Clinical Toxicology (2009) 47, 393–406 Copyright © Informa UK, Ltd.ISSN: 1556-3650 print / 1556-9519 onlineDOI: 10.1080/15563650902997849

LCLTREVIEW

Technologically enhanced naturally occurring radioactive materials

TENORMDAVID VEARRIER, JOHN A. CURTIS, and MICHAEL I. GREENBERG

Department of Emergency Medicine, Drexel University College of Medicine, Philadelphia, PA, USA

Introduction. Naturally occurring radioactive materials (NORM) are ubiquitous throughout the earth’s crust. Human manipulation ofNORM for economic ends, such as mining, ore processing, fossil fuel extraction, and commercial aviation, may lead to what is known as“technologically enhanced naturally occurring radioactive materials,” often called TENORM. The existence of TENORM results in anincreased risk for human exposure to radioactivity. Workers in TENORM-producing industries may be occupationally exposed to ionizingradiation. TENORM industries may release significant amounts of radioactive material into the environment resulting in the potential forwidespread exposure to ionizing radiation. These industries include mining, phosphate processing, metal ore processing, heavy mineralsand processing, titanium pigment production, fossil fuel extraction and combustion, manufacture of building materials, thoriumcompounds, aviation, and scrap metal processing. Methods. A search of the PubMed database (www.pubmed.com) and Ovid Medlinedatabase (ovidsp.tx.ovid.com) was performed using a variety of search terms including NORM, TENORM, and occupational radiationexposure. A total of 133 articles were identified, retrieved, and reviewed. Seventy-three peer-reviewed articles were chosen to be cited inthis review. Results. A number of studies have evaluated the extent of ionizing radiation exposure both among workers and the generalpublic due to TENORM. Quantification of radiation exposure is limited because of modeling constraints. In some occupational settings, anincreased risk of cancer has been reported and postulated to be secondary to exposure to TENORM, though these reports have not beenvalidated using toxicological principles. Conclusions. NORM and TENORM have the potential to cause important human health effects.It is important that these adverse health effects are evaluated using the basic principles of toxicology, including the magnitude and type ofexposure, as well as threshold and dose response.

Keywords Radioactive materials; TENORM; Occupational exposures

Introduction

Naturally occurring radioactive materials (NORM) areradionuclides that occur spontaneously in nature and are not aproduct of human activities. These radionuclides can be clas-sified as primordial, secondary, or cosmogenic. Primordialradionuclides are byproducts of the fusion that occurs in starsand were deposited in the earth’s crust during its formation.Their continued persistence is explained by the extremelylong degradation half-lives. Secondary radionuclides aredecay products of primordial radionuclides that are them-selves radioactive and will decay to other secondary radionu-clides or stable isotopes. Cosmogenic radionuclides areformed from stable isotopes by the action of cosmic rays inthe atmosphere.

Human exposure to NORM may be increased as a result ofhuman manipulation of raw materials from the earth’s crust.This technologically enhanced NORM (TENORM) may res-ult as a byproduct of a variety of industrial and other activi-ties including mining, extracting, concentrating, processing,or combusting raw materials containing NORM.

TENORM poses a number of potential human healthconcerns. Workers in TENORM-producing industries may beoccupationally exposed to ionizing radiation. TENORMindustries may release significant amounts of radioactivematerial into the environment resulting in the potential forwidespread exposure to ionizing radiation. Radioactive wasteproducts of TENORM industries may contaminate industrialsites or may be spread by wind or water to contaminate otherareas. Radionuclides in soil or water may be incorporatedinto crops or livestock and subsequently be consumed byhumans.

Methodology

We searched the PubMed (www.pubmed.com) and OvidMedline (ovidsp.tx.ovid.com) databases using the search

Received 19 April 2009; accepted 27 April 2009.Address correspondence to Michael I. Greenberg, Division of

Medical Toxicology, Drexel University College of Medicine, 245North 15th Street, MailStop 1011, Philadelphia, PA 19102, USA.E-mail: mgreenbe@drexelmed.edu

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terms “NORM,” “naturally occurring radioactive materials,”“TENORM,” “technologically enhanced naturally occurringradioactive materials,” “technologically enhanced NORM,”and “occupational radiation exposure.” We identified,retrieved, and reviewed a total of 133 articles. Seventy-threepeer-reviewed articles were chosen to be cited in this review.The articles not cited were rejected because of lack of clinicalrelevance as well as the fact that some contained datedinformation that was superseded in more recent articles. Inaddition, the reference lists in each article retrieved werereviewed for additional relevant references that might havebeen missed in the original search strategies. The 2000 reportof the United Nations Scientific Committee on the Effects ofAtomic Radiation was also utilized as a resource. Searchresults were evaluated for their relevance and the validity oftheir methods.

Principles of radiation

Ionizing radiation exerts its biological effects through fourmechanistic pathways, involving the production of alphaand beta particles, gamma rays, and neutrons. Neutronemission does not occur with NORM or TENORM radionu-clide decay, though it may account for up to 50% of cosmicradiation.1

Alpha particles are identical to helium nuclei (two protonsand two neutrons) and, because of their relatively large sizeand charge, can only penetrate the outermost layers of theepidermis of the skin and not beyond. Alpha emitters, there-fore, pose their primary risk only if they are ingested, inhaled,injected, or contaminate a wound. Once inside the body,

however, alpha particles are substantially more biologicallydangerous than beta or gamma particles.

Beta particles are high-energy electrons or positrons. Theyhave a limited depth of penetration in human tissue (on theorder of millimeters), though external exposure may causecutaneous burns. Systemic radiation poisoning may onlyoccur when beta emitters are ingested or inhaled. Gammarays are high-energy photons with a high depth of penetrationin human tissue that may cause systemic radiation poisoningfrom external exposure.

The effects of TENORM and ionizing radiation in generalmay be expressed using a variety of nomenclature. A detaileddiscussion of measures of ionizing radiation is found in basictexts and is summarized in Table 1. As quantification ofradiation exposures in occupational scenarios is based onestimates and a significant amount of modeling is involved incalculating doses, results have been reported to vary by twoorders of magnitude.2 Some have reported that calculatedeffective doses related to occupation may overestimate theactual received effective dose by 86- to 2000-fold dependingon the industry.2 Over the last 10 years, as TENORM hasbecome an important focus of concern, one major goal ofTENORM research has been to improve the accuracy ofmeasurements and models of radiation exposure.

Radionuclides involved in TENORM

The radionuclides concentrated or emitted by industrieswhere TENORM may be an issue may differ depending onthe raw materials and the specific human activity involved. Inaddition, it is important to remember that radionuclides may

Table 1. Definitions of terms used in TENORM literature to describe radioactivity and its human effects

Term Definition SI units Units Conversion factor

Radioactivity, activity

The number of decays per unit time

Becquerel (Bq): 1 decay per second

Curie (Ci): no longer widely used

1 Bq = 2.70 × 10−11 Ci1 Ci = 3.7 × 10 exp 10 Bq

Specific activity The concentration of radioactivity in a substance or sample

Becquerel per gram (Bq/g) or Becquerel per kilogram (Bq/kg)

Curie per gram (Ci/g) As above

Radium equivalent activity

A measurement of the gamma radioactivity of a substance or sample

Milligrams radium equivalent (mgRaeq)

NA

Absorbed dose The amount of energy absorbed by a human body from exposure to ionizing radiation

Gray (Gy): 1 joule of energy per kilogram

Radiation absorbed dose (rad)

1 Gy = 100 rad

Effective dose A weighted version of absorbed dose that more accurately measures the biological effects of the radiation exposure

Sievert (Sv) Roentgen equivalent in man (rem)

1 Sv = 100 rem

Cumulative effective dose

The cumulative effective dose to which a group of workers or population is exposed

Man-Sievert (mSv) NA

SI, international system of units.

