Episodes of thoron exposure due to consumer products claiming health benefits of negative ions

Jaiki Lee

(Korean Association for Radiation Protection,Seoul,Korea)

Abstract:In May 2018,the primetime news casted a shocking report saying that radon concentration on a certain model of bed mattress found to be as high as 2 200 Bq/m3.After a humble,the Nuclear Safety and Security Commission(NSSC) of Korea confirmed that significant amount of thoron gas is emanated from several mattress models marketed by a company claiming beneficial health effects of negative ions.Laboratory analysis showed that some internal fabric sheets of those mattresses contain high concentration of Th-232.It was revealed that the manufacture treated the material with so-called ‘negative ion powder’ procured from the market and NSSC found that its radioactive content is the monazite powder.Although measurements with reliable instruments resulted in somewhat lower values,the tentative but conservative estimates of doses to the users are still remarkable,ranging from a few to 14 mSv a year.Most of the affected models have been marketed from 2010 but earlier models,with lower thorium content,were supplied from 2006.As many as 88,000 mattresses have been produced.The manufacturer with help of the government,recalled all the affected models and separated the radioactive internals.A large amount of waste is waiting for the government decision on disposal method.Similar problems were identified in other consumer products including latex mattresses and pillows imported,hot pads,and several models of sanitary or health-aid goods.These episodes called for revisiting NORM control strategy in Korea.

Key words:negative ions;health effect myth;consumer products;monazite;thoron exposure

1 Introduction

On May 3,2018,the evening news of a major TV channel of Korea casted a shocking report saying that radon concentration on a certain model of bed mattress found to be as high as 2 200 Bq/m3of radon gas[1].The reporter showed a scene of measurement with a handy model of radon detector,Radon Eye?,displaying the number.In response,the Nuclear Safety and Security Commission(NSSC) of Korea with help of technical staff of the Korea Institute of Nuclear Safety(KINS) acquired samples of some relevant mattress models and measured radon with a dedicated radon detector,Rad-7?,but got much lower values.On May 9,NSSC hurriedly called a press conference and explained that the thoron levels are no more than 100 Bq/m3and radon levels near background to soothe worried users of relevant mattress models.For the reported high number,NSSC assumed some technical problems in the handy instrument which cannot distinguish radon from thoron.

Unfortunately for NSSC,soon after the 1stpress conference,from other samples collected later high concentrations of thoron gas,up to 1 500 Bq/m3,were detected at close contact to the surface of mattress.

Situations changed abruptly.NSSC and KINS collected many samples of several models produced by the manufacturer of the thoron prone mattress and made numerous measurements to conclude the event is a serious one.With conservative scenarios,it was revealed that users of the highly thoron prone model could get over 10 mSv of effective dose a year.On May 14,NSSC again held a press conference to confirm radiological significance of several mattress models and announced a recall order had been into action against the affected models marketed after 2010.NSSC also confirmed that the emanation of thoron gas is due to misuse of so-called ‘negative ion powder’ which is produced from monazite sand.

2 Development of the episode

2.1 Further investigations for bed mattresses

Upon confirming monazite content of several models of mattress,NSSC and KINS made investigations against all the mattress models produced by that particular company,including earlier models before 2010.It was found that some models marketed before 2010 were also affected although the thoron emanation rates were lower than later models and the recall order was amended.The fabric samples treated with the negative ion powder were analyzed to confirm their high contents of Th-232.

According to the manufacturer’s report,around 89,000 affected mattresses have been sold in total.Due to the long time period concerned,earlier records are lost so that exact number is unknown.Since the quality program of manufacturer,a small industry,the thoron levels varied even among individual mattresses of the same model.

Naturally,lots of enquiries were received by NSSC and KINS on possible health effects and other potential use of radioactive substance in consumer products.Many people attempted to get a radon detector and to measure radon from not only their bed mattresses,even of other makes,but also other suspected items.Many of them posted the results on internet sites,largely ones operated by environmental activist groups,or communicated through their social network service(SNS).NSSC and KINS monitored such activity and made screening measurements on mattress models from other manufacturers in Korea but none was found to be significant.

2.2 Recall campaign of affected mattresses

Because costumer records of the affected models are available only for recent sales,the manufacturer and NSSC opened online registration sites for the users of affected models.Around 50,000 users were registered.The reason of discrepancy between the sale number and the registered number is unknown.

(Photo credit:Yonhap News)Fig.1 Recall campaign of the affected mattresses with help of the national post service(June 16,2018)

Initially,only the manufacturer conducted the recall operation from late May.Large polyethylene tube capable to accommodate king-size mattress were sent to the registered users to put aside the affected mattress.Recall proceeded very slow due to limited capacity of the company.Discontent built up among the users and complains increased.The Government had to be involved in the recall campaign and the President committed the recall operation be quickened.On June 16 and 17,Saturday and Sunday,around 30,000 crew members and 3,200 vehicles of the national post service were put into the operation to end the recall campaign.

