Micronuclei in human peripheral blood lymphocytes exposed to mixed beams of X-rays and alpha particles

The purpose of this study was to analyse the cytogenetic effect of exposing human peripheral blood lymphocytes (PBL) to a mixed beam of alpha particles and X-rays. Whole blood collected from one donor was exposed to different doses of alpha particles ((241)Am), X-rays and a combination of both. All exposures were carried out at 37 °C. Three independent experiments were performed. Micronuclei (MN) in binucleated PBL were scored as the endpoint. Moreover, the size of MN was measured. The results show that exposure of PBL to a mixed beam of high and low linear energy transfer radiation led to significantly higher than expected frequencies of MN. The measurement of MN size did not reveal any differences between the effect of alpha particles and mixed beam. In conclusion, a combined exposure of PBL to alpha particles and X-rays leads to a synergistic effect as measured by the frequency of MN. From the analysis of MN distributions, we conclude that the increase was due to an impaired repair of X-ray-induced DNA damage.     

Gamma densitometry for the measurement of skeletal density

A method is described for the measurement of the density of calcium carbonate materials from the attenuation of a narrow, collimated beam of gamma photons. For the measurement of density for slices, approximately 0.5 to 1.0 cm thick, from the skeletons of reef building corals, the optimum beam energy is 30–34 keV; and measurement is practical from approximately 22 to 100 keV. The potential utilities of five commercially available isotopic sources (¹⁰⁹Cd,¹²⁵I,²⁵³Gd,²¹⁰Pb and²⁴¹Am) are evaluated. Methods and results are presented for gamma densitometry using²¹⁰Pb and²⁴¹Am. The²¹⁰Pb point source had its principal gamma emission at 46.5 keV. Bremsstrahlung and high energy (800 keV) gamma emissions associated with the²¹⁰Pb decay grand-daughter were detected, and procedures were developed to accommodate the contribution of these emissions to the overall count rate. The attenuation of count rate by aluminium and aragonite absorbers closely followed simple theoretical considerations provided that narrow energy window settings were used at the radiation monitor. These theoretical considerations take account of the density of the material absorbing the radiation, and hence the density could be determined from the attenuation of the gamma beam. Increased accuracy was achieved by the use of²⁴¹Am and high speed counting equipment.²⁴¹Am has its principal gamma emission at 59.6 keV. The attenuation of this gamma beam follows simple theoretical considerations for targets with mass thicknesses from 0 to 6 g cm^-2. Aragonite from the shell of a giant clam was found to have slightly different properties in the absorption of gamma photons to aragonite from a coral skeleton. The differences were small but statistically significant.     

Estimation of rate constant for dissolution of radioactive fuel particles

Some theoretical of the experimental investigation of solubility of radioactive aerosols were examined. Filters, which were exposed during October-November 1987 in Pripyat town, were studied. Measurements on 22 November 1987 showed that an activity in the air was 12.1-20.8 mBq/m3 for 137Cs, 34.9-89.3 mBq/m-3 for 144Ce, 24.3-30.5 mBq/m-3 for 106Ru. Disperse structure of aerosol hot particles and the number of hot particles on each filter fragment was estimated by radiography. To determine a dissolution rate constant a static system with two 0.14 micron pore size membrane MFE filters (Dubna, Russia) enclosing fragments of Petryanov filters was selected. The composition was held in Gamble's solution lung fluid anf then in 0.1 mol/l HCl as dastic juice simulation. The activity of 90Sr, 238Pu, 239 + 240Pu, 241Am and 244Cm in aerosol filters and solutions was measured by radiochemical methods. It was shown that leaching of radionuclides from aerosol hot particles in lung fluid simulation decreases in line 137Cs > 90Sr > 239 + 240Pu > or = 241Am, depending om particle diameter and time. Dissolution constants were presented. Dissolution of aerosol particles in 0.1 mol/l HCl is also shown (dissolution time was 3 days). A radionuclide transition to HCl solution decreases in line 90Am 241Am > 137Cs > 239 + 240Pu. A transition degree reached 21% for 90Sr and extraction of 241Am was 3-17%.     

