A practical method for assessment of dose conversion coefficients for aquatic biota

Radiological impact assessment for flora and fauna requires adequate dosimetric data. Due to the variability of habitats, shapes, and masses of the non-human biota, assessment of doses is a challenging task. External and internal dose conversion coefficients for photons and electrons have been systematically calculated by Monte Carlo methods for spherical and ellipsoidal shapes in water medium. An interpolation method has been developed to approximate absorbed fractions for elliptical shape organisms from absorbed fractions for spherical shapes with reasonable accuracy. The method allows an evaluation of dose conversion coefficients for arbitrary ellipsoids for photon and electron sources with energies from 10 keV to 5 MeV, and for organism masses in the range from 10(-6) to 10(3) kg. As an example of the application of the method, a set of dose coefficients for aquatic organisms discussed as reference animals and plants in a draft of an up-coming publication of the International Commission on Radiological Protection has been determined.     

An analytical model for calculating internal dose conversion coefficients for non-human biota

To assess the radiation burden of non-human living organisms, dose coefficients are available in the literature, precalculated by assuming an ellipsoidal shape of each organism. A previously developed analytical method was applied for the determination of absorbed fractions inside ellipsoidal volumes from alpha, beta, and gamma radiations to the calculation of dose conversion coefficients (DCCs) for 15 reference organisms, animals and plants, either terrestrial, amphibian, or aquatic, and six radionuclides (¹⁴C, ⁹⁰Sr, ⁶⁰Co, ¹³⁷Cs, ²³⁸U, and ²⁴¹Am). The results were compared with the reference values reported in Publication 108 of the International Commission on Radiological Protection, in which a different calculation approach for DCCs was employed. The results demonstrate that the present analytical method, originally intended for applications in internal dosimetry of nuclear medicine therapy, gives consistent results for all the beta-, beta–gamma-, and alpha-emitting radionuclides tested in a wide range of organism masses, between 8 mg and 1.3 kg. The applicability of the method proposed can take advantage from its ease of implementation in an ordinary electronic spreadsheet, allowing to calculate, for virtually all possible radionuclide emission spectra, the DCCs for ellipsoidal models of non-human living organisms in the environment.     

External exposure of deciduous tooth enamel to photons: dose conversion coefficients for standard radiation fields

Dose conversion coefficients for teeth of children were computed for external photon sources by means of Monte Carlo methods using a modified MIRD-type mathematical phantom of a 5-year-old child. The tooth region is separated into eight smaller regions that represent incisors, canines, first and second molars. Each of these sub-regions is separated into enamel and dentin parts. Dose conversion coefficients were computed as ratio of absorbed dose in the enamel and air kerma. They are given for unidirectional (AP, PA, RLAT, LLAT), rotational (ROT) and isotropic (ISO) photon sources in the energy range from 10 keV to 10 MeV. All computations were performed with the MCNP4 code including coupled electron-photon transport. The computed coefficients demonstrate a significant non-linearity versus photon energy, which is more pronounced than that observed for adult phantoms. Due to this non-linearity, use of the EPR-measured doses in human teeth requires information on the incident photon fluence spectra. The data presented can be used for assessment of public exposure.     

Dose coefficients of percentile-specific computational phantoms for photon external exposures

The use of dose coefficients (DCs) based on the reference phantoms recommended by the International Commission on Radiological Protection (ICRP) with a fixed body size may produce errors to the estimated organ/tissue doses to be used, for example, for epidemiologic studies depending on the body size of cohort members. A set of percentile-specific computational phantoms that represent 10th, 50th, and 90th percentile standing heights and body masses in adult male and female Caucasian populations were recently developed by modifying the mesh-type ICRP reference computational phantoms (MRCPs). In the present study, these percentile-specific phantoms were used to calculate a comprehensive dataset of body-size-dependent DCs for photon external exposures by performing Monte Carlo dose calculations with the Geant4 code. The dataset includes the DCs of absorbed doses for 29 individual organs/tissues from 0.01 to 104 MeV photon energy, in the antero-posterior, postero-anterior, right lateral, left lateral, rotational, and isotropic geometries. The body-size-dependent DCs were compared with the DCs of the MRCPs in the reference body size, showing that the DCs of the MRCPs are generally similar to those of the 50th percentile standing height and body mass phantoms over the entire photon energy region except for low energies (≤ 0.03 MeV); the differences are mostly less than 10%. In contrast, there are significant differences in the DCs between the MRCPs and the 10th and 90th percentile standing height and body mass phantoms (i.e., H10M10 and H90M90). At energies of less than about 10 MeV, the MRCPs tended to under- and over-estimate the organ/tissue doses of the H10M10 and H90M90 phantoms, respectively. This tendency was revised at higher energies. The DCs of the percentile-specific phantoms were also compared with the previously published values of another phantom sets with similar body sizes, showing significant differences particularly at energies below about 0.1 MeV, which is mainly due to the different locations and depths of organs/tissues between the different phantom libraries. The DCs established in the present study should be useful to improve the dosimetric accuracy in the reconstructions of organ/tissue doses for individuals in risk assessment for epidemiologic investigations taking body sizes into account.     

