Importance of Uranium Recovery Facility Product Characteristics for Dose Assessment and Assignment.

Two traditional methods are used, often in combination, for assessing the intake and resulting dose from the inhalation of radioactive aerosols. The first calculates the intake based on air sampling programs and assessing and assigning dose using published dose conversion factors. The second approach assigns dose from the results of bioassay programs using measurements of radionuclides in human excreta (ex vivo, sometimes referred to as "in vitro") or via direct measurements of radionuclides in the body (in vivo) in combination with metabolic models. This paper describes standard practices using each of these methods to assess and assign worker dose from inhalation of uranium products produced at natural uranium processing facilities, namely uranium mills and in-situ uranium recovery facilities (ISRs). Chemical speciation is an important consideration, which relates directly to solubility in body fluids and associated metabolic behavior. The concepts are illustrated by specific examples applicable to the products to which workers can be exposed at natural uranium processing facilities.

Deterministic Effects to the Lens of the Eye Following Ionizing Radiation Exposure: is There Evidence to Support a Reduction in Threshold Dose?

Ionizing radiation exposure to the lens of the eye is a known cause of cataractogenesis. Historically, it was believed that the acute threshold dose for cataract formation was 5 Sv, and annual dose limits to the lens were set at 150 mSv. Recently, however, the International Commission on Radiological Protection has reduced their threshold dose estimate for deterministic effects to 0.5 Gy and is now recommending an occupational limit of 20 mSv per year on average. A number of organizations have questioned whether this new threshold and dose limit are justified based on the limited reliable data concerning radiation-induced cataracts. This review summarizes all of the published human epidemiological data on ionizing radiation exposure to the lens of the eye in order to evaluate the proposed threshold. Data from a variety of exposure cohorts are reviewed, including atomic bomb survivors, Chernobyl liquidators, medical workers, and radiotherapy patients. Overall, there is not conclusive evidence that the threshold dose for cataract formation should be reduced to 0.5 Gy. Many of the studies reviewed here are challenging to incorporate into an overall risk model due to inconsistencies with dosimetry, sample size, and scoring metrics. Additionally, risk levels in the studied cohorts may not relate to occupational scenarios due to differences in dose rate, radiation quality, age at exposure and latency period. New studies should be designed specifically focused on occupational exposures, with reliable dosimetry and grading methods for lens opacities, to determine an appropriate level for dose threshold and exposure limit.

Degradation of Crude 4-MCHM (4-Methylcyclohexanemethanol) in Sediments from Elk River, West Virginia.

In January 2014, approximately 37 800 L of crude 4-methylcyclohexanemethanol (crude MCHM) spilled into the Elk River, West Virginia. To understand the long-term fate of 4-MCHM, we conducted experiments under environmentally relevant conditions to assess the potential for the 2 primary compounds in crude MCHM (1) to undergo biodegradation and (2) for sediments to serve as a long-term source of 4-MCHM. We developed a solid phase microextraction (SPME) method to quantify the cis- and trans-isomers of 4-MCHM. Autoclaved Elk River sediment slurries sorbed 17.5% of cis-4-MCHM and 31% of trans-4-MCHM from water during the 2-week experiment. Sterilized, impacted, spill-site sediment released minor amounts of cis- and up to 35 µg/L of trans-4-MCHM into water, indicating 4-MCHM was present in sediment collected 10 months post spill. In anoxic microcosms, 300 µg/L cis- and 150 µg/L trans-4-MCHM degraded to nondetectable levels in 8-13 days in both impacted and background sediments. Under aerobic conditions, 4-MCHM isomers degraded to nondetectable levels within 4 days. Microbial communities at impacted sites differed in composition compared to background samples, but communities from both sites shifted in response to crude MCHM amendments. Our results indicate that 4-MCHM is readily biodegradable under environmentally relevant conditions.

Uranium Mining and Norm in North America-Some Perspectives on Occupational Radiation Exposure.

All soils and rocks contain naturally occurring radioactive materials (NORM). Many ores and raw materials contain relatively elevated levels of natural radionuclides, and processing such materials can further increase the concentrations of naturally occurring radionuclides. In the U.S., these materials are sometimes referred to as technologically-enhanced naturally occurring radioactive materials (TENORM). Examples of NORM minerals include uranium ores, monazite (a source of rare earth minerals), and phosphate rock used to produce phosphate fertilizer. The processing of these materials has the potential to result in above-background radiation exposure to workers. Following a brief review of the sources and potential for worker exposure from NORM in these varied industries, this paper will then present an overview of uranium mining and recovery in North America, including discussion on the mining methods currently being used for both conventional (underground, open pit) and in situ leach (ISL), also referred to as In Situ Recovery (ISR), and the production of NORM materials and wastes associated with these uranium recovery methods. The radiological composition of the NORM products and wastes produced and recent data on radiological exposures received by workers in the North American uranium recovery industry are then described. The paper also identifies the responsible government agencies in the U.S. and Canada assigned the authority to regulate and control occupational exposure from these NORM materials.

Determination of (4-methylcyclohexyl)methanol isomers by heated purge-and-trap GC/MS in water samples from the 2014 Elk River, West Virginia, chemical spill.

