Introducing DEPDOSE, a Tool to Calculate Dose Coefficients to Members of the Public for Radioactive Aerosols

ABSTRACT

This paper presents DEPDOSE, an open-source computer application that combines the KDEP respiratory tract deposition fractions for inhaled aerosols with DC_PAK committed equivalent dose coefficients for a unit deposition in each region of the respiratory tract. DEPDOSE allows the user to rapidly produce tables of dose coefficients for workers and members of the public inhaling precisely defined, user-specified aerosols using the ICRP Publication 60 methodology. Combined with a plume dispersion modeling system, such as the Quick Urban & Industrial Complex (QUIC) Dispersion Modeling System, this makes it possible to predict radiation doses downstream from an accidental or intentional release of radioactive materials. For this work, a radioactive plume was calculated to members of the public downstream from a dirty bomb in Chicago. DEPDOSE is published under an open source license, and can be downloaded at https://github.com/lanl/DEPDOSE .

Chelation Model Validation: Modeling of a Plutonium-238 Inhalation Incident Treated with DTPA at Los Alamos National Laboratory

Accidental inhalation of plutonium at the workplace is a non-negligible risk, even when rigorous safety standards are in place. The intake and retention of plutonium in the human body may be a source of concern. Thus, if there is a suspicion of a significant intake of plutonium, medical countermeasures such as chelation treatment may be administered to the worker. The present work aimed to interpret the bioassay data of a worker involved in an inhalation incident due to a glovebox breach at Los Alamos National Laboratory's plutonium facility. The worker was treated with intravenous injections of calcium salts of diethylenetriaminepentaacetic acid (DTPA) in an attempt to reduce the amount of plutonium from the body and therefore reduce the internal radiation dose. It is well known in the internal dosimetry field that the administration of chelation treatment poses additional challenges to the dose assessment. Hence, a recently developed chelation model was used for the modeling of the bioassay data. The objectives of this work are to describe the incident, model the chelation-affected and non-affected bioassay data, estimate the plutonium intake, and assess the internal radiation dose.

Dose Assessment Following a 238 Pu Inhalation Incident at Los Alamos National Laboratory

A glovebox breach at the plutonium facility at Los Alamos National Laboratory potentially exposed 15 individuals to 238 Pu aerosols. One of the individuals (P0) received two 1-g intravenous DTPA treatments, one on the day of the intake and another the following day. Several urine samples were collected from the individuals involved in the incident. Particle size analysis on the PPE and solubility analysis of the particles on a filter sample were conducted in vitro. The applicability of the results from the in vitro studies for dose assessment was questionable because of the effect of the cloth mask the workers were wearing for COVID-related protection. Based on several considerations, including the effect of cloth masks on the "effective" particle size inhaled and the analysis of fecal-to-urine ratio, the default Type M 1 μm AMAD model was used to estimate intakes and doses. Using the urinary excretion data collected after 100 d post last chelation treatment, the committed effective dose, E(50), for P0 was calculated to be 5.2 mSv. For all others, the bioassay data were consistent with no intakes or very small intakes [corresponding to E(50) less than 0.1 mSv].

Localized Instantaneous Dose Rates from Inhaled Particles of 239 Pu

In this work, the authors present instantaneous local dose rates from particles of plutonium-239 oxide ( 239 PuO) embedded in various regions of the respiratory tract. For comparison, a small number of simulations were performed in a representative region of the respiratory tract with other chemical compounds including pure metallic 239 Pu, 239 PuO 2 , 239 PuO 3 , 239 Pu 2 O 3 , and 239 Pu(NO 3 ) 4 . A small number of simulations were also performed with 238 PuO, weapons grade Pu, and Pu from a typical radioisotope thermoelectric generator (RTG) source for the same reason. The self-shielding effect is minor for very small particles but gradually becomes more significant as the particle size increases. For particles that are 0.1 μm and larger (excluding Pu nitrate), the calculated dose rate within several microns of the particle may be sufficient to damage lung cells, but the implications of damage to such a small volume of tissue are unclear. However, it is reasonable to assume that clinical effects will be observed if a large enough volume of tissue is damaged, as might happen when large numbers of particles are inhaled. The instantaneous dose rate around a particle may be predictive of deterministic effects, scar tissue formation, and biokinetics.

