RADON MONITORING IN AUSTRALASIAN TOURIST CAVES: THE WHY, WHAT AND WHEREFORE OF THE WORKSAFE STUDY

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

INTRODUCTION

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.

REGULATIONS

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.

MOTIVATION FOR THE WORKSAFE STUDY

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:

• Economies of scale, both financial and in effort.
• Directly comparable results from all caves measured, due to a common method and common calibration standard.
• The possibility of external funding, relieving smaller and remote operations in particular of a disproportionately heavy expense.
• A 'screed' of all caves so that further monitoring and research, if necessary, could be targeted to those areas which had the potential to result in high doses to employees.
• The provision of data on which wise management decisions could be taken, given that the best available data, that from Buchan in Victoria, was almost certainly not applicable to other caves nor, indeed, even to other times in the same cave.
• The study would be the most comprehensive and geographically diverse study of radon concentrations in caves to date and would add significantly to our knowledge of radon in caves on an international basis.

THE TEAM

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.

THE METHODOLOGY

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:

• A total of 270 sites, covering 57 cave systems in 23 locations from all states in Australia are being monitored in the Worksafe study.
• The monitors are passive track etch detectors, calibrated by Australian Radiation Laboratory. Four monitors in each site cover the four seasons, while an additional monitor remains in situ for the whole year to collect an annual average and provide a cross-check with the seasonal data. Sites have been selected to be representative of each cave, and the times which tour guides spend in the areas of the caves represented by each site have been noted. Not every tour stop has been individually monitored, as some are expected to have very similar readings to nearby sites, and we needed to maximise the use of our resources.
• The study is collecting seasonal average radon concentrations. These values may not be typical of the times at which most tours occur, eg day and night values may be very different, but this will not be observed in seasonal averages. In addition, it is not radon itself that constitutes a potential health risk but the products of radon, known as radon daughters or, to be politically correct, radon progeny. Why then do we measure radon instead of its offspring?
  Firstly because radon is easier to measure. Secondly, because if radon is low then so will be the number of radon progeny. So if we can show that average seasonal radon is very low, it will not be necessary to measure the radon progeny directly and we can eliminate caves from further monitoring. If the average radon values are high, these caves will require further work, and this is where future efforts should be targeted.

RESULTS TO DATE

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.

IMPLICATIONS

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

• We can close the caves and all go home — a knee-jerk response.
• We can ventilate the caves to dilute the radon. In a gathering such as this I don't need to spell out the possible adverse effects of this on the cave biota and the speleothems which are one of the principal attractions of many of the caves. It is also not always effective and may in fact even draw more radon into the cave air. NOT RECOMMENDED!
• The probable dose received by an employee can be calculated and action taken if this, rather than the concentrations are high (this has been done in the since-published Worksafe Report). When the actual hours worked are taken into account, the dose due to exposure even to relatively high levels of radon, may still be low enough not to be of concern.
• Personal dosimeters can be provided and employees taken off underground duties when their accumulated dose reaches the maximum permitted - a reactive management response. Effective in fulfilling legal requirements and ensuring employee safety standards are met, but may have undesirable social consequences, or make fostering of duties difficult.
• Seasonal data can be used to estimate dose for different tours in different seasons. Tour duties for individual guides and maintenance could be scheduled to minimise expected doses. For example, we might know one area of a cave is high in summer and but low in winter (a scenario we might find if a cave's ventilation system is driven by external/internal temperature differences). It makes sense to schedule maintenance work in this area in winter, and allocate work in a low summer/high winter area in summer if possible.
• Estimates can be refined so they are more accurate. For example, standard factors used to convert radon concentrations into dose from radon progeny can be actually measured instead of assuming a value based on measurements taken in houses and mines.
• We can carry out more in-depth research to find out how, when and why radon and radon progeny concentrations vary, in greater detail than the relatively coarse estimate provided by average seasonal data. We can then use this information to plan tours and rosters to minimize doses to any one employee. The more we know and understand, the greater the opportunity for proactive management. And the less we will be restricted by the necessary safety regulations.

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.

REFERENCE

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.