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Biomedical subjects

J W Baum

Publications and source records attributed to J W Baum.

At least 19 recordsLinked to original sources
PubMed1991

A system for simultaneous exposure of small animals to 60-Hz electric and magnetic fields.

Equipment designed for simultaneous exposure of rodents to 60-Hz electric and magnetic fields is described. Three identical systems were constructed, each capable of continuous exposure of 256 rats or 640 mice to a nominal electric field at less than 50 kV/m, and to horizontal and vertical magnetic fields at less than 1 mT. Design features, construction details, and results of various tests of the systems are described. Tests were made: of phase relations between electric and magnetic fields; of uniformity of electric and magnetic fields; of changes across time in electric-field intensity as a result of animals' soiling of cages and various washing routines; of resistance of bedding material during humid and dry conditions; and of acoustic noise due to background, to field-generation equipment, and to air conditioning equipment. The results demonstrated that fields were effectively generated but that significant and troublesome changes in electric-field intensity occurred because of cage-soiling. However, when cages were frequently cleaned, field intensities were consistent from one exposure to another.

Animals↗
PubMed1989

Probabilistic approach to obtain hit-size effectiveness functions which relate microdosimetry and radiobiology.

A probabilistic approach has been developed to relate microdosimetry, biological effects, and radiation quality. It is used to derive, and subsequently apply, microdosimetry-based cellular response functions for different biological end points of relevance for radiological protection. The approach makes use of measurable microdosimetry spectra and avoids assumptions concerning the course of mechanisms of radiation action. Instead, it postulates a response function that is, and behaves like, the cumulative probability that a subcellular target structure will respond to a specific target-averaged ionization density. Statistical distributions are applied and their parameters are evaluated to characterize the randomness involved in the localization of sensitive sites and in the reactivity of the whole sensitive structure. The resulting response functions can be used for prediction of the effects of low-level radiation. Such predictions for some selected effects of a stochastic nature (mutagenesis, chromosome abnormalities, etc.) are presented as relative biological effectiveness values based on low doses of radiations with a wide range of linear energy transfer and compared with various quality factor specifications. Cellular response relationships, termed hit-size effectiveness functions, can also be applied directly in radiation protection metrology by incorporating them into the software used to process the readings of microdosimetric spectrometers. The derivation of the functions, rather than their uses in radiation protection, is the principal subject of this report.

Animals↗
PubMed1989

Ionization yields in hydrocarbons under electron irradiation.

Ionization yields and W-values in several hydrocarbon gases under electron irradiation have been calculated using Inokuti's solution of the Fowler equation, i.e., incorporating a linear dependence of ionization yield on source electron energy. Collision stopping powers of hydrocarbons were evaluated using the Bethe formula with mean excitation energies determined using the additivity rule with modification based on molecular bond strengths. Contributions to the collision stopping powers from discrete level excitations were estimated by multiplying collision stopping powers by the excitation fractions constructed from atomic calculations. Average energy transfers for ionizing collisions producing subionization electrons were calculated using differential ionization cross sections proposed by Khare and co-workers. The calculated W-values are in good agreement with those recommended by ICRU.

Electrons↗
PubMed1984

Influence of strong magnetic fields on genetic endpoints in Tradescantia tetrads and stamen hairs.

Inflorescences from Tradescantia clones 4430 and 02 were subjected to mean magnetic field intensities of 0.16 or 0.76 to 0.78 tesla for 6 to 11 days. Following exposures to both intensities, damage to pollen mother cell chromosomes at early prophase was determined by scoring the frequency of micronuclei in early tetrads. Pink mutations in stamen hair cells of clone 4430 were scored for 15 days after a 6-day exposure to the higher intensity level while clone 02 was scored during and for 6 days after an 11-day exposure to the 0.16 tesla field. Comparison of micronuclei results from exposed groups to those for control groups that were scored concurrently showed that there was no significant difference in frequency for either clone or either field intensity (P values in contingency table analyses were between 0.42 and 0.6); similarly, pink mutation frequencies for clone 4430 exposed and control groups did not differ significantly (a contingency test yielded X2 = 1.4 and P = 0.26). Comparisons of pink mutation frequencies during the first 6 days of clone 02 exposure to those in the period when an effect should be greatest (days 7 through 17 revealed no significant difference (X2 = 2.6 and P = 0.1) between the two scoring periods, through frequencies were higher during the early scoring period.

