INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF RADIOLOGICAL PROTECTION

J. Radiol. Prot. 24 (2004) 295–305 PII: S0952-4746(04)83706-6

High radon exposure in a Brazilian underground coalmine

L H S Veiga1,3, V Melo1, S Koifman2 and E C S Amaral1

1 Instituto de Radioprotecao e Dosimetria, Avenida Salvador Allende s/n, Caixa Postal; 37750,Rio de Janeiro—CEP 22642-970, Brazil2 Escola Nacional de Saude Publica, Fundacao Oswaldo Cruz, Avenida Leopoldo Bulhoes, 1480,Rio de Janeiro, RJ 21041-210, Brazil

E-mail: lene@ird.gov.br

Received 19 September 2003, in final form 20 March 2004, accepted forpublication 30 June 2004Published 27 August 2004Online at stacks.iop.org/JRP/24/295doi:10.1088/0952-4746/24/3/008

AbstractThe main source of radiation exposure in most underground mining operationsis radon and radon decay products. The situation of radon exposure inunderground mining in Brazil is still unknown, since there has been no nationalregulation regarding this exposure. A preliminary radiological survey in non-uranium mines in Brazil indicated that an underground coal mine in the southof Brazil had high radon concentration and needed to be better evaluated.This paper intends to present an assessment of radon and radon decay productexposure in the underground environment of this coal mining industry and toestimate the annual exposure to the workers. As a product of this assessment, itwas found that average radon concentrations at all sampling campaign andexcavation sites were above the action level range for workplaces of 500–1500 Bq m−3 recommended by the International Commission on RadiologicalProtection—ICRP 65. The average effective dose estimated for the workerswas almost 30 times higher than the world average dose for coal miners.

1. Introduction

Underground mining is one of the most important technologically enhanced causes of radiationexposure that greatly contributes to occupational risk since radon gas and ore dust containingmembers of the uranium and thorium decay series are transported to the galleries through wateror air circulation during mining operations.

A considerable amount of evidence has established that prolonged exposure to the α-emitting decay products of Rn, more precisely 222Rn and its progeny 214Po and 218Po, increasesthe risk of lung cancer among underground miners (NRC 1988, 1999, Lubin et al 1994).

3 Author to whom any correspondence should be addressed.

0952-4746/04/030295+11$30.00 © 2004 IOP Publishing Ltd Printed in the UK 295

296 L H S Veiga et al

In response to the abundant evidence of the carcinogenic potential of inhaled radon,occupational standards for Rn progeny concentrations in mines have been implemented inmany countries and exposures have declined since then (Lubin et al 1994). The InternationalCommission on Radiological Protection (ICRP), in publication 65, derives a range of actionlevels for radon at workplaces in the range between 500 and 1500 Bq m−3 (ICRP 1993).

In Brazil, the situation of radon exposure in underground mines is still unknown, sincethere is no national regulation regarding this exposure. There are 74 underground mines inBrazil, according to the National Department of Mineral Production—DNPM (DNPM 1997).Of these, approximately 33 are in operation, with approximately 3200 workers in undergroundactivities. Of the 33 mines, eight are coal mines and seven are gold mines. Among the othersare fluoride, beryllium, feldspar, lead, iron/manganese, zinc/cadmium and tungsten mines.

In 1995, the Brazilian Nuclear Energy Commission conducted a national programmein order to investigate the potential environmental and occupational radiological impactsassociated with some non-uranium mining and milling industries (Fernandes et al 1997, Piresdo Rio et al 2002, Lipsztein et al 2001). The results of this project called attention to thecoal mining industry located in the south of Brazil, which presented high levels of radonconcentration (Matta et al 1998, Veiga et al 2000, Fernandes et al 2002). High values of 210Poin urine samples of some workers from this mine indicated the inhalation of radon progeny asa relevant source of occupational exposure as reported by Lipsztein et al (2001).

Workers from this mine have been working in underground activities since 1942 withoutany compliance with radioprotection regulatory standards, once there is no national regulationto deal with the radiological impact of non-uranium mining activities.

This paper presents an evaluation of radon and radon decay product exposure in theunderground environment of the coal mining industry and an estimation of the workers’ annualexposure.

These results may aid in the preparation of corrective actions,as well as in the improvementof safety measures, where needed. At present, the Brazilian Nuclear Energy Commission isformulating a national regulation to deal with this kind of situation.

2. Area under study

The coal mining industry is located in a very small county with 9000 people, located in thenortheast region of the Parana state in the south of Brazil. The mining industry is in chargeof mining and milling activities and also of the electric energy production at a thermoelectricfacility.

