Medical science is fairly clear on the subject. Smoking cigarettes seriously damages one’s health. It is estimated that approximately half of all smokers die from a smoking-related illness. Long-term smokers live approximately 10 years less than non-smokers. Typically, smoking-related deaths are not quick affairs. Yet, there are plenty of people who smoke.

And I have absolutely no problem with smokers at all. Smokers know the risks. Smokers are generally well-informed about such risks as medical science has made its position very clear. And, in possession of that evidence, smokers have still decided to smoke. Good luck to them. 

Where I have a problem, however, is a situation where there is a clear medical risk yet, for some unfathomable reason, it is not understood or more cynically the facts are misrepresented or simply just not made evident. Radioactive watches are in this category. This article sets out to present the points about the health hazards of wearing a watch with high radioactivity levels. As watch collectors, it seems only right that there is some clarification on the issue. So many vintage dealers brush us off with the idea that a radium watch is only dangerous if one inhales/ingests some of the radium dust. This is disingenuous at best.

The issue of radioactive watches is complex. For one thing, watch manufacturers used a wide variety of different radioactive substances including amongst other, Radium-226, Radium-228, Promethium-147, Strontium-90 and Tritium. In order to enhance clarity, I will examine just one variant: Radium-226. I will focus on this isotope for two main reasons. First, this was the isotope that was most commonly used by watchmakers from the 1920s through to the 1960s era - until it was made illegal to use. By far the majority of radioactive watches from this era contain Radium-226. Secondly, Radium-226 has a half-life of 1600 years, whereas other isotopes typically have much shorter half-lives (Radium-228: 5 years, Strontium-90: 29 years, Promethium-147: 3 years, Radium-228: 6 years, Tritium: 12 years). 

For watches, then, that had radioactive material applied with relatively short half-lives, the problem has largely decayed away. Many wonderful vintage watches exist today with very low levels of radioactivity courtesy of the specific isotope applied when first manufactured. Those that had Radium-226, however, are still not even in the adolescence of their prospective radioactive lives. Such watches are, today, very much alive. The question is, are they dangerous? Potentially, yes.

What is the nature of the danger?

Radioactive emission comes in different forms depending on the nature of the isotope. Radium-226 emits Alpha and Gamma particles, though other steps in its decay chain also emit Beta. For the purposes of this article, it is sufficient to consider just Alpha and Gamma. This also makes it easy to understand since Alpha particles cannot penetrate a piece of paper whilst Gamma particles can penetrate virtually anything. This makes the analysis of the radioactive material much easier to interpret. 

Radium-226 and Gamma emission

Radium-226 emits Gamma. Now, this will vary from one watch to another. Amounts used will have varied from one manufacturer to another. Indeed the amount used on one specific watch could vary quite considerably from another of exactly the same reference. It is relatively easy to determine how much Gamma is being produced by a watch. In the past, i have stated very clearly that a simple Geiger counter is totally inappropriate as a tool to determine what type of radiation is in a watch for the purpose of authenticating a dial. I stand 100% behind that statement. However, a simple Geiger counter is very effective at evaluating how much radiation is being emitted. Given that Alpha particles will not pass through a plexiglass and Beta particles, if present, will only penetrate a centimetre or so of aluminium, if a watch is recording high radioactivity readings through more than a centimetre, then what it will be recording is Gamma emission. I took one of my watches and placed it behind 6cm of lead. Gamma was still finding its way through the obstacle. It is, then, quite plausible to evaluate how much Gamma a specific watch is emitting using a Geiger counter.

Does Gamma matter?

Gilmore et al. (2012) at the University of Kingston, cite a study on workers in the luminising industry published in 1981 that indicated that women under the age of 30 had a significantly raised risk of dying from breast cancer. Bruenger et al. (1994) stated that it is not clear whether this mortality risk was due to internal exposure to Radium isotopes (i.e. ingestion/inhalation) or to external radiation from elevated Gamma or Radon gas. It should be noted here that Radon gas is one of the by-products that results from Radium-226 decay (and will be addressed later in this article).

