Material Anxieties

Soaps - and their newer synthetic cousin detergents - are substances that play an important role in cleaning by removing dirt and grease from our bodies and lived environment. Although there are many different recipes for soap, the basic chemistry involves boiling an oil or fat with an alkali. The ensuing reaction, called ‘saponification’, produces soap and glycerine.

Historically, the fats used for soap production would have been either animal fats like tallow and bone grease or vegetable oils such as olive oil, palm oil or coconut oil. The alkali component, potash or soda, would have been derived from the ashes of plant matter. Developments in the chemistry of cleaning agents have since led to the production of a plethora of different kinds of soap: from beauty soaps to antibacterial and medicated soaps. Non-soap synthetic detergents were also introduced after WWII following a shortage of animal and vegetable fats and in response to the need for cleansing agents that would work in mineral-rich and cold water.

Both soaps and detergents work to remove ‘soils’: the combination of bacteria, moulds, yeasts, fats, grease, proteins and minerals that build up on surfaces and our skin. Soils are often hard to remove from surfaces because they are hydrophobic and repel water molecules. At the same time, the surface tension of water (the strong attraction of water molecules to each other) causes it to bead and stops it properly wetting or saturating a surface. Soaps and detergents are surfactants: compounds that reduce the surface tension of water, allowing it to flow more freely over a surface. Their molecules also contain both hydrophobic and hydrophilic components that attach to the oil and water respectively and form a bridge between them. This allows the oil and dirt to mix with and become suspended in the water as an emulsion that can then be removed.

Today we mainly associate soap with cleanliness and health, and in particular with personal hygiene. However, early forms of soap were used for everything except cleaning the body. The earliest evidence of soap-making can be found in ancient Sumerian and Babylonian texts that date back to the 3rd century BC. The Phoenicians, Gauls and Romans also made saponaceous substances, but these were largely used in the preparation of wool for dying or for bleaching and styling hair: not for personal hygiene. Naturally occurring ‘soapweeds’, clays, perfumed oils and mechanical cleaning implements were used to clean the body instead (Levey 1954; Bradley 2002).

It is still debated exactly when soap was first used for personal hygiene and prevention of disease, with some arguing that the Greek physician Galen discussed its medicinal and body-purifying benefits as far back as the 2nd century AD (Partington 1960). The manufacture and use of soap grew slowly in Europe from the 7th until the 18th centuries, existing as localised and small scale craft production centred around cities like Malaga and Alicante in Spain, Genoa and Venice in Italy, Marseilles in France and Bristol, Coventry and London in England. The period between the late 18th and 19th centuries saw a series of significant advances in chemical knowledge that led to the birth of the modern soap-making industry, including the development of inexpensive synthetic caustic soda (Gibbs 1939). These technical developments allowed soap-making to move from a small-scale craft to an industry.

The late 19th century saw a massive and rapid expansion in soap production and sales, particularly in Britain. The emergence of germ theory – the idea that microbes caused disease - played a very important role in soap’s transition from luxury good to everyday necessity. Against a prevailing idea that infection and disease were caused by ‘miasmas’, vapours or smells coming from stagnant water and waste matter, medics like American physician Oliver Wendell Holmes and Hungarian obstetrician Ignaz Semmelweiss began to put forward the idea that they might be transmitting disease to patients by contact. They instituted handwashing or disinfecting techniques in hospitals that substantially reduced death rates (Tebbe-Grossman and Gardner 2011).

The virtues of handwashing and antisepsis were not immediately recognized. Historian of science Steven Schaffer argues that the ‘fight for soap’ required a ‘distinctive late Victorian combination of scientific authority, respectable domesticity and mass advertising’ to succeed (2004). He discusses the role of public lectures and demonstrations of scientists like Huxley and Tyndall in this popularisation of pathologies of infection (2004). Anthropologists Jamie Cross and Alice Street (2009) also discuss the importance of marketing strategies like Lifebuoy soap’s campaigns, which emphasised the dangers of invisible germs on door handles, banisters and other people, in creating new consumer subjectivities.