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be released into the air as particulates from combustion orhigh-temperature manufacturing processes, into water asaqueous sludge or from fossil fuel extraction, or as solidwaste products or scale on pipes and in facilities.

The radionuclides involved in TENORM include those ofthe radium, thorium, and actinium decay series and potas-sium-40. Specific radionuclides measured in TENORM andthe industry with which they are associated are summarizedin Table 2.

Radon-222 (alpha emitter) is possibly the most importantradionuclide involved in TENORM. It may be released invarying amounts during some mining operations, extractionof oil or natural gas, combustion of natural gas, and produc-tion of phosphates or cement.3 Radon-222 is a secondary

radionuclide produced from the decay of uranium. It exists asa gas that may undergo decay to form alpha particles afterinhalation giving it the potential to have profound biologicaleffects. Lead-210 (beta emitter) may be released into the airduring the production of phosphorus, iron, and steel, whereaspolonium-210 (alpha emitter) may be released into the airduring cement production.3 Neither lead nor polonium existas gases, and these materials may be released into the air asparticulates. The concentration of those radionuclides in theair rapidly attenuates with increasing distance from the site ofproduction. The risk for radiation exposure, therefore, isextremely limited, though the potential for exposure doesexist both for unprotected workers at the site of productionand for persons living or working in proximity to the plant.Although the amount of radiation exposure, as well as anyconsequent dose, because of the release of these radionu-clides is likely to be minimal, each case of potential exposuremust be assessed individually and based on the governingscientific principles of medical toxicology and radiation med-icine. In other words not every exposure will be associatedwith an absorbed dose and not every dose will have medicalimportance.

Oil and gas extraction and phosphate processing have beenassociated with TENORM releases into ocean or seawater.Historically, the vast majority of lead-210 and polonium-210and a substantial amount of the radium-226 released into sea-water were related to phosphate processing. This effect hasdeclined in recent years with the storage of phosphate wasteson land in the so-called phosphogypsum stacks. Radium-226may be released into water by offshore oil extraction.4 Simi-larly, some coal mines may release radium-226 and radium-228 into rivers.3

Other radionuclides are concentrated as solid waste prod-ucts. Following extraction of the desired minerals from ore,the leftover waste product, termed “tailings,” may containTENORM, which may also be found in scale-coating storagetanks and pipes of phosphate factories and oil refineries.These solid waste products may represent less of a humanhealth hazard as they are not generally ingested or inhaled,though they may have important environmental impacts. Themagnitude and importance of any potential environmentalimpact must be assessed using accepted principles of science,medicine, and toxicology on a case-by-case basis.

TENORM industries and occupational exposures

The greatest potential for individual exposures to TENORMexists among workers in TENORM industries. The primaryindustries that may contribute to TENORM include mining,phosphate processing, metal ore processing, heavy mineralsand processing, titanium pigment production, fossil fuelextraction and combustion, manufacture of building materials,thorium compounds, aviation, and scrap metal processing.3

Table 3 lists some reported effective dose exposures forworkers in these industries.

Table 2. Some radionuclides released by TENORM industries

Lead-210 (beta emitter)

- Released as airborne particulate during the production of phosphorus, iron, and steel

- Historically released into water during phosphate processing

- Released as dust during zircon processing

Polonium-210 (alpha emitter)

- Released as airborne particulate during cement production

- Released as dust during zircon processing

- Historically released into water during phosphate processing

Radium-226(alpha emitter)

- Released into seawater during offshore oil extraction

- Released by coal mines into rivers- Accumulated as scales or sludge during

fossil fuel processing- Accumulated in blast furnace slag and

tin slag- Elevated concentrations in some

phosphate oresRadium-228

(beta emitter)- Released by coal mines into rivers

- Accumulated as scales or sludge during fossil fuel processing

- Elevated concentrations in some phosphate ores

Radon-222 (alpha emitter)

- Concentrated in underground mines resulting in possible occupational exposures

- Released during extraction of oil or natural gas

- Released during the production of phosphates and cement

Thorium-232 (alpha emitter)

- Elevated concentrations in niobium and phosphate ores

- Used in gas mantles, high intensity discharge lamps, and some welding rods

Uranium-238 (alpha emitter)

- Concentrated in niobium ores

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Mining

Mining is an industry of economic import employing nearly5 million workers worldwide.5 The amount of radiation towhich miners may be exposed varies with the type of mine,the ore being mined, time spent in the mine, the use ofpersonal protective equipment, and the degree of ventilation.Some ores, such as coal, uranium, and phosphates, arenaturally higher in radionuclides than others. Because of thelarge numbers of workers employed in mines worldwide, acumulative effective dose of TENORM exposure may beattributed to mining. However, it is important to rememberthat the medical importance of TENORM exposure in miningactivities should not be generalized and must be evaluated ona case-by-case basis.

Coal mining employs approximately 84% of all minersworldwide, with the mining of all other ores making up theremainder.5 Coal mining involves lower TENORM exposures

than other mining. This may be related to the fact that coal minesare more thoroughly ventilated in order to attempt to limit work-ers’ exposure to coal dusts in hopes of preventing coal workersfrom pneumoconiosis. This additional ventilation also tends todecrease the amount of inhaled radon-222. A report fromGermany estimated that most miners in that country are exposedto between 1,000 and 3,000 Bq/m3 of radon gas, whereas aminority are exposed to radon gas levels above 3,000 Bq/m3.6

A study of miners in the United Kingdom reported that theaverage annual effective dose to coal miners because of radonwas 0.6 mSv, whereas the average annual effective dose tononcoal miners was 4.5 mSv. In both coal and other miners,there was significant heterogeneity in TENORM exposurewith some miners in noncoal mines being exposed to anexcess of 50 mSv/year.7 The cumulative effective dosebecause of radon from coal mining worldwide is estimated tobe 1,400 mSv, whereas that of noncoal mining (excludinguranium mining) is estimated at 1,800 mSv.5

Table 3. Annual exposures to ionizing radiation by industry

Industry Reported annual effective doses Notes

Air travel crews 0.2–9.1 mSv Professional air couriers may have similar radiation exposure*

Ethylene/polyethylene production

Up to 1.6 mSv Exposure may occur during the production of ethylene/polyethylene from natural gas*

Fossil fuel extraction and processing

0.27–0.32 mSv (range: 0.02–1 mSv) Highest risk of exposure may be to workers involved in cleaning or removing pipe scale*