The coal basin region is situated near a uranium deposit. The uranium mineralisationis located in the sedimentary sequence between the coal seam and the calcareous horizoncomprising siltite and limestone. Coal is associated with sandstones, carbonaceous siltitesand coal seams. In sandstones, the uranium mineralisation is found in the form of uraninite,between the interstices of quartz grains cemented by calcareous cement; in carbonaceoussiltites and coal, the uranium mineralisation occurs in the form of organo-mineral complexes.70% of the uraninite is present in the sandstone and 30% in carbonaceous siltites and coal(Daemon et al 1982).

This mine is characterised as one without a methane hazard. In mines with a methanehazard the intensity of the ventilation is always higher, occasioning lower radon concentrationthan that found in non-methane mines (Skubacz and Michallik 2002).

The uranium and thorium content in coal samples of this mine is reported to be 28 and8 ppm, respectively (Fernandes et al 1997). The average activity concentration of coal minesamples from 15 countries is given as 1.6 ppm for both U and Th (UNSCEAR 1982).

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The mining complex comprises the excavation sites, the physical processing unit and solidwaste stocking areas. A total of seven excavation sites have been open since 1942. Six of themhad their activities completely closed. Some of these sites were as deep as 200 m.

A ventilation system was introduced early in the past but it was precarious at that timeand since then radon concentrations in workplace have never been monitored.

3. Methodology

3.1. Radon and radon daughter concentration measurements

Measurements of radon concentration and potential alpha energy concentration of radondecay products—WL4 —were performed inside the underground galleries in order to havean estimation of radon and radon daughter exposure.

For radon concentration measurements,an ‘Alpha Guard’ portable radon monitor (GentronInstruments) was used. For potential alpha energy concentration of radon decay products, a‘WLM-200 plus’ working level monitor (Tracerlab Instruments) was used. Individual radonmeasurements were also performed by using etched track dosimeters fixed to the workers’helmets during the working period.

Radon gas concentration was determined using an alpha particle sensitive Makrofoldetector prepared and analysed according to Urban et al (1985) and Binns et al (1998).

Three sampling campaigns took place. The first campaign was in December 1999.Excavation site 1 was the first one to be explored in the past and it was re-opened to assessthe remaining coal reserves. Excavation site 1 was 138 m deep with a vertical access byelevator. Measurements of radon concentration were performed along the main gallery, fromthe entrance (elevator) until the mining shaft, where most of the underground activities occur.The distance from the entrance to the mining shaft was about 1600 m.

Individual radon measurements were also performed by selecting 12 undergroundworkersto use an alpha track detector fixed to their helmets during working time. Detectors wereattached to the helmets for six working days. Between working hours, the helmets with the fixeddetectors were stored at a room in the surface, where radon concentration was about 10 Bq m−3.This low background radon value was considered negligible. After the measurement period,detectors were removed, sealed in appropriate transport bags and sent by mail to the laboratoryof the Institute of Radiation Protection and Dosimetry to be processed. Detectors were kept ina low radon environment prior to use.

The second campaign was held in May 2000 and site 1 was still active. At this time,the mining shaft was 800 m distant from the entrance. Radon and WL measurements wereperformed continuously during 31 working hours at the front of the mining shaft and 32underground workers were selected to use the alpha track detectors fixed to their helmetsduring their working hours.

The third sampling campaign was in April 2003. At this time, site 1 was completelydisabled and a new site was investigated—excavation site 7, which is of 35 m depth with anaccess by foot through a slanted ramp. Measurements of radon concentration were performedcontinuously during 71 h at the front of the mining shaft and radon individual measurementswere also performed on 44 underground workers using alpha track dosimeters.

4 One working level (WL) equals any combination of radon progeny in one litre of air which results in the ultimateemission of 130 000 MeV of energy from alpha particles. It corresponds to an activity concentration of 3700 Bq m−3

for 222Rn. One WLM is exposure of 1 WL in 170 h per month or 3.5 × 10−3 J h m−3.

298 L H S Veiga et al

Table 1. Results of radon concentration and WL measurements at excavation site 1 of the Braziliancoal mining. Range of values in brackets.

