The role of nuclear fragmentations in high energy transfers to a micro-object exposed to primary space radiation

This paper describes events of anomalously high energy transfer to a micro-object by fragments of nuclei generated in nuclear interactions in the environment on board a spacecraft in flight in low-Earth orbit. An algorithm has been developed that allows for the calculation of the absorbed energy from one or more fragments - products of nuclear interaction. With this algorithm the energy distributions for a spherical micro-volume in an aqueous medium were calculated. And the resulting absorbed energy spectra from nuclear fragments and from primary cosmic rays were compared. The role of nuclear interactions in events of large energy transfers in micro-objects in the field of primary cosmic radiation has been evaluated. The calculations performed in this study showed that the energy in a micro-volume from nuclear events can be several times higher compared to the energy imparted by primary space radiation.

Distributions of energy imparted to a micro-volume by secondary charged fragments of nuclear interactions in space radiation field

The field of cosmic radiation at low-Earth orbit (LEO) has a complex composition. It always contains a component of secondary charged particles, formed by the products of nuclear interactions of the primary high-energy radiation with the nuclei of spacecraft's shielding material, electronic components and biological matter on board. Generation of this secondary radiation can be observed in some track detectors in the form of "stars" formed by tracks-fragments with a common vertex. The energy absorbed by the medium in the region adjacent to the interaction vertex can reach abnormally high values because of its intersection by several particle fragments. In the present paper, a methodology is considered to calculate the energy imparted by such fragments to a spherical sensitive volume in an aqueous medium. The energy distributions for three fragment events were calculated for different positions of the vertex relative to the spherical volume. The obtained data were analyzed and were compared with the distribution for a uniform fluence of secondary particles. It was shown that as the fragmentation vertex approaches the boundary of the sensitive micro-volume, the probability of events with anomalously high energy transfers, higher than the energies from single fragments, increases. The method can be applied to calculate absorbed energy distributions from secondary radiation in media of different elemental composition than that used in the present work. In the future, it is of interest to apply the method for example to study the energy imparted from secondary fragments to a silicon medium, to quantify the number of single event upsets in electronic components.

Commercial Air And High-Altitude Travel by Pregnant Women: A scientific review commissioned by the European Board and College of Obstetrics and Gynaecology (EBCOG)

Air travel and long distance travel may have adverse effect on the pregnancy-induced physiology and these effects are more marked among those with pre-existing medical conditions. There are significantly increased risks of deep venous thrombosis, inflight transmission of infections, preterm labour, and other significant obstetric and medical complications that may be exacerbated by the flight and may require emergency care. Transient changes in cardiotocographic tracings during third trimester of pregnancy have been reported following air travel. It has been suggested that pregnant members of the flight crew may be at a slightly higher risk of spontaneous miscarriages. There are no contra-indications for healthy pregnant women on air travel. Those with underlying medical conditions should only embark on long distance travel following consultation with their obstetrician. Pregnant women should be advised to familiarise themselves with the healthcare system in the country/region they will be visiting and draw up an emergency plan of how they will contact the healthcare system at their destination.

External background ionizing radiation and childhood cancer: Update of a nationwide cohort analysis

BACKGROUND

Exposure to high doses of ionizing radiation is known to cause cancer. Exposure during childhood is associated with a greater excess relative risk for leukemia and tumors of the central nervous system (CNS) than exposure in later life. Cancer risks associated with low-dose exposure (<100 mSv) are uncertain. We previously investigated the association between the incidence of childhood cancer and levels of exposure to external background radiation from terrestrial gamma and cosmic rays in Switzerland using data from a nationwide census-based cohort study. Here, we provide an update of that study using an extended follow-up period and an improved exposure model.

METHODS

We included all children 0-15 years of age registered in the Swiss national censuses 1990, 2000, and 2010-2015. We identified incident cancer cases during 1990-2016 using probabilistic record linkage with the Swiss Childhood Cancer Registry. Exposure to terrestrial and cosmic radiation at children's place of residence was estimated using geographic exposure models based on aerial spectrometric gamma-ray measurements. We estimated and included the contribution from ¹³⁷Cs deposition after the Chernobyl accident. We created a nested case-control sample and fitted conditional logistic regression models adjusting for sex, year of birth, neighborhood socioeconomic position, and modelled outdoor NO₂ concentration. We also estimated the population attributable fraction for childhood cancer due to external background radiation.

RESULTS

We included 3,401,113 children and identified 3,137 incident cases of cancer, including 951 leukemia, 495 lymphoma, and 701 CNS tumor cases. Median follow-up in the cohort was 6.0 years (interquartile range: 4.3-10.1) and median cumulative exposure since birth was 8.2 mSv (range: 0-31.2). Hazard ratios per 1 mSv increase in cumulative dose of external background radiation were 1.04 (95% CI: 1.01-1.06) for all cancers combined, 1.06 (1.01-1.10) for leukemia, 1.03 (0.98-1.08) for lymphoma, and 1.06 (1.01-1.11) for CNS tumors. Adjustment for potential confounders had little effect on the results. Based on these results, the estimated population attributable fraction for leukemia and CNS tumors due to external background radiation was 32% (7-49%) and 34% (5-51%), respectively.