Image credit: Wellcome Library, London.

The widespread availability and increased use of low-cost soap did a lot to improve levels of hygiene in 19th century Britain, and led to many of our contemporary cleaning practices. Soap-like substances had been used medically as purgatives and to treat skin conditions since the Egyptians and Greeks (Gibbs 1939). However, the development of specially made medicated soaps was first taken up in a scientific manner between the 19th and early 20th centuries (Appleton & Simmons 2007). At the advice of surgeons and dermatologists these medicated soaps incorporated ingredients like phenol (carbolic acid), sphagnol (peat tar), glycerine, salicylic acid, formaldehyde or mercury salts that were effective as germicides and for skin conditions like eczema and psoriasis. However, as Steven Connor shows, some of the health claims made for medicinal soaps were ‘large and improbable’, such as the use of Amiral as a topical treatment for obesity (2013). Some medicated soap additives like mercury compounds were also later shown to have serious long-term negative health effects and were banned from soaps and cosmetics in Europe and the US, although they are still found in cosmetics globally.

Photo credit: Adrian Wressell, Heart of England NHSFT. Wellcome Image Library, London.

The efficacy of different formulations of soaps and detergents continue to be debated by medical professionals and in the public domain. The most well-known example of this is probably the debate surrounding the widespread use of antiseptic agents such as triclosan that are incorporated into soaps and sutures used in hospitals as well as toothpastes and plastics in consumer products (Page et al. 2009). The main concern in the scientific community focuses on the overuse of disinfectants and the role that may play in inducing antimicrobial resistance (McMurray et al. 1998), whereas the media furore, since rebuffed by the NHS (2014), focused on triclosan’s potential toxicity (Willey 2014). Laboratory tests and clinical trials have both reinforced and contested concerns around resistance (Aiello et al. 2007), but in the UK clinicians remain in favour of using triclosan in, for example, sutures, where demonstrable health benefits can be shown as opposed to in consumer applications where no benefits have been shown (Leaper at al. 2011).   

References

Appleton, H.A. and Simmons, W.H., 2007. The Handbook of Soap Manufacture. Project Gutenberg.

Bradley, M., 2002. ‘It all comes out in the wash’: Looking harder at the Roman fullonica. Journal of Roman Archaeology, 15, pp.20-44.

Connor, S., 2013. Soap, Senstance and Semblance. [Online] Available at: http://stevenconnor.com/senstance/senstance.pdf

Tebbe-Grossman, J. and Gardner, M.N., 2011. Germ Free: Hygiene History and Consuming Antimicrobial and Antiseptic Products. In Dayan, N. and Wertz, P.W. (eds.), Innate Immune System of Skin and Oral Mucosa: Properties and Impact in Pharmaceutics, Cosmetics, and Personal Care Products. John Wiley & Sons.

Gibbs, F.W., 1939. The history of the manufacture of soap. Annals of Science, 4(2), pp.169-190.

Leaper, D., Assadian, O., Hubner, N.O., McBain, A., Barbolt, T., Rothenburger, S. and Wilson, P., 2011. Antimicrobial sutures and prevention of surgical site infection: assessment of the safety of the antiseptic triclosan. International Wound Journal, 8(6), pp.556-566.

Levey, M., 1954. The early history of detergent substances: A chapter in Babylonian chemistry. J. Chem. Educ, 31(10), p.521.

McMurray, L., Oethinger, M. and Levy, S. 1998.Triclosan Targets Lipid Synthesis. Nature 394: 531-532.

NHS, 2014. Triclosan soap linked to mouse liver cancers. Behind the Headlines [Online] 18th Nov. Available at: http://www.nhs.uk/news/2014/11November/Pages/triclosan-soap-link-with-mouse-liver-cancers.aspx

Page, K., Wilson, M. and Parkin, I.P., 2009. Antimicrobial surfaces and their potential in reducing the role of the inanimate environment in the incidence of hospital-acquired infections. Journal of Materials Chemistry, 19(23), pp.3819-3831.