Use of Nasal Swab Activity to Estimate Intake in Internal Dosimetry

In addition to a review of theoretical analyses, this work presents an empirical study of nasal swab data from the Los Alamos National Laboratory (LANL) database correlated with intake obtained from plutonium internal dosimetry calculations. As a result of this work, several "intake-versus-nasal-swab" models were derived. We advocate quantitative use of nasal swab measurements in dose assessment calculations and discuss ways that this can be done. The best description of the LANL plutonium internal dose database is arguably intake = A + Bx, where A = 2.7 Bq, B = 3.8, and x = summed nasal swab activity. The geometric standard deviation was found to be 8.2. This relationship, obtained using plutonium data, should apply also for other radionuclides.

Alternate Analysis of an In Vitro Solubility Study on the Lung Dissolution Rate of 238PuO2 Material Involved in the 2020 Incident at Los Alamos National Laboratory

This work presents an alternate analysis of an in vitro solubility study on the lung dissolution rate of 238PuO2 material involved in a recent inhalation incident at Los Alamos National Laboratory (LANL). The original dataset used in this work was retrieved from a recently published report. The present work shows an analysis of the same dataset by modeling the dissolution in separate time intervals rather than modeling the cumulative dissolution.

Side Effects and Complications Associated with Treating Plutonium Intakes: A Retrospective Review of the Medical Records of LANL Employees Treated for Plutonium Intakes, with Supplementary Interviews

ABSTRACT

Anecdotal evidence indicates there may be unpublished physical and psychological events associated with the medical treatment of plutonium intakes. A thorough review was conducted of the medical and bioassay records of current and previous Los Alamos National Laboratory (LANL) employees who had experienced plutonium intakes via wound or inhalation. After finding relatively incomplete information in the medical records, the research team interviewed current LANL employees who had undergone chelation therapy and/or surgical excision. Although the dataset is not large enough to reach statistically significant conclusions, it was observed that adverse events associated with treatment appear to be more frequent and more severe than previously reported.

Maximum Possible Doses for a Cohort of Individuals with Intakes Possibly Containing a Component of a Ceramic-type Material

ABSTRACT

Recently, a glovebox breach led to the potential exposure of 15 Los Alamos National Laboratory employees to 238Pu. Given what is known about the material involved in the incident, the possibility of an intake with a ceramic-type component must be considered. Incidents in which intakes of ceramic solubility-type material is suspected represent a challenge for internal dose assessment via urine bioassay because even relatively large doses cannot be detected in urine until many months after the intake. Ideally, in these situations fecal samples should be collected to assess the intake, but in this case fecal sampling was delayed. This paper presents a method to calculate the maximum possible doses for all individuals involved in an incident using only early time-decreasing urine bioassay measurements.

Implications of Cloth COVID Masks for Size Distribution of Inhaled Plutonium, Respiratory Deposition, and Fecal Bioassay Monitoring

This work considers the implications of cloth masks due to the COVID-19 pandemic on suspected plutonium inhalations and dose assessment. In a plutonium inhalation scenario, the greater filtration efficiency for large particles exhibited by cloth masks can reduce early fecal excretion without a corresponding reduction in dose. For plutonium incidents in which cloth masks are worn, urinary excretion should be the preferred method of inferring dose immediately after the inhalation, and fecal excretion should be considered unreliable for up to 10 days.

Response to a Skin Puncture Contaminated with 238Pu at Los Alamos National Laboratory

The three principal pathways for intakes of plutonium are ingestion, inhalation, and contaminated wounds. In August 2018, a glovebox worker at Los Alamos National Laboratory (LANL) sustained a puncture from a thread of a braided steel cable contaminated with Pu. The puncture produced no pain, no blood, and little or no visible mark. As a result, the potential for a contaminated wound was not immediately recognized, and a wound count was not conducted until elevated urine bioassay results were received 12 d after the incident. This paper discusses the circumstances of the incident, along with the medical response and dose assessment, and a discussion of the risks and benefits of the medical interventions.

IMPROVED EMPIRICAL LIKELIHOOD FUNCTION BASED ON NORMALIZATION-DEPENDENT REPLICATE MEASUREMENTS

Based on $n$ replicate measurements that require known normalization factors and assuming an underlying normal distribution for individual measurements but with unknown standard deviation, a combined likelihood function is derived that takes the form of a Student's $t$-distribution with $\nu = n-1$ degrees of freedom and $t=(\psi -\overline{Y})/s$, where $\psi $ is the true value of the measurement quantity calculated from the forward model, and $\overline{Y}$ and $s$ are average and standard error of the mean obtained from the $n$ measurements defined with weighting proportional to the inverse of the normalization factor squared. Assuming an underlying triangle distribution rather than a normal distribution does not produce a large change for six replicates. Examples of replicate data from an animal study and sequential occupational urine and fecal monitoring are given. The use of the empirical likelihood function in data modeling is discussed.

