Uranium in vitro bioassay action level used to screen workers for chronic inhalation intakes of uranium mill tailings.

A uranium in vitro bioassay (urinalysis) action level was derived for use at the Department of Energy's Uranium Mill Tailings Remedial Action Project sites to identify chronic inhalation intakes of uranium mill tailings causing 0.5 mSv (50 mrem) annual effective dose equivalent. All radionuclides in the 238U decay chain that contribute 1% or more to the annual effective dose equivalent from an inhalation intake of uranium mill tailings were included in the derivation of the urinalysis action level. Using a chronic inhalation intake model, the uranium urinalysis action level for a 24-h urine sample, collected on a quarterly schedule, was calculated to be 1.5 micrograms.     

Study of radon daughter concentrations in Polk and Hillsborough counties

The present study finds the average excess dose equivalent resulting from external gamma radiation on reclaimed land to be 17 mrem/yr (whole body); the highest excess is 166 mrem/yr, well below the NCRP limit that might be compared (500 mrem/yr). In contrast, the annual average excess exposure from radon-daughter inhalation on reclaimed land has been found to be 540 mrem/yr to the whole lung, more than twice that resulting from natural background in the study area and more than 5 times the national average dose equivalent reported in NCRP 45 (100 mrem/yr). Moreover, a significant number of individuals presently receive lung doses exceeding limits inferred from NCRP recommendations. These results indicate the need for corrective action to reduce radiation exposure of members of the general population whose exposure exceeds dose limiting recommendations and possibly to reduce radiation exposures well below these limits, thereby lowering risks even further.     

Radiological risk from consuming fish and wildlife to Native Americans on the Hanford Site (USA)

Historical operations at the Hanford Site (Washington State, USA) have released a wide array of non-radionuclide and radionuclide contaminants into the environment. As a result of stakeholder concerns, Native American exposure scenarios have been integrated into Hanford risk assessments. Because its contribution to radiological risk to Native Americans is culturally and geographically specific but quantitatively uncertain, a fish and wildlife ingestion pathway was examined in this study. Adult consumption rates were derived from 20 Native American scenarios (based on 12 studies) at Hanford, and tissue concentrations of key radionuclides in fish, game birds, and game mammals were compiled from the Hanford Environmental Information System (HEIS) database for a recent time interval (1995-2007) during the post-operational period. It was assumed that skeletal muscle comprised 90% of intake, while other tissues accounted for the remainder. Acknowledging data gaps, median concentrations of eight radionuclides (i.e., Co-60, Cs-137, Sr-90, Tc-99, U-234, U-238, Pu-238, and Pu-239/240) in skeletal muscle and other tissues were below 0.01 and 1 pCi/g wet wt, respectively. These radionuclide concentrations were not significantly different (Bonferroni P>0.05) on and off the Hanford Site. Despite no observed difference between onsite and offsite tissue concentrations, radiation dose and risk were calculated for the fish and wildlife ingestion pathway using onsite data. With median consumption rates and radionuclide tissue concentrations, skeletal muscle provided 42% of the dose, while other tissues (primarily bone and carcass) accounted for 58%. In terms of biota, fish ingestion was the largest contributor to dose (64%). Among radionuclides, Sr-90 was dominant, accounting for 47% of the dose. At median intake and radionuclide levels, estimated annual dose (0.36 mrem/yr) was below a dose limit of 15 mrem/yr recommended by the United States Environmental Protection Agency (USEPA), as well as below a dose limit of 100 mrem/yr proposed by the International Commission on Radiation Protection (ICRP). Similarly, lifetime cancer risk (1.7E−5), calculated with median inputs, was below risk levels corresponding to these dose limits. However, our dose and risk estimates apply to only one pathway within a multidimensional exposure scenario for Native Americans. On the other hand, radiation dose and risk corresponding to onsite tissue concentrations were not significantly different from those corresponding to offsite (background) concentrations. Recognizing uncertainties in exposure and toxicity assessments, our results may facilitate informed decision making and optimize resource allocation within a risk assessment framework at the Hanford Site.     

