Population dose due to natural radiation in Hong Kong.

In densely populated cities such as Hong Kong where people live and work in high-rise buildings that are all built with concrete, the indoor gamma dose rate and indoor radon concentration are not wide ranging. Indoor gamma dose rates (including cosmic rays) follow a normal distribution with an arithmetic mean of 0.22 +/- 0.04 microGy h(-1), whereas indoor radon concentrations follow a log-normal distribution with geometric means of 48 +/- 2 Bq m(-3) and 90 +/- 2 Bq m(-3) for the two main categories of buildings: residential and non-residential. Since different occupations result in different occupancy in different categories of buildings, the annual total dose [indoor and outdoor radon effective dose + indoor and outdoor gamma absorbed dose (including cosmic ray)] to the population in Hong Kong was estimated based on the number of people for each occupation; the occupancy of each occupation; indoor radon concentration distribution and indoor gamma dose rate distribution for each category of buildings; outdoor radon concentration and gamma dose rate; and indoor and outdoor cosmic ray dose rates. The result shows that the annual doses for every occupation follow a log-normal distribution. This is expected since the total dose is dominated by radon effective dose, which has a log-normal distribution. The annual dose to the population of Hong Kong is characterized by a log-normal distribution with a geometric mean of 2.4 mSv and a geometric standard deviation of 1.3 mSv.

Radon mitigation by depressurization of concrete walls and slabs.

A special laboratory, the Radioisotope Unit Radon Analysis Laboratory, has been built for the study of radon mitigation in high-rise buildings. Reduction of radon exhalation rate from concrete walls as a result of depressurizing the interior of the wall was studied by embedding tunnels in a wall and pumping away the radon in the wall. The reduction in exhalation rate was quantified against the applied depressurization, the separation of the tunnels, the depth of the tunnel, and the thickness of the wall. Results show that radon exhalation rate from a wall embedded with tunnels can be reduced significantly by applying depressurization. For example, the radon exhalation rate from a wall of 20 cm thickness containing tunnels separated by 0.7 m can be reduced by 60% at a depressurization of 67 kPa (20 in Hg). This paper summarizes the effect of depressurization and suggests practical ways of applying the technique in radon mitigation in high-rise commercial buildings.

Radon action level for high-rise buildings.

Radon and its progeny are the major contributors to the natural radiation dose received by human beings. Many countries and radiological authorities have recommended radon action levels to limit the indoor radon concentrations and, hence, the annual doses to the general public. Since the sources of indoor radon and the methods for reducing its concentration are different for different types of buildings, social and economic factors have to be considered when setting the action level. But so far no action levels are specifically recommended for cities that have dwellings and offices all housed in high-rise buildings. In this study, an optimization approach was used to determine an action level for high-rise buildings based on data obtained through previous territory-wide radon surveys. A protection cost of HK$0.044 per unit fresh air change rate per unit volume and a detriment cost of HK$120,000 per person-Sv were used, which gave a minimum total cost at an action level of 200 Bq m(-3). The optimization analyses were repeated for different simulated radon distributions and living environment, which resulted in quite significantly different action levels. Finally, an action level of 200 Bq m(-3) was recommended for existing buildings and 150 Bq m(-3) for newly built buildings.

Behavior of 222Rn and its progeny in high-rise buildings.

Unlike detached or semi-detached houses, the main source of indoor radon in high-rise buildings is the building material. Radon released from the building material will be removed by ventilation, either forced or natural, so that its concentration, its progeny's concentration, and the equilibrium between the two will be different for different types of buildings and environmental factors. A number of surveys were carried out in buildings throughout the territory to look at the seasonal variation of indoor 222Rn levels; the dependence of indoor 222Rn concentration on the living environment; the indoor gamma dose rate and its relation to indoor 222Rn concentration; and the dependence of 222Rn progeny concentration and equilibrium factor on the environment in high-rise buildings.

Stability of gastrin in the gastrointestinal lumen of suckling, weanling and adult pigs.