Dual-age-class population model to assess radiation dose effects on non-human biota populations

In the present paper, a two-age-class group, logistic growth model for generic populations of non-human biota is described in order to assess non-stochastic effects of low linear energy-transfer radiation using three endpoints: repairable radiation damage, impairment of reproductive ability and, at higher radiation dose rates, mortality. This model represents mathematically the exchange between two life stages considering fecundity, growth and mortality. Radiation effects are modeled with a built-in self-recovery pool whereupon individuals can repair themselves. In acute effects mode, the repairing pool becomes depleted due to radiation and the model tends to lethality mode. A base calibration of the model's two free parameters is possible assuming that in acute mode 50% of the individuals die on 30 days when a radiation dose equal to the LD(50/30) is applied during that period. The model, which requires 10 species-dependent life-history parameters, was applied to fish and mammals. Its use in the derivation of dose-rate screening values for the protection of non-human biota from the effects of ionizing radiation is demonstrated through several applications. First, results of model testing with radiation effects data for fish populations from the EPIC project show the predictive capability of the model in a practical case. Secondly, the model was further verified with FREDERICA radiation effects data for mice and voles. Then, consolidated predictions for mouse, rabbit, dog and deer were generated for use in a population model comparison made within the IAEA EMRAS II project. Taken together, model predictions suggest that radiation effects are more harmful for larger organisms that generate lower numbers of offspring. For small mammal and fish populations, dose rates that are below 0.02 Gy day(-1) are not fatal; in contrast, for large mammals, chronic exposure at this level is predicted to be harmful. At low exposure rates similar to the ERICA screening dose rate of 2.4 × 10(-4) Gy day(-1), long-term effects on the survivability of populations are negligible, supporting the appropriateness of this value for radiological assessments to wildlife.     

Eurados review of retrospective dosimetry techniques for internal exposures to ionising radiation and their applications

Radiation and Environmental Biophysics - This work presents an overview of the applications of retrospective dosimetry techniques in case of incorporation of radionuclides. The fact that internal...     

Effective dose conversion coefficients for radionuclides exponentially distributed in the ground

In order to provide fundamental data required for dose evaluation due to environmental exposures, effective dose conversion coefficients, that is, the effective dose rate per unit activity per unit area, were calculated for a number of potentially important radionuclides, assuming an exponential distribution in ground, over a wide range of relaxation depths. The conversion coefficients were calculated for adults and a new-born baby on the basis of dosimetric methods that the authors and related researchers have previously developed, using Monte Carlo simulations and anthropomorphic computational phantoms. The differences in effective dose conversion coefficients due to body size between the adult and baby phantoms were found to lie within 50?%, for most cases; however, for some low energies, differences could amount to a factor of 3. The effective dose per unit source intensity per area was found to decrease by a factor of 2–5, for increasing relaxation depths from 0 to 5?g/cm², above a source energy of 50?keV. It is also shown that implementation of the calculated coefficients into the computation of the tissue weighting factors and the adult reference computational phantoms of ICRP Publication 103 does not significantly influence the effective dose conversion coefficients of the environment. Consequently, the coefficients shown in this paper could be applied for the evaluation of effective doses, as defined according to both recommendations of ICRP Publications 103 and 60.     

Chromosome aberrations in relation to radiation dose following partial-body exposures in three populations

Structural chromosome aberrations were evaluated in peripheral blood samples obtained from three populations exposed to partial-body irradiation. These included 143 persons who received radiotherapy for enlarged thymus glands during infancy and 50 sibling controls; 79 persons irradiated for enlarged tonsils and 81 persons surgically treated for the same condition during childhood; and 77 women frequently exposed as young adults to fluoroscopic chest X rays during lung collapse treatment for tuberculosis (TB) and 66 women of similar ages treated for TB with other therapies. Radiation exposures occurred 30 and more years before blood was drawn. Doses to active bone marrow averaged over the entire body were 21, 6, and 14 cGy for the exposed thymic, tonsil, and TB subjects, respectively. Two hundred metaphases were scored for each subject, and the frequencies of symmetrical (stable) and asymmetrical (unstable) chromosome aberrations were quantified in 97,200 metaphases. Cells with stable aberrations were detected with greater frequency in the irradiated subjects compared with nonirradiated subjects in all three populations, and an overall test for an association between stable aberrations and partial-body ionizing radiation was highly significant (P less than 0.001). We found no evidence that radiation-induced aberrations varied by age at exposure. These data show that exposure of children or young adults to partial-body fractionated radiation can result in detectable increased frequencies of stable chromosome aberrations in circulating lymphocytes 30 years later, and that these aberrations appear to be informative as biological markers of population exposure.     