In the December 1985 NAWCC bulletin (vol 27/6 num 239 page 729) it is argued that since some people wear wristwatches 24hrs a day and often sleep with the watch resting against their head, the radioactive Gamma dosage would be “far in excess” of the recommended maximum for the head and eyes. Different parts of the body will be affected differently to Gamma radiation. The study conducted by Gilmore et al. (2012) suggested that the effective dose to the trunk of the body is approximately 80 times greater than to the wrist. For the wristwatch wearer, this would be fine if the watch was exposed solely to the wrist. But with Gamma radiation, the wrist is just the closest area. Gamma will penetrate throughout. Again, here is clear evidence highlighting the risks from Gamma exposure and spelt out clearly by Gilmore in his study.

“Collectors are unaware of the dangers of radio-luminescent material. These dangers might not be insignificant given the radioactivities encountered.”

One of the issues that the Gilmore study did not touch upon was the potential for Gamma radiation to affect people other than the wearer of the watch. For example, babies and small children and spouses who are in regular contact with the exposure. Young children, in particular, can be particularly sensitive to radiation exposure, as detailed in the attached WHO report (http://www.who.int/ceh/capacity/radiation.pdf). 

How much Gamma radiation is on a watch?

There is no standard answer to this. Given that Radium-226 has such a long half-life, one cannot expect its decay to have put much of a dent in its Gamma emissions. Rather, what will determine the extent of Gamma will be how much Radium-226 was applied when the watch was made. This will vary from very small to very significant. Indeed, some watch manufacturers gave their customers a choice in how much luminescence they wanted on a watch. 

The result, today, is that a Radium-226 watch can emit next-to-no Gamma (if minimal Radium-226 was applied) to very high Gamma emissions. One unit of measure that is typically found on a Geiger counter is Micro-Sieverts (uSv). This unit can be defined as a measure of the health effect of ionizing radiation on the human body. Given that this article evaluates health risks, it seems an appropriate measure to use. It is, handily, also what my Geiger counter measures.

In my experience measuring watches on my Geiger counter that I am confident have Radium-226, I have seen readings that have ranged from 1.0 uSv per hour up to 130 uSv. Background radiation usually comes out at between 0.1-0.2 uSv per hour. Clearly, some watches emit significantly more than others. A watch that emits 130 uSv per hour is approximately 1000 times greater than background radiation. I have asked a number of my watch-collecting colleagues to let me know what type of readings they see. The range that I have experienced is fairly common. Readings at 130 uSv are not common, but there are certainly enough to make it important to mention. I am genuinely not sure that there is a typical reading. There does not appear to be a normal curve for the distribution of readings. Rather, between 1.0 up to 20.0, there seems to be an even distribution. This empirical evidence, of course, begs an important question. 

What is a dangerous amount of Gamma exposure?

In just the same way that one knows smoking is dangerous, quantifying just how dangerous it is proves tricky as it varies from one person to another. Further, for watches there are so many variables that will affect the answer that it makes it difficult to be conclusive. For example, how many hours per day is a watch worn? Is the watch worn overnight and hence close to the head or even near the trunk of the body? Is the watch especially high or low in Gamma emissions? Although there are several variables that need to be taken into account, health organisations have tried to give some guidelines into what is equivalent radiation risk. There appears to be a reasonable consensus on what is and what is not dangerous exposure. The following link shows the associated risks as provided by the Senior Reactor Operator at the Reed Research Reactor (https://xkcd.com/radiation/). 

According to this source, the lowest accumulated one-year dose that has been clearly linked to increased cancer risk is 100,000 uSv. Taking its data from the World Nuclear Association, a recent article in the UK Guardian newspaper provided a similar guideline. A dose of 10 million uSv was deemed to be lethal. The typical dosage recorded in those Chernobyl workers who died within a month was 6 million uSv. The accumulated dosage estimated to cause a fatal cancer in 5% of people is 1 million uSv. And, as described above, the lowest annual dose that's been clearly linked to increased cancer risk is 100,000 uSv. For comparison, a full-body CT scan is the equivalent exposure of uSv 10,000. This framework provides a very good guideline for comparison.

