R G Lyonsl, S B Solomon2, R Langroo2, J R Peggie2 and J M James3

lDepartment of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand, 2Australian Radiation Laboratory, Lower Plenty Rd, Yallambie, Victoria 3085, 3Dept of Chemistry, F11, University of Sydney, Sydney, New South Wales 2006


Recently the attention of the media has been grabbed by the fascinating combination of those dark threatening places, caves, with the dread spectre of cancer-causing radiation, which, you will agree, is not good for tourism or peace of mind. Those of us who have been approached by the media - including journalists from every major newspaper from the Sydney Herald to the Te Kuiti Times, as well as national radio and television - have been at some pains to prevent a totally unnecessary and counterproductive feeding frenzy. As flavour of the month radon in caves is, hopefully, now somewhat passé, but that does not negate the original concern which prompted our study, that some caves overseas had been shown to have sufficiently high levels of the radioactive gas, radon, to pose an increased risk to the health of people who spend extended periods of time in them, and that we in Australasia knew little about the levels of radon in the caves in which many of us work.

First, let's be clear about what precisely the risk of exposure to radon may be. The risk is NOT that anyone exposed to radon will turn green and collapse, or develop acute radiation poisoning, bums, nausea and die within days! Our caves are not bombs waiting to go off - in fact, in the event of a nuclear holocaust, our caves would be one of the safest places to be! It is that, with prolonged exposure to high levels of radon, a person will have an increased risk of developing lung cancer or other cancers of the respiratory tract. In this case it is similar to smoking - it doesn't follow that in either case, the person WILL develop cancer, or that, if they do, the cancer will be due to exposure to cigarette smoke or radon, simply that exposure to either substance will increase the risk of developing cancer.

The relationship between low levels of exposure to radon or any other radioactive substances, or to environmental factors such as Agent Orange or smoking, is always difficult to establish precisely. It has taken years of extensive studies involving large numbers of people to convince people of the link between smoking and lung cancer, indeed the tobacco companies still claim that the evidence is "inconclusive". This difficulty of proof is inherent in any study of environmental factors. Because there are so many factors that may affect each individual, for example, age, diet, genetic predisposition, race, sex, other illnesses, lifestyles, etc etc, it requires a very large number of people to participate in a study in order to isolate any one factor such as smoking, to show a statistically convincing link. A classic example is the US government claiming, correctly, that there was no statistically proven link between the exposure of service personnel in Vietnam to Agent Orange and the medical problems so many of them were having.

No wonder! To achieve the level of proof they demanded, would have required a study involving no less than four times the total number of people who served in Vietnam during the whole of the war!

How then can we hope to demonstrate a conclusive link between radon in caves and an increased health risk to people who work in them? Because we can't prove radon is a cause in any one case of lung cancer for example, does that mean there is no risk? Our concerns are the result of the study of radiation, such as X-rays, nuclear fall-out, medical uses of radiation, where health risks have been clearly demonstrated for higher doses. From these proven links for high dose cases, scientists extrapolate to determine the much lower risk for low doses. There is some controversy whether the risk for low doses is simply proportional to the risk for higher doses, or whether, as was once believed, there was no risk for doses below a certain level. The jury is still out on this, but it is worth noting that recommended 'safe' levels, are continually being revised downwards. On the other hand, we should also remember that every living thing on earth, including ourselves, is constantly exposed to low levels of various types of radiation and indeed the damage caused by radiation to our cells has probably been an essential part of evolution.


The level which the International Commission on Radiological Protection (ICRP) proposed as a 'safe' level, below which no action is necessary, corresponds to 2-3 times a normal 'background' level, to which the average person is exposed in normal daily living. These recommendations are in the process of being adopted by individual state governments. Specifically they are, that when a working environment has concentrations of radon which exceed 1000 Becquerels per cubic metre, either levels must be reduced by intervention such as ventilation, or people working in that environment must be monitored to ensure the total dose they receive at work is less than 20 mSv per year.

At the maximum levels of exposure recommended by the ICRP, the increased risk is comparable to that of smoking 2-3 cigarettes a day, or to passive smoking. Why then, should we be concerned? Particularly when many cave workers are heavy smokers and indulge in other hazardous activities, such as driving on our roads or even caving? The difference is clear-cut. If people are exposed to increased risk of any sort through their work, this is ethically and legally very different from a voluntarily assumed risk - the Marlborough Man is currently suing his erstwhile employer because he has developed lung cancer which he maintains may be due to his smoking cigarettes in making the advertisements.