Partington, J.R., 1960. A History of Greek Fire and Gunpowder. JHU Press.

Schaffer, S., 2004. A science whose business is bursting: Soap bubbles as commodities in classical physics. In Daston, L. (ed.), Things That Talk. Object Lessons From Art and Science. Zone Books, New York.

Willey, J. 2014. Cancer scare: Could your liquid hand gel be harming your health? Daily Express [Online]. 

I began writing this blog post having just got back from the International Agatha Christie Festival where I spent the weekend talking about murderous materials with fellow Poirot fans, so the dynamic relationship between poisonous and medicinal materials was very much at the forefront of my mind.

In particular, I’d been thinking about stainless steel and its relationship to health: in terms of the occupational risks of producing and working with it as well as its many beneficial medical uses. In the first part of this three part blog post, I explore the gradual historical domination of stainless steel in surgical tools and medical implants.

Stainless steel is so-called because of its corrosion-resistance, a property largely afforded by the addition of chromium (Cr) to the alloy. This chromium content reacts with oxygen to form a very stable chromium oxide bond at the surface, which means it does not rust. Nickel (Ni) is also well-known for being a key ‘stainless metal’, and plays a crucial role in the production of austenitic stainless steels where it gives these non-magnetic grades their strength, ductility and toughness as well as making them more inert inside the body (Street and Alexander 1994; Kirkup 1993).

As a result of these properties, stainless steel has become a stalwart of the modern hospital. Various grades of this material are used in a wide range of medical applications, from the mundane to the specialized, for everything from hospital beds and handrails to hip replacements, prosthetics and sterilisable surgical instruments. This material domination is relatively new though: a much wider palette of materials used to be common in hospitals.

Early 19th century stethoscopes, for example, like the one pictured below, were often made from the same finely grained and lightweight woods used for wind instruments (e.g. boxwood and fir). And before the introduction of thermal sterilization (between 1885 and 1910), when surgery was conducted without asepsis (or anaesthetic!) (Fitzharris 2017), surgical instruments were commonly made using ivory, tortoiseshell, wood, copper, bronze, iron, silver and gold (Gugliemino et al. 2016).

Thermal sterilisation revolutionised the surgeon’s armoury: it proved destructive to the organic materials on instruments (e.g. bacteria, blood) but also to the wood, ivory and tortoiseshell used to make these tools (Kirkup 1993). All-metal instruments became the norm, and because thermal sterilisation accelerated steel corrosion, these were further protected by plating them with nickel and chrome. However, these plated steels still had the tendency to peel, flake and rust underneath: a problem eventually eliminated by the introduction of stainless steel in the early 20th century. Between 1913 and 1925 stainless steel gradually superceded most other materials in surgical instruments.

Having discussed the surgical advances and new hygienic environments that stainless steels made possible, the next part of this blog post turns to the negative effects of steel on the human body. Nickel and chromium, the constituent ingredients of stainless steel, are both known carcinogens, and nickel also has the dubious honour of having been voted ‘Allergen of the Year’ in 2008 by the American Contact Dermatitis Association. So why do people use stainless steels for medical purposes if their component parts have this potential to cause adverse health effects?

Well, one of the central principles of toxicology is that the effects of a material on the human body depend on the form of the material, the volumes we are exposed to, and the context in which we encounter them. The risk from nickel, for example, largely comes from encountering it in its raw form: once alloyed with steel it presents little risk to the consumer encountering it in everyday use.

The health effects of chromium also depend on the form in which we encounter them: whilst the high levels of toxicity and carcinogenic properties of hexavalent chromium (Cr+6) have been known about since the late 1800’s (Antonini 2003), metallic chromium (Cr) and trivalent chromium (Cr+3) (the same substance in different oxidation states) are both of a low order of toxicity and are found in trace amounts in food and water. The chromium that most patients and consumers will encounter in finished stainless steel in surgical tools and the hospital environment is not hazardous.