降札异常高氡温泉天然辐射外照射水平调查

目的调查降札温泉区域的天然1辐射水平,掌握温泉区域的人员外照射剂量。方法采用便携式x-1剂量率仪和x-γ射线巡测仪对周围环境7照射量率进行测量,采用高纯锗γ谱仪进行土壤、河床沙样品进行比活度测量。结果该区域1辐射水平和放射性核素含量都很高,温泉小院中1辐射均值9630nGy／h,为四川省室外平均水平的150倍。温泉周围建筑物室内均值为3461nGy／h,最高值28718nGy／h,为四川省室内平均水平的38和312倍。结论该区域异常高水平γ照射量率,主要是该区域存在铀矿浅层露头、矿渣铺垫院子、采用铀矿石修建房屋、土壤中含高比活度放射性核素238u、236Ra等因素所致,温泉水流入牛棚沟,使放射性核素随河流迁移,对环境造成一定的污染。     

Investigation of magnetic nanoparticles for the rapid extraction and assay of alpha-emitting radionuclides from urine: demonstration of a novel radiobioassay method

In the event of an accidental or intentional release of radionuclides into a populated area, massive numbers of people may require radiobioassay screening as triage for dose-reduction therapy or identification for longer-term follow-up. If the event released significant levels of beta- or alpha-emitting radionuclides, in vivo assays would be ineffective. Therefore, highly efficient and rapid analytical methods for radionuclide detection from submitted spot urine samples (≤50 mL) would be required. At present, the quantitative determination of alpha-emitting radionuclides from urine samples is highly labor intensive and requires significant time to prepare and analyze samples. Sorbent materials that provide effective collection and enable rapid assay could significantly streamline the radioanalytical process. The authors have demonstrated the use of magnetic nanoparticles as a novel method of extracting media for four alpha-emitting radionuclides of concern (polonium, radium, uranium and americium) from chemically-unmodified and pH-2 human urine. Herein, the initial experimental sorption results are presented along with a novel method that uses magnetic nanoparticles to extract radionuclides from unmodified human urine and then collect the magnetic field-induced particles for subsequent alpha-counting-source preparation. Additionally, a versatile human dose model is constructed that determines the detector count times required to estimate dose at specific protective-action thresholds. The model provides a means to assess a method's detection capabilities and uses fundamental health physics parameters and actual experimental data as core variables. The modeling shows that, with effective sorbent materials, rapid screening for alpha-emitters is possible with a 50-mL urine sample collected within 1 wk of exposure/intake.     

Population exposure from nuclear medicine procedures: measurement data

In order to estimate the public radiation burden from nuclear medicine studies, a TLD chip in a sealed plastic bag was taped on the abdomen of patients who received 111In as chloride or oxine, 201T1 chloride, or one of four common 99mTc agents. The TLD chip was removed after 24 h. Additionally, abdominal skin surface exposure rate measurements were performed with an ionization chamber survey meter at various times (0 to about 60 h). There was superb correlation between TLD and integrated exposure rate measurements and between TLD and ionization chamber measurements and MIRD calculated doses. Scenarios postulated for exposure of co-workers and family members yielded doses between 7 muSv (0.7 mrem) and 20 muSv (2 mrem) for the selected radiopharmaceuticals. Calculations of the total population exposure from nuclear medicine procedures indicate the per capita dose (amortized over the entire population) is approximately 0.4 muSv (0.04 mrem), a negligible dose compared to natural background and total medical irradiation.     

Accumulation and distribution of uranium in rats after chronic exposure by ingestion

Data describing the biokinetics of radionuclides after contamination come mainly from experimental acute exposures of laboratory animals and follow-up of incidental exposures of humans. These data were compiled to form reference models that could be used for dose calculation in humans. In case of protracted exposure, the same models are applied, assuming that they are not modified by the duration of exposure. This work aims at testing this hypothesis. It presents new experimental data on retention of uranium after chronic intake, which are compared to values calculated from a biokinetic model that is based on experiments of acute exposure of rats to uranium. Experiments were performed with 56 male Sprague Dawley rats, from which 35 were exposed during their whole adult life to 40 mg L of uranyl nitrate dissolved in mineral water and 21 were kept as controls. Animals were euthanatized at 32, 95, 186, 312, 368, and 570 d after the beginning of contamination. Urine and all tissues were removed, weighted, mineralized, and then analyzed for uranium content by Kinetics Phosphorescence Analysis (KPA) or by ICP-MS. Experimental data showed that uranium accumulated in most organs, following a nonmonotonous pattern. Peaks of activities were observed at 1-3, 10, and 19 mo after the beginning of exposure. Additionally, accumulation was shown to occur in tissues such as teeth and brain that are not usually described as target organs. Comparison with model prediction showed that the accumulation of uranium in target organs after chronic exposure is overestimated by the use of a model designed for acute exposure. These differences indicate that protracted exposure to uranium may induce changes in biokinetic parameters when compared to acute contamination and that calculation of dose resulting from chronic intake of radionuclides may need specific models that are not currently available.     