Magnetics↗
PubMed1983

Sensitivity of Drosophila melanogaster to low concentrations of gaseous mutagens. IV. Mutations in embryonic spermatogonia.

Drosophila embryos were treated with gaseous ethylene dibromide at concentrations ranging from 0.26 to 200 ppm, thereby exposing a homogeneous and non-dividing population of primordial spermatogonia. Mutations were induced at exposures as low as 1 ppm for 3 h indicating the sensitivity of spermatogonia and the usefulness of this life-cycle stage for detection of mutagens. Other advantages of using embryos are also discussed. The relations between exposure vs. percentage of mutations per chromosome tested and vs. percentage of positive males were linear at low exposures indicating the possibility of extrapolation of the data to very low doses and lack of a threshold. For some males 50% of the progeny carried a mutation, and mutations continued to appear in all tested broods providing evidence of damage to stem cells undergoing quasi-dichotomous divisions. Damage to the stem cells is important in terms of total effects on the gene pool and may contribute more mutations than that due to damage in the more sensitive spermatocytes and spermatids. Spermatogonial stages, therefore, should also be considered in mutagen screening and risk-benefit analyses.

Animals↗
PubMed1982

Genetic effects of 1,2-dibromo-3-chloropropane (DBCP) in Drosophila.

Induction of sex-linked recessive lethal mutations, heritable translocations and genetic crossing-over were studied in Drosophila melanogaster males treated as adults and as embryos with different concentrations of gaseous DBCP. Adults exposed to 30 ppm/hr of the compound did not produce a significant number of sex-linked recessive lethal mutations in treated spermatozoa, spermatids, or spermatocytes. However, at an exposure of 17.7 ppm/hr, a weak mutagenic effect was observed in embryonic spermatogonia. No translocation was scored in 4032 tested chromosomes from adults treated with 150 ppm/hr. However, a significant number of spermatocytial crossovers were induced after an exposure of 120 ppm/hr.

Animals↗
PubMed1981

Sensitivity of Drosophila melanogaster to Low concentration of gaseous mutagens: III. Dose-rate effects.

Sex-linked recessive lethal mutations were induced in D melanogaster males by chronic as well as acute treatments of gaseous 1,2-dibromoethane ranging from 2.3 to 31 ppm.hr. Acute treatments corresponding to each chronic treatment were made by increasing chemical concentration approximately 30 times with a concomitant decrease in exposure period. Germ cell stages sampled, in order of decreasing sensitivity, were spermatocytes, spermatids, and spermatozoa. The most significant finding is that no consistent pattern of difference is observed between acute and chronic exposure for three of the four exposure levels. Only at the highest exposure level (30-31 ppm.hr) was any consistent difference observed between chronic and acute exposure levels. At the higher exposure level in all three germ cell stages the acute exposure showed a significant increase in mutation frequency over the chronic exposure. The greater acute vs chronic mutation frequency for spermatozoa, a metabolically inactive cell stage, leads to the conclusion that the exposure rate effect at high exposure levels is due to systemic factors such as metabolic deactivation or elimination rather than repair of premutational damage in the target cells. The significance of these observations in risk assessment for environmental pollutants is discussed.

Animals↗
PubMed1980

Genetic effects of strong magnetic fields in Drosophila melanogaster: II. lack of interaction between homogeneous fields and fission neutron-plus-gamma radiation.

Interaction between mutagenic effects of strong homogeneous magnetic fields and fission neutron-plus-gamma radiation was investigated, using the sex-linked, recessive, lethal test in Drosophila melanogaster. Drosophila males were exposed chronically, for seven days, to a 37,000-G homogeneous magnetic field and/or 3 doses of neutron-plus gamma radiation. Mutations in spermatozoa, spermatids, and spermatocytes were scored. There was no evidence of interaction between the effects of the two types of exposure in causing genetic damage in any of the three cell types. Dose-response relations for the radiation doses were linear for spermatozoa and spermatids for all three doses and for spermatocytes, up to 300 rads. Spermatozoa appear to be most sensitive to neutron-radiation-induced, recessive lethal mutations.