CONCLUSIONS

Our results suggest that background ionizing radiation contributes to the risk of leukemia and CNS tumors in children.

Short-term metabolic disruptions in urine of mouse models following exposure to low doses of oxygen ion radiation

Molecular alterations as a result of exposure to low doses of high linear energy transfer (LET) radiation can have deleterious short- and long-term consequences on crew members embarking on long distance space missions. Oxygen ions (¹⁶O) are among the high LET charged particles that make up the radiation environment inside a vehicle in deep space. We used mass spectrometry-based metabolomics to characterize urinary metabolic profiles of male C57BL/6J mice exposed to a single dose of 0.1, 0.25 and 1.0 Gy of ¹⁶O (600 MeV/n) at 10 and 30 days post-exposure to delineate radiation-induced metabolic alterations. We recognized a significant down regulation of several classes of metabolites including cresols and tryptophan metabolites, ketoacids and their derivatives upon exposure to 0.1 and 0.25 Gy after 10 days. While some of these changes reverted to near normal by 30 days, some metabolites including p-Cresol sulfate, oxalosuccinic acid, and indoxylsulfate remained dysregulated at 30 days, suggesting long term prognosis on metabolism. Pathway analysis revealed a long-term dysregulation in multiple pathways including tryptophan and porphyrin metabolism. These results suggest that low doses of high-LET charged particle irradiation may have long-term implications on metabolic imbalance.

Mitigation of helium irradiation-induced brain injury by microglia depletion

Background

Cosmic radiation exposures have been found to elicit cognitive impairments involving a wide-range of underlying neuropathology including elevated oxidative stress, neural stem cell loss, and compromised neuronal architecture. Cognitive impairments have also been associated with sustained microglia activation following low dose exposure to helium ions. Space-relevant charged particles elicit neuroinflammation that persists long-term post-irradiation. Here, we investigated the potential neurocognitive benefits of microglia depletion following low dose whole body exposure to helium ions.

Methods

Adult mice were administered a dietary inhibitor (PLX5622) of colony stimulating factor-1 receptor (CSF1R) to deplete microglia 2 weeks after whole body helium irradiation (⁴He, 30 cGy, 400 MeV/n). Cohorts of mice maintained on a normal and PLX5622 diet were tested for cognitive function using seven independent behavioral tasks, microglial activation, hippocampal neuronal morphology, spine density, and electrophysiology properties 4–6 weeks later.

Results

PLX5622 treatment caused a rapid and near complete elimination of microglia in the brain within 3 days of treatment. Irradiated animals on normal diet exhibited a range of behavioral deficits involving the medial pre-frontal cortex and hippocampus and increased microglial activation. Animals on PLX5622 diet exhibited no radiation-induced cognitive deficits, and expression of resting and activated microglia were almost completely abolished, without any effects on the oligodendrocyte progenitors, throughout the brain. While PLX5622 treatment was found to attenuate radiation-induced increases in post-synaptic density protein 95 (PSD-95) puncta and to preserve mushroom type spine densities, other morphologic features of neurons and electrophysiologic measures of intrinsic excitability were relatively unaffected.

Conclusions

Our data suggest that microglia play a critical role in cosmic radiation-induced cognitive deficits in mice and, that approaches targeting microglial function are poised to provide considerable benefit to the brain exposed to charged particles.

Reproducible changes in the gut microbiome suggest a shift in microbial and host metabolism during spaceflight

BACKGROUND

Space environment imposes a range of challenges to mammalian physiology and the gut microbiota, and interactions between the two are thought to be important in mammalian health in space. While previous findings have demonstrated a change in the gut microbial community structure during spaceflight, specific environmental factors that alter the gut microbiome and the functional relevance of the microbiome changes during spaceflight remain elusive.

METHODS

We profiled the microbiome using 16S rRNA gene amplicon sequencing in fecal samples collected from mice after a 37-day spaceflight onboard the International Space Station. We developed an analytical tool, named STARMAPs (Similarity Test for Accordant and Reproducible Microbiome Abundance Patterns), to compare microbiome changes reported here to other relevant datasets. We also integrated the gut microbiome data with the publically available transcriptomic data in the liver of the same animals for a systems-level analysis.

RESULTS

We report an elevated microbiome alpha diversity and an altered microbial community structure that were associated with spaceflight environment. Using STARMAPs, we found the observed microbiome changes shared similarity with data reported in mice flown in a previous space shuttle mission, suggesting reproducibility of the effects of spaceflight on the gut microbiome. However, such changes were not comparable with those induced by space-type radiation in Earth-based studies. We found spaceflight led to significantly altered taxon abundance in one order, one family, five genera, and six species of microbes. This was accompanied by a change in the inferred microbial gene abundance that suggests an altered capacity in energy metabolism. Finally, we identified host genes whose expression in the liver were concordantly altered with the inferred gut microbial gene content, particularly highlighting a relationship between host genes involved in protein metabolism and microbial genes involved in putrescine degradation.