Radioactivity in municipal sewage and sludge.

OBJECTIVE: To determine the environmental consequences of discharges of radioactivity from a large medical research facility into municipal sewage, specifically 131I activity in sewage sludge, and the radiation exposures to workers and the public when sludges are incinerated. METHODS: The authors measured radioactivity levels in the sludge at the Ann Arbor, Michigan, Waste Water Treatment Plant following radioiodine treatments of two patients at the University of Michigan hospital complex and performed a series of calculations to estimate potential radiation doses due to releases of 131I from incineration of sewage sludge. RESULTS: Approximately 1.1% of the radioactive 131I administered therapeutically to patients was measured in the primary sludge. Radiation doses from incineration of sludge were calculated to be 0.048 millirem (mrem) for a worker during a period in which the incinerator filtration system failed, a condition that could be considered to represent maximum exposure conditions, for two nine-hour days. Calculated results for a more typically exposed worker (with the filtration system in operation and a 22-week period of incineration) yielded a committed effective dose equivalent of 0.066 mrem. If a worker were exposed to both conditions during the period of incineration, the dose was calculated to be 0.11 mrem. For a member of the public, the committed effective dose equivalent was calculated as 0.003 mrem for a 22-week incineration period. Exposures to both workers and the public were a very small fraction of a typical annual dose (about 100 mrem excluding radon, or 300 mrem with radon) due to natural background radiation. Transport time to the treatment plant for radioiodine was found to be much longer than that of a normal sewage, possibly due to absorption of iodine by organic material in the sewer lines. The residence time of radioiodine in the sewer also appears to be longer than expected. CONCLUSION: 131I in land-applied sludge presents few health concerns because sufficient decay occurs before it can reach the public however, incineration, which is done in winter months, directly releases the 131I from sewage sludge to the atmosphere, and even though exposures to both workers and the public were found to be considerably lower than 1% of natural background, incineration of sludge in a pathway for public exposure. Although 131I was readily measurable in sewage sludge, only about 1% of the radioione administered to patients was found in the sludge. The fate of the remaining radioactivity has not been established; some may be in secondary and tertiary residuals, but it is quite likely that most passed through the plant and was discharged in dilute concentrations in plant emissions. The behavior of radioiodine and other radioactive materials released into municipal seweage systems, such as those from large medical facilities, is not yet well understood.     

Fifteen years of radiological protection experience in a regional radiopharmacy

Radiological protection experience in a regional radiopharmacy, currently handling 28.5 TBq (770 Ci) 99mTc y-1, is reviewed for the period 1974-1988. The results of personnel monitoring have shown a downward trend (by more than a factor of two) in radiation exposure of individual staff members, despite the workload per person [6000 GBq (162 Ci) 99mTc y-1] remaining virtually constant. Adequate staff selection and training contribute to the reduction in dose. A significant reduction in dose to the eyes was achieved by installing lead glass screens in the radiopharmacy work stations, and tungsten syringe shields reduced radiation dose to the hands. The use of commercially available kits for producing 99mTc radiopharmaceuticals, rather than relying on in-house preparations that require more operator handling, has also contributed to reduction in radiation exposure. Internal contamination of staff members with 125I was markedly reduced when the practice of sub-dispensing high-specific activity solutions of the radionuclide was discontinued. Annual doses from external radiation currently average less than 6 mSv (600 mrem) to the trunk, less than 7 mSv (700 mrem) to the eyes, and 50 mSv (5 rem) to the hands. Internal contamination of personnel with 125I, 131I, and 99mTc, as detected by thyroid and whole-body monitoring, contributed less than 65 mSv y-1 (6.5 rem) to the thyroid gland and less than 0.1 mSv y-1 (10 mrem) to the whole body.     

Effective half-life of 131I in thyroid cancer patients

The oral administration of radioactive 131I is a standard treatment for thyroid carcinoma. One consideration for this therapy is assuring that other people do not receive significant radiation exposure. In particular, federal and state regulatory authorities stipulate that no individual should receive more than 5 mSv (500 mrem) effective dose-equivalent from the released patient. Patients receiving more than 1.11 GBq (30 mCi) of 131I were traditionally confined as in-patients by regulation until their burdens of radioactivity fell below that level or until the external dose rates were less than 50 microSv (5 mrem) per hour at 1 m. Recent regulatory guidance recommends the use of biological elimination as well as physical decay in calculating the confinement time to keep the effective dose-equivalent to members of the public less than 5 mSv. Analysis of a database of more than 250 administrations of 131I for thyroid cancer shows a median effective half-life of at least 14 h, with substantial variation. Thus, discharge criteria for radiation safety purposes should be calculated on the basis of individual measurements. The release of these patients should not always be as prompt as the guidance indicates. The results also challenge some long-used assumptions regarding iodine excretion in this patient population.     