Heavy mineral sands processing

6 mSv (range: 6–125 mSv) Effective dose may be minimized by reducing inhalation of ore dusts*

Mining – coal 1.2 mSv (range: 0.6–1.2 mSv) Effective dose depends on the characteristics of the mine*

Mining – phosphate 12–15 mSv (range: <1–53 mSv) Effective dose depends on the radioactivity of the phosphate ore and characteristics of the mine*

Mining – uranium 4.5 mSv (range: 1–20 mSv) There is significant heterogeneity in radiation exposure in this industry

Mining – other 3.2 mSv (range: 2.55–50 mSv) There is significant heterogeneity in radiation exposure in this industry*

Ore processing 0.4–2 mSv Effective dose depends on the specific activity of the ore*

Phosphate-containing fertilizers

1–6 mSv Occupational exposure may occur during the retail sale of or application of fertilizers*

Phosphate processing Range 1.6–11 mSv Occupational exposures may occur during ore crushing, transport, ore separation, and storage

Phosphogypsum stacks 0.71 μSv Minimal occupational exposure from aerosolized radionuclides*

Phosphoric acid plants May exceed 1 mSv Highest radiation exposures may be associated with filter pan cleaning and maintenance*

Pyrochlore mining and niobium processing

2.4–3.5 mSv (range: 1.3–3.5 mSv) The use of respiratory protection minimizes effective dose*

Scrap processing 0.3 mSv Workers involved in the recycling of thorium-containing scrap or materials from oil and gas extraction may be most likely to be exposed*

Thorium manufacturing processes

1–10 mSv (range: negligible–10 mSv) Highest exposures may be to workers in the manufacturing of gas mantles while the production of thorium lamps and thorium oxide welding rods is associated with lower exposures*

Titanium dioxide production

Up to 1 mSv Standard precautions limit effective dose to workers

Uranium milling 3.3 mSv Exposure is primarily due to inhaled ore dust*

Zircon sands industry 0.1–1 mSv (range: 0.07–6 mSv) Effective dose may be minimized by reducing inhalation of dusts*

*Medical importance must be evaluated on a case-by-case basis.

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All the above dose data may, in some cases, underestimatethe total TENORM exposure of miners as the numbers arebased on radon inhalation only and do not account for exter-nal radiation exposure or internal exposures due to inhalationof ore dust. These pathways have been estimated to result inan additional annual effective dose of 0.75–1 mSv/year.5

When taking these pathways into account, the annual effect-ive doses for coal and noncoal (excluding uranium) miners isapproximately 1.2 and 3.2 mSv, respectively, and cumulativeannual worldwide effective doses of 4,500- and 2,400 mSv,respectively.5

TENORM exposure for South African gold miners hasbeen studied. Gold mines in South Africa tend to be verydeep underground (average depth of 1,600 m). Mining at thisdepth tends to be protective against TENORM because thedegree of cooled air ventilation that is necessary at thatdepth dilutes the concentration of radon gas. The averageeffective dose of radon gas for the miners was calculatedto be 2.55 mSv/year with 71, 25, and 4% of the radiationexposures attributable to radon gas, external radiation, andinhalation of ore dust, respectively.5 The cumulative annualeffective dose was estimated to be 640 mSv.5

Countries with large mining industries account for a largeshare of the worldwide cumulative TENORM exposure.South Africa, Poland, and the former USSR, are estimated tocontribute 39, 22, and 19%, respectively of the cumulativeannual effective dose.5

Uranium mining and milling

Uranium may be mined using traditional underground mines,open pit mines, in situ leaching, or extraction from oresmined for other minerals. In addition to radon-222, uraniummining operations, including open pit mines and in situ leach-ing, carry an additional risk of inhalation of radioactive oredust. The amount of TENORM to which workers are exposedis a function of the type of mine, quality of the uranium ore(higher grade ore being more radioactive), time spent in themine, and the size and concentration of ore dust particulates.A report from Germany, where uranium mining is no longerperformed, estimated that most uranium miners in that coun-try were exposed to 1–6 mSv/year, with about one-sixth ofthe workforce having exposures between 6 and 20 mSv/year.6

Uranium mining has declined over the last two decades withthe most recent estimates reporting a worldwide 69,000uranium miners, an average annual effective dose of 4.5 mSv,and a cumulative effective dose of 310 mSv/year.5

The average annual effective dose for uranium minersshould be interpreted cautiously. Uranium miners working inunderground mines may be exposed to larger doses of radon-222and radioactive ore dusts than their colleagues involved inopen pit mining or in situ leaching, because of the enclosedspace and practical limits on mine ventilation. For example,an open pit mine in Namibia reported an average effectivedose of 1.8 mSv to workers, with an upper limit of 5 mSv.8

Those working in underground mines are protected by radia-tion exposure regulations, and one study performed in Spainfound that radiation exposure due to radon-222 inhalationwas 2–10 times lower in uranium mines than in touristcaves.9

Uranium milling involves the crushing of ore to a finepowder followed by leaching of the uranium using aqueousperoxides, acids, or bases to produce the material known as“yellowcake.” Workers may receive external exposure result-ing from proximity to radioactive ore and internal exposurefrom inhaled ore dust. In an Egyptian study of uraniummilling facilities, airborne uranium dust was estimated to res-ult in worker exposures of 1–80 μSv/h and urinary uraniumconcentrations were as high as 29.2 μg/L.10 As with uraniummining, uranium milling has declined in recent years with anestimated 6,000 workers worldwide reportedly engaged inthis work. These workers may be exposed to an averageannual effective dose of 3.3 mSv and a cumulative effectivedose of 20 mSv.5

Workers involved in uranium enrichment, beyond the pro-duction of the so-called yellowcake or urania (the uraniumconcentrate obtained from the milling, processing, and dryingof uranium ore), also may be occupationally exposed toionizing radiation. However, this exposure generally falls out-side the scope of TENORM and therefore will not be discussedhere. Radiation exposure due to enrichment of uranium foreconomic or military uses is widely considered to be a resultof human activities and not strictly due to NORM.

Phosphates and phosphorus

Phosphate-containing rock varies considerably in its degreeof radioactivity. Some phosphate deposits are estimated toresult in less than 1 mSv/year of occupational exposure forminers.5 However, phosphate mines in Egypt and Tanzaniathat also yield uranium are estimated to result in averageannual doses of 15 and 12 mSv for miners, respectively, witha maximum annual dose of 53 mSv.11,12 Highly radioactivephosphate rock has elevated concentrations of radium-228,radium-226, and thorium-232.11 Miners working in mainten-ance or ore crushing, transport, beneficiation (separation ofvaluable mineral from waste materials), and storage are esti-mated to average 10–11 mSv/year.12

During the processing of the phosphate ores at phosphoricacid plants, TENORM exposure may occur from externalexposures or inhalation of dusts. Some Florida phosphoricacid plants have been found to have elevated gamma radia-tion levels with calculated occupational exposures up to0.4 mSv per week, with the highest radiation exposures beingassociated with filter pan cleaning and maintenance. Cumula-tive annual doses to workers are undetermined but arehypothesized to exceed 1 mSv/year.13 More recently, revisedestimates of occupational TENORM exposure duringphosphate processing using more accurate dust inhalationparameters are calculated to be up to 1.6 mSv/year.2 Pipes