Investigation of the radiation risk due to environmental contamination by <Superscript>241</Superscript>Am from lightning rods disposed at uncontrolled garbage dumps

Radioactive lightning rods were manufactured in Brazil until 1989, when the licenses for using radioactive sources in these products were lifted by the national nuclear authority. Since then, these rods have been replaced by the Franklin type and collected as radioactive waste. However, only 20% of the estimated total number of installed rods has been delivered to the Brazilian Nuclear Commission. This situation causes concern, since there is the possibility of the rods to be disposed as domestic waste. In Brazil, 64% of the municipal solid waste is disposed at garbage dumps without sufficient control. In addition, ²⁴¹Am, the radionuclide most commonly employed, is classified as a high-toxicity element, when incorporated. In the present study, ²⁴¹Am migration experiments were performed by means of a lysimeter system, in order to evaluate the risk of contamination caused by radioactive lightning rods disposed as common solid waste. ²⁴¹Am sources removed from lightning rods were placed inside lysimeters filled with organic waste that was collected at the restaurant of the Instituto de Pesquisas Energéticas e Nucleares. The generated leachate was periodically analyzed, and characteristics such as pH, redox potential, solid content and the concentration of the radioactive material were determined. The equivalent dose for members of the public was calculated considering ingestion of contaminated drinking water as the major path of exposure. Estimated doses were about 20-times below the effective dose limit of 1 mSv year⁻¹ for members of the public as recommended by the International Commission on Radiological Protection. This suggests the radiation risk caused by lightning rods disposed at uncontrolled garbage dumps to be low. It should be noted, however, that the number of investigated lightning rods was quite small. The results of this study might therefore not be entirely representative and should be interpreted with care. They provide, however, a very first basis for characterizing the transfer of ²⁴¹Am from lightning rods to the human food chain.     

Relative biological effectiveness of 241Am relative to 192Ir for continuous low-dose-rate irradiation of BA1112 rat sarcomas

Sealed sources of 241Am have been developed for intracavitary irradiation of gynecological cancers. Relative to conventional isotopes (that is, 226Ra, 137Cs, 192Ir), 241Am allows for better shielding of dose-limiting normal tissues in the patient. In addition, the long half-life of 241Am (432 years) makes it an attractive isotope both for clinical use and for long-term radiobiology studies. Using a previously developed in vivo applicator system, BA1112 sarcomas on WAG/Rij Y rats were irradiated using 241Am or 192Ir at three different dose rates. Following in vivo treatment of the sarcomas with graded doses of radiation, cell survival curves were determined using an in vitro colony formation assay. The slopes of the resulting cell survival curves were observed to increase significantly as the dose rate increased from 0.30 to 0.60 Gy/h, then to decrease slightly as the dose rate increased from 0.60 to 0.95 Gy/h. The relative biological effectiveness (RBE) of 241Am relative to 192Ir was observed to increase linearly with increasing dose rate; the RBEs were 0.96 +/- 0.009, 1.09 +/- 0.12, and 1.17 +/- 0.11 at dose rates of 0.30, 0.60, and 0.95 Gy/h, respectively.     

Effect of gavaged chemical form of 241Am on its retention in mice

The retention of 241Am in mice 48 h after administration by gavage is reported here. The 241Am was given to mice in the form of either 241Am nitrate or 241Am citrate. The 241Am was also injected into rats in the same form. The homogenized livers of those rats were subsequently administered by gavage to another group of mice. The retention of 241Am citrate was 1.5 X 10(-2)% of the original dose and was the highest among the compounds examined. The retention of biologically incorporated 241Am into the liver as 241Am nitrate and as 241Am citrate was 2.4 X 10(-3) and 2.6 X 10(-3)%, respectively, and was similar to the retention of 241Am nitrate, which was 2.8 X 10(-3)%. The ratio of the retention in the carcass to that in the liver for the 241Am citrate was lower than that of the 241Am nitrate and the biologically incorporated 241Am. This difference indicates that the distribution of 241Am in the animal body depends on the chemical form administered. The retention of liver-incorporated 241Am as citrate after autolysis of the liver is similar to that of fresh liver-incorporated 241Am citrate.     