A field study of Ra accumulation in trout with assessment of radiation dose to man

The purpose of this study was to determine the concentrations of 226Ra in edible fish from surface ponds near an open pit U mine. Because one reclamation plan for the U mine proposed formation of an artificial lake in the open pit, potential radiation dose to man from ingestion of fish needed to be investigated. Trout were collected from four existing ponds which varied in mean 226Ra concentration from 12-33 pCi/l. and in Ca concentration from 30-330 mg Ca/l. Radium and Ca accumulation in trout flesh, skin, fins and bone were measured. Geometric mean concentrations of 226Ra in trout flesh from four ponds ranged from 6.3-30 pCi/kg wet weight. The distribution of Ra in the trout body was similar to that of Ca. Of the total 226Ra in trout carcasses, 6% was in flesh, 25% was in skin, 28% was in fins, and 41% was in bone. Mean concentration factors for 226Ra in trout flesh from the four ponds ranged from 0.29-2.5. Bone concentration factors were up to 260 times higher than for flesh. Observed ratios (Ra/Ca in fish tissue divided by Ra/Ca in water) were used to normalize the differences in Ca availability among the locations. Observed ratios were higher in all tissues of fish which had been in the ponds for a longer time, indicating that 226Ra concentrations in fish may increase with continued exposure to the nuclide. The calculated dose equivalent commitment to human endosteal tissue ranged from 0.2-2 mrem per fish consumed, depending on the assumed dietary and environmental parameters. Neglecting the consumption of trout skin underestimated the ingestion dose from 226Ra by a factor of 5-10. Estimated annual dose equivalent rates to human endosteal tissue ranged from 1.0-83 mrem/yr for an individual who consumed one fish per week for a 50-yr period. The dose to man from ingestion of 226Ra in fish would not likely preclude the establishment of a recreational lake at this site.     

A proposal for a generally applicable de minimis dose

This paper presents a proposal for a generally applicable de minimis radiation dose for members of the general public. A de minimis dose defines a level below which control of radiation exposures would be deliberately and specifically curtailed. Thus, such a dose must be set well below established limits on acceptable dose from all sources of exposure and, furthermore, must be below any established dose limit for specific practices. The proposed de minimis level consists of two dose limits: a principal limit on annual committed effective dose equivalent averaged over a lifetime of 0.01 mSv (1 mrem) and a subsidiary limit on committed effective dose equivalent in any year of 0.05 mSv (5 mrem). The proposed values are 1% of the limits on acceptable dose from all sources currently recommended by the International Commission on Radiological Protection (ICRP85), and correspond to a lifetime risk from continuous exposure of about 10(-5).     

Drinking-water contribution to natural background radiation

The average concentrations of naturally occurring radionuclides in drinking water are estimated from recent measurements and are used to estimate the annual effective dose equivalent associated with drinking water due to the different radionuclides. The annual effective dose equivalents are determined from the annual intake of these radionuclides using dosimetric information based on ICRP Publication 30 dosimetric models and cohort analysis considering risk coefficients developed by the U.S. Environmental Protection Agency using data from the report of the Biological Effects of Ionizing Radiation Committee (BEIR III) of the National Academy of Sciences. The resulting contribution from drinking water sources to the annual effective dose equivalent is in the range of 0.002 to 0.05 mSv/y (0.2-5 mrem/yr) for those using community drinking water supplies (approximately 216 million people in the United States). The contribution to the annual effective dose equivalent from 222Rn dissolved in water is in the range of 0.8-30 mu Sv/y (0.08-3 mrem/yr) based on the inhalation pathway following the release of 222Rn from drinking water.     