Considerations for Bioassay Monitoring of Mixtures of Radionuclides

Complying with regulations for bioassay monitoring of radionuclide intakes is significantly more complex for mixtures than it is for pure radionuclides. Different constituents will naturally have different dose coefficients, be detectable at significantly different levels, and may require very different amounts of effort to bioassay. The ability to use certain constituents as surrogates for others will depend on how well characterized the mixture is, as well as whether the employee is also working with other radionuclides. This is further compounded by the fact that the composition of a mixture (or even of a pure radionuclide) is likely to change over time. Internal dosimetrists must decide how best to monitor employees who work with radionuclide mixtures. In particular, they must decide which constituents should be monitored routinely, which constituents only need to be monitored in the case of an intake, and how to estimate doses based on intakes of monitored and unmonitored constituents.

KDEP: A Resource for Calculating Particle Deposition in the Respiratory Tract

This paper presents KDEP, an open-source implementation of the ICRP lung deposition model developed by the authors. KDEP, which is freely available to the public, can be used to calculate lung deposition values under a variety of different conditions using the ICRP methodology. The paper describes how KDEP implements this model and discusses some key points of the implementation. The published lung deposition values for intakes by workers were reproduced, and new deposition values were calculated for intakes by members of the public. KDEP can be obtained for free at github.com or by emailing the authors directly.

Interpretation of Nasal Swab Measurements Following Suspected Releases of Actinide Aerosols

For radionuclides such as plutonium and americium, detection of removable activity in the nose (i.e., nasal swab measurements) are frequently used to determine whether follow-up bioassay measurements are warranted following a potential intake. For this paper, the authors analyzed 429 nasal swab measurements taken following incidents or suspicious circumstances (such as an air monitor alarming) at Los Alamos National Laboratory (LANL) for which the dose was later evaluated using in vitro bioassay. Nasal swab measurements were found to be very poor predictors of dose and should not be used as such in the field. However, nasal swab measurements can be indicative of whether a reliably detectable committed effective dose (CED) occurred. About 14% of nasal swab measurements between 1.25 and 16.7 Bq corresponded to CEDs greater than 1 mSv, so in general, positive nasal swabs always indicate that follow-up bioassay should be performed (positive nasal swabs less than 1.25 Bq are considered separately). This probability increased significantly for nasal swabs greater than 16.7 Bq. Only about 3% of nasal swabs with no detectable activity (NDA) corresponded to reliably detectable CEDs. A nasal swab with NDA is therefore necessary, but not sufficient, to negate the need for a follow-up bioassay if it was collected following other workplace indicators of a potential intake.

Potential of phage cocktails in the inactivation of Enterobacter cloacae--An in vitro study in a buffer solution and in urine samples

The objective of this study was to compare the dynamics of three previously isolated phages for Enterobacter cloacae in order to evaluate their ability to treat urinary tract infections (UTI). The phages genomes, survival, host range, were characterized, and the host-phage dynamics was determined in culture medium and urine samples. The presence of prophages in bacteria, host recovery and development of resistance to phage after treatment was also evaluated. The growth of the E. cloacae was inhibited by the three phages, resulting in a decrease of ≈3 log. The use of cocktails with two or three phages was significantly more effective (decrease of ≈4 log). In urine, the inactivation was still effective (≈2 log). Both phages were considered safe to inactivate the bacteria (no integrase and toxin codifying genes). Some bacteria remained viable in the presence of the phages, but their colonies were smaller than those of the non-treated control and were visible only after 5 days of incubation (visible after 24h in the control). A high bacterial inactivation efficiency with phage cocktails combined with the safety of the phages and their long periods of survival, even in urine samples, paves the way for depth studies, especially in vivo studies, to control urinary tract infection and to overcome the development of resistances by the nosocomial bacterium E. cloacae.

First detection of Klebsiella variicola producing OXA-181 carbapenemase in fresh vegetable imported from Asia to Switzerland

Background

The emergence and worldwide spread of carbapenemase-producing Enterobacteriaceae is of great concern to public health services. The aim of this study was to investigate the occurrence of carbapenemase-producing Enterobacteriaceae in fresh vegetables and spices imported from Asia to Switzerland.