Sampling campaign 1 Sampling campaign 2(December 1999) (May 2000)

Type of measurement N Mean value N Mean value

Workplacea radonconcentration 25 6.0 28 2.4(kBq m−3) (5.1–7.2) (1.7–3.4)

Workplaceb WLconcentration 15 614 9 346(mWL) (458–780) (255–638)

Equilibrium factor, F 15 0.36 9 0.53(0.28–0.46) (0.37–1.05)

Individual radonc

concentration 16 2.8 32 1.1(kBq m−3) (0.7–6.1) (0.2–3.4)

a Instantaneous measurements using Alpha Guard equipment.b Instantaneous measurements using WLM-200 instrument.c Integrated measurements using track etching detector.

3.2. Radon dose and exposure assessment

The annual radon dose was determined employing data from individual radon measurementsand the methodology described by the International Commission on Radiological Protectionin ICRP-65 report (ICRP 1993) and the United Nations Scientific Committee on the Effectsof Atomic Radiation (UNSCEAR 2000). Average individual radon concentration was usedinstead of workplace measurements as it seems to be a more representative measure of radonexposure since it was time integrated.

Average equilibrium factor values can only be estimated for sampling campaigns 1 and2. In sampling campaign 3, no WL measurements were performed. As can be seen in theresults, the average equilibrium factor in sampling campaign 1 was 0.36, ranging from 0.28 to0.46. In the second sampling campaign, it was 0.53, ranging from 0.37 to 1.05. Since thesemeasurements reflect only a portion of the total working hours and can vary with parameterssuch as humidity, ventilation and aerosol concentration, the authors considered the 0.4 defaultvalue for underground mining (ICRP 1993) as more representative for the three samplingcampaigns.

Radon concentration was converted to WL assuming 1 WL is present when 3700 Bq m−3

of radon is in radioactive equilibrium with its daughters. The occupancy in the mine was takento be 1848 h/year for workers, assuming 7 h per day, 6 days per week and 11 months per year.Working level month (WLM) values were estimated using the conversion factor of 5 mSv perWLM at work as suggested by ICRP (1993).

4. Results and discussion

Results of workplace and individual radon concentration and also radon progeny concentrationat excavation site 1 during the sampling campaigns of December 1999 and May 2000 arepresented in table 1.

It can be observed that average values of radon and WL concentrations were lower duringthe second sampling campaign than during the first one (December 1999). Average values

Radon exposure in Brazilian coal mine 299

Figure 1. Variation of radon concentration along the main underground gallery of site 1—firstsampling campaign.

of radon and WL concentration were 6.0 kBq m−3 and 614 mWL, respectively in December1999 and 2.4 kBq and 345 mWL, respectively, in May 2000.

Lower individual radon measurements were also observed for the second campaigncompared to the first one. In the first campaign the average value for individual radonconcentration was 2.8 kBq m−3, while in the second campaign the average value of individualradon concentration was 1.1 kBq m−3.

The average equilibrium factor for the May campaign (0.53) is higher than for theDecember campaign (0.36), suggesting a lower ventilation rate for the second campaign.Nevertheless, the equilibrium factor can vary with many parameters such as ventilation rate,humidity and aerosol concentration in the air, increasing with decreasing ventilation rate andincreasing aerosol concentration.

In this specific situation, different sampling campaigns were realised in different partsof excavation site 1, where conditions of ventilation rate, humidity and aerosol concentrationcould be different. The only certainty is that the mine shaft in the second campaign waslocated closer to the entrance and, therefore, in a more ventilated area. Therefore, the mostplausible explanation for the different average results between the two campaigns would bea better ventilated environment in the second campaign. Other parameters such as aerosolconcentration and air humidity could also be contributing to the equilibrium factor discrepancy.

It can also be observed that individual measurements were almost 50% lower thanworkplace measurements in both campaigns. This can be explained by the fact that values ofindividual radon concentrations were time-integrated measurements over six working days,where the worker is always moving. On the other hand, workplace values were localmeasurements related only to some hours in front of the mine shaft. A radon survey carriedout in South African gold mines also reported individual dosimetry 50% lower than areameasurements (UNSCEAR 2000).

Radon concentration at underground locations can have a great variability, as can be seenin figure 1, which presents measurements along the main underground gallery of excavationsite 1. Radon concentration increases gradually towards the mine shaft, from 1000 Bq m−3 at

300 L H S Veiga et al

Figure 2. Variation of radon concentration and potential alpha energy of radon daughters (mWL)in front of the mining chain of site 1—first sampling campaign.

Figure 3. Variations of radon concentration and potential alpha energy of radon daughters (mWL)in front of the mining chain of site 1—second sampling campaign.

the entrance of the gallery, where ventilation was more efficient, to about 7000 Bq m−3 in themine shaft.