It has been reported in the literature that a large quantity of gastrin is released into the gastric lumen in various species. This study was aimed to examine the stability of gastrin in the gastrointestinal (GI) lumen of pigs. Iodine-labelled little (G17) and big gastrin (G34) were incubated in vitro with the GI luminal fluids of suckling, weanling and adult pigs at 37 degrees C for 20 min, and the degradation of the peptide was measured by monitoring the generation of trichloroacetic acid soluble radioactivity. The degradation rate of G17 in the gastric fluids of all animals was less than 10%, while the degradation of G34 was less than 15% in the gastric fluids of suckling and adult pigs and about 25% in the gastric fluids of weanling pigs. The degradation rates of G17 and G34 in the small intestinal fluids of suckling pigs were between 18 and 30%, and were significantly lower than the corresponding rates in the intestinal fluids of weanling and adult pigs, the latter were between 35 and 67%. Addition of defatted porcine colostrum or its components, the casein or acid-soluble fraction, inhibited gastrin degradation in the intestinal fluids with the casein fraction having highest inhibition potency. These results indicate that gastrin is stable in the GI lumen of the suckling pigs and porcine colostrum protects gastrin from luminal hydrolysis in the small intestine, suggesting a potential physiological role of luminally released gastrin in suckling animals.

Radon release from building materials in Hong Kong.

Indoor 222Rn in high-rise buildings originates inside the building materials, then diffuses gradually through the intergranular spaces of the material into the room atmosphere. Therefore, the radionuclide contents and the physical properties of the building materials are important for indoor 222Rn levels in Hong Kong. In this paper, the radionuclide contents of typical building materials used locally were determined by gamma spectrometry, and the results indicate that the average 226Ra, 232Th, and 40K contents in Hong Kong concrete are the highest known in the world. Physical properties, such as the emanation coefficients and 222Rn diffusion coefficients, were measured in these materials and they are not much different from those in other countries. The effect of surface coatings on 222Rn exhalation rate was studied and the observed reduction was from 2-68%. The 222Rn exhalation rate was found to increase steadily with temperature up to 50 degrees C; at 50 degrees C, the 222Rn exhalation rate can be as high as four times the rate at 20 degrees C.

Terrestrial gamma radiation dose in Hong Kong.

The first reactor of the Daya Bay nuclear power plant, 30 km from Hong Kong, is expected to begin operation in 1992. As a result, residents in Hong Kong are concerned with potential exposure to man-made and natural radiation. Therefore, the Radioisotope Unit of the University of Hong Kong performed studies to estimate Hong Kong's natural background radiation and the potential exposure to local residents, the results of which are presented here.

The structural specificity of carbohydrate in the initiation of rat sperm motility.

Mammalian spermatozoa are stored in the cauda epididymis (CE) in a quiescent state and become motile when diluted with seminal plasma upon ejaculation. The structural specificity of a variety of sugars and sugar derivatives as diluents that are capable of initiating a transition of CE spermatozoa from the quiescent to the actively motile state was examined. It was found that monosaccharides, except those containing less than five-carbon skeletons, were good motility initiators; a trisaccharide tested showed reduced activity. The initiation activity was also independent of the structural stereospecificity and the nutritional value of the sugar. Based on these observations, a mechanism involving a receptor which handles sugar transport or sugar recognition in a transport process is proposed to be responsible for generating a signal that triggers CE spermatozoal motility.

Effect of gossypol on boar spermatozoal adenosine triphosphate metabolism.

The effect of gossypol on boar spermatozoal adenosine triphosphate (ATP) metabolism was investigated. Gossypol has little effect on the activities of the total spermatozoal ATPase, the spermatozoal flagellar ATPase, and the mitochondrial fragment ATPase. The membrane ATPase, being exceedingly low, has not been considered for its susceptibility toward gossypol. Gossypol uncouples spermatozoal oxidative phosphorylation. A biphasic response (stimulation at low concentration and inhibition at high concentration) has been noticed in anaerobic lactate production and hypotonically treated spermatozoal mitochondrial ATPase activity. The ATP content, either under aerobic or anaerobic condition was reduced by gossypol with the reduction threshold of ATP more sensitive in the latter. The reduction of ATP follows two different reaction kinetics in which it is stabilized at moderate gossypol concentrations but progresses along with time at high concentrations. Since the drop in motility is more sensitive than the drop in ATP content and since the flagellar ATPase is not significantly inhibited by gossypol, a motility controlling component that is more sensitive to gossypol antimotility inhibition is proposed.