Findings

Twenty-two different fresh vegetable samples were purchased in March 2015 from different retail shops specializing in Asian food. The vegetables included basil leaves, bergamont leaves, coriander, curry leaves, eggplant and okra (marrow). Samples had been imported from Thailand, the Socialist Republic of Vietnam and India. After an initial enrichment-step, carbapenemase-producing Enterobacteriaceae were isolated from two carbapenem-containing selective media (SUPERCARBA II and Brilliance CRE Agar). Isolates were screened by PCR for the presence of bla_KPC, bla_NDM, bla_OXA-48-like and bla_VIM. An OXA-181-producing Klebsiella variicola was isolated in a coriander sample with origin Thailand/Vietnam. The bla_OXA-181 gene was encoded in a 14′027 bp region flanked by two IS26-like elements on a 51-kb IncX3-type plasmid.

Conclusions

The results of this study suggest that the international production and trade of fresh vegetables constitute a possible route for the spread of carbapenemase-producing Enterobacteriaceae. The presence of carbapenemase-producing organisms in the food supply is alarming and an important food safety issue.

Simultaneous Source Detection and Analysis Using a Zero-inflated Count Rate Model

This paper proposes a novel Bayesian technique that allows for simultaneous source detection and count rate analysis. The technique involves using priors, which include a finite probability that the source count rate is exactly zero. Such priors are called "zero-inflated." Solving the posterior distribution of a zero-inflated count rate model provides the probability that the sample contains a source and a probability distribution for the source count rate if the source exists, without the need to perform redundant computations. Sampling from zero-inflated distributions is straightforward and can be accomplished with easily accessible open source software. In addition, zero-inflated priors lead to finite posterior probabilities of "no source," which is an easy-to-understand and satisfying result.

Characterisation of non-constant background in counting measurements

A 'moving-target' method for characterising background in a counting measurement in which the instantaneous background count rate is a function of time, rather than being fixed, is proposed. This model treats the average Poisson mean in observation period P as coming from a gamma distribution with parameters αP and βP. This model is applied to a large dataset of replicate observations, consisting of 242 (234)U method blank measurements collected over a 2-y period. Point estimates of the model parameters are determined by comparing the mean and variance of the observed data and by maximising the likelihood function. Posterior distributions of the parameters are obtained by Markov Chain Monte Carlo. Assuming time-invariant fluctuations of the background count rate, the variation of the instantaneous count rate is described by a correlation function, which can be interpreted as describing how rapidly the background changes with time, or how likely the background is to change between measurements. An 'exponential-correlation' model of background time dependence is proposed, with parameters α, β and correlation time τ. Once determined, these parameters fully describe the distribution of background, just as NB and TB in the fixed-target model.

Bayesian analysis of energy and count rate data for detection of low count rate radioactive sources

A particle counting and detection system is proposed that searches for elevated count rates in multiple energy regions simultaneously. The system analyzes time-interval data (e.g., time between counts), as this was shown to be a more sensitive technique for detecting low count rate sources compared to analyzing counts per unit interval (Luo et al. 2013). Two distinct versions of the detection system are developed. The first is intended for situations in which the sample is fixed and can be measured for an unlimited amount of time. The second version is intended to detect sources that are physically moving relative to the detector, such as a truck moving past a fixed roadside detector or a waste storage facility under an airplane. In both cases, the detection system is expected to be active indefinitely; i.e., it is an online detection system. Both versions of the multi-energy detection systems are compared to their respective gross count rate detection systems in terms of Type I and Type II error rates and sensitivity.

Inhalation scintigraphy with an ultrafine aerosol in infants with functional bronchial stenoses

Evaporation of Tc-99m pertechnetate at about 2500 degrees C on a carbon surface generates an ultrafine aerosol of Tc-99m-labeled carbon clusters (Technegas). The small particle size of about 100 nm enables the aerosol to behave similarly to a gas in its ability to penetrate. After inhalation, the radioactive particles adhere to the walls of the respiratory bronchioles and alveoli, or to the greater bronchial tubes if the airflow is not laminar. The high concentration of radioactivity in the argon carrier gas makes it possible to perform inhalation scintigraphy after only a few breaths. The authors investigated 24 infants with multiple events of bronchitis, most of whom had pneumonia. Seventeen patients had inhalation scintigraphy and bronchoscopy. Of these, 11 had scans diagnostic of bronchial stenosis and 6 had normal scans. Except for two pathologic scans, all scintigraphic findings matched well with the results of bronchoscopy. Seven patients had scintigraphy only, of which four were normal. Inhalation scintigraphy with Technegas is a reliable, nonhazardous procedure to preselect young patients for directed bronchoscopy.