The variability of radon concentration and the potential alpha energy of radon decayproducts (WL) at the mine shaft during the working time in the first and the second samplingcampaign are presented in figures 2 and 3, respectively.

In the first sampling campaign 1, values of radon concentration range from 5.1 kBq m3

to 7.2 kBq m−3 (average = 6.0 kBq m−3) and WL ranges from 458 to 780 mWL(average = 614 mWL). The estimated equilibrium factor was 0.4.

During sampling campaign 2, efforts were made to measure radon concentration for alonger period (31 h) in order to observe variation of radon concentration during the ventilationstops, when detonations occurred.

Radon measurements started at 10:00 (23 May 2000) and finished at 9:00 (24 May 2000).WL measurements were performed only for some of this time due to operational problems.

Radon exposure in Brazilian coal mine 301

Figure 4. Variations of radon concentration in front of the mining chain of site 7—third samplingcampaign.

Table 2. Results of individual and workplace radon concentration at excavation site 7 of theBrazilian coal mine. Range of values in brackets.

Type of measurement N Mean value

Working placea radonconcentration 333 1.25(kBq m−3) (0.78–1.8)

Individual radonb

concentration 44 1.83(kBq m−3) (0.45–3.99)

a Instantaneous measurements using Alpha Guard equipment.b Integrated measurements using track etching detector.

During the working time, the ventilation system stopped three times: the first stop at 11:30(23 May) was due to operational problems. The second and third stops at 17:00 (23 and 24May) were due to detonation activities. No workers were inside at these times.

It can be observed from the data that when ventilation stopped radon and potential alphaenergy concentration increased to values up to 10 kBq m−3 and 2800 mWL, respectively.As soon as the ventilation system was activated, radon and WL concentrations droppeddramatically. The average radon concentration during the ventilated working time periodwas estimated to be 2.4 kBq m−3 as reported in table 1.

In the third sampling campaign, a new excavation site had been opened (excavation site7) Individual and workplace area radon concentrations were investigated in this site and theresults are presented in table 2.

Radon concentrations found at excavation site 7 were lower than at excavation site 1.Excavation site 1 was deeper than excavation site 7 (138 and 37 m, respectively). Besidesthe depth, many factors can contribute to this, such as geology, ventilation circuit and minearchitecture.

In contrast to the observed values at excavation site 1, individual radon measurements atthis site were higher than the working place measurements.

Figure 4 presents the variation of radon concentration during 71 h at the mine shaft ofexcavation site 7.

302 L H S Veiga et al

Table 3. Average radon concentration in some coal mines of the world. Range of values inbrackets.

Average radonNumber of coal concentration

Country minesa (Bq m−3) Source

Britain 12 74 Duggan et al 1968(22–518)

Godavarikhani, India 2 145 Vishnuprasad Rao et al 2001(46–354)

Iran 10 320 Ghiassi-Nejad et al 2002(146–520)

Poland 71 740 Chruscielewski et al 1984(0–7000)

Turkey 5 (31–185) Yener and Kucuktas 1998Pakistan 6 192

(121–408) Qureshi et al 2000Brazil 1 1650

(170–6100) Present study

a Number of coal mines included at the study.

Two programmed stops of the ventilation system occurred at 17:45 and 21:15 in the threedays of measurements. At these periods, auxiliary fans were used during maintenance activitiesthat were performed by eight workers at other locations underground. It can be observed thatthe radon concentration increased from 1.3 to 4.0 kBq m−3 at the mine shaft. After ventilationbegan, it took almost 4 h of continuous ventilation to reach the previous radon concentration.Nevertheless, a group of workers used to start working just 45 min after the beginning ofventilation.

When comparing radon concentration values observed during the unventilated period atboth sites, it can be observed that radon concentrations at excavation site 7 were still lowerthan those observed at excavation site 1. This may indicate that lower radon concentrations atthis site cannot be regarded as only a matter of better ventilation efficiency.

Average radon concentrations at all sampling campaign and excavation sites were aboveor in the range of the action level for workplaces of 500–1500 Bq m−3 recommended by ICRP(1993).

About 92% of radon individual personnel measurements were higher than 500 Bq m−3

and 40% exceeded the upper value of 1500 Bq m−3. If the workplace measurements weretaken into account, 100% were above 500 Bq m−3 and 36% exceeded the upper limit.

Average radon concentrations in some coal mines of the world have been summarised andare given in table 3. In the last row of this table is given the overall average value of individualradon concentrations for the Brazilian coal mine.