Assay of progressive motion of boar spermatozoa.

The motility of ejaculated boar spermatozoa was assayed by measuring the number of organisms which have entered a capillary tube in an experimental setup with the spermatozoal suspension as well as the capillary content containing the same chemically defined motility medium. This medium, used both for washing and suspending spermatozoa, contained only an isotonic tris HCl (isotris) buffer at pH 7.0. The recommended assay conditions are the following: (1) wash the spermatozoa three times with isotris buffer, (2) suspend the spermatozoa in a concentration of 10(6) spermatozoa/ml, and (3) assay at 25 degrees C with an incubation period of 60 min.

Actin and myosin-linked calcium regulation in the nematode Caenorhabditis elegans. Biochemical and structural properties of native filaments and purified proteins.

Calcium regulation of actomyosin activity in the nematode, Caenorhabditis elegans, has been studied with purified proteins and crude thin filaments. Actin and tropomyosin have been purified from C. elegans and shown to be similar in most respects to actin and tropomyosin from rabbit skeletal muscle. The actin comigrates with rabbit actin on polyacrylamide-sodium dodecyl sulfate gel electrophoresis, forms similar filaments and paracrystals, and activates the Mg2+-ATPase of rabbit myosin heads as efficiently as rabbit actin. Nematode tropomyosin has a greater apparent molecular weight (estimated by mobility on polyacrylamide-sodium dodecyl sulfate gels) than the rabbit protein, yet it forms Mg2+-paracrystals with a slightly shorter periodicity. Native thin filaments extracted from nematodes activate rabbit myosin subfragment 1 Mg2+-ATPase in a calcium sensitive manner; the extent of activation is threefold greater in 0.2 mM CaCl2 than in the absence of calcium. This observation suggests that the thin filaments contain components which are functionally equivalent to vertebrate troponins. Calcium is also required for maximal activation of the Mg2+-ATPase of purified nematode myosin by pure rabbit F-actin. C. elegans therefore has both myosin and thin filament-linked calcium regulatory systems. The origin of the actin, tropomyosin, and myosin from different tissues and the use of genetic analysis to answer questions about assembly and function in vivo are discussed.

Electron paramagnetic resonance of nitrogenase and nitrogenase components from Clostridium pasteurianum W5 and Azotobacter vinelandii OP.

The electron paramagnetic resonance of nitrogenase components, separately and together with the other reactants in the nitrogenase system (namely, reductant and Mg.ATP), have been examined at low temperatures (<20 degrees K). The MoFe protein, component I or molybdoferredoxin, in the oxidized (but not oxygen-inactivated) state yields signals with g-values of 4.3, 3.7, and 2.01, and when reduced has no observable electron paramagnetic resonance. The Fe protein, component II, or azoferredoxin, yields a signal with g-values of 2.05, 1.94, and 1.89 in the reduced state that is converted by Mg.ATP into an axial signal with g-values near 2.05 and 1.94, and a second split signal near g = 4.3. The Fe protein has no definite electron paramagnetic resonance in the oxidized (not oxygen-denatured) state under these conditions. The Mg.ATP complex of reduced Fe protein reduces the MoFe protein, whereas dithionite alone does not reduce the MoFe protein. Reoxidation of the system by substrate leads to disappearance of the Fe protein signal and the reappearance of the MoFe protein signal. Thus Mg.ATP, which is hydrolyzed during substrate reduction, converts the Fe protein to a reductant capable of transferring electrons to MoFe protein, after which substrate reduction occurs.