Size distributions and growth of natural and chernobylderived submicron aerosols in Tennessee

The median aerodynamic diameters of aerosol-associated SO₄²⁻, ²¹⁰Pb, ⁷Be, and Chernobyl-derived fission products in Tennessee were examined using high-volume cascade impactors. Regardless of season, the ‘steady-state’ size distributions of SO₄²⁻ shifted to larger sizes than found for either ²¹⁰Pb or ⁷Be, and for ⁷Be sizes showed a weaker seasonal dependency than for either SO₄²⁻ or ²¹⁰Pb. It is suggested that the size differences are the result of the different spatial distributions of these species in the atmosphere during aerosol formation and growth. The mean growth rate of aerosols between ≈0·2 μm and ≈0·4 μm was estimated to be ≈0·03 μm d⁻¹ from a comparison of the median diameter of ²¹⁰Pb when it is first produced from ²¹⁴Po decay with the median diameter after a mean atmospheric residence time of 7 d.Measurements of the size distributions of radioactive aerosols released during the nuclear reactor accident at Chernobyl were made in May and June 1986, and provided rare information on growth rates of aerosols released to the atmosphere over a short time period. A linear growth rate of ≈0·013 μm d⁻¹ was observed in the lower troposphere after the median diameter had reached ≈0·4 μm. Chernobyl-derived ^134,137Cs was less soluble than ⁷Be, suggesting the presence of an aerosol core derived from reactor constituents. An analysis of time intervals and trends in both concentrations and isotopic ratios, when compared to Soviet data on the time course of radioactive releases from the damaged reactor, suggested that the large releases which occurred in early May were an important component of the globally transported ¹³⁷Cs.     

Determination of dose rates from natural radionuclides in dental materials

Different types of materials used for dental prosthetics restoration, including feldspathic ceramics, glass ceramics, zirconia-based ceramics, alumina-based ceramics, and resin-based materials, were investigated with regard to content of natural radionuclides by means of thermoluminescence beta dosimetry and gamma spectrometry. The gross beta dose rate from feldspathic and glass ceramics was about ten times higher than the background measurement, whereas resin-based materials generated negligible beta dose rate, similarly to natural tooth samples. The specific activity of uranium and thorium was significantly below the levels found in the period when addition of uranium to dental porcelain materials was still permitted. The high-beta dose levels observed in feldspathic porcelains and glass ceramics are thus mainly ascribable to (40)K, naturally present in these specimens. Although the measured values are below the recommended limits, results indicate that patients with prostheses are subject to higher dose levels than other members of the population. Alumina- and zirconia-based ceramics might be a promising alternative, as they have generally lower beta dose rates than the conventional porcelain materials. However, the dosimetry results, which imply the presence of inhomogeneously distributed clusters of radionuclides in the sample matrix, and the still unsuitable structural properties call for further optimization of these materials.     

Viruses in wastewater aerosols

Agricultural land application of wastewater is becoming a widely used means of dealing with water scarcity and diminishing sources of unpolluted water. One of the most common forms of land application—sprinkler irrigation—poses an environmental problems in that it created wastewater aerosols. Air sampling experiments done at distances of up to 100 meters from wastewater irrigation sprinklers have detected several airborne enteroviruses: echovirus 1, 25, 29; poliovirus II, and coxsackie B1. The levels of airborne viruses found in wastewater aerosols may be potentially hazardous at any level. Since the impact of these findings on public health is not clear, epidemiological investigations by standard techniques should be conducted. It is estimated that the number of viruses isolated in environmental samples may be smaller by one or two orders of magnitude (90%–99%) than their actual number due to the limitations of virus recovery procedures. The unvailability of a reliable indicator microorganism which fulfills all the requirements for a biological indicator also makes it difficult to determine the virus level in the aerosols. Thus the scientific knowledge available today is insufficient to determine with certainty that no public health risk is created by wastewater aerosols. A comprehensive prospective study will, in all likelihood, provide answers to most questions and make it possible to assess more reliably the extent of the health risk due to wastewater aerosols.     