Tens of thousands mattresses were mounted on the loading area of the manufacturer factory and on the idle transit area at Dangjin seaport.The mattresses were dismantled to retrieve the affected fabric parts at the factory.Those stacked at Dangjin transit area had to be relocated later to the factory due to strong opposition of residents nearby the seaport against on-site dismantle work.

(Photo credit:SBS)Fig.2 Thoron affected bed mattresses stacked on the transit area of Dangjin seaport(June 2018)

2.3 Estimation of annual doses to users

An ad hoc task group was established to make tentative estimation of doses to the users of each model of mattress in response to the questions poured from many directions.Conservative assumptions were applied to the exposure parameters,e.g.taking the measured thorn concentrations at 3 cm from the mattress surface as references and 10 hours as the sleeping time a day.This very conservative value of the distance was selected to accommodate argument that many people sleep in prone position instead of supine.However,the breathing rate of the users were adjusted to 37% of the reference rate,1.1 m3/h,considering less breathing while sleeping[2].

It is recommended to use measured thoron progeny concentrations to assess thoron doses because of the high variability of the equilibrium factors between thoron gas and its progenies[3].However,the task group applied the equilibrium factor to the measured thoron gas concentrations,partly because of lack of time and partly because it is difficult to reconstruct the various home environment conditions where the mattresses were used.After reviewing the reported values of thoron equilibrium factor[4-8],varying from <0.01 to 0.8 depending on the environmental conditions,the task group chose a value of 0.04 for the purpose of tentative dose assessment.Consensus were reached among the task group members that this value of equilibrium factor would not result underestimation of doses to the users.The dose coefficient recommended by ICRP[3]for thoron progeny was used to evaluate the effective doses from the equilibrium equivalent thoron concentrations.

Table 1 shows the mattress models affected with the thoron concentration on them and the estimated annual doses.All the thoron concentrations measured with Rad-7 were less the background of the counting room.The thoron concentrations are in the range from a few hundred Bq/m3to over 1 000 Bq/m3.The estimated annual effective doses are in the range of 1～14 mSv,which are remarkable doses for members of the public unknowingly exposed.Note that these doses may not representative values because the quality control program of the manufacturer was poor at least for the process of imbedding the negative ion powder into the fabrics or ‘eco-form’ and the KINS team collected only a few samples for each model.Depending on models,radon exceeding the background level was also detected but the levels were negligible compared to those of thoron.

In terms of cumulative exposure,the model New Western Sleeper is most dominant because its annual dose is higher(6.97 mSv),the sales number is large,and was marketed ever since 2010.The model giving the highest annual dose,Power Green Sleeper R,was marketed only in the year of 2014 and total sales was only 344.Whereas the most popular model,Western Sleeper,gave around 2 mSv a year,although it has been on market from 2010.

2.4 Waste problems

By the end of 2018,all the recalled mattresses were dismantled and the affected materials were separated.As a result,some hundreds of tons of waste affected by Th-232 was generated and is currently stored in the manufacturer’s facility.Since Korea does not have regulations or guidelines established for dealing with such waste affected by NORM.Discussions among governmental agencies are in progress under lead of Ministry of Environment to resolve various problems interfering disposal of the waste,including amendment of laws and regulations if needed.

Tab.1 Thoron concentration and estimated tentative annual doses from different models affected

2.5 Other consumer products

Soon after the shocking news,many people purchased radon detectors like Radon Eye and began to measure radon near suspected articles in their home,not only bed mattresses,whatever the makes,but other consumer products advertised ‘negative ion’ or ones contain ceramic materials.Local governments and some companies also acquired radon detectors and rented them to people who want to measure.Upon finding suspected readings,they notify their results to press or NGO’s addressing environmental issues,and also posted on the online communities.

Many kinds of products were on the suspected list:latex mattresses and pillows(mostly carried in from Southeast Asian countries by tourists),heating mats,hot pads,stomach bands,ankle bands,hygienic bands,eyepatches,patches of various sizes,necklaces and bracelets,underwear and socks,hair dryers,shower nozzles,air purifiers,etc.Thoron emanation from most of the products was not significantly high but some products called concerns.Certain models of latex mattress and heating mats emitted thoron gas at similar levels as the affected mattress models.For these products,NSSC ordered the makers to recall.

Those latex goods pose particular problems.Firstly,most of them have been imported on individual basis and hence there are no liable parties to conduct recall.Secondly,radioactive substance is distributed throughout the whole bulky volume to make the disposal process difficult.Thirdly,there is no record informing how many such products are in the country.While NGO’s estimation is much larger,quite sizable numbers of user have registered yet.

3 Lessons learned

3.1 Cause of the event

The root cause of the event is the myth of negative ion effects on health.It claims that negative ions in air is beneficial to human health in various ways;strengthens the functions of autonomic nerves,reinforces collagen,improves the permeability of the cell’s prototype plasma membranes to improve metabolism,strengthens the body’s immune system,etc.[9].From half a century ago,there were articles from time to time in popular magazines and even in science journals,of which authors including medical doctors.Many books are also published.But due to stochastic nature of such effects,like the hermetic effects of ionizing radiation,the evidence is not strong enough to get agreement of scientific community at large.