In its finished form, stainless steels is relatively inert, strong, corrosion-resistant and durable, so it is understandable that it has become one of the materials of choice for use inside the body. Before the advent of stainless steel, a wide variety of metals like gold, brass, aluminium, platinum and nickel-plated steels were used for dentistry, prostheses and to fix fractures, but most of these were later found to be unstable with a tendency to corrode or leach into the body (Agrawal 1998). Materials implanted in the body are in continuous or intermittent contact with bodily fluids, so have to be corrosion-resistant, biocompatible, nontoxic and non-carcinogenic, and in the case of a joint prosthesis for example, have the physical and mechanical properties to withstand heavy loads and strains. These stringent requirements eliminate all but a few engineering materials. For this reason, from the 19th century onwards corrosion-resistant metals like stainless steel and titanium came to displace all other metals for in vivo applications, and stainless steel is still one of the most frequently used materials for fracture fixation.

However stainless steel is not suitable for all biomedical applications. This is because the health effects of a biomaterial are not just about the interaction between one material and the human body: interactions between different materials or components also have to be considered. Stainless steel was used in a variety of early metal-on-metal hip implant designs between the 1930s and 1950s (Reynolds & Tansey 2007), but it is now known that the abrasive action of the two parts of the steel hip joint rubbing together resulted in the release of toxic metal ions into the body. Equally, the metal-on-plastic (stainless steel and PTFE) implants developed in the 1960s released harmful metal and plastic wear debris into the body. The long-term physiological effects are still not entirely understood, but the metal debris in particular includes nanoparticles of chromium (Cr), cobalt (Co), nickel (Ni) and iron (Fe). These particles accumulate locally causing allergic reactions that can lead to infections, the failure of the implant and tumours (Schaffer et al. 1999; Keegan et al. 2008). Because these metal particles are so small they are thought to be more toxic and to travel around the body interfering with the a variety of wider biological functions including the vascular system, immune system, reproductive function and DNA repair. This is not a new problem, and stainless steel is not the only problematic material: there have since been concerns about the body’s reaction to a variety of structural biomaterials, including cobalt-chromium alloys, titanium and polyethylene (PTFE). The debate about the best material for these kinds of implants still continues.

Stainless steel’s harmful effects can also be seen in its industrial production, where it is by no means a docile material. As well being subject to all the usual risks of hot and noisy metal work, stainless steels welders are at a higher than normal risk of respiratory illnesses like occupational asthma, bronchitis, metal fume fever and lung cancers (Simonato et al. 1991, Hansen et al. 1996, Antonini 2003). Vaporized chromium, nickel, manganese, zinc oxide, iron and silica present in the welding fumes are thought to be the cause of these particular occupational health hazards. Hexavalent chrome also manifests itself during the hot work of production.

Even a very brief survey of the history of pharmaceuticals highlights the fact the same substance can be considered both a poison and a medicine. Radon, for example, can be both a toxin, as a major cause of lung cancer, and a medicine, as a gas used therapeutically for its analgesic and anti-inflammatory effect (Erickson 2007). The materials that we consider to be medicinal or harmful also vary cross-culturally and historically. Arsenic, for example, one of Agatha Christie’s poisons of choice, was used medicinally by early Chinese healers as a bacteriocide (Hulse 2004), by the Greeks for hair removal and the treatment of ulcers, and by the Victorians as a cure-all ‘therapeutic mule’ (Bentley & Chasteen 2002) used to treat everything from malarial fever, skin disease, neuralgia and even finding its way into everyday hand soap.

The same is true of materials like stainless steel and silicone rubber: their health and societal impacts are not just the result of a fixed set of physical properties, but depend on how and where we use those materials, and in what volumes. Substances that are known to be hazardous in some forms, contexts and volumes can be useful and protective in others. Although it has been banned for use in most applications by the European Chemicals Agency as a substance of very high concern (SVHC), hexavalent chrome is still authorised for use by the aerospace and automotive industries. Because of the unparalleled hardness, shininess and corrosion resistance it gives alloys, it is still used in the as a primer for parts whose failure could have a catastrophic impact on the safety of the car or plane passenger (Wilkes 2014). This known carcinogen can have an indirect and positive impact on human wellbeing.