Hazards of X-ray radiation on the quantitative and phagocytic functions of polymorphonuclear neutrophils in X-ray technicians

Over exposure to X-ray radiation is detrimental to the living cells and may lead to development of life-threatening diseases. It is intuitive to postulate that a low level exposure may lead to functional abnormalities in human immune cells. Therefore, the objective of the present study was to study the effects of X-ray radiation on the total leukocyte count (TLC) and phagocytic activity of Polymorphonuclear neutrophils (PMN). A group of 42 apparently healthy X-ray technicians were recruited with age ranging from 25-50 years. They were matched with another group of 42 control healthy volunteer subjects in terms of age, sex and ethnic variation. The mean exposure level of X-ray radiation in X-ray technicians was 72.4 mrem per calendar quarter and 289.6 mrem per year. TLC was performed by using a Beckman Coulter counter and phagocytic activity of whole blood and PMN was determined by measuring chemiluminescence (CL) response with a chemiluminescence luminometer. The mean value of CL response was significantly decreased (p<0.0005) in X-ray technicians, even though they had low levels of exposure, compared to their controls. However, no significant difference was observed in TLC between the two groups at this low level of exposure. Exposure to X-ray radiation decreases the physiological functions of PMN as measured by decreasing chemiluminescence response even at low levels of exposure.     

Radiological assessment of petroleum pipe scale from pipe-rattling operations

Petroleum pipe scale, consisting of concentrated inorganic solids such as barium sulfate, can deposit on the inside of down-hole pipes during the normal course of oil field pumping operations. A portion of this scale has been shown to contain naturally occurring radioactive materials (NORM), predominantly compounds of radium. When these pipes are removed from the well, there is a potential for radiation doses to the oil field workers handling the pipes, especially as the pipes are cleaned for reuse. A thorough sampling and measurement protocol was applied under a variety of weather conditions in an outdoor laboratory to obtain an accurate indication of the radiological and aerodynamic characteristics of scale release and dust dispersion during petroleum pipe scale removal from out-of-service pipes with a restored, historically relevant outdoor pipe-cleaning machine. Exposure rate data were also obtained for both the pre-cleaned pipes, and the general area inhabited by workers during the descaling operation. Four radiation exposure pathways were investigated: inhalation of pipe scale dust generated during pipe rattling, incidental ingestion of the pipe scale dust, external exposure from uncleaned pipes, and external exposure from pipe scale dispersed on the ground. Pipes from three oil fields were rattled to collect as much industry-representative data as possible. The Ra specific activity of the pipe scale ranged from 33.6 +/- 0.4 to 65.5 +/- 0.7 Bq g, depending on the formation. A median atmospheric dust loading of 0.13 mg m was measured in the operator breathing zone. The respirable fraction was observed to be about 42% to 46%. Based on cleaning 20 pipes per day,250 d per year on average, annual committed effective doses for the operator and helper ranged from 0.11 mSv (11 mrem) to 0.45 mSv(45 mrem) for inhalation and from 19 microSv (1.9 mrem) to 97 microSv (9.7 mrem) for incidental ingestion. Worker annual external dose from the pipe racks ranged from 0 to 0.28 mSv (28 mrem). In the deposition experiment, more than 99% by weight of the deposited scale fell within 2 m of the machine centerline, the vast majority of which was in the downwind direction. The dose from this deposited material dominated the worker dose estimates. The annual external dose from dispersed material was estimated to be 2.8 mSv (280 mrem) for the operator and 4.1 mSv (410 mrem) for the helper.     

Radionuclides in Peconic River fish, mussels, and sediments.

For regulatory oversight and quality control of Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) actions, fish, mussels, and sediments were analyzed from the Peconic River system on Long Island, NY, downstream of the Brookhaven National Laboratory, as well as from control locations. The analyses were for photon-emitting radionuclides (notably 60Co and 137Cs), uranium, plutonium, and americium. Sediments were cored in 4 sections to 0.37 m depth, whole fish were analyzed, and mussels were separated into flesh and shells. Radioisotopes of the cited elements were detected in sediment, some of the fish contained 137Cs, 241Am, and uranium, and mussel flesh contained 137Cs and uranium. All of the 60Co, 233U, and enriched uranium, and some of the 137Cs and 241Am, can most likely be attributed to Brookhaven National Laboratory. The other radionuclides (and some of the 137Cs and 241Am) are believed to have either fallout or nature as their origin. The New York State Department of Health (NYSDOH) evaluated the radiological data in terms of adverse health implications due to consumption of fish with the levels of reported radioactivity. The NYSDOH determined that the added radiation doses likely to result from eating this fish are a small fraction of the radiation dose that normally results from radionuclides present in the body from natural sources.     