The accumulation of 241Am by suspended matter of the Yenisei River

Laboratory experiments were performed to determine parameters of accumulation of 241Am by suspended particulate matter (seston) of the Yenisei River, with particles larger than 1 microm, and the diatoms A. formosa and D. vulgare. Concentration factors for seston were (2.8-4.1) x 10(5) and for diatoms--(1.5-4.2) x 10(4). As phytoplankton's contribution to the seston mass is rather small (< 10%), we assume that suspended matter contains other particles similar in size to the Yenisei River phytoplankton, which make larger contribution to 241Am concentration of seston than the studied algae. No energy-dependent accumulation of americium by algae was detected in the experiments. Addition of dissolved organics and hydrogen carbonates led to a lower uptake of 241Am from the Yenisei water by seston.     

Retention and dosimetry of injected 241Am in beagles

Equations have been derived, from the results of total-body and partial-body counting and gamma-ray counting of individual bones and soft tissues, which describe the retention of injected 241Am in the liver, in the nonliver tissue (including skeleton), and in the skeleton of young adult beagles. Retention was found to be dependent upon injection level, and different sets of equations were developed for dogs given about (a) 2.8 microCi/kg (b) 0.9 microCi/kg (c) 0.3 microCi/kg, and (d) 0.1 microCi/kg and less. Liver rention, RL, was characterized by a single exponential equation of the form RL = ce-beta t, with c = 0.49 +/- 0.04 and beta = a function of injection level. Nonliver tissue was assigned a retention equation of the form RNL = d + alpha + J(l - e-mt), with d = 0.102 +/- 0.024 e-1.22t, alpha = 0.41 +/- 0.04, and both J and m as a function of injection level. Skeletal retention was found to be about 0.885 +/- 0.037 of nonliver retention with no significant dependence upon either injection level or time after 241Am injection. Dosimetry equations based on these retention expressions were derived. Individual bones of 55 beagles were assayed at death for their 241Am content for a determination of 241Am distribution within the skeleton.     

Experimental investigations of 211Am accumulation by macrophytes of the Yenisei River

Experiments were carried out in which 241Am was added to water samples containing macrophytes of the Yenisei River, and the radionuclide absorption rates and concentration factors were determined for the plants. It has been shown that the water moss (Fontinalis antipyretica) has a higher capacity to accumulate 241Am than the Canadian pondweed (Elodea canadensis) does. The laboratory experiments revealed that the capacity of dead biomass of the Canadian pondweed to accumulate 241Am is twice higher than that of living biomass. In contrast, no significant increase in 241Am accumulation by dead biomass of the water moss has been recorded. The transuranic element 241Am was firmly fixed by the plant biomass and was not released into water in the course of long-duration experiments.     

Effect of low-level alpha-radiation on bioluminescent assay systems of various complexity.

This study addresses the effects of low-level alpha-radiation on bioluminescent assay systems of different levels of organization: in vivo and in vitro. Three bioluminescent assay systems are used: intact bacteria, lyophilized bacteria, and bioluminescent system of coupled enzyme reactions. Solutions of 241Am(NO3)3 are used as a source of alpha-radiation. It has been shown that activation processes predominate in all the three bioluminescent assay systems subjected to short-term exposure (20-55 h) and inhibition processes in the systems subjected to longer-term exposure to radiation. It has been found that these effects are caused by the radiation component of 241Am3+ impact. The intensity of the 241Am3+ effect on the bioluminescent assay systems has been shown to depend on the 241Am3+ concentration, level of organization and integrity of the bioluminescent assay system. The bioluminescent assay systems in vivo have been found to be highly sensitive to 241Am3+ (up to 10(-17) M).     