CONCLUSIONS

These observations shed light on the specific environmental factors that contributed to a robust effect on the gut microbiome during spaceflight with important implications for mammalian metabolism. Our findings represent a key step toward a better understanding the role of the gut microbiome in mammalian health during spaceflight and provide a basis for future efforts to develop microbiota-based countermeasures that mitigate risks to crew health during long-term human space expeditions.

Comments on "Incidence of cancer among licensed commercial pilots flying North Atlantic routes"

Gudmundsdottir et al. in their paper entitled "Incidence of cancer among licensed commercial pilots flying North Atlantic routes" published in Environmental Health have evaluated the effects of exposure to higher levels of cosmic radiation on cancer incidence in the pilots of commercial flights. Despite its remarkable strengths, the paper authored by Gudmundsdottir et al. has some shortcomings. The shortcomings of this paper such as not determining the shape of dose-response relationship for radiation-induced cancers, limitations in flight dose calculations, the weaknesses of CARI-6 as the program used by Gudmundsdottir et al. to estimate the effective dose of galactic cosmic rays, and the problems associated with unpredictable nature of the magnitude and duration of solar particle events are discussed.

Incidence of cancer among licenced commercial pilots flying North Atlantic routes

BACKGROUND

To evaluate cancer incidence among licenced commercial pilots in association with cosmic radiation.

METHODS

Cohort study where ionizing radiation dose of cosmic radiation was estimated from airline data and software program and cancer incidence was obtained by record linkage with nation-wide cancer registry. All licenced commercial male airline pilots were followed from 1955 to 2015, ever or never employed at airline with international routes. Standardized incidence ratios were calculated and relative risk by Poisson regression, to examine exposure-response relation.

RESULTS

Eighty three cancers were registered compared with 92 expected; standardized incidence ratios were 0.90 (95% CI 0.71 to 1.11) for all cancers, 3.31 (95% CI 1.33 to 6.81) for malignant melanoma, and 2.49 (95% CI 1.69 to 3.54), for basal cell carcinoma of skin. The risk for all cancers, malignant melanoma, prostate cancer, basal cell carcinoma of skin, and basal cell carcinoma of trunk increased with an increase in number of employment years, cumulative air hours, total cumulative radiation dose, and cumulative radiation dose sustained up to age of 40 years. The relative risk for the highest exposure categories of cumulative radiation dose were 2.42 (95% CI 1.50 to 3.92) for all cancers, 2.57 (95% CI 1.18 to 5.56) for prostate cancer, 9.88 (95% CI 1.57 to 190.78) for malignant melanoma, 3.61 (95% CI 1.64 to 8.48) for all basal cell carcinoma, and 6.65 (95% CI 1.61 to 44.64) for basal cell carcinoma of trunk.

CONCLUSIONS

This study was underpowered to study brain cancer and leukaemia risk. Basal cell carcinoma of skin is radiation-related cancer, and may be attributed to cosmic radiation. Further studies are needed to clarify the risk of cancers in association with cosmic radiation, other workplace exposure, host factors, and leisure sun-exposure, as clothes, and glass in cockpit windows shield pilots from the most potent ultraviolet-radiation.

Assessment of radiological hazard parameters due to natural radioactivity in soils from granite-rich regions in Kütahya Province, Turkey

The analysis of natural radioactivity from ²³⁸U, ²³²Th and ⁴⁰K in 357 soil samples collected from the province of Kütahya was carried out using a NaI(Tl) gamma-ray spectroscopy system at the Nuclear Physics Research Laboratory, Dumlupınar University, Kütahya, Turkey. The specific activities of ²³⁸U, ²³²Th and ⁴⁰K in the soil samples were evaluated. From the activity concentrations of ²³⁸U, ²³²Th and ⁴⁰K, the total absorbed outdoor gamma-ray dose rates and the corresponding annual effective dose rates were determined. The corresponding values of the external and internal hazard indices of all the soil samples were also calculated. The external gamma-ray dose rate at 1 m above the ground was directly measured at each collected soil sample location. The results obtained in this study were compared within the limits of values obtained in other cities of Turkey, those in other countries. Radiological maps of Kütahya Province were constructed from the results of this study.

Understanding existing exposure situations

International Commission on Radiological Protection (ICRP) Publication 103 removed the distinction between practices and interventions, and introduced three types of exposure situation: existing, planned, and emergency. It also emphasised the optimisation principle in connection with individual dose restrictions for all controllable exposure situations. Existing exposure situations are those resulting from sources, natural or man-made, that already exist when a decision on control has to be taken. They have common features to be taken into account when implementing general recommendations, such as: the source may be difficult to control; all exposures cannot be anticipated; protective actions can only be implemented after characterisation of the exposure situation; time may be needed to reduce exposure below the reference level; levels of exposure are highly dependent on individual behaviour and present a wide spread of individual dose distribution; exposures at work may be adventitious and not considered as occupational exposure; there is generally no potential for accident; many stakeholders have to be involved; and many factors need to be considered. ICRP is currently developing a series of reports related to the practical implementation of Publication 103 to various existing exposure situations, including exposure from radon, exposure from cosmic radiation in aviation, exposure from processes using naturally occurring radioactive material, and exposure from contaminated sites due to past activities.