The conversion of exposures due to radon into the effective dose: the epidemiological approach

The risks and dose conversion coefficients for residential and occupational exposures due to radon were determined with applying the epidemiological risk models to ICRP representative populations. The dose conversion coefficient for residential radon was estimated with a value of 1.6 mSv year^?1 per 100 Bq m^?3 (3.6 mSv per WLM), which is significantly lower than the corresponding value derived from the biokinetic and dosimetric models. The dose conversion coefficient for occupational exposures with applying the risk models for miners was estimated with a value of 14 mSv per WLM, which is in good accordance with the results of the dosimetric models. To resolve the discrepancy regarding residential radon, the ICRP approaches for the determination of risks and doses were reviewed. It could be shown that ICRP overestimates the risk for lung cancer caused by residential radon. This can be attributed to a wrong population weighting of the radon-induced risks in its epidemiological approach. With the approach in this work, the average risks for lung cancer were determined, taking into account the age-specific risk contributions of all individuals in the population. As a result, a lower risk coefficient for residential radon was obtained. The results from the ICRP biokinetic and dosimetric models for both, the occupationally exposed working age population and the whole population exposed to residential radon, can be brought in better accordance with the corresponding results of the epidemiological approach, if the respective relative radiation detriments and a radiation-weighting factor for alpha particles of about ten are used.     

土壤生物对地上生物的反馈作用及其机制

长期以来对陆地生态系统的研究主要集中于地上部分。由于测度上的困难, 人们对地下部分(belowground)的认识还处于相当模糊的状态。当今的生态学家已经越来越强烈地认识到, 地上生态系统与地下生态系统存在着不可分割的相互联系。100多年来的研究表明, 作为地下生态系统最活跃部分的土壤生物, 是联结地上部分与地下部分物质循环和能量流动的纽带, 对地上部分的结构、功能及过程起着重要的反馈调控作用。土壤生物受资源的时空异质性、营养的可获得性以及非生物因素的选择性所驱动, 通过直接作用于根系, 或通过改变养分的矿化速率及其在土壤中的空间分布, 改变植物根际的激素状况以及土壤环境等间接作用方式, 对地上生物产生正、负反馈作用。因此, 从土壤生物和地上生物的相互作用过程、土壤生物功能群及土壤食物网等角度分析土壤生物反馈作用的时空尺度、生物组织形式、方式、模型、驱动因素及其机制, 能为理解地下生态学过程、维持生态系统稳定性以及制定生物多样性保护策略提供参考, 并有助于理解全球变化下陆地生态系统结构及功能的动态和响应过程。     

Inter-comparison of absorbed dose rates for non-human biota

A number of approaches have been proposed to estimate the exposure of non-human biota to ionizing radiation. This paper reports an inter-comparison of the unweighted absorbed dose rates for the whole organism (compared as dose conversion coefficients, or DCCs) for both internal and external exposure, estimated by 11 of these approaches for selected organisms from the Reference Animals and Plants geometries as proposed by the International Commission on Radiological Protection. Inter-comparison results indicate that DCCs for internal exposure compare well between the different approaches, whereas variation is greater for external exposure DCCs. Where variation among internal DCCs is greatest, it is generally due to different daughter products being included in the DCC of the parent. In the case of external exposures, particularly to low-energy beta-emitters, variations are most likely to be due to different media densities being assumed. On a radionuclide-by-radionuclide basis, the different approaches tend to compare least favourably for (3)H, (14)C and the alpha-emitters. This is consistent with models with different source/target geometry assumptions showing maximum variability in output for the types of radiation having the lowest range across matter. The intercomparison demonstrated that all participating approaches to biota dose calculation are reasonably comparable, despite a range of different assumptions being made.     