Around year of 2000,the myth was revived in Japan with great popularity.The wind landed Korea and varieties of goods and services claiming negative ion effects have been on market since around 2005.Koreans in general are particularly keen on health of own or family members.Such goods and services made a good business so.Probably,import of the negative ion powder began at this stage.Ionizing radiation creates ion pairs in the air by its nature.Monazite powder,whose specific activity is in the range of 200～300 Bq/g presented very high readings on the conventional ion counters.Users of negative ion powder were attracted by such outcome but may not be aware of its radioactive contents.

On the other side,there were no laws and regulations regulating potential hazard of NORM before 2011.Unlike most of the foreign countries,Korea has no ‘radiation protection acts’ which can cover broad aspects of radiation protection.The ‘nuclear safety acts’ only deals with protection of human and environment from harmful effects of radiation as a result of utilizing nuclear energy.Hence,natural radiation is intrinsically out of the scope.Diagnostic x-rays are regulated by Ministry of Health after ‘medicine acts’,while radon in indoor air is regulated by the Ministry of Environment after ‘environment acts’.There was no agency regulating NORM.

After the Fukushima accident in 2011,people started to care about radiation in living environment.Some acquired radiation detectors and took measurements here and there.In due course,many abnormal radiological situations were found.Most of the cases were attributed to simply slightly higher radiation levels than typical background due to local geology features.However,one case revealed that part of the asphalt pavement on a street in Seoul was contaminated with Cs-137.In another case,steel dish racks contaminated with Co-60 were found.

In response to these social concerns,NSSC promulgated the new ‘laws controlling radiation in living environment’.These laws include provisions regulating raw material containing significant amount of uranium and thorium.With these laws,NSSC can regulate bulk use of raw material.However,there is the exemption level on amount of annual use,which is 1 ton.Import amount of ‘negative ion powder’ was usually much less than the exemption level and this was the blind spot.

The initial draft laws included a chapter on protection against radon and radioactivity in construction materials,but the chapter was deleted in the final rules because of different opinions from Ministry of Environment.This could be a part of the reason leading to the episode.However,a more direct cause may be our negligence of thoron by relying on the common sense that thoron does not carry radiological significance in general.Consumer products containing monazite powder create completely different situations when used at home.

3.2 Understanding the exposure situations

Many people,including not only media reporters but also so-called experts,usually compare such doses as ones incurred to the mattress users with the dose limits for members of the public in planned exposure situations,i.e.1 mSv a year.They often say like ‘14 times of dose limit’ to scare people.If the manufacture of consumer products knowingly put peoples into the exposure situation,such expression must be corrected and doing so constitutes a crime.

However,if the exposure is unintentional at all,such an exposure is simply an accident.The resulting dose should not be compared with any dose guidelines but reviewed in terms of the risk accompanied by the dose.

3.3 NORM regulation

The episode clearly called for review of regulatory system of the country for controlling use of raw materials,particularly ores,from view point of NORM hazard.Attitude of regulatory bodies tends to strengthen regulations after such events,e.g.lowering the exclusion of exemption levels for naturally occurring radioactive substance.Such attempt would cause more problems than solving ones because the international recommended levels,e.g.1 Bq/g for U and Th,are rather optimized.Prudent approaches are needed.

Consumer products made of NORM containing U or Th in the order of 100 Bq/g may not be justified in general.Below this level,careful justification is needed case by case.It may be inappropriate to prohibit use of NORM only on the basis of potential radiation hazard.If a product accompanies reasonable evidence of any positive health effects,radiation hormesis,negative ion effect or whatever,the associate costs and benefits should be carefully compared.It should be kept in mind that harmful effect of radiation at very low dose is hardly more scientifically evident than beneficial effects of negative ions.

Common senses should be revisited their validity.Negligence of thoron in Korea,relied on a common sense,caused the painful episode.There is another common sense related to radon:Radon may be a concern only at ground floor and underground floors.It revealed however that air tightness of modern system windows is so good to buildup radon from typical construction material over 300 Bq/m3.This calls for setting criteria of Ra and Th content in construction material.

4 Conclusion

Tens of thousands people unknowingly got significant doses from consumer products affected by NORM.Although the estimated annual doses to the user are tentative and based on conservative assumptions,the values are in the range of a few to a few tens mSv a year.The exposure time spans to over ten years.Whatever the root causes are,the episode is a failure of regulation of radioactive substance and calls for prudent regulatory approaches on controlling NORM uses.

NSSC is preparing a white paper on the episodes which should include refinement of dosimetry and proposed revision of radiation protection regulations.

Acknowledgements:The author thanks Dr.Yongjae Kim,KINS,for providing valuable information and comments.