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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
PubMed2001

Analysis of potential radiobiological effects related to a unified skin dose limit.

A unified skin dose limit of 0.5 Sv at a depth of 70 microm averaged over the highest 10 cm2 of skin exposed was evaluated to replace the existing limit of 0.5 Sv averaged over 1 cm2. This limit would apply to all exposures including non-uniform exposures such as from hot particles on or off skin, skin contamination, or beams of charged particles or photons. The probabilities and severity of both stochastic and deterministic risks were estimated for a wide range of worst-case exposure scenarios using published radiobiological data and calculations of radial- and depth-dose distributions. Results indicate that exposures at the unified dose limit have the potential to cause effective doses of about 17 microSv (1.7 mrem), estimated stochastic risks of <3.3 x 10(-7) fatal skin cancers, and <1.6 x 10(-4) non-fatal skin cancers. The worst deterministic effects were estimated to be (a) based on a 2 Gy threshold, transient erythema induction to an area of 2.5 cm2 for uniform skin contamination over this same area and 0.65 cm2 for a 60Co hot particle 3 mm off of skin, (b) based on data for pig skin, 50% probability that 0.5 cm2 of skin would suffer 20% dermal thinning for uniform contamination with 106Rh spread over the same area, and (c) 10% probability of barely detectable transient acute necrosis or ulceration for 60Co or activated fuel particles 0.4 mm off of skin. It was concluded that the unified limit would provide a more logical system of dose control with possible savings of whole-body dose and other benefits.

Animals↗
PubMed2001

Scab diameters on pig skin resulting from hot particle exposures under varying conditions.

The National Council on Radiation Protection and Measurements (NCRP) in NCRP Report Number 106 recommended a limit of 10(10) beta particles emitted from radioactive particles with sizes less than 1 mm (hot particles) to prevent acute deep ulceration. This recommendation was determined, in part, by regressing the diameter of the scabs induced by fissioned 235UC2 hot particles as a function of the logarithm of the number of beta particles emitted from the sources for one study. To validate this recommendation and the approach used by the NCRP, external irradiations of pig skin using radioactive sources of less than 600 microm in the largest dimension were carried out. The hot particles used included fissioned 235UC2 and activated 170Tm, 175Yb, and 46Sc. Results indicated a strong correlation between scab diameter and dose for scabs induced using fissioned 235UC2, activated 170Tm, and 46Sc, but not for 175Yb. The correlation value decreased with decreasing beta particle energy, with the exception of 46Sc, which had scabs with diameters greater than twice the maximum beta particle range. The larger scabs from 46Sc are thought to be due to dose contributions from the gamma rays. The results also give an ulceration threshold less than that given by NCRP to prevent acute deep ulceration. It was concluded that regression analysis of scab diameter as a function of either number of beta particles emitted from the hot particles or dose did not yield either precise or accurate thresholds but was useful in determining probable ranges of doses which lead to scab induction.

Animals↗
PubMed2001

Scab incidence on pig skin resulting from hot particle exposures under varying conditions.

External irradiations of pig skin using radioactive sources of less than 600 microm in the largest dimension (hot particles) were carried out. The objective of the study was to determine a threshold for scab induction. Hot particles used included fissioned 235U and activated 170Tm, 17SYb, and 46Sc with maximum beta-particle energies of approximately 1.8 (average), 0.97, 0.47, and 0.35 MeV, respectively. The photon emissions from the fissioned 235U were about 1 MeV per disintegration. The photon emissions from 46Sc were 0.89 and 1.12 MeV, with 100% abundance. Photon emissions from 170Tm and 175Yb were negligible. Responses followed cumulative normal probability distributions; thus, no true thresholds could be determined. Hence, 10% and 50% scab incidence rates (ED10 and ED50, respectively) were determined using probit analysis. For dose averaged over 1 cm2 at a depth of 70 microm, the ED10 (and 95% confidence limits) were 5.1 (2.7-7.2) Gy for 46Sc, 1.3 (0.89-1.8) Gy for 175Yb, 2.8 (1.9-3.5) Gy for 170Tm, 8.5 (5.7-9.8) Gy for on-skin fissioned UC2, and 4.5 (0.9-7.2) Gy for off-skin fissioned UC2. The ED50 values were 12 (8.8-17) Gy for 46Sc, 6.0 (4.3-9.7) Gy for 175Yb, 5.9 (5.1-6.7) Gy for 170Tm, 11 (9.9-19) Gy for on-skin fissioned 235UC2, and 11 (6.2-14) Gy for off-skin fissioned 235UC2.

Animals↗
PubMed2000

Effective half-lives for patients administered radiolabeled antibodies and calculated dose to the public in close proximity to patients.

Effective half-lives (T(e)) for radiolabeled antibodies can be much longer than that of traditional radiopharmaceuticals, potentially resulting in larger doses to members of the public. Clearance-rate data from patients treated with radio-labeled antibodies (RABs) were obtained from ten institutions. Calculations were made to determine if a single- or bi-exponential clearance-rate model was statistically justified; the results indicated that the former model was justified for more than 95% of the data. Values of T(e) for the different RABs are summarized. To plan actions to limit doses to less than 5 mSv annually for individuals continuously close to the patient (at 1 m), dose rates from patients at the time of release also are given as a function of T(e).

Antibodies, Monoclonal↗
PubMed1997

Assessment of plutonium exposure in the Enewetak population by urinalysis.

Since 1980, the inhabitants of Enewetak Atoll have been monitored periodically by scientists from Brookhaven National Laboratory for internally deposited radioactive material. In 1989, the establishment of fission track analysis and of a protocol for shipboard collection of 24-h urine samples significantly improved our ability to assess the internal uptake of plutonium. The purpose of this report is to show the distribution of plutonium concentrations in urine collected in 1989 and 1991, and to assess the associated committed effective doses for the Enewetak population based on a long-term chronic uptake of low-level plutonium. To estimate dose, we derived the plutonium dose-per-unit-uptake coefficients based on the dosimetric system of the International Commission on Radiological Protection. Assuming a continuous uptake, an integrated Jones's plutonium urine excretion function was developed to interpret the Enewetak urine data. The Appendix shows how these values were derived. The committed effective doses were 0.2 mSv, calculated from the 1991 average plutonium content in 69 urine samples.

Adolescent↗
PubMed1995

Assessment of plutonium exposures in Rongelap and Utirik populations by fission track analysis of urine.

A nuclear device, code-named Bravo, detonated at Bikini Atoll at 6:45 a.m. on 1 March 1954, unexpectedly released a large amount of radioactivity. Over 40 years after this incident, the study of its impact on the radiological health and environmental safety of the residents of Rongelap and Utirik Atolls continues. In 1987, researchers at Brookhaven National Laboratory established a fission track analysis (FTA) method for low-level 239Pu urinalysis. Two years later, a new shipboard protocol was developed for collecting 24-h radiologically clean urine samples. The purpose of this paper is to update information on the FTA method for measuring low-levels of plutonium, and to summarize results on the distribution of 239Pu in the populations of Rongelap and Utirik between 1981-1991. Plutonium detection levels (99% confidence level) in these samples were 2-3 microBq, which is equivalent to 0.2-0.3 mSv effective dose equivalent (EDE) to age 70 for Marshallese. The latest 1991 FTA data indicate average EDE of 0.62 mSv and 1.6 mSv for the people of Rongelap and Utirik, respectively, which both are the highest values since 1988.

Adolescent↗
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↗