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Biomedical subjects

P K Hopke

Publications and source records attributed to P K Hopke.

At least 19 recordsLinked to original sources
PubMed1992

Measurement of SO2 effects on the 218Po ion mobility spectrum by alpha-track detection.

A number of investigators have reported the formation of radiolytic ultrafine particles produced by the interaction of ionizing radiation with atmospheric trace gases. Previous studies have suggested that a very high localized concentration of the OH radical produced by the radiolysis of water can react with atmospheric trace gas, like SO2, to produce lower vapor pressure compounds that can then nucleate. To determine trace-gas dependence of the active, positively charged, first decay product of radon, the mobility spectrum of the decay products in the range of 0.06-3.0 cm2 V-1s-1 was measured in a flow-through radon chamber using a specially designed mobility spectrometer. Measurements were taken for different relative humidities and concentrations of SO2 in purified laboratory compressed air. The resultant mobility spectra were compared with radiolytic ultrafine particle activity distribution data. In the case of low humidities, the reduction of available OH concentration and hence neutralization rate led to the increasing intensity of the shoulder around 1.35 cm2 V-1s-1 with increasing SO2, suggesting SO2 clustering around the PoOx+ ion. For high humidity conditions (5 ppm SO2, 30% RH), there was clear droplet formation, H2SO4, clustering around the ion, and also an increase in the background level between the high mobility peak and droplet peak.

Bismuth↗
PubMed1992

Some thoughts on the "unattached" fraction of radon decay products.

A problem exists in the meaning and use of the term "unattached fraction" to describe the highly diffusive portion of the airborne radon progeny. The term was originally developed to aid in lung dosimetry but now that more detailed size measurements can be made, there are ambiguities in its definition between a physical size basis and a dosimetric definition. Some possible ways to resolve these ambiguities are presented and discussed. It is suggested that the term only be used in the context of complete size information rather than as the conventional operationally defined term.

Radon↗
PubMed1992

The measurement of activity-weighted size distributions of radon progeny: methods and laboratory intercomparison studies.

Over the past 5 y, there have been significant improvements in measurement of activity-weighted size distributions of airborne radon decay products. The modification of screen diffusion batteries to incorporate multiple screens of differing mesh number, called graded screen arrays, have permitted improved size resolution below 10 nm such that the size distributions can now be determined down to molecular sized activities (0.5 nm). In order to ascertain the utility and reliability of such systems, several intercomparison tests have been performed in a 2.4 m3 radon chamber in which particles of varying size have been produced by introducing SO2 and H2O along with the radon to the chamber. In April 1988, intercomparison studies were performed between direct measurements of the activity-weighted size distributions as measured by graded screen arrays and an indirect measurement of the distribution obtained by measuring the number size distribution with a differential mobility analyzer and multiplying by the theoretical attachment rate. Good agreement was obtained in these measurements. A second set of intercomparison studies among a number of groups with graded screen array systems was made in April 1989 with the objective of resolving spectral structure below 10 nm. Again, generally good agreement among the various groups was obtained although some differences were noted. It is thus concluded that such systems can be constructed and can be useful in making routine measurements of activity-weighted size distributions with reasonable confidence in the results obtained.

Air↗
PubMed1991

Source apportionment with site specific source profiles.

A receptor modeling study was performed to identify and apportion the sources of PM10 mass in Granite City, Illinois, an area of historic TSP nonattainment. Samples of the ambient aerosol were collected using a dichotomous sampler. Each sample was analyzed by x-ray fluorescence and instrumental neutron activation analysis. To begin the study, a factor analysis was performed. Two different chemical mass balance (CMB) analyses were then made. The first CMB analysis used only source profiles available from the literature while the second included twelve source profiles developed from dust samples collected in Granite City. Both CMB analyses used 20 of the 33 analyzed elements since many of the source profiles in the literature did not include the other thirteen elements. The results from both sets of CMB analyses were grouped by the predominate wind direction at the site during the time each sample was taken to identify the direction of each source relative to the sampler. It was found that regional sources were the primary contributors to the fine fraction while the coarse fraction was composed of material from local industries. These sources were generally the ones identified during the Regional Air Pollution Study previously conducted in the area. However, the emission profiles from these sources were observed to have changed between the studies. It was also found that the use of the locally generated profiles greatly improved the results of the CMB analysis.

Air↗
PubMed1991

Study of neutralization of 218 Po ions by small ion recombination in O2, Ar, and N2.

Three mechanisms of neutralization of Po(+)--electron transfer, electron scavenging, and small ion recombination--have previously been suggested. Considerable work has been conducted on the first two mechanisms. However, little information about small ion recombination is available. In the present study, this mechanism was studied by examining the neutralization rates of different Rn concentrations in N2, Ar, and O2 with the aid of a continuous Rn progeny monitoring system. The results showed that the neutralization rates in the three gases are of the order 1-4 s-1 at high Rn concentrations (higher than 40,000 Bq m-3). A linear relationship between the neutralization rate and the square root of Rn concentration (from 40,000 Bq m-3 to 810,000 Bq m-3) was obtained. Neutralization rates were higher in the gas with lower ionization potential. Further, the existence of a neutralization rate plateau at high Rn concentrations was strongly suggested.

Air Pollutants, Radioactive↗
PubMed1991

Efficacy of air cleaning systems in controlling indoor radon decay products.