Plasma growth hormone-releasing hormone levels in type 1 (insulin-dependent) diabetic children following a mixed meal

Following a mixed meal, plasma hormone responses were measured in four type 1 diabetic children and in eight short normal children. Between 60 and 150 min after ingestion of the mixed meal there was a significant increase in circulating growth hormone-releasing hormone values both in diabetic and in normal children. Mean plasma GHRH peak values were not different between diabetic patients (27.0 +/- 3.9 ng/l) and controls (24.6 +/- 4.9 ng/l). No time relationship to spontaneous growth hormone peaks was observed. Whereas normal children showed a characteristic biphasic plasma somatostatin response, somatostatin plasma levels in diabetic children did not change. In normal children plasma insulin values increased between 30 and 150 min, but remained unchanged in type 1 diabetic patients. Blood glucose response was more pronounced in diabetic children than in short normal children. These results indicate that circulating growth hormone-releasing hormone does not play a dominant role in the regulation of insulin and somatostatin.

Plasma levels of growth hormone-releasing hormone and somatostatin in response to a mixed meal and during sleep in children

Following a mixed meal, plasma levels of GHRH, GH, SRIH and insulin were measured in 7 prepubertal children with constitutional delay of growth and adolescence (CDGA) and in 3 children with proven GH-deficiency which responded to GHRH-injection. In children with CDGA, plasma levels of GHRH increased between 60 and 120 min (10.1 +/- 1.2 ng/l vs 25.5 +/- 4.4 ng/l; P less than 0.01). Although no GH increase occurred in patients with GH-deficiency, their plasma GHRH increases were comparable to those in CDGA children. No time relationship was present between circulating GHRH and GH, SRIH, or insulin, nor was there any correlation between their integrated hormone response areas. Sleep-induced plasma GHRH, GH and SRIH values were determined in 10 prepubertal children with CDGA. Spontaneous variations of plasma GHRH and GH values occurred with no temporal or quantitative relationship. SRIH values did not change during nocturnal sleep. In one child with GH-deficiency, comparable GHRH plasma fluctuations occurred, although GH values were all below 1 microgram/l. Our results support the concept that circulating GHRH does not only represent hypothalamic GHRH, but derives mainly from extrahypothalamic sources, possibly from the gastrointestinal tract.

Insulinhypoglycemia but not arginine infusion stimulates circulating plasma growth hormone-releasing hormone (GHRH) concentrations in children

The effect of insulinhypoglycemia and arginine infusion on circulating concentrations of plasma growth hormone-releasing hormone (GHRH) and growth hormone (GH) has been studied in 24 children (4.4 to 14.3 years). Plasma GH and GHRH concentrations were determined by RIA. Basal plasma GHRH levels were detectable in the plasma of all patients ranging from 6.8 to 27.1 pg/ml. Injection of 0.1 U/kg body wt. insulin i.v. resulted in an increase of plasma GHRH levels (11.1 +/- 1.4 pg/ml vs. 18.8 +/- 2.6 pg/ml; P less than 0.01) preceding that of plasma GH (1.5 +/- 0.4 ng/ml vs. 13.6 +/- 1.3 ng/ml; P less than 0.01). Infusion of 0.5 gm/kg body wt. arginine hydrochloride did increase GH concentrations (2.0 +/- 0.6 ng/ml vs. 13.9 +/- 2.3 ng/ml; P less than 0.01) but did not change circulating plasma GHRH levels. Since the source of peripheral GHRH concentrations is not known the importance of these findings remains to be determined.

Effect of insulin-induced hypoglycemia on circulating levels of plasma growth hormone-releasing hormone and somatostatin in children

In response to insulin-induced hypoglycemia (0.1 U insulin/kg body weight, i.v.) plasma levels of growth hormone-releasing hormone (GHRH), somatostatin (SLI), and growth hormone (GH) were measured by radioimmunoassay in 10 children with short stature. Insulin injection resulted in a significant increase in plasma GHRH values at 15 min (10.0 +/- 0.5 vs. 17.1 +/- 3.1 pg/ml; p less than 0.05) preceding the increase in plasma GH levels (1.5 +/- 0.4 vs. 13.6 +/- 1.2 ng/ml; p less than 0.001). SLI concentrations peaked between 15 and 60 min after insulin injection (20.9 +/- 1.2 vs. 47.1 +/- 6.2 pg/ml; p less than 0.01). No correlation was present between plasma GHRH or SLI levels and plasma GH concentrations. A significant negative correlation could be established between maximum increments of plasma GHRH and SLI levels (r = -0.843; p less than 0.01) in response to insulin injection. This finding suggests a possible relationship between these two hormones at peripheral level.