It can be observed that the Brazilian coal mine presented the highest average radonconcentration value among all coal mines. Brazilian and Polish coal mines were the only onesthat had radon concentration measurements above the action level range of 500–1500 Bq m−3.Nevertheless, in Polish coal mines only 10% of measurements were higher than 1500 Bq m−3

(Chruscielewski et al 1984).An overall average individual radon concentration can be estimated as 1.7 kBq m−3,

ranging from 0.2 to 6.1 kBq m−3, considering all individual measurements.Taking into account this average individual radon concentration, the average annual radon

progeny exposure in WLM and radon effective doses was estimated, as described previously.

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Average annual exposure to radon progeny was estimated to be 2.1 WLM, ranging from0.2 to 7.2 WLM, and average radon effective dose was estimated to be 10.7 mSv yr−1, rangingfrom 1.0 to 36.0 mSv yr−1.

The world average annual effective dose for underground coal miners and otherunderground ore miners (except uranium miners) was estimated to be 0.36 and 2.4 mSvrespectively, according to UNSCEAR (2000).

The estimated radon effective dose for these Brazilian coal miners is almost 30 timeshigher than the world average dose for coal miners. It is also above the intervention limit forthe workplace of 3–10 mSv yr−1 recommended by ICRP (1993).

Notwithstanding these considerations, the estimate of annual exposure to workers doesnot exceed the annual radon progeny exposure limit of 4 WLM for nuclear industries (ICRP1993). It must, however, be emphasised that these dose estimations take into account only theindividual radon measurements. For instance, the overall average WL radon progeny exposureat excavation site 1 was 514 mWL, ranging from 255 to 780 mWL. If these measurements wereconsidered, it would represent an annual exposure of 5.6 WLM, ranging from 2.7 to 8.5 WLM,which would exceeds the annual limit for radon progeny exposure to workers.

Considering an average of 5 years for an underground exposure time, a cumulative WLMexposure of 28 WLM can be estimated. This cumulative exposure is closer to the exposureestimated for the Ontario uranium cohort study in Canada, which was 30 WLM for an averageexposure duration of 3 years (Kusiak et al 1993).

It can be stated that underground workers of this Brazilian coal mine have been exposedto radon and radon progeny concentration levels that cannot be considered safe from theradioprotection point of view.

In the absence of national regulations to deal with this situation, international regulationsshould be applied. According to ICRP 65 and the European Commission (1997), remedialmeasures should be implemented to reduce this exposure to values below the action level. Ifthis is not possible or if the remedial measures are not successful the exposure of the workershas to be controlled as in nuclear industries.

The most effective radiation protection measure for reducing this exposure has beenimprovements in ventilation. For this, three components are particularly important: the airvolume of the ventilated area, the air throughput and the direction of ventilation (change fromunderpressure to overpressure) (Kraus and Schedt 2002).

In general, exposure in coal mines is low because good ventilation is required toreduce the risk of methane. Nevertheless, coal mines without a methane hazard seem topresent a radiological problem as presented in this paper and also in most Polish coal mines(Chruscielewski et al 1984).

Another relevant aspect to be considered is that these measurements reflect only presentexposure, since radon exposure in the past is unknown. This coal mining industry has beenoperating since 1942 and almost 4000 workers have since then worked in underground activitieswithout any compliance with regulatory standards.

Considering that ventilation systems and mine architectures have been improving throughtime, it could be assumed that radon concentrations in the past should be much higher than atpresent.

Recognising that workers from this coal mine could have been exposed to higher radonconcentrations in the past that were not safe from the health hazards related to decay products,a retrospective mortality study was initiated by the Institute of Radioprotection and Dosimetryand the National School of Public Health to evaluate the possible health effects related toradon exposure. Results from this first radon epidemiological study in Brazil will be publishedsoon.

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5. Conclusions

The average individual radon concentration values at this Brazilian coal mine were above therecommended action level of ICRP 65. If workplace measurements were taken into account,exposure in annual WLM exceeds the annual limit for workers of 4 WLM.

The estimated effective dose is almost 30 times higher than the world average doseestimates for coal miners. It can be concluded that these mine workers have not been workingsafely from the perspective of the health hazard related to radon and radon progeny exposure.Proper remedial measures should be implemented in order to reduce exposure below the actionlevel.

Regarding this opportunity, a retrospective mortality study has been conducted to evaluatepossible health effects related to radon exposure.

Acknowledgments

The authors acknowledge Dr Nilo Schneider, Regional Manager of the Coal Industry, for thesupport given during the sampling campaigns, and all miners who took part in the study.

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