Easy projection of stereo movies

A method is described of showing colour stereo movies with arbitrary movie projectors by means of a small portable adapter. The beam from an ordinary movie projector is passed through a linear polarizer and then a crystal, which rotates the angle of polarization under voltage control so that alternating left and right images are polarized 90° apart. A photodiode and a sensing circuit synchronize the polarization shift to the flicker of the projector shutter. The adapter is small and self contained and needs only to be placed in the path of the projected beam.     

Metal corrosion by aerobic bacteria isolated from stimulated corrosion systems: Effects of additional nitrate sources

Many microorganisms are reported to influence the corrosive behaviour of mild steel and stainless steel in different habitats. In this study, 40 bacterial strains were isolated from corroded mild steel and stainless steel coupons in the nitrate supplemented environments. The corrosion abilities of the isolates against the mild steel and stainless steel coupons were tested with or without additional nitrate sources. The presence of bacterial isolates alone stimulated the corrosion of mild steel coupons. Most of the bio-corrosion processes of mild steel coupons were mitigated by adding nitrate supplement with bacterial isolates. The effects of bacterial isolates and additional nitrogen sources on corrosion of stainless steels were varied. Not all bacterial isolates stimulated the corrosion on stainless steel during the study period. Unlike the effects on mild steel coupons, additional NaNO₃ might stimulate, retard the corrosion rate by the bacterial isolates or have limited effects. Similar results were obtained when NH₄NO₃ was used. Phylogenetic analysis demonstrated that all isolates were closely related. The majority of the bacterial isolates from corroded metal coupons were identified as Bacillus species. Others were identified as Pseudomonas sp., Marinobacter sp., and Halomonas species. The results prove that the isolated aerobic microorganisms do play a role in the corrosion process of stainless and mild steel. Adding additional nitrate sources might be a tool to mitigate corrosion of mild steel which was stimulated by the presence of bacteria. However, to prevent the corrosion of stainless steels, it might need a trial and errors approach in each case.     

Mutagenicity of fume particles from metal arc welding on stainless steel in the Salmonella/microsome test.

Mutagenic activity of fume particles produced by metal arc welding on stainless steel (ss) is demonstrated by using the Salmonella/microsome mutagenicity test described by Ames et al., with strain TA100 (base-pair substitution) and TA98 (frame-shift reversion). Results of a representative but limited selection of processes and materials show that mutagenic activity is a function of process and process parameters. Welding on stainless steel produces particles that are mutagenic, whereas welding on mild steel (ms) produces particles that are not. Manual metal arc (MMA) welding on stainless steel produces particles of higher mutagenic activity than does metal inert gas (MIG) welding, and fume particles produced by MIG welding under short-arc transfer. Further studies of welding fumes (both particles and gases) must be performed to determine process parameters of significance for the mutagenic activity.     

Biochemical alterations in human cells irradiated with alpha particles delivered by macro- or microbeams