Internal dose assessment of natural uranium from drinking water based on biokinetic modeling and individual bioassay monitoring: a study of a Finnish family

Since the later 1960's, a nationwide survey on natural radionuclides in drinking water showed high concentrations of natural uranium (U) in Finland, especially in uraniferous granite areas. In order to assess the radiation dose from the natural uranium to individuals, the concentrations of natural uranium in drinking water of the drilled wells were determined by radiochemical and alpha spectrometric methods. Uranium contents were measured in the urinary samples of five members of a Finnish family by means of inductively coupled plasma-mass spectrometry. Correspondingly, theoretical biokinetic modeling of natural uranium incorporated for the same persons were performed with the aid of follow-up interviews. The ICRP biokinetic compartmental model and the age-dependent transfer rates for uranium were used to model the intake, transfer, distribution, retention, and excretion of (234)U and (238)U, respectively, from the drinking water for each person of the family. The organ absorbed dose, equivalent dose, and effective dose were evaluated for each family member at time intervals using specific effective energy values calculated by the SEECAL program and compared with recommended values. The modeled urinary excretion rates were found to be mostly higher than the measured values by a factor of three. The mean annual effective dose for this family is 8 muSv y(-1). By comparing the measured and calculated data, estimation of retrospective radiation exposure based on biokinetic modeling and bioassay method is enhanced and, vice versa, the biokinetic and dosimetric models are tested and verified.     

Reconstruction of radionuclide contamination of the Techa River caused by liquid waste discharge from radiochemical production at the Mayak Production Association

Because of its importance to reconstructing radiation doses for ongoing epidemiological studies, a feasibility study was undertaken to determine if the source term of radioactive materials released to the Techa River from the Mayak Production Association, the first facility in the former Soviet Union for the production of plutonium, could be reconstructed from historical measurements made at a limited number of downriver locations. The feasibility study used historically measured water flow rates and total-beta radioactivity measurements, and considered the processes of radioactive decay and of sorption/desorption. A simple radionuclide mass balance approach was used. To determine the rate of input of radionuclides to the Techa River system, the Techa River was depicted as a series of segments for which measurements are available. For each segment of the river, a system of recurrent (with time) equations was compiled for radioactivity balance accounting for the radioactivity inflow at the inflowing end, activity discharge with water at the outflowing end, and the reduction of activity because of radioactive decay. The equations change with time to account for the changing nature of the river regime. Effective sorption constants for 90Sr and 137Cs, which characterize the transport of radionuclides among the river system components (water and bottom sediments), were defined based on the inventory of these radionuclides deposited at each of the studied river segments and data on water concentration and radioactive removal. All the information on radioactive contamination of the river system components during the period 1949-1996 was used. Solution of the series of equations provided information on the rate of input of these radionuclides into the upper end of the river. The pilot study indicated that it is possible to determine the historical releases of a wider suite of radionuclides using the historical monitoring data from numerous locations along the river, rather than relying on a more uncertain reconstruction of quantities released at the point of discharge. Radionuclides considered include 90Sr, 106Ru, 137Cs, and 144Ce. Estimated concentrations of selected radionuclides at various times are presented.     

Exposure assessment for a cohort of workers at a former uranium processing facility

Exposure was assessed for a cohort of 6409 workers at a former uranium processing facility as part of a mortality study. Workers at the facility had potential for exposure to a wide variety of radiological and chemical agents including uranium, thorium, radon, external ionizing radiation, acid mists, asbestos, and various solvents. Organ dose from internal exposure to uranium was assessed, along with dose from external ionizing radiation and exposure to radon. Qualitative assessment of exposure to thorium, acid mists, asbestos, coal dust, welding fumes, and other chemicals was also performed. Mean cumulative organ dose from internal uranium exposure ranged from 1.1 mGy (lung) to 6.7 μGy (pancreas). Mean cumulative external ionizing radiation dose was 13.4 mGy. Mean cumulative radon exposure was 26 working level months (WLMs). The chemical agents to which the largest numbers of study subjects were exposed were acid mists, machining fluids, and a tributyl phosphate/kerosene mixture used in the refining process.     

Source inventory limits

A new set of values has been developed for exempting sealed sources of radioactive materials from inventory. The criteria for exemption are: (a) the annual occupational dose from external radiation at 1 m from the source is approximately 100 microSv (10 mrem) or less; and (b) the source activity is approximately equal to the annual limit on intake by inhalation or less than 4 X 10(7) Bq (1000 microCi). These criteria were selected to correspond to an annual occupational dose of approximately 50 to 500 microSv (5 to 50 mrem) and a small potential annual risk of approximately 1 X 10(-6) to 1 X 10(-5) fatal cancers or less.