RADON AT THE ISTARSKE TOPLICE HEALTH RESORT

Nevenka Lokobauer, Zdenko Franić, Dragan Kubelka, Jasminka Senčar, Enis Sokolović

Institute for Medical Research and Occupational Health, Zagreb

Ksaverska cesta 2, PO Box 291, HR-10001 Zagreb, Croatia

Tel.: +385-1-4673188, Fax: +385-1-4673303

Abstract

This paper deals with the determination of radon concentrations and estimations of radiation risk from radon inhalation in the spa of Istarske Toplice which is known as "sulfur radioactive spa".

Investigations include indoor measurements around the pool and premises used for a medical cure with spring water or healing mud (fango). Since all the premises in a therapeutic ward of Istarske Toplice were interconnected, measurements were also performed in the premises for rehabilitation and electrotherapy.

Taking into account observed variations in 226Ra concentrations in spring water, which lead to variability in indoor radon concentrations, measurements were repeated several times in one year in order to assess occupational exposure as accurate as possible. Indoor measurements were mostly performed at the level of about 2m above a water surface. Average annual radon activity concentrations measured at selected measuring sites inside the spa ranged from 98 ± 25 to 872 ± 112 Bqm-3. Estimated effective doses for workers who spend the whole working day at selected measuring sites ranged from 1.5 ± 0.1 to 6.3 ± 0.8 mSvy-1.

Analyses of chromosome aberration in the blood samples of eleven workers were also included in the study.

Introduction

The assessment of the radiation doses in humans due to natural sources is of particular importance because natural radiation is the largest contributor to a collective dose of the world population. Off all natural sources of radiation, it has been estimated that inhalation of radon (222Rn) and its short-lived decay products accounts on average for about one half of the effective dose (1).

Over the past few years the Radiation Protection Unit of the Institute for Medical Research and Occupational Health, Zagreb, has been engaged in the study of indoor radon activity concentrations in the Republic of Croatia. Elevated concentration of radon detected at certain locations pointed to a need for more detailed assessment of radon levels and associated risk to some population groups.

This paper deals with the investigations of radon concentrations and estimations of radiation risk from radon inhalation for occupationally exposed persons who work around the indoor swimming pool and premises used for a medical cure at the Istarske Toplice health resort. The spa of Istarske Toplice (Istrian Peninsula) is known as "a sulphur radioactive spa". Investigations of radon activity concentrations in the spa have been conducted since 1992. Detailed investigations at selected measuring sites inside the spa of Istarske Toplice were performed from March 1994 to March 1995 as a part of a project with International Atomic Energy Agency entitled "Elevated radon concentration and related health effects ". The primary aim of the investigations was to estimate exposure doses from radon inhalation to relevant occupationally exposed persons.

Methods

Radon activity concentrations were measured by solid state nuclear track detectors - Kodak Pathe LR-115 films, type II. Investigations were performed by means of open (cassette) and filtered detectors (diffusion chamber). Detectors in a diffusion chamber with a volume of 0.24 dm3 were covered with a glassfiber filter of 0.07 kgm-2 surface density. The detectors were exposed indoors ( at the locations of interest ) over the period of two to six months, and were then etched in 2.5 N NaOH aqueous solution at 60 °C for 90 min. The track densities of bare and filtered detectors were counted visually using an optical microscope, magnification 10 x 15. Kodak LR-115 films in a diffusion chamber and in a cassette were calibrated in National Radiological Protection Board, Chilton, Didcot, Great Britain. For the purpose of intercomparison of the obtained results, at several locations radon activity concentrations were measured by means of a Radhome silicon detector (CMPR, France) and by KfK radon diffusion chamber (MAKROFOL E). In the spa detectors were mostly installed at the level of about 2 m and, if feasible, 0.5 m above water surface or floor.

Results and discussion

Preliminary investigations of radon activity concentrations in the spa of Istarske Toplice started in 1992. They included indoor measurements around the swimming pool and in some premises used for a medical cure. The elevated radon activities detected in preliminary measurements performed in 1992 and 1993 in the spa of Istarske Toplice called for further investigations.

Taking into account observed variations in 226Ra concentrations in spring water (2) which leads to variability in indoor radon concentrations from March 1994 to March 1995 measurements were repeated several times in order to assess occupational exposure as accurate as possible. Investigation included indoor measurements around the pool and premises used for a medical cure with spring water or healing mud (fango). Since all the premises in a therapeutic ward of the Istarske Toplice were interconnected, measurements were also performed in the premises for rehabilitation and electrotherapy. Results of radon activity concentrations in the spa of Istarske Toplice are given in Table 1.