Gamma dose rates and distribution of natural radionuclides in sand beaches--Ilha Grande, Southeastern Brazil

In order to study the process of dispersion and the activity concentration of 232Th and 238U series and 40K radionuclides in two island beaches in southeastern Brazil, analyses was made of sand samples of 0-10 cm profile, during a 12-month period. Moreover, the monthly variations of gamma dose rates were studied to determine the local environment absorbed dose rate. The average activity concentration of primordial radionuclides 232Th, 238U and 40K at Preta beach, they were 239, 121 and 110 Bq kg(-1), while at Dois Rios beach they were 48, 39 and 412 Bq kg(-1), respectively. The absorbed dose rate in air, observed at 1 m above the ground, ranged from 54 to 228 nGy h(-1) at Preta beach and from 39 to 110 nGy h(-1) at Dois Rios beach. The annual effective dose equivalent corresponding to Preta beach is 0.15 mSv a(-1) and to Dois Rios 0.08 mSv a(-1).     

Gamma radiation measurements and dose rates in commercially-used natural tiling rocks (granites)

The gamma radiation in samples of a variety of natural tiling rocks (granites) imported in Cyprus for use in the building industry was measured, employing high-resolution gamma-ray spectroscopy. The rock samples were pulverised, sealed in 1-l plastic Marinelli beakers, and measured in the laboratory with an accumulating time between 10 and 14 h each. From the measured gamma-ray spectra, activity concentrations were determined for (232)Th (range from 1 to 906 Bq kg(-1)), (238)U (from 1 to 588 Bq kg(-1)) and (40)K (from 50 to 1606 Bq kg(-1)). The total absorbed dose rates in air calculated from the concentrations of the three radionuclides ranged from 7 to 1209 nGy h(-1) for full utilization of the materials, from 4 to 605 nGy h(-1) for half utilization and from 2 to 302 nGy h(-1) for one quarter utilization. The total effective dose rates per person indoors were determined to be between 0.02 and 2.97 mSv y(-1) for half utilization of the materials. Applying dose criteria recently recommended by the EU for superficial materials, 25 of the samples meet the exemption dose limit of 0.3 mSv y(-1), two of them meet the upper dose limit of 1 mSv y(-1) and only one clearly exceeds this limit.     

Soil-to-plant transfer factors for natural radionuclides and stable elements in a Mediterranean area

The transfer factors (TF) for natural uranium isotopes (238U and 234U), thorium isotopes (232Th, 230Th and 228Th), and 226Ra were obtained in plant samples (grass-pasture) growing in granitic and alluvial soils around a disused uranium mine located in the Extremadura region in the south-west of Spain. Affected and non-affected areas of the mine presented large differences in the activity concentrations of radionuclides of the uranium series. We also determined transfer factors for several stable elements (essential and non-essential). A set of statistical tests were applied to validate the data. The results showed that the transfer factors for both the natural radionuclides and the stable elements are independent of the two substrate types involved and also of the two areas considered in the study.     

The adverse health effects of biological aerosols, other aerosols, and indoor microclimate on asthmatics and nonasthmatics

Asthmatic and nonasthmatic families in a representative community population sample have been monitored over a 2-year period using daily diaries. Simultaneous micro-indoor and outdoor monitoring has been conducted in a representative sample of houses for air pollutants, pollen, fungi, algae, and climate. Macromonitoring of air pollutants and pollen was conducted simultaneously. The relationship of indoor to outdoor and micro to macro factors can be demonstrated. Acute symptoms were strongly related to age, weakly related to sex, and not related to smoking habits. The qualitative relationship of these micro and macro factors to symptoms in asthmatic and nonasthmatic families have been explored. Suspended particulate matter and pollen were related to symptoms in asthmatics and nonasthmatics. Fungi might be related to