Irradiation of individual cell nuclei with charged-particle microbeams requires accurate identification and localization of cells using Hoechst staining and UV illumination before computer-monitored localization of each cell. Using Fourier-transform infrared microspectroscopy (FT-IRM), we investigated whether the experimental conditions used for cell recognition induce cellular changes prior to irradiation and compared biochemical changes and DNA damage after targeted and nontargeted irradiation with alpha particles delivered by macro- or microbeams, using gamma radiation as a reference. Molecular damage in single HaCaT cells was studied by means of FT-IRM and comet assay (Gault et al., Int. J. Radiat. Biol. 81, 767-779, 2005). Hoechst 33342-stained HaCaT cells were exposed to single doses of 2 Gy (239)Pu alpha particles from a broad-beam irradiator, five impacted alpha particles from a microbeam irradiator, or 6 Gy gamma rays from (137)Cs, each of which resulted in about 5% clonogenic survival. FT-IRM of control cells indicated that Hoechst binding to nuclear DNA induced subtle changes in DNA conformation, and its excitation under UV illumination induced a dramatic shift of the DNA conformation from A to B as well as major DNA damage as measured by the comet assay. Comparison of the FT-IRM spectra of cells exposed to gamma rays or alpha particles specifically targeted to the nucleus, alpha particles from a broad-beam irradiator revealed spectral changes corresponding to all changes in constitutive bases in nucleic acids, suggesting oxidative damage in these bases, as well as structural damage in the deoxyribose-phosphate backbone of DNA and the osidic structure of nucleic acids. Concomitantly, spectral changes specific to protein suggested structural modifications. Striking differences in IR spectra between targeted microbeam- and nontargeted macrobeam-irradiated cells indicated greater residual unrepaired or misrepaired damage after microbeam irradiation. This was confirmed by the comet assay data. These results show that FT-IRM, together with the comet assay, is useful for assessing direct radiation-induced damage to nucleic acids and proteins in single cells and for investigating the effects of radiation quality. Significantly, FT-IRM revealed that Hoechst 33342 binding to DNA and exposure to UV light induce a dramatic change in DNA conformation as well as DNA damage. These findings suggest that fluorochrome staining should be avoided in studies of ionizing radiation-induced bystander effects based on charged-particle microbeam irradiation. An alternative cell nucleus recognition system that avoids nuclear matrix damage and its possible contribution to propagation of biological effects from irradiated cells to neighboring nontargeted cells needs to be developed.     

Inhalation carcinogenesis of high-fired 241AmO2 in rats

Wistar rats were given a single inhalation exposure to high-fired 241AmO2 particles and examined over their life span. A total of 310 rats were used: 259 exposed to 241Am for life-span study, 30 exposed to 241Am for early metabolism study, and 21 unexposed life-span controls. The activity median aerodynamic diameter of the aerosols was 0.75-1.39 microns. About 55% of alveolarly deposited 241Am was cleared from the lung with a half-life of 0.5 days, 37% with a half-life of 7 days, and 8% with a half-life of 580 days. Group mean lung doses ranged from less than 5.7 rad up to 1500 rad. Significant early mortality due to radiation pneumonitis was seen only in the highest exposure group. The percentage of rats with lung tumors was 0% for controls (21 rats), 1% at lifetime lung doses less than 10 rad (139 rats), 7% at 10-50 rad (86 rats), 0% at 50-100 rad (9 rats), 60% at 100-500 rad (10 rats), and 7% at 500 rad (15 rats). Only one liver and one bone tumor were found in all exposed rats, both at lifetime tissue doses less than 10 rad. The fate and carcinogenicity of inhaled 241AmO2 in the lung of rats were similar to what has previously been described for inhaled 244CmO2.     

241Am dating of lake sediments

²⁴¹Am derived from decay of fallout ²⁴¹Pu is now frequently detected in analyses of lake sediments by low-background gamma assay, and offers an alternative to weapons test ¹³⁷Cs in dating recent sediments at those sites where the ¹³⁷Cs record has been degraded by post-depositional mobility or obliterated by Chernobyl fallout. Calculations of the in-growth of ²⁴¹Am from ²⁴¹Pu indicate a nominal distribution broadly similar to that of ¹³⁷Cs, with the maximum ²⁴¹Am activity occuring in fallout dating from 1963. Results from a number of sites suggest that ²⁴¹Am is significantly less mobile in lake sediments than ¹³⁷Cs, and that its distribution in cores reflects more closely the fallout record. Since further decay of existing weapons debris will increase ²⁴¹Am concentrations by about 24% over the next 40 years, ²⁴¹Am is likely to play an increasingly important role in assessing the validity of ²¹⁰Pb dates at sites with varying sediment accumulation rates.     

