whole business is based on health and safety and the environment. We source our products only from respected, ethical manufacturers with whom we have a solid trust relationship. We use our products all the time - as does our 6 year old son - and he is largely why we first started the company. We wouldn't sell these products if we weren't confident of their high quality and safety.
We think, on balance, that stainless steel is far safer than various plastics, which release endocrine disruptors and other synthetic chemicals. But of course, it is a personal decision you must make on your own.
Stainless Steel and the Environment
Stainless steel is one of the most environmentally efficient raw materials available because of its durability and ability to be recycled. That said, the making of stainless steel is a polluting and energy-intensive process that uses mined metals, such as iron, chromium and nickel. Over the past two decades, improved process technology has enabled manufacturers to decrease significantly the amount of embodied energy required to produce stainless steel. The mined materials used to make the stainless steel may have travelled significant distances to arrive at the manufacturing facility, and then the final product often travels great distances through various supply chains to reach the final consumer. So there is a significant carbon footprint attached to stainless steel.
Stainless steel products should last an extremely long time under normal usage. Generations. And even once their service life is over or they become irreparably damaged, stainless steel items should never enter the waste stream. Stainless steel is 100% recyclable and can be reused to make new products without loss of any of the original properties, such as tensile strength, ductility and corrosion-resistance. Valuable raw materials like chromium and nickel can be easily separated from the iron and similarly recycled. The scrap material can be used to make brand new products of the highest quality. On the average, any stainless steel item is made of approximately 60% recycled material, with 25% of that derived from end-of-life products, and the other 35% from manufacturing processes. The recycled content is limited only by the amount of scrap steel available. The global market for scrap stainless steel is active. As it is a commodity constantly in demand, its recyclability is not just economically viable, but lucrative. Anything made of stainless steel should never end up in a landfill! Take a look at this presentation on stainless steel recycling, keeping in mind it was made by the stainless steel industry.
We balance the environmental issues associated with stainless steel against those of plastics. Comparatively, plastics break down much faster and may release dangerous synthetic chemicals, including endrocrine disruptors, in the process. Plastic production and manufacturing are extremely polluting and energy-intensive processes. Most plastics are derived from petroleum, a non-renewable often imported resource with serious issues of its own - environmental, energy, health, global security. And plastic waste is an enormous environmental problem that is spurring jurisdictions around the world to ban or tax various forms of plastic packaging. The plastics recycling industry and processes are complex and not well understood by the general public. Far fewer plastics are recycled than people think. Much of it still ends up in landfills or oceans. An Earth-shaking example of the plastic problem lies in the oceans, literally. Plastic pollution in the Pacific Ocean has reached epidemic proportions as indicated by the powerful research being carried out by the Long Beach, Calfiornia-based Algalita Marine Research Foundation. Broken, degraded pieces of all kinds of plastic outnumber surface plankton in the Central North Pacific by a ratio of 6 to 1, over an area the size of Texas. Estimates of the amount of plastics in the world's oceans exceed 100 million tons.
Some Handy Stainless Steel Links
British Stainless Steel Association (http://www.bssa.org.uk/faq.php?id=10)
European Stainless Steel Development Association (http://www.euro-inox.org/)
International Stainless Steel Forum (http://www.worldstainless.org/)
Steel Recycling Institute (http://www.recycle-steel.org/)
Wikipedia entry on stainless steel (http://en.wikipedia.org/wiki/Stainless_steel)
World Steel Association (http://www.worldsteel.org/)