A heated purge-and-trap gas chromatography/mass spectrometry method was used to determine the cis- and trans-isomers of (4-methylcyclohexyl)methanol (4-MCHM), the reported major component of the Crude MCHM/Dowanol™ PPh glycol ether material spilled into the Elk River upriver from Charleston, West Virginia, on January 9, 2014. The trans-isomer eluted first and method detection limits were 0.16-µg L(-1)trans-, 0.28-µg L(-1)cis-, and 0.4-µg L(-1) Total (total response of isomers) 4-MCHM. Estimated concentrations in the spill source material were 491-g L(-1)trans- and 277-g L(-1)cis-4-MCHM, the sum constituting 84% of the source material assuming its density equaled 4-MCHM. Elk River samples collected⩽3.2 km downriver from the spill on January 15 had low (⩽2.9 µg L(-1) Total) 4-MCHM concentrations, whereas the isomers were not detected in samples collected 2 d earlier at the same sites. Similar 4-MCHM concentrations (range 4.2-5.5 µg L(-1) Total) occurred for samples of the Ohio River at Louisville, Kentucky, on January 17, ∼630 km downriver from the spill. Total 4-MCHM concentrations in Charleston, WV, office tap water decreased from 129 µg L(-1) on January 27 to 2.2 µg L(-1) on February 3, but remained detectable in tap samples through final collection on February 25 indicating some persistence of 4-MCHM within the water distribution system. One isomer of methyl 4-methylcyclohexanecarboxylate was detected in all Ohio River and tap water samples, and both isomers were detected in the source material spilled.

Worker protection implications of the solubility and human metabolism of modern uranium mill products in the U.S.

This paper presents an analysis of the implications of some recent studies performed to characterize uranium products from modern uranium recovery facilities important for worker protection. Assumptions about the solubility (related to the molecular species being produced) of these materials in humans are critical to properly assess radiation dose from intakes, understand chemotoxic implications, and establish protective exposure standards (airborne concentrations, limits on intake, etc.). Recent studies, as well as information in the historical professional literature, were reviewed that address the issue of solubility and related characteristics. These data are important for the design of programs for assessment of both chemical and radiological aspects of worker exposure to the products of modern uranium recovery plants (conventional uranium mills and in situ recovery plants; i.e., ISRs). The data suggest strongly that the oxide form produced by these facilities (and therefore, product solubility) is related to precipitation chemistry and thermal exposure (dryer temperature). Given the peroxide precipitation and low temperature drying methods being used at many modern uranium recovery facilities in the U.S. today, very soluble products are being produced. The dosimetric impacts of these products to the pulmonary system (except perhaps in case of an extreme acute insult) would be small, and any residual pulmonary retention beyond a month or two would most likely be too small to measure by traditional urinalysis sampling or the current state-of-the-art of natural uranium in vivo lung counting techniques. Uranium recovery plants should revisit the adequacy of current bioassay programs in the context of their process and product specifics. Workers potentially exposed to these very soluble yellowcake concentrates should have urine specimens submitted for uranium analysis on an approximately weekly basis, including analysis for the biomarkers associated with potential renal injury [e.g., glucose, lactate dehydrogenase (LDH) and protein albumen]. Additionally, implications for compliance with current U.S. Nuclear Regulatory Commission (NRC) regulations (e.g., 10 CFR20) are discussed. NRC, the applicable Agreement State agencies, and licensees need to recognize the importance of the uranium chemotoxicity versus dose relationship in the interest of worker protection.

Prediction of the variation in risks from exposure to radon at home or at work.

On the basis of a review of recent epidemiology, the ICRP recently issued a statement outlining a new approach to radon. The ICRP indicates that the Publication 65 dose conversion convention will be replaced using the dosimetric approach currently used for other radionuclides. Moreover, the ICRP indicates that the dose conversion factor is expected to increase by about a factor of 2. This paper independently examines the risks associated with exposure to radon and decay products through estimation of lifetime excess absolute risks per WLM for a variety of epidemiological risk projection models and baseline cancer and mortality rates. This paper suggests that current ICRP dosimetric models do not reflect the effect of smoking and suggest that basic risk estimates and dose conversion factors be based on risks to non-smoking populations with recognition that lifestyle choices, especially smoking, have a large effect on the risk from exposure to radon.

Choosing an alpha radiation weighting factor for doses to non-human biota.

The risk to non-human biota from exposure to ionizing radiation is of current international interest. In calculating radiation doses to humans, it is common to multiply the absorbed dose by a factor to account for the relative biological effectiveness (RBE) of the radiation type. However, there is no international consensus on the appropriate value of such a factor for weighting doses to non-human biota. This paper summarizes our review of the literature on experimentally determined RBEs for internally deposited alpha-emitting radionuclides. The relevancy of each experimental result in selecting a radiation weighting factor for doses from alpha particles in biota was judged on the basis of criteria established a priori. We recommend a nominal alpha radiation weighting factor of 5 for population-relevant deterministic and stochastic endpoints, but to reflect the limitations in the experimental data, uncertainty ranges of 1-10 and 1-20 were selected for population-relevant deterministic and stochastic endpoints, respectively.