Osteosarcoma development following single inhalation exposure to americium-241 in beagle dogs

Young, mature Beagle dogs underwent single inhalation exposure to respirable aerosols of 241AmO2 to determine the radiation dose distribution to tissues. The dogs were serially sacrificed to assess the clearance of 241Am from the lung, the rate of translocation to internal organs, the pattern of retention in the organs, and the rates and modes of excretion. Americium dioxide was relatively soluble in the lung, leading to the translocation of significant quantities of 241Am to bone and liver, thus delivering radiation doses to these tissues nearly equal to that received by the lung. Osteoblastic osteosarcomas developed in four dogs surviving more than 1000 days after exposure. Histologically, all of the osteosarcomas were associated with areas of radiation osteodystrophy characterized by bone infarction, peritrabecular new bone formation, marrow fibrosis, and microresorptive cavities. The retention and translocation of inhaled 241Am in dogs is similar to that of man, indicating that 241Am inhaled by humans may potentially result in significant risk of bone tumor development.     

Toxicity of 241Am in male C57BL mice: relative risk versus 226Ra

A life-span study on male C57BL mice after injection of various doses of 241Am was conducted. The effects on life span were evaluated and the incidence of tumors was determined by procedures that take competing risks into account. Bone tumors were induced in the mice by injections of 22 and 58 Bq 241Am per g. The mice died early from nonneoplastic diseases at the higher dose levels (190, 373, and 1197 Bq 241Am/g). Additionally, spontaneously occurring tumors such as liver carcinomas, lymphosarcomas, and lymphoreticulosarcomas occurred at an enhanced rate with increasing dose level. The data for survival time after 241Am injection and death with bone tumor were compared to data collected previously for 226Ra-injected mice of the same C57BL strain. This enabled direct comparison in the same strain of the effects of the bone-surface seeker 241Am to the effects of the bone-volume seeker 226Ra. The proportional hazards model was applied and the rate of death with bone tumor was 12.9 +/- 5.2 times higher after 241Am injection than after 226Ra injection if the regression covariate was the average dose to the skeleton. The relative risk was 3.5 +/- 1.7 if regressed on the injected radioactivity. The mortality rate after 241Am injection was 20.4 +/- 3.6 times higher than after 226Ra injection if regressed on average dose to the skeleton.     

The "windows", scales, and bristles of the tropical moth Rothschildia lebeau (Lepidoptera: Saturniidae)

The common Spanish name of the moth Rothschildia lebeau (Saturniidae) is cuatro ventanas (four 'windows'), because it exhibits a transparent oval path in each wing. The scales of the colored areas and the bristles from the "window" were analyzed. We developed a simple device to measure transmittance across the "windows" with an spectrophotometer. A square section of "window" was mounted onto a flat black card and placed onto a clamp that hung in the path of the light - beam of the spectrophotometer. Absorbance was measured at 350 and 550 nm, with the "window" positioned perpendicular to the light beam (incidence of 90 degrees); then the measurements were repeated with the "window" moved at an angle of 45 degrees. Each measurement was replicated 5 times. Wing color spots were analyzed with a light dissection microscope (stereoscope) and with scanning electron microscopy. The scales have a minimum of 4 morphological types, 3 of them showed the typical appearance of unspecialized scales described for other butterflies; whereas the fourth has features particular to this species. On the "window" the scales are transformed in hair-like bristles that do not interfere with light, conferring the transparency that characterizes the "windows". However, if the wing is illuminated at an almost grazing-incidence, they reflect the light as a mirror. Two hypothetical functional explanation for the windows are mimicry and interspecies communication.     

Inactivation of influenza A virus on copper versus stainless steel surfaces

Influenza A virus particles (2 x 10(6)) were inoculated onto copper or stainless steel and incubated at 22 degrees C at 50 to 60% relative humidity. Infectivity of survivors was determined by utilizing a defined monolayer with fluorescent microscopy analysis. After incubation for 24 h on stainless steel, 500,000 virus particles were still infectious. After incubation for 6 h on copper, only 500 particles were active.