Table 2 gives average indoor radon activity concentrations measured from March 1994 to March 1995 at selected measuring sites inside the spa. The table also gives the estimated annual effective doses from inhalation of radon and radon progeny for workers who spend the whole working day at selected measuring sites (annual occupancy of 2,000 hours per year).

Table 1	Indoor radon activity concentrations in the spa of Istarske Toplice measured from March 1994 to March 1995

MEASURING SITE	EXPOSURE PERIOD
March-May 1994	May-July 1994	July-Sep.1994	Sep.1994-March1995
Activity concentration (Bqm-3)
Swimming pool	932	± 38	882	± 31	985	± 42
944	± 35	689	± 22º	1100	± 55 K
903R	735	± 28
Therapeutic bath	695	± 30	659	± 31	722	± 23
605	± 26º
Electrotherapy	140	± 14	84	± 9	77	± 7
90	± 10º
Gymnasium	434	± 24	270	± 19	227	± 17	294	± 18
Inhalatory room	958	± 35	348	± 22	459	± 24	398	± 23
Fango preparation	1022	± 36	546	± 24	657	± 28	539	± 24
500	880	± 32
540	± 49K
646	± 29
Fango therapy	184	± 16	229	± 17	218	± 16
192	± 12º

diffusion chamber damaged or taken away	R	activity measured by Radhome detector

º	data from bare detector	K	activity measured by KfK detector

detector was set up 0.5 m above the water level

Table 2	Average annual radon activity concentrations in the spa of Istarske Toplice and the estimated effective doses for the workers who spend the whole working day at selected measuring sites

MEASURING SITE	Activity concentration

(Bqm-3)	Effective dose

(mSvy-1)
Swimming pool	872	± 112	6.3	± 0.8
Therapeutic bath	670	± 44	4.8	± 0.3
Electrotherapy	98	± 25	0.7	± 0.2
Gymnasium	306	± 78	2.2	± 0.6
Inhalatory room	541	± 244	3.9	± 1.8
Fango preparation	691	± 197	5.0	± 1.4
Fango therapy	206	± 18	1.5	± 0.1

The maximal radiation dose was received by the workers who spend the whole working day around the swimming pool or in the room for fango preparation. The estimated annual effective doses for them are 6.3 mSv and 5.0 mSv, respectively.

Since the premises in the therapeutic ward of the spa of Istarske Toplice were interconnected, all workers (medical nurses in particular) are occupationally exposed to elevated radon concentrations. Assuming that they spend one hour a day at selected sites where radon measurements were carried out, and an additional hour at a canteen (measured radon activity was found to be 60 Bqm-3) each worker would receive the annual effective dose of 3.3 mSv.

Genetic damage is (owing to its consistency, universality and sensitivity) a good parameter for measuring the effect of ionizing radiation on different biological system (3). For this reason analysis of chromosome aberrations was chosen to determine possible effect of radon in the working environment, in all workers occupationally exposed to elevated radon concentrations. The investigation was carried out in the sample of 11 workers who differed by age, sex and occupation. The frequencies of chromosomal aberrations (200 metaphases per each subject) are given in Table 3.

Table 3	Frequencies of chromosomal aberrations (200 metaphases per each subject)

Subject I	∝	Subject VII	∝∝
Subject II	∝	Subject VIII	∝
Subject III	∝∝	Subject IX
Subject IV	∝	Subject X	∝
Subject V	∝	Subject XI	∝
Subject VI
Chromatid break

∝	Chromosomal break

Accentric chromosome

Analysis of chromosome aberration showed that obtained values were in accordance with the control values for general population of the Republic of Croatia. Future investigation of indoor radon activity concentrations in the spa of Istarske Toplice will be continued and cytogenetic investigation of ambiental exposure to radon in the working environment should be repeated in the period of maximal radon concentration.

References

1.	UNSCEAR. Sources and Effects of Ionizing Radiation. United Nations, New York, USA 1993.

2.	IAEA. The Environmental Behaviour of Radium. Technical Reports Series No. 310. Vol. 1. International Atomic Energy Agency, Vienna, Austria, 1990.

3.	Pohl-Ruling J.: "Chromosome aberrations of blood lymphocytes induced by low level doses of ionizing radiation", Advances in Mutagenesis Research. Ed.: Obe G. 2, Springer-Verlag, Berlin, Deutchland, 1992, pp155-190.