Measurement of radiation levels. and radon in particular, are not straightforward. Because the health effect of radiation depends on many things, not just the crude measurement of how much radiation there is, but also on how long the person is exposed to the radiation, what type of radiation it is, where it is absorbed in the body (in the case of radon and its products, in the lungs themselves), and on other external factors such as the health, age and lifestyle of the person, radiation dosimetry is very complex. It's important to understand one thing in particular, though: the risk depends on the TOTAL dose, which is the concentration multiplied by the time during which the person is exposed - a high concentration for a short time has exactly the same risk as half the concentration for twice the time. The guidelines are based firstly on a sample easily carried out measurement of overall levels, below which there is no cause for concern and no more complex monitoring needs to be carried out. At these levels even if a person spent 2000 hours per year working in the area their total dose would still be less than recommended maximum. If these levels are exceeded, then personal monitoring needs to be undertaken which will give the total dose received by that individual during the time they actually spend underground. If these also show high risk levels, then further action needs to be taken (see later). Personal monitoring, though more informative, is more expensive than simple measurements of average radon concentrations; where the simpler measurements of radon levels are low enough, clearly it's easier for all concerned.


The motivation behind this study was NOT to disrupt the operation of tourist caves, nor to provide scientists with things to do - we, like you, have plenty to keep us busy! - but to avoid blind bureaucratic sledge hammers and public panic. The alternative, of course, was to wait for the regulations to be passed - and I remind you that the recommended regulations were initiated by the ICRP quite independently - sit back and collect consultancy fees. Given that it is a legal responsibility of employers to provide a safe environment for employees, and that some overseas caves had been shown to have elevated levels of radon, it would be rash for any operation not to carry out monitoring and this additional expense might well have strained the resources of smaller operations. We saw the advantages of a single Australasian wide study as:


The study was a cooperative effort, with each of us contributing a different expertise.

Critically important was the contribution of Julia James: without Julia as an Australian academic, we would not have been eligible for funding from Worksafe Australia; neither Australian Radiation Laboratory, as a government body, nor myself (R.G.L.) as a non-Australian, were eligible. The Australian Radiation Laboratory contingent were responsible for the laboratory analysis and technical input while I carried out the fieldwork "you can have the caves, we'd rather not" - "thanks guys, each to their own".

A study such as this is simply not possible without the cooperation of those on site. We are deeply indebted to those of you who assist by changing the seasonal monitors - while it would be lovely to visit each cave every 3 months, it just isn't practical. We are also most grateful for feed-back and the careful observations many of you have contributed. Your knowledge of your own caves is extremely valuable, and not something that can be obtained in any "expert's" short visits to your caves. Special thanks are due to many of you who have contributed in so many ways, with hospitality and practical help. Most of you are here today, and I can express our gratitude to you directly, but we would like to thank especially Bill Chandler of Western Radiation Services, who facilitated the work in the Margaret River caves - Bill regretted he could not be with us at this ACKMA conference.


Details of the methodology are given in the full report of the study which has been published since this talk was presented (Solomon et al, 1996).

Features worth noting are:


At time of the ACKMA conference in Tasmania at which this paper was presented results were in the mail to each cave manager detailing the first results, for winter and spring seasons. Now that the complete report is available, it is superfluous to present the detailed preliminary results in this report (if you have not got a copy and would like one, feel free to request one from the Australian Radiation Laboratory.) General points worth noting are:

Firstly, that most cave sites are sufficiently low to fall below the levels at which further monitoring is required. However approximately 20% are above the cut-off level, above which the problem cannot be ignored — the study is definitely worthwhile and indeed necessary!

Secondly, there is a great variation, not only between regions and caves within any region, but even between sites in the same cave. There is also very marked seasonal variation — low concentrations in spring do not mean that there will be low concentrations in winter, nor do high values in one season imply high values in another. Because of this, it is imperative that data be collected for the full year.


IF the high values measured in some locations prove to be typical of annual concentrations, there are a number of possible management options:

Once more, we would like to thank you all for your cooperation in what must seem at times a tedious exercise, and maybe even of dubious relevance given all the other risks that living entails. We assure you, however, that the study is proving that it is indeed a necessary exercise. We hope the study will show that most of us do not need to carry out further monitoring, and where that fortunate result is not obtained, that the data gathered will be of significant value as a management tool.


SOLOMON, S.B, LANGROO, R., PECGIE, J.R., LYONS, R.C. and JAMES, J.M. 1996. Occupational exposure to Radon in Australian tourist caves. An Australia - wide study of Radon levels. Final report of Worksafe Australia Research Grant (93/0436) Aust. Rad. Lab. Rept ARL/TR119 16pp.