Source: WNA, Reuters, Radiologyinfo.org g

Prima facie, this would suggest a fairly material risk from wearing Radium-226. Unfortunately it is not as simple as that. Collectors rarely wear the same watch all year. The proximity of the watch to especially vulnerable body parts is also a major criterion. The area around the genitals is 20 times more “vulnerable” than the wrist. The main body organs are approximately 80 times more “vulnerable”. The effective dose from the Gamma will, then, vary according to where it is located. Pocket watches, for example, typically emit a much higher effective dose of Gamma as the watch is located in the vest. Notwithstanding this caveat, a study conducted by Haybittle (1958), showed that  significant dose rates have been measured through the back cover of timepieces containing Radium-226.

Boerner and Buchholz (2007) presented nine exposure scenarios in a study for the U.S. Nuclear Regulatory Commission in order to assess the potential dose from Radium-226 wristwatches. The first of these scenarios (Gamma dose to the skin from wearing a Radium-226 timepiece for 16 hours per day) estimated the exposure  at 16000 uSv/year. However, the assumption made in this study was that the average emission rate from the Radium-226 was uSv 2.8 per hour. Gilmore et al. (2012) made a similar assumption based on a sample of 18 watches they had purchased for the purpose of the study. It should be noted that although the mean emission was around uSv 3 per hour, the sample had a standard deviation of 4.5, with one watch emitting uSv 20.0 per hour. In my experience, the majority of watches with Radium-226 emit over uSv 5.0 per hour and readings of over uSv 10.0 are not at all unusual. It may be that higher quality manufacturers tended to use more Radium than used in cheaper watches. 

So, based on these academic studies, and assuming an emission rate of around uSv 3 per hour, the average watch wearer will be exposed to approximately uSv 16,000 per year. On these calculations, it would take about 6 years before a clearly defined cancer risk was evident. Of course, we come back to the issue of whether the wearer is exposed to an effective dose or not and also the same imponderables about whether the wearer sleeps with the watch or not. There are many imponderables. The purpose here is to create a reasonable framework for assessing the risks.

An emission rate of uSv 3 per hour, however, as assumed by the academic studies, appears low. For a watch that has an emission rate of uSv 10 per hour, the cancer risk threshold is reached in under two years. For the more aggressive emitters of uSv 130+ per hour, it takes about 50 days. This all assumes the watch is removed during sleep. If it isn’t, then the threshold is reached much sooner.  It would be the equivalent of having a full CT scan every 3 days.

The risks from Gamma from a watch with Radium-226 appear not just evident but also elevated. Regrettably, the risk from Gamma is not the only factor to consider.

Radium-226 and Alpha emission

If you are wearing a watch with Radium-226, the alpha emissions will not penetrate the case or the plexiglass. They will never reach the body. Even if they did, they would not be able to penetrate the skin. The risk from Alpha particles comes almost entirely from the prospect of ingesting or inhaling some of the radium dust. If you take off the plexi from a radium watch or you decide to replace hands or inspect the movement, then this type of workmanship will, quite plausibly, lead to the possibility of inhaling or ingesting some of the dust. There is, regrettably, substantial amounts of scientific evidence showing that the inhalation/ingestion of Radium-226 causes very severe and fatal illness. The well-documented effects of radium inhalation that occurred amongst the users of radium paint in the watch industry in the first two decades of the 20th century bears sad testimony to this issue. 

https://en.wikipedia.org/wiki/Radium_Girls

Inhalation/ingestion of Radium-226 “dust” and subsequent fatality is not a subject that carries much contrary argument. A study by a Harvard University team led by Cecil Drinker confirmed another study by Frederick Hoffman, the former president of the American Statistical Association,showing overwhelming evidence of direct causation.