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and tanks in phosphate processing plants accumulate scalewith activities of 100 kBq/kg as a result of radium-226.Occupational TENORM exposure may occur with mainten-ance or cleaning of the pipes and tanks.14 Workers, in retailestablishments, who sell phosphate-containing fertilizer orare engaged in the application of phosphate-containing fertil-izers reportedly may be exposed to 1–6 mSv/year.5

Phosphogypsum is the waste byproduct formed during theprocessing of phosphate ore into fertilizer and, like phosphateore, is radioactive because of the presence of uranium andradium. Historically, radioactive phosphogypsum was dumpedinto waterways and the sea. However, recent restrictions onmarine dumping of radioactive wastes now require that phos-phogypsum with elevated levels of radioactivity be stored onland in large “stacks.” Workers at phosphogypsum stacks areunlikely to receive significant occupational TENORM expo-sure. One study, conducted in Spain, estimated that workersat phosphogypsum stacks may receive doses in the range of0.71 μSv/year, primarily from aerosolized radionuclides.15

Workers involved in the production of elemental phosphorus,used in various industrial and consumer applications, are esti-mated to receive an average effective dose of 1 mSv/year.2

Ore processing

The same geological processes that lead to the concentrationof desirable rare earth elements in certain ores also lead toincreased concentrations of uranium and thorium in the samedeposits. During the mining, milling, and processing of theseores, these radionuclides and their decay progeny may be con-centrated in the finished product, waste products (tailings),scale in boilers or pipes, and aqueous effluent.16 Workersinvolved in mineral processing industries therefore may havethe potential for TENORM exposure.

TENORM exposure during ore processing may includeexternal exposure from proximity to radioactive ore orinternal exposure from radon gas or the inhalation of dustfrom ore or scale. The International Commission on Radio-logical Protection (ICRP) has estimated that occupationalexposure to ores with between 1 and 10 kBq/kg may result inan annual effective dose between 1 and 2 mSv.5 Anotherreport demonstrated that working with ores with less than 1kBq/kg could lead to an annual effective dose of less than 1mSv, the cutoff for nonexposed workers.5

One study of the Egyptian aluminum industry found somebauxite ores with activities in the range of 800 Bq/kg withworkers receiving an effective dose of 0.4 mSv/year.17

Heavy mineral sands

Heavy mineral sands (a class of ore containing zirconium,titanium, tungsten, and rare earth elements) represent a poten-tially important industrial source of TENORM exposure inthe mineral processing industry. These heavy mineral sandsmay contain elevated concentrations of thorium and uranium.

Monazite may contain 5–7% thorium and 0.1–0.5% uraniumby weight. By comparison, the earth’s crust generally containsonly 0.5–5 parts per million (ppm) uranium and 2–20 ppmthorium.5 Monazite is also concerned with internal exposuresbecause of its tendency to concentrate in airborne dust.5 Inone heavy mineral sand processing plant in Australia, exter-nal exposure was estimated to be about 1 mSv/year whereasinternal exposure due to inhalation of dust was estimated at7 mSv/year. The mean annual effective dose to workers in theWestern Australia heavy mineral sand processing industry isthought to be 6 mSv.5 Annual effective doses at a heavy miner-als separation plant in Brazil were estimated to be 8–125 mSv/year, most of which was received by inhalation of dust,though that plant has since implemented changes to reducethe inhalation hazard.2 Another source reports that workersinvolved in separation of heavy minerals from monazite oreor the later step of extraction of rare earths from monazitereceive annual effective doses between 1 and 9 mSv.2

Zirconium is a transitional metal that finds use in a varietyof industries, including industries using alloys, refractories,jewelry manufacturing industry, and nuclear power plant, andis found in nature in zircon sands or baddeleyite ore. In addi-tion, industries manufacturing or using abrasives that may beextracted from the mineral baddeleyite or zircon sands maybe at risk. Baddeleyite and zircon sands typically containaround 30 and 10 kBq/kg of radionuclides, respectively,whereas zircon flue dusts have concentrated levels of lead-210and polonium-210 with a typical activity of 800 kBq/kg.18

Workers involved with the processing or bulk storage of bad-deleyite and zircon sands are estimated to receive around 1 and0.1 mSv/year, respectively; workers responsible for clearingzircon flue sands wear protective equipment and respiratoryprotection and are estimated to receive 0.07 mSv/year.18

In one study5 of a factory using zircon sand to producerefractory material, in the area where the sand was heated andground, it was estimated that the effective dose would equal5 mSv/year. Another estimate put these workers as receivingbetween 0.72 and 1.84 mSv/year depending on the respira-tory protection.18 Another German report suggested thatworkers involved with zircon sands (5–10 kBq/kg), pyrrhiteore (30 kBq/kg), or copper slag received annual effectivedoses between 1 and 6 mSv/year.5

Another source2 disputes the quantity of TENORMradiation in zirconium storage, milling, and manufacturingoperations, contending that the above results are excessivelyhigh because of overly conservative assumptions and reportsthat average actual occupational annual effective doses varybetween 0.28 and 1 mSv in these industries, though max-imum annual effective doses to workers thermally processingzircon could still reach 3.1 mSv.

Titanium dioxide production

The process of manufacturing titanium dioxide has thepotential to result in occupational exposures up to 6 mSv/year

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though standard precautions limit annual effective doses toup to 1 mSv.2 The bulk storage of ilmenite, another mineralfound in heavy mineral sands and one of the industrial pre-cursor to titanium, may cause occupational annual effect-ive doses of 0.03–0.08 mSv.2 Radium-rich scale, withactivities in excess of 300 kBq/kg, is produced during theprocessing of ilmenite or rutile into titanium dioxide lead-ing to the risk of TENORM exposure during maintenanceor scale removal.14

Pyrochlore mining and niobium production

Niobium is a transition metal used in a variety of alloys, super-conducting magnets, and internal medical devices. Pyrochlore,the most important economic source for niobium, containsuranium-238 and thorium-232 with a typical activity of270 kBq/kg.16 Workers involved in the processing or bulk stor-age of pyrochlore have been estimated to receive 2.4–3.5 mSv/year, though wearing a dust mask can be expected to decreasethe effective dose to 1.30 mSv/year.18 Workers in a niobiummine in Brazil were found to have elevated urinary levels ofniobium, tin, and uranium, suggesting possible occupationalTENORM exposure.19

Fossil fuel extraction and processing

Oil and natural gas reservoirs frequently contain an aqueouslayer. Additional quantities of water are injected into these res-ervoirs during extraction to force the fossil fuels to the surfaceto facilitate separation and removal. This water becomes radio-active, to varying degrees, as radionuclides present in the fossilfuels dissolve into the aqueous phase. This material is known as“produced water” in the industry. Produced water has a radioac-tivity that is variable and in the order of 10 Bq/L.20 Althoughoccupational exposure from this water is usually minimal,disposal of the produced water has the potential to pose import-ant environmental risks as discussed below.