Field evaluations of an air filtration system and an electronic air cleaner to remove Rn decay products were performed in a single-family house located in the Northford, CT area. Field measurements included the Rn concentration, particle number concentration, and concentration and activity size distribution of Rn decay products. A semi-continuous screen diffusion battery system with six parallel sampler/detector units was used to determine the concentrations and size distributions of the Rn decay products. Indoor particles were generated by common activities such as vacuuming, washing and drying clothes, opening the outside door, and cooking. Influences on the size distributions over the size range from 0.5 nm to 500 nm of Rn decay products were investigated in the domestic environment. The effect of the air cleaners was to decrease the concentration of the decay products and to reduce the equilibrium fraction. For the filtration system in particular, the activity fractions in the smallest size range were increased. However, the overall effect of the air cleaners was to reduce the median dose. The filtration unit was found to be more effective than the electronic air cleaner.

Air Pollution, Indoor↗
PubMed1990

A measurement system for Rn decay product lung deposition based on respiratory models.

Using models of particle deposition in the nasal cavity and in the tracheobronchial region of the respiratory tract, it is possible to design a measurement system based on wire screen penetration theory. This system provides direct estimates for the quantities of Rn decay product activity deposited in the nasal cavity and in the tracheobronchial region. Historically, measurements of the "unattached" fraction of the airborne Rn decay product size distribution have been made in order to better estimate the dose resulting from the deposition of these 222Rn progeny in the human respiratory tract. However, previous measurement systems have been developed based on choices of screen parameters and sampling flow conditions in an attempt to separate the "unattached" fraction from the rest of the activity size distribution. By taking into consideration the deposition behavior of particles in the respiratory tract, a specific choice of wire screens and flow rates can be made that can provide better information for the estimation of deposited dose in the respiratory tract.

Air Pollutants↗
PubMed1989

On improving the validity of wire screen "unattached" fraction Rn daughter measurements.

Wire screens are commonly used to estimate "unattached" Rn daughter fractions in ambient and mine atmospheres. However, it is now recognized that the "unattached" fraction is in reality an ultrafine cluster mode in the 0.5-3 nm size range and that the collection efficiency versus particle diameter characteristics of wire screens do not permit a distinct separation of the "unattached" and "attached" fractions. Wire screen penetration theory and a semi-empirically corrected diffusion coefficient equation are used to characterize "unattached" fraction measurements as a function of experimental parameters. Collection efficiency curves are estimated for previously published wire screen "unattached" fraction measurements, and improvements in wire screen methods for such measurements are discussed.

Air Pollutants, Radioactive↗
PubMed1989

Use of electrostatic collection of 218Po for measuring Rn.

The decay of 222Rn produces a positively charged 218Po ion 88% of the time. The electrostatic collection of this ion has served as the basis of a number of systems for measuring Rn concentrations. However, there are neutralization processes that restrict the time available to collect the ion. The measured rates of neutralization by water vapor and by trace gases have been used to determine the applied field strengths necessary to ensure complete collection of the ions and thus interference-free Rn determinations.

Electrons↗
PubMed1988

Radon adsorption on activated carbon and the effect of some airborne contaminants.

The adsorption and desorption of radon on five types of activated carbon and the effect of various airborne contaminants on the adsorption process was studied, the dynamic adsorption coefficient for the carbon samples tested was found to range from 2.4 +/- 0.2 to 7.1 +/- 0.71 g-1. Iso-octane was found to reduce the dynamic adsorption coefficient significantly.

Adsorption↗
PubMed1988

Investigation of the geographical distribution of female cancer patterns in Belgium using pattern recognition techniques.

Different multivariate methods have been applied to obtain an overview of the Belgian female cancer mortality distribution. The resulting maps and figures show the patterns of female cancer mortality to be strongly geographically determined. Two major trends can be derived namely along the north-south axis and along the east-west axis of the country. The cancer sites responsible for these patterns are identified.

Belgium↗
PubMed1987

Reduction of mutagenicity of municipal wastewaters by land treatment.

The disposal of complex mixtures such as wastewater on agricultural lands poses known and unknown environmental risks. Mutagens may be introduced into the ecosystem and perhaps concentrated by crop plants or leached into ground water supplies. The purpose of this study was to determine the biological effect of a mutagenic wastewater before and after application to soil. An XAD-8 methanol extract of wastewater from the municipal sewage treatment facility at Sauget, IL, was a potent, direct acting mutagen when assayed with Salmonella typhimurium. One and 3 ml of extract were brought up to 10 ml volumes with water and added to 10 g of sterile or nonsterile native clay loan. These mixtures were incubated at room temperature for 0, 24 and 48 h. After separation of solid and liquid portions by filtration, dichloromethane was added to extract the organic fractions from each component. Solvent extractions were evaporated to dryness under vacuum and brought up in DMSO. Tests for mutagenic activity were conducted using Ames strain TA98. Addition to the soil for greater periods of time decreased the mutagenic activity. The solid component exhibited greater mutagenic activity than the liquid.

Illinois↗
PubMed1975

The dynamics of diquat in a model eco-system.

Muskelung (Esox-masquinongy chiensis) fry were used in a 96 hour toxicity study with diquat and simazine. Although the death of sufficient control fish invalidated the test as a whole, some interesting observations were made. At the end of 48 hours 4 out of 10 fish had died in the control tank and 8 had died in the simazine tank while all 10 diquat-treated fish appeared healthy. Two model eco-systems with components from Chautauqua Lake, N.Y. were constructed in 20 gallon glass aquaria to trace the movement of 14C labeled diquat. After activity had reached near background levels in the water from the test tank, fish, plants, sediments and snails were counted in a liquid scintillation counter to discover the fate of diquat within the system. The concentration of diquat was found to be highest in sediments, followed by fish tissue, snail parts, with plants having the lowest measured concentration.

Animals↗