Animals↗
PubMed1979

Sensitivity of Drosophila melanogaster to low concentrations of the gaseous 1, 2-dibromoethane: I. acute exposures.

Drosophila melanogaster males were exposed to gaseous 1, 2-dibromoethane at concentrations lower than those used in aerosol treatments of suspected mutagens by other investigators. Premeiotic stages appear to be more sensitive than postmeiotic stages to gaseous mutagens. At an exposure of 125 ppm . hr, significant numbers of mutations were induced in spermatids, spermatocytes, and spermatogonia. Since this exposure increased the mutation rate in spermatogonial stages by a factor of 20--40 over the spontaneous rate, it appears that the lowest detectable exposures may be much lower than 125 ppm . hr for 1, 2-dibromoethane.

Aerosols↗
PubMed1979

Sensitivity of Drosophila melanogaster to low concentrations of gaseous mutagens. II. Chronic exposures.

Sex-linked recessive lethal mutations were induced in Drosophila melanogaster males by gaseous 1,2-dibromoethane at concentrations ranging from 0.2 to 2 parts per million. Significant numbers of mutations could be induced at all these concentrations. Pronounced germ-cell sensitivity differences were observed. For low exposures, spermatids and spermatocytes were about 10--20 times more sensitive than spermatozoa. The dose-effect relation was linear below 60 ppm . h for the 3 cell types. At higher exposures, sterility prevented mutation detection in spermatocytes and in spermatogonia. The lowest effective exposure for spermatozoa was 18 ppm . h (0.25 ppm for 72 h). In spermatids, the lowest exposure tested, 2.3 ppm . h (0.2 ppm for 11 h) induced 4 times the spontaneous mutation rate. Therefore, using prolonged exposure periods one may be able to detect concentrations in the range of parts per billion. Thus, Drosophila appears suitable as a system for detecting very low concentrations of gaseous mutagens in industrial, agricultural and environmental atmospheres.

Animals↗
PubMed1979

Relative determination of W-values for alpha particles in tissue-equivalent and other gases.

W (the average energy to form an ion pair) for 5.4 MeV 241Am alpha particles in a Rossi-type tissue-equivalent (TE) gas, argon and methane was determined to an accuracy better than 0.2% using a new automated data handling system. A vibrating reed electrometer and current digitiser were used to measure the current produced by completely stopping the alpha particles in a large cylindrical ionisation chamber. A multichannel analyser, operating in a slow multiscaler mode, was used to store pulses from the current digitiser. The dwell time, of the order of 60 min per channel, was selected with an external timer gate. Current measurements were made at reduced pressures (200 Torr) to reduce ion recombination. The average current, over many repeated measurements, was compared to the current produced in nitrogen and its previously published W-value of 36.39+/-0.04 eV per ion pair. The resulting W-values were, in eV per ion pair, 26.29+/-0.05 for argon, 29.08+/-0.03 for methane and 30.72+/-0.04 for TE gas, which had an analysed composition of 64.6% methane, 32.4% CO2 and 2.7% nitrogen. Although the methane and argon values agree within 0.1% with previously published values, the value for TE is 1.2% lower than the single previously reported value.

Alpha Particles↗
PubMed1978

Energy dependence of W for alpha particles in N2, CO2, CH4, Ar, H2 and Rossi-type tissue-equivalent gases.

Average energy required to form an ion pair (W) was determined in N2, CO2, CH4, Ar, H2 and Rossi-type tissue-equivalent gas. Alpha particles from a 241Am source were used. W was determined at alpha energies of 5.37, 3.12, 1.08 and 0.46 MeV. The ratio of total ionisation produced (for fixed alpha particle energy) in experimental gas to that produced in argon was measured. This ratio was then multiplied by the previously determined W value for argon gas (26.29 eV per ion pair) to yield W for various experimental gases. Energy of the 241Am alpha particles was degraded by using air as an absorbing material. Empirical relations W = alpha + betaE-1/2 and W = alpha1 + beta1E-1 were fitted to the experimental data. Both functions fit reasonably well in the range 0.4--5.37 MeV. Below about 0.4 MeV the first function provides a better fit to the data of Boring et al. (1965).

Alpha Particles↗