The role of marine biota in the evolution of terrestrial biota: Gases and genes

There is greater biodiversity (in the senseof genetic distance among higher taxa) ofextant marine than of terrestrialO₂-evolvers. In addition tocontributing the genes from one group ofalgae (Class Charophyceae, DivisionChlorophyta) to produce by evolution thedominant terrestrial plants (Embryophyta),the early marine O₂-evolvers greatlymodified the atmosphere and hence the landsurface when the early terrestrialO₂-evolvers grew. The earliestterrestrial phototrophs (from geochemicalevidence) occurred 1.2 Ga ago, over 0.7 Gabefore the Embryophyta evolved, but wellafter the earliest marine (cyanobacterial)O₂ evolvers (3.45 Ga) and marineeukaryotic O₂ evolvers (2.1 Ga). Evenby the time of evolution of the earliestterrestrial O₂-evolvers the marineO₂-evolvers had modified the atmosphereand land environment in at least thefollowing five ways. Once photosyntheticO₂ paralleling organic C burial hadsatisfied marine (Fe²⁺, S^2-reductants, atmospheric O₂ built (1) upto a considerable fraction of the extantvalue (although some was consumed inoxidising terrestrial exposed Fe²⁺ and(2) provided stratospheric O₃ and thusa UV-screen. (3) CO₂ drawdown to20-30times the extant level is attributableto net production, and burial, of organic Cin the oceans (plus other geologicalprocesses). Furthermore, (4) theirproduction of volatile organic S compoundscould have helped to supply S to inland sitesbut also (5) delivered Cl and Br to thestratosphere thus lowering the O₃ leveland the extent of UV screening.     

Whole-body to tissue concentration ratios for use in biota dose assessments for animals

Environmental monitoring programs often measure contaminant concentrations in animal tissues consumed by humans (e.g., muscle). By comparison, demonstration of the protection of biota from the potential effects of radionuclides involves a comparison of whole-body doses to radiological dose benchmarks. Consequently, methods for deriving whole-body concentration ratios based on tissue-specific data are required to make best use of the available information. This paper provides a series of look-up tables with whole-body:tissue-specific concentration ratios for non-human biota. Focus was placed on relatively broad animal categories (including molluscs, crustaceans, freshwater fishes, marine fishes, amphibians, reptiles, birds and mammals) and commonly measured tissues (specifically, bone, muscle, liver and kidney). Depending upon organism, whole-body to tissue concentration ratios were derived for between 12 and 47 elements. The whole-body to tissue concentration ratios can be used to estimate whole-body concentrations from tissue-specific measurements. However, we recommend that any given whole-body to tissue concentration ratio should not be used if the value falls between 0.75 and 1.5. Instead, a value of one should be assumed.     

Cultivation-based and molecular approaches to characterisation of terrestrial and aquatic nitrifiers

Increased awareness of the metabolic diversity within autotrophic nitrifying bacteria has led to a re-evaluation of their role in the cycling of nitrogen in terrestrial and aquatic ecosystems. This has been accompanied by improvements in our ability to characterise natural populations of autotrophic ammonia oxidising bacteria through the application of molecular techniques. Molecular approaches indicate considerable diversity within natural populations and the association of different groups of ammonia oxidisers with different environments and changes in populations in response to environmental factors. To some extent, results from molecular approaches are consistent with those adopting laboratory enrichment and isolation strategies. Physiological studies on the latter demonstrate links between phylogenetic groups and possession of characteristics of relevance to ecological studies. Understanding of the significance of ammonia oxidiser species and functional diversity for global cycling of nitrogen require greater links between molecular analyses, physiological studies and measurements of nitrogen cycling processes. However, there is increasing evidence for physiological properties driving the environmental distribution of particular groups of ammonia oxidisers and for associations between nitrification process rates and ammonia oxidiser community structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

Triadic IBD coefficients and applications to estimating pairwise relatedness

Knowledge of the genetic relatedness among individuals is essential in diverse research areas such as behavioural ecology, conservation biology, quantitative genetics and forensics. How to estimate relatedness accurately from genetic marker information has been explored recently by many methodological studies. In this investigation I propose a new likelihood method that uses the genotypes of a triad of individuals in estimating pairwise relatedness (r). The idea is to use a third individual as a control (reference) in estimating the r between two other individuals, thus reducing the chance of genes identical in state being mistakenly inferred as identical by descent. The new method allows for inbreeding and accounts for genotype errors in data. Analyses of both simulated and human microsatellite and SNP datasets show that the quality of r estimates (measured by the root mean squared error, RMSE) is generally improved substantially by the new triadic likelihood method (TL) over the dyadic likelihood method and five moment estimators. Simulations also show that genotyping errors/mutations, when ignored, result in underestimates of r for related dyads, and that incorporating a model of typing errors in the TL method improves r estimates for highly related dyads but impairs those for loosely related or unrelated dyads. The effects of inbreeding were also investigated through simulations. It is concluded that, because most dyads in a natural population are unrelated or only loosely related, the overall performance of the new triadic likelihood method is the best, offering r estimates with a RMSE that is substantially smaller than the five commonly used moment estimators and the dyadic likelihood method.