The primary occupational TENORM exposure risk associ-ated with fossil fuels occurs during fossil fuel processing.Radium-226 and radium-228 and, to a lesser extent other radio-nuclides, accumulate as scales or sludge in piping or areadsorbed onto pipe metal during normal operation.21 The scalesmay accumulate an activity of 1–1000 Bq/g though concentra-tions as high as 15,000 Bq/g have been reported.2,5,20,22

Between 25,000 and 225,000 tons of scale are generated annu-ally industry-wide.22 Workers who perform repairs and/orclean, or remove scale may be exposed to up to 1 mSv/yearwith an average effective dose of 0.27–0.32 mSv/year.20,22,23

Workers involved in the refurbishment of oil extraction equip-ment may receive effective doses as high as 0.93 mSv/year.2

Additionally, workers involved in the fractionation of nat-ural gas may receive minimal effective doses of up to 0.02mSv/year. The production of ethylene and polyethylene fromnatural gas is estimated to result in annual effective doses ofup to 1.6 mSv.2

Thorium compounds

Thorium is currently used in gas mantles, high-intensitydischarge lamps, and certain welding rods. Workers involvedin the production of gas mantles reportedly may receivebetween 1 and 10 mSv/year of radiation.2 In contrast, the pro-duction of thorium lamps is thought to involve minimal expo-sure. The use of thorium oxide welding rods, used in tungsteninert gas welding, may involve exposures up to 0.15 mSv/year,whereas workers involved in the recycling of lamps orwelding rods may be exposed to up to 0.3 mSv/year.2 The useof thorium for these applications is declining as more producersswitch to substitutes.

Scrap processing and waste management

Scrap metals may contain elevated concentrations of NORM.Consequently, workers involved in melting thorium-containingscrap metal may be exposed to effective doses of up to0.3 mSv/year.2

Blast furnace slag in Sweden has been reported to containradium-226 at a concentration of 0.25 Bq/g and is recycledfor use in the construction of roads and buildings. Similarly,burnt alum shale is used in Sweden as a filling material forthe construction of open air facilities (e.g., parks and tenniscourts) though it is not used to construct residential buildingsbecause of the accumulation of radon indoors.2 Tin slag witha radium-226 activity of 4 Bq/g has been used in Malaysia toreclaim areas for industrial use with calculated maximumannual effective dose of 0.45 mSv.2

Recycling of pipes and other materials from oil and gasextraction and processing plants containing scale must beaccomplished either at a dedicated facility or first be washedto remove radioactivity; calculated occupational exposuredoses for workers involved in the former were less than0.3 mSv/year, whereas the workers involved in the latterwere estimated to receive less than 1 mSv/year.2

Aviation

Flight personnel in commercial aviation are exposed toincreased levels of cosmic radiation, and in this setting,cosmic radiation may be considered to be TENORM. Theamount of cosmic radiation exposure increases with alti-tude and with polar latitudes. At an altitude of 8 km(∼26,000 ft) in temperate latitudes, the effective dose ratehas been estimated to be in the range of 3 μSv/h. An alti-tude of 12 km (∼39,000 ft) doubles this rate.5 Approxi-mately 50% of the ionizing radiation during aviation resultsfrom neutrons.

The effective dose from cosmic radiation for typicalflight routes can be estimated using computer modeling.Relatively short-haul routes (e.g., London to Rome) gener-ally may be associated with cosmic radiation exposure ofless than 10 μSv, whereas long-haul routes (e.g., Dublin to

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New York) may be associated with exposures in the orderof 25–70 μSv.24 Therefore, ionizing radiation exposurefrom a single plane flight is minimal, though cumulativeexposure to aircrews has been estimated to be in the rangeof 0.2–9.1 mSv/year.1,5,25 Crews, on long-haul routes, whospend longer times at higher altitudes at more polar lati-tudes receive higher TENORM exposure than crews onshort-haul flights. Approximating a worldwide populationof 250,000 aircrew, the cumulative effective dose for thatpopulation may be estimated at 800 mSv/year.5

Air couriers and those who may fly consistently and con-tinuously may also be exposed to significant doses of cosmicradiation. Professional couriers may spend more time aloftthan flight crews. For example, a courier flying 1,200 h/yearreceives an estimated effective dose of 6–10 mSv/year.5

A German study suggested that, in that country alone, thereare 20,000 civilians who fly frequently enough to receiveannual doses of 1 mSv or above.5

An additional variable affecting the effective dose ofcosmic radiation received during aviation is the amount ofsolar activity. The amount of cosmic radiation produced bythe sun varies with an approximately 11-year cycle. Yearswith increased levels of solar activity translate to a higherfrequency of solar flares, some of which may increase theamount of cosmic radiation in the earth’s atmosphereresulting in higher annual effective doses to aircrews dur-ing those years.5

Other industries

Pulp and paper mill workers may be exposed to TENORM inthe form of alum (252 Bq/g) or other precipitates (15–44 Bq/g).Some, but not all, mills have been reported to produce poten-tially excessive amounts of TENORM. Paper-recycling millsappear to be less likely to result in occupational radiationexposure than other types of mills. Maintenance workers maybe most likely to have TENORM exposure but are estimatedto receive less than 1 mSv/year.26

In the sandblasting industry, the use of coal slag haslargely replaced sand because of the risk of silicosis,bronchitis, and cancer from the latter. Coal slag containsminimally elevated levels of TENORM, and sand blasterslikely receive insignificant radiation exposure as a result.Nonetheless, appropriate respiratory protection is advisedfor these workers.27

Geothermal power plants that derive energy from high-temperature subterranean brine may produce substantialquantities of dissolved solids with elevated radioactivityrequiring special disposal, though occupational TENORMexposures have not been studied in this setting.28

Drinking water treatment plants that use lime softening orion exchange and activated charcoal produce TENORM asradionuclides that accumulate in the sludge from these pro-cesses. Occupational exposure to TENORM has not beenstudied in this industry.

Population exposure because of TENORM

Persons not exposed to TENORM through occupation arestill exposed to a background amount of radiation from nat-ural sources (NORM) and cosmogenic radiation. The quan-tity of background radiation varies geographically with someareas having higher levels of radiation. The United NationsScientific Committee on the Effects of Atomic Radiationcalculates the average global effective dose of radiation fromnatural background sources to be 2.4 mSv/year with mostindividuals being exposed to between 1 and 10 mSv/year.29

Population exposure to TENORM may be divided intocritical groups and the population-at-large, where the formeris a group of people living in the vicinity of a TENORMindustrial site and possibly exposed to larger quantities ofTENORM than the population-at-large.30

Generally, external radiation exposures to critical groupsfrom individual TENORM industrial sites are thought to beinsignificant. Because of the rapid attenuation of radiationintensity with distance, local residents generally do notreceive a significant quantity of gamma radiation from nearbyTENORM sites.3 One exception may be phosphogypsumstacks: terrestrial gamma radiation rates near one phospho-gypsum stack were reported to be 0.3–0.85 mGy/year.31