Although it is important to avoid generalisations, for a watch that has been lumed with Radium-226, it is extremely likely that the radium decay that has taken place will have bombarded the lume paste in place to such an extent that considerable amounts of lume will have been displaced into dust. It should be recognised that such decay in Radium-226 breaks down into daughter elements such as Radon-222, which can be every bit as lethal as Radium-226. The bottom line is quite simple. if you own a vintage watch that has Radium-226 on its dial, then it is highly advisable never to remove the plexi from the watch or the caseback. The dust can readily find its way under the fingernails and then subsequently into food. That, of course, presents risks to not only the individual inspecting the watch, but also those around him. In the event that the plexi gets cracked or breaks, it would be advisable to handle the dial with extreme caution. Robert Free, of the Texas Department of Health, Bureau of Radiation Control wrote an article in the June 1988 NAWCC Bulletin. To quote from that article;

“Individuals manufacturing the jewelry [made from old watch parts] are exposed to dusts containing radium from buffing and brushing exposed watch faces, dials and hands. As a result, they run an increased risk of cancer from ingestion and inhalation of radioactive particles. People who repair and refurbish old watches are also at risk.”

In reality, just like our hypothetical smoker, many vintage watch collectors will be happy to live with the risks from Alpha particles because in all likelihood, most collectors never really get close to inhaling or ingesting the Radium dust. This seems a risk that some are prepared to take. Indeed, many experts often end their analysis at this point, stressing that so long as you don’t inhale or ingest Radium dust, risks are minimal. I believe it is very premature to argue that inhalation risk is the extent of the problem. It is, clearly, a risk, but by no means the main risk. To my mind, courtesy of its unobtrusiveness to the casual collector, Gamma poses a much more material risk. Again, however, the analysis doesn’t end there. Gamma also poses an additional risk. This additional risk comes from a direct by-product of Radium-226 decay in the form of Radon gas.

What about Radon gas risk?

When Radium-226 starts to decay, Radon gas is one of the by-products. There is no disputing this. Every watch with Radium-226 will release Radon gas. Is Radon gas dangerous? Radon is a cancer-causing radioactive gas. In the US, the Surgeon General has warned that Radon is the second leading cause of lung cancer in the United States today. It cannot be smelt or tasted. And it is being released every second on a watch with Radium-226. Furthermore, where a collector has a large collection of watches kept in a specific room, the build-up of Radon can be quite material, affecting the entire household. This issue was one tested by Gilmore et al. (2012). The findings are quoted directly below:

“Significantly, there is also a risk to amateur collectors from radon gas emitted from the radium. Routine radon concentrations of ca. 200 Bq/ cubic metre peaking to over 3000 Bq/ cubic metre, were recorded in this study: such levels represent a significant potential health hazard.”

The WHO quantify the risks quite clearly. For each additional 100 Bq/cubic metre of exposure to Radon gas, lung cancer risk rises by 16%. A more detailed review is given in the attached WHO report; http://www.who.int/phe/radiation/backgrounder_radon/en/. So, taking the Gilmore study as a reference range, lung cancer risk from the wristwatches in his study was raised between 32% and 480% directly as a result of Radon gas exposure. Gilmore’s watches, of course, only emitted Gamma at an average rate of uSv 3 per hour. If a watch emits at a much higher level, then expect a much higher emission of Radon. Further, as Gilmore points out, if a watch is worn overnight, the risk to the wearer is seen as significantly greater as the Radon emission is much more likely to be inhaled. Indeed, the Gilmore study stated:

“Furthermore, in the light of the Radon results, it would highly inadvisable to sleep wearing such a watch with the possibility that the watch-bearing wrist – where the Radon will be most concentrated – can be very close to the wearer's nose and mouth for extended night-time periods exposing the wearer to significantly increased inhalation of radon.”

It should be understood that the half-life of Radon gas is just 3.8 days. Hence, if it is inhaled into the lungs, there is a high probability that it will decay whilst in the body, thereby emitting Alpha particles directly into the body. It is the equivalent of breathing in Radium-226 dust.

The authors of this paper concluded in the following way:

“There is a need in the authors view to acknowledge that health risks associated with radium artefacts are a serious issue. The results presented in this study may in fact be just the tip of the iceberg. The risks of radioluminescent materials has been largely forgotten as most modern materials are much less radiotoxic because each isotope emits only low energy beta, being based on tritium or promethium  particles, or even non-radioactive luminous material (e.g. ‘Lumibright’). This suggests that more publicity to emphasise the risks would be an appropriate course of action.”