In thinking through the ways in which stainless steel influences human health and wellbeing this blog post demonstrates that the same material can be both poison and panacea. The health of a material is not just a question of its physical properties and effects on the human body; it is also related to the material’s applications and societal benefits. This post also shows that the perceived health of a material is dynamic, and is as much a question of politics and ethics as it is one of toxicology and materials science: depending as it does on culturally- and historically-specific understandings of toxicology and levels of acceptable risk.

References

Agrawal, C. M. (1998). Reconstructing the human body using biomaterials. Journal of the Minerals, Metals and Materials Society, 50(1), 31-35.

 Antonini, J. M. (2003). Health effects of welding. Critical reviews in toxicology, 33(1), 61-103.

Bentley, R., & Chasteen, T. G. (2002). Arsenic curiosa and humanity. The Chemical Educator, 7(2), 51-60

Erickson, B. E. (2007). Toxin or medicine? Explanatory models of radon in Montana health mines. Medical anthropology quarterly, 21(1), 1-21.

Fitzharris, L. (2017). The Butchering Art: Joseph Lister's Quest to Transform the Grisly World of Victorian Medicine. Scientific American/Farrar, Straus and Giroux.

Gugliemino, B., Lake Thomas, Z., Curtis, B., Baranow, S. and Lotzof, K. 2016. Robert Liston’s Surgical Instruments. UCL Collection Curatorship Project. Available at: https://www.academia.edu/30768024/Robert_Listons_Surgical_Instruments_UCL_Scientific_and_Engineering_Collections_Research

Hansen, K. S., Lauritsen, J. M., and Skytthe, A. (1996). Cancer incidence among mild steel and stainless steel welders and other metal workers. Am. J. Ind. Med. 30:373–382.

Haudrechy, P., Mantout, B., Frappaz, A., Rousseau, D., Chabeau, G., Faure, M., & Claudy, A. (1997). Nickel release from stainless steels. Contact Dermatitis, 37(3), 113-117.

Hulse, J. H. (2004). Biotechnologies: past history, present state and future prospects. Trends in food science & technology, 15(1), 3-18.

Kanerva, L., Sipiläinen‐Malm, T., Estlander, T., Zitting, A., Jolanki, R., & Tarvainen, K. (1994). Nickel release from metals, and a case of allergic contact dermatitis from stainless steel. Contact Dermatitis, 31(5), 299-303.

Keegan, G. M., Learmonth, I. D., & Case, C. (2008). A systematic comparison of the actual, potential, and theoretical health effects of cobalt and chromium exposures from industry and surgical implants. Critical reviews in toxicology, 38(8), 645-674.

Kirkup, J. (1993). From flint to stainless steel: observations on surgical instrument composition. Annals of the Royal College of Surgeons of England, 75(5), 365.

Reynolds, L. A., & Tansey, E. M. (2007). Early development of total hip replacement. Wellcome Trust Centre for the History of Medicine at UCL.

 Schaffer, A. W., Schaffer, A., Pilger, A., Engelhardt, C., Zweymueller, K., & Ruediger, H. W. (1999). Increased blood cobalt and chromium after total hip replacement. Journal of Toxicology: Clinical Toxicology, 37(7), 839-844.

 Simonato, L., Fletcher, A. C., Andersen, A., Anderson, K., Becker, N., Chang-Claude, J., ... & Hansen, K. S. (1991). A historical prospective study of European stainless steel, mild steel, and shipyard welders. Occupational and Environmental Medicine, 48(3), 145-154.

Street, A., & Alexander, W. (1994). Metals in the Service of Man. Penguin Books.

Wilkes, S. (2014). In Search of Sustainable Materials: Negotiating Materiality and Morality in the UK Materials Industry. PhD Thesis, University College London.