Internal exposures to some population groups mayoccur from inhalation of gaseous radionuclides such asradon-222, inhalation of airborne particulate radionuclidesin the vicinity of a TENORM industrial site, drinkingTENORM-contaminated water, and/or ingestion of crops, live-stock, or fish that have incorporated TENORM radionuclides.Generally, inhalation of airborne particulate radionuclides onlycauses measurable radiation exposure in the immediate vicin-ity of a TENORM site where it may reach 50 μSv/year.32

Internal radiation exposure from consumption of crops, live-stock, or fish in the general public is generally thought toequal 1–10 μSv/year, whereas consumption of crops grownin the vicinity of a phosphorus plant could lead to radiationexposure of 100 μSv/year.32 A South African study reportedthat residents in the vicinity of a mining and mineral process-ing complex may receive 58–254 μSv/year, primarily frominhalation and ingestion routes.2 It has been estimated thatuse of thorium gas mantles for 20 h per year may lead toradiation exposures of 100 and 50 μSv to children and adults,respectively, chiefly because of the inhalation of volatilizedthorium radionuclides.16

At the population-wide level, phosphoric acid production,processing of ores, and coal-powered electricity plants contrib-ute most to population-wide TENORM exposures becauseof emission of large quantities of radionuclides to waterand air. Current global oil production is estimated to intro-duce 10 TBq/year of radium isotopes into the biosphere.33

Population-wide average effective doses have been estimatedto be in the order of 1–10 μSv/year, and residents living nearthose industries may be exposed to 100 μSv/year.29 In theUnited Kingdom, steel-sintering plants are estimated to causean annual population-wide effective dose of between 2.9 and

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5.5 mSv, whereas residents living close to plants could indi-vidually receive between 1.5 and 18 μSv/year.3 Similarly,coal-powered electricity plants in the United Kingdom wereestimated to cause annual exposures of 0.07–55 μSv/year tolocal residents, though the use of pulverized fuel ash, a by-product of coal-fired power plants, as building materialscould cause exposures of 200–250 μSv/year.3,34

One study that attempted to quantify the amount of TENORMreleased into the northeast Atlantic Ocean from 1981 to 2000found that the two main sources of TENORM were phospho-gypsum waste and produced water from offshore fossil fuelextraction. The highest amount of human radiation exposurebecause of this TENORM occurred in 1984 with a cumula-tive effective dose of 606 mSv/year with human exposureoccurring primarily through consumption of marine biota.The dumping of phosphogypsum (and other TENORM)either directly or indirectly into the ocean has declined con-siderably after modifications of the London Convention in1993 prohibited the dumping of all types of radioactivewastes at sea. As a result, the cumulative effective humanexposure has correspondingly decreased, being 195 mSv/year in2000. Fossil fuel extraction remains the major contributor ofTENORM radionuclides into the northeast Atlantic.4 Largequantities of produced water are released into the coastalwaters of the United States, particularly coastal Louisiana,though studies quantifying human exposure have not beenperformed.35

Of theoretical concern is the long-term release of radonand its progeny from uranium-mining and uranium-millingsites, whether active or abandoned. Radon gas may beexhaled from these sites and thereby result in radiation expo-sure on both a local and a global scale. Individual sites mayvary considerably in their radon exhalation rates depending onspecific activity of the soil or tailings and soil functions such asmoisture, density, and porosity. Therefore, the calculateddegree of radiation exposure received by the general public isunclear, and estimates depend considerably on modelingfactors. Further study of this area is needed for an adequateassessment of its contribution to public radiation exposure.36

Another concern is when TENORM materials are inadvert-ently sent for recycling at conventional facilities raising theconcern for radioactive contamination of materials that couldresult in TENORM exposure to the general public. It hasbeen estimated that between 37 and 43% of cases in whichradioactive material was inadvertently sent to plants forrecycling were TENORM in origin.2,33 To date, there are 91confirmed reports in the United States of the accidentalrecycling of TENORM-contaminated material with thou-sands of cases in which radioactive scrap metal was identifiedat a recycling plant prior to recycling taking place.37,38 World-wide, the frequency and severity of accidental recycling ofTENORM materials is even more severe.38 A primary concernis that TENORM-contaminated recycled steel or othermaterials could subsequently be used in office or residentialbuildings resulting in substantial public radiation exposure. Fol-lowing radionuclide-contaminated steel being inadvertently

used in construction in Taiwan, radiation levels of 0.5–120μSv/h were reported in one building.39

Industrial site pollution because of TENORM

Following the decommissioning of a TENORM industrial ormining site, contaminated equipment must either be washedof activity and recycled or disposed of conventionally or berecycled or disposed of as radioactive waste at special facilit-ies. Additionally, contamination of soil or groundwater at asite may limit future use or development of the area untilremediation is made.40

Scale or sludge from fossil fuel extraction or other process-ing activities, such as the processing of monazite, phosphates,and other minerals, may exhibit radioactivity on the level ofthousands of becquerels per gram.2,41 Scale or sludge accu-mulates on the inside of pipes, boilers, and storage contain-ers. These must generally be disposed of as radioactive wasteusing special handling and containment, though in manycountries appropriate facilities do not exist at this time.2,42

Other lower activity wastes may be disposed of convention-ally with no risk to the general public.43 Failure to remediatesites of scale or sludge may allow leaching of radionuclidesinto groundwater leading to non-negligible radiation expo-sure for local residents.44 Phosphate scale, in particular, hasbeen shown to readily leach into groundwater.41

Similarly, furnace dust from thermal processing of phos-phorus, zircon, or ceramic tiles may exhibit low to moderatelevels of activity and disposal may require temporary storagein dedicated facilities until activity levels have declined toacceptable values. Of specific concern is the leachability ofsuch dusts at unremediated sites with resulting contaminationof groundwater or water runoff.2 Slag from the pyrolysis ofpyrochlore during the production of niobium may containelevated concentrations of uranium-238 and thorium-232.16

Large quantities of low-activity tailings are produced duringmining, beneficiation, and processing activities, and conse-quently, the ground surface immediately above abandonedcoal-mining sites may have elevated radioactivity.45 Gener-ally, these tailings are disposed of in surface repositoriesdesignated for hazardous waste.