I think it is worth re-iterating that the authors of this published academic paper reached this conclusion based on Gamma emission rates averaging just uSv 2.0-3.0 per hour (depending whether it was the front or the back of the watch). In reality, emission rates can rise materially higher than this. I have seen others test watches that have reached well over 200 uSv per hour. And with higher emission rates come increased Radon gas emissions too. Where a collector has a large collection of Radium-226 watches, the accumulation and concentration of Radon gas can, plausibly, reach very extreme limits that will be significantly in excess of the WHO recommendation of a maximum of 100 Bq/cubic metre. This will impact on all members of the household and especially those who spend long periods of time in the household. The issue is put well by the US Environmental Protection Agency:

"Any radon exposure has some risk of causing lung cancer. The lower the radon level in your home, the lower your family's risk of lung cancer.”

Why is this issue not at the forefront of the vintage collectors attention?

Why are watch experts not paying attention to this? Well, I think there are many possible answers to this. 

• For some collectors, the joy of the watch overrides all associated risks. This is our happy smoker. This collector knows the risks, but just doesn't care. Each to their own.

• For some vintage collectors, the risks are just not known. I think it is fair to say that these risks are not generally well-highlighted. 

• The vintage watch industry is big business. Does it have an interest in advertising the associated health risks? Maybe it is assumed that buyers should do their own homework? Nobody denies that smoking can cause cancer. Nobody denies that high levels of radiation can also cause cancer. But cigarette companies still sell cigarettes. And I am sure vintage dealers will continue to sell Radium-226 watches. But should it not be done with more disclosure of the risks, just as in the warning on cigarette packets?

• Watch manufacturers used many different types of radioactive material. Being able to identify what is being used and how radioactive a specific watch is can be hard in the absence of a usable Geiger. Two identical watches, from the same manufacturer, same reference and even similar serial numbers can vary widely in terms of how radioactive they are. In short, its hard for a collector to know if a watch he is buying is or is not at a dangerous level of radioactivity. 

• The science behind what is and what is not dangerous is not foolproof. Just like cigarettes, it is difficult to prove that exposure to high levels of Gamma radiation are lethal (in all but the most extreme examples!). Gamma exposure can plausibly kill over a number of years, making it hard for collectors to evaluate the risks.

A personal view

I think there are clear and identifiable risks associated with wearing a vintage watch with Radium-226. Those risks vary, but in certain circumstances are very high. Collectors should appreciate that a Radium-226 dial poses a real health risk not only to the wearer but also to those in regular close proximity to the wearer. That risk will vary depending on a number of factors and I would put forward the following checklist;

• A simple Geiger counter can be purchased at a reasonably low price. This will enable a quick test to evaluate how much Gamma radiation is evident in a watch. Generally speaking, watches with radioactive lume manufactured between the 1920s and the 1960s will, typically, have had Radium-226 applied. That is a decent working assumption. Some will have different isotopes with much shorter half-lives. For Radium-226, however, expect the Geiger counter to light up.

• If a watch is identified with Gamma radiation, evaluate at what point you feel comfortable with the risks. Clearly, a watch that emits over 10 uSv per hour is one that I would simply not want to wear. It would be the equivalent of having 1-2 chest X-rays every single day. One that emitted at 1 uSv per hour might be something I would wear intermittently. Everyone will have their respective tolerance levels. uSv 100/hour? I actually wouldn't want to be next to someone with such a watch. 

• With Radium-226, be aware that it carries a much greater risk to health if the watch is worn overnight courtesy of the Radon gas emission as well as the higher vulnerability of the head to Gamma.

• Radiation dust that will exist on the dial is toxic. Never open a watch. I think this rule needs to be quite categorical.

• Radon testing kits are very cheap and easy to use. For collectors that have Radium-226 watches, especially those with large collections concentrated in the same place, it would be a great idea to test for Radon.

This article aims to provide a starting point from which collectors can build upon in making an evaluation. The issue needs much greater openness. One could further argue that legislation should be considered for emission rates that are above certain levels. Radium was banned from use in the 1960s. It was deemed dangerous enough to pass legislation preventing the use of Radium. That was 50 years ago. Since the 1960s, much more evidence has emerged regarding the danger from Gamma exposure and Radon gas to make the issue pertinent to legislation today. At a minimum it requires much more scrutiny.