A German investigation of a large red mud (waste productformed during bauxite processing) disposal site reportednegligible leaching into surface and groundwater and trivialinhalational exposures to the public. Similar results have beenreported for residues from mining, mineral processing, andcoal-fired power plants.2,46 Soils in the vicinity of former min-eral processing plants may be contaminated with TENORMtailings; activities of 300 and 40 kBq/kg have been reported inthe vicinity of a former uranium factory and monazite factory,respectively.42

In some areas, produced water from fossil fuel extractionmay be released into soil at the site leading to elevated levelsof radioactivity in the soil, in some cases into the thousandsof kilobecquerels per kilogram.47

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Radiological waste may also enter the environment througheffluent water from plants into streams or rivers. In somecases, environmental regulations already in place to protectecosystems from heavy metals also remove radionuclides fromeffluent. Strategies include recycling, neutralization, settling,and precipitation. In many cases, treatment of effluent waterresults in radioactivity similar to background NORM levelsand may even result in radioactivity lower than the inflowupstream of the plant.2

A study of waste effluent ponds at a tin tailings plant inMalaysia found sediment with activities ranging from 244.2to 933.5 Bq/kg.48 The authors raised concern that if the landis later reclaimed for residential use, residents could receiveeffective dose exposure of up to 3.15 mSv/year.48

Phosphogypsum is a low-activity tailing that is of particularconcern. Large quantities of phosphogypsum are producedduring the processing of phosphate ore. Previously phospho-gypsum was disposed of into streams or the sea, though thatprocess has largely been abandoned because of marine pollu-tion in favor of creating phosphogypsum stacks. The UnitedStates has produced 7.7 billion metric tons since 1910, withapproximately 1 billion metric tons of phosphogypsum stacksand an annual production of 40–47 million metric tons.49,50 Inthe United States, phosphogypsum with an average activityabove 10 pCi/g (0.37 Bq/g) because of radium is classified bythe Environmental Protection Agency (EPA) as toxic wasteand must be disposed of accordingly, whereas phosphogypsumwith lower levels of activity may be used for fertilizer or otherpurposes. Because of the large volumes of phosphogypsumproduced and requiring storage in stacks as toxic waste,efforts to find suitable alternative uses of phosphogypsum areongoing. One study in Spain, where phosphogypsum is usedas a fertilizer, reported no increase in radon exhalation ratesor concentrations of radionuclides in the soil and inconse-quential contamination of foodstuffs by radionuclides despite30 years of use of phosphogypsum as a soil amendment.2

Uranium mill tailings are also of concern.51 Although manyformer uranium- and radium-mining sites have no enhancedradionuclide concentrations, former uranium-milling sites maycontain tailings with up to 200 times the radioactivity of sur-rounding soils.52,53 Large quantities of tailings were producedduring the nuclear arms race of the cold war. The formerSoviet Union is estimated to have 5 billion tons of uraniummill tailings to give a total activity of 2 × 1016 Bq.33 A concernin the United States is that uranium tailings have historicallybeen disposed of in ways that are no longer deemed adequateby the EPA and that those sites now require remediation.33 InPortugal, river basins that formerly received wastewater fromuranium-milling facilities contained elevated concentrations ofradionuclides in their sediment, though estimated radiationexposure to local residents (through consumption of fish) wasestimated to be minimal (0.032 mSv/year).54

Residents living in the vicinity of a uranium mine tailingdump in Kyrgyzstan have been estimated to receive between 4.2and 11.2 mSv/year of radiation with an additional 10–30 mSvannually from local crops and livestock.55

Estimation of health risks

Excess exposure to radiation can manifest as acute radiationpoisoning, skin burns, or an increased risk for cancers andother disease processes following a latent period. Radiationexposure because of TENORM is generally not severeenough to cause acute radiation poisoning or skin burns.

Increased risk for fatal cancer, nonfatal cancers, and terato-genic effects can be calculated in a stochastic fashion for lowdoses of radiation, similar to those received from TENORM.Probability coefficients for each of the above effects havebeen historically estimated using data from Japanese survi-vors of the atomic bombs and animal data; for example, in anadult worker, the “detriment” in probability coefficient forfatal cancer has been estimated at 0.04/Sv.56 “Detriment” is aterm denoting the probability of causing a level of total harmjudged to be equivalent to one death causing a loss of lifetimeof 15 years on average.56 Additionally, data from atomicbomb survivors suggest that in the low-dose exposure range,the risk of cancer and radiation dose are linearly related,though a recent report on leukemia suggests that a linear-quadratic relationship may be more appropriate.57,58

More recently, meta-analyses of studies of nuclear industryworkers, whose long-term low-dose radiation exposure is simi-lar to TENORM workers, have been reported to have a decre-ment in probability coefficient for fatal cancer of 0.07/Sv andan excess relative risk for death from leukemia of 2.2/Sv.59,60

The only cancer statistically associated consistently with radia-tion dose is leukemia, excluding chronic lymphocytic leuke-mia, though recent studies have suggested a statisticallysignificant relationship for multiple myeloma and nonleukemiacancers as well.60,61

Data from atomic bomb survivors who received low dosesof ionizing radiation also show that cancer risk is higher witha younger age at the time of radiation exposure, that theincreased risk for cancer is lifelong, and that the risk for somesolid tumor cancers – cancers of the rectum, gallbladder, anduterus – may not increase with radiation exposure. Addition-ally, women may be at a higher risk for cancer followingradiation exposure than men – female : male ratio of 1:4 forexcess absolute cancer rate – though this appears to be due tosex-specific cancers only.62

Atomic bomb survivors with exposure in the 0–4 Sv rangeappear to have an elevated risk for heart disease and stroke.63

Yet, a number of subsequent studies examining subjects withoccupational radiation exposure have produced inconsistentresults, and at this time, it is unclear whether low-doseradiation exposure is associated with an increased risk ofcirculatory diseases.64

Traditional theories regarding risk of cancer because ofradiation exposure are based on the linear no-threshold modelthat states that any amount of ionizing radiation is dangerousand that the risk for cancer increases with increasing radiationdose. On the other hand, proponents of hormesis contend thatin very small doses, similar to the doses seen in TENORMexposures, radiation exposure may actually be protective by

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stimulating DNA repair mechanisms, inducing apoptosis incells with pre-existing mutations, and by other mecha-nisms.65,66 Although some in vivo and in vitro studies havereported that low-dose radiation exposure may be protectiveagainst a later high-dose radiation challenge, other in vivostudies have failed to show a hormetic effect.67–69 Addition-ally, if hormesis does occur, it may be that only low-linearenergy-transfer (LET) radiation, such as X-rays and gammarays, would be protective, whereas alpha radiation would notoffer any such adaptive effect.70

Detecting excess cases of cancer in individual industriesbecause of TENORM may be difficult. The low incidence ofcancer and the relatively small increment in relative risk forcancer from long-standing exposure to low doses of ionizingradiation can make it difficult to achieve statistical signifi-cance when comparing cancer rates between TENORM-exposed patients and controls, especially if a study is notadequately powered.71 As a result, studies may falsely reportno excess risk of cancer because of some occupational orgeneral public TENORM exposure.

A pooled analysis of 11 cohort studies of undergroundminers with radon exposure reported a linear dose–responserelationship between radon exposure and cancer risk, thatlong-term lower exposure rates were more dangerous thanshort-term higher exposure rates, and that smoking and radonexposure were synergistic in causing lung cancer.71 Radonexposure was a significant factor in lung cancer mortality inthis population, causing 70 and 40% of excess lung cancerdeaths in nonsmokers and smokers, respectively.71 A cohortof Newfoundland fluorspar miners exposed to radon fromwater running through the mine had a mortality rate becauseof lung cancer that was 3.09 times that of the general popula-tion when controlling for age and cigarette smoking.72 A Pol-ish study reported that the coefficient of annual cancer riskinduction is 1.5 × 10–4 for coal miners, 1.4 × 10–4 for metalore miners, and 1.5 × 10–4 for chemical raw material miners.The average lost life expectancy coefficient for radiation riskwas 0.6/year.73

In addition to the radon found in all underground mines,some uranium mines contain higher concentrations of air-borne particulate radionuclides from ore dust. Because ofuranium’s known radioactivity, there have been a number ofstudies investigating cancer risks in uranium miners. A studyof German uranium miners reported that lung cancer mortal-ity in this population is 2.9 times higher than that of amatched cohort and that both moderate and high exposures toradon were risk factors for lung cancer with odds ratio of 1.2and 1.4, respectively.74 Studies of French uranium minersreport an excess 0.71–0.85% risk for lung cancer per 100working level months.75,76 Another study reported thaturanium miners lose on average of 1.5 years of potential lifebecause of mining related lung cancer or 3 months of life foreach year employed as a uranium miner.77 As with otherminers, lung cancer is reportedly the only cancer found to beconsistently associated with uranium-mining occupationalexposures, and higher radiation exposure tends to increase

the relative frequency of squamous cell and small cell lungcancer.71,78 Several studies have reported an increasednumber of chromosomal aberrations among uranium min-ers.79–81

Workers at tin tailing processing plants in Malaysia havebeen reported to have higher numbers of chromosomal aberra-tions than controls and workers who had been in the field formore than 5 years had more aberrations than those in the fieldfor less than 5 years. Their annual occupational radiation expo-sure has been estimated to range from 5 to 15 mSv.82

Studies suggest that aircrews may be at higher risk for mel-anoma, nonmelanoma skin cancers, and breast cancer.1 Twocohort studies of male pilots reported increased incidence ofprostate cancer, leukemia, nonmelanoma skin cancers, braincancer, and Hodgkin’s disease in that population.25,83 Addi-tionally, cohort studies and nested case–control studies withadjustment for reproductive factors have reported anincreased risk of breast cancer among female aircrew withreported standardized incidence ratios of 1.6–2.0.84–87 Femaleaircrew may also be at higher risk of malignant melanomawith a standardized incidence ratio of 3.0 though sunbathinghabits may be a confounding factor.88

There are fewer studies investigating the risk of cancerbecause of TENORM in the general public than there are forworkers, likely because of the relatively low radiationexposures to the general public attributable to TENORM. Asmentioned above, global oil production is one of the leadingcontributors of TENORM to the biosphere through the radio-activity of produced water. Fuzzy modeling suggests that theindividual excess cancer risk in the general public due toproduced water is around 4.4 × 10–7 and is from ingestion offish and seafood harvested in the vicinity of offshore oilrigs.89 Critical groups, defined above as persons residing inthe vicinity of a TENORM facility, are also less well studied.

Current regulations

The fundamental principle behind NORM and TENORMregulations and, more broadly, radiation exposure as a wholeis to keep radiation exposures as low as reasonably achiev-able (ALARA). The ALARA principle is based on the morewidely accepted linear no-threshold model of radiationeffects. Although some recommend the revision of radiationprotection regulations to account for hormesis, the level ofevidence for that position is currently inadequate.90

One difficulty with regulating NORM and TENORM isdetermining what substances need to be regulated. All naturalmaterials have some degree of radiation, yet regulating theentire natural world and all industries that use components ofthe natural world would be impossible. The InternationalAtomic Energy Agency’s Basic Safety Standards suggeststhat regulation of materials with activities below 1 Bq/g ofuranium and thorium decay series radionuclides and 10 Bq/gpotassium-40 is generally unnecessary.91 For transport ofradioactive materials, the International Atomic Energy

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Agency proposes the same cutoffs for uranium and thoriumdecay series radionuclides and 100 Bq/g of potassium-40.92

Regulation of TENORM in the United States is minimal as itis not subject to regulatory control under the Atomic EnergyAct of 1954 or the Low Level Radioactive Waste PolicyAct.43 As a result, most regulation of TENORM occurs at thestate level.93

The National Council on Radiation Protection (NCRP), abody chartered by the United States Congress in 1964, publishesrecommendations for occupational exposure limits. For occupa-tional exposures, the recommended annual limit is 50 mSv witha cumulative limit of 10 mSv × age. Lower limits are recom-mended for exposure of the general population, with a recom-mended annual effective dose limit of 1 mSv. A recommendedembryo–fetus exposure limit of 0.5 mSv/month in pregnantwomen is recommended. The NCRP also publishes recom-mended levels for remedial action for natural sources.94 TheICRP, an independent international scientific body not associ-ated with any government, makes similar recommendations onoccupational limits, limits on embryo–fetus exposure, and limitsto the general public.56 ICRP recommendations are generally asrestrictive or more restrictive as NCRP recommendations. As aresult of NCRP/ICRP recommendations on radiation exposureto pregnant women, many airlines transfer pregnant flight crewto ground duties for the duration of their pregnancy.1

Generally, occupational activities and industries that donot result in exposure exceeding 1 mSv/year are de facto notsubjected to regulation. The European Commission is consid-ering including exemption criteria of 1 and 0.3 mSv/year foroccupational and public exposures, respectively, into therevised Euratom Directive.2 There is currently no generallyaccepted criteria for exemption of activity per unit surfacearea, which would be useful in regulating TENORM surfacecontamination or scale.2

The United States EPA has established maximum concen-trations for various radionuclides in drinking water includingradium-226/228 (5 pCi/L), gross alpha emitter activity notincluding radon or uranium (15 pCi/L), beta emitters (4 mrem/year), and uranium (30 μg/L).95

Dumping of radioactive waste at sea was prohibited by themodification of the London Convention in 1993. Previously,only the dumping of high-level waste had been prohibited.

Norway is undertaking measures to establish limits for thedischarge of produced water from offshore fossil fuel extrac-tion with the goal of limiting human exposure through con-sumption of marine animals. A discharge limit based on anabsorbed dose to marine biota of 5 mGy/h has been proposed.2

Rehabilitation of polluted sites may be required by regula-tions or advocated by environmental groups. Rehabilitationmay be very expensive and may raise concerns among localresidents about exposure to radioactivity.96

Of continuing controversy today is the lack of protectiveequipment and ventilation in American uranium mines fol-lowing World War II.97 In consideration of the health effectsexperienced by American uranium miners, the RadiationExposure Compensation Act was passed by the US Congress in

1990, providing compensation to miners who developed healthproblems related to their radiation exposure. Despite beingamended in 2000, controversy remains as to whether RadiationExposure Compensation Act adequately covers all those withadverse health effects from working in uranium mines.98

Conclusions

TENORM is produced in large quantities in association witha number of industries. The most important industries whereTENORM may be at issue are mining, ore processing andextraction of minerals, fossil fuel extraction, and commercialaviation.

Although most occupational and general public exposuresare minimal, there is the potential for TENORM exposuresamong certain workers and critical groups. Excess cancer hasbeen linked to certain TENORM exposures though in mostcases the quantity of TENORM exposure is not sufficient toallow a correlation to be made. Regulations, especially in theUnited States, are minimal and are created on the state level,with the potential for inadequate protection of workers andthe general public. To properly evaluate whether TENORMposes a health risk to any given individual or group of indi-viduals, a careful evaluation of all facts and issues surround-ing each given circumstance must be undertaken inaccordance with the generally accepted principles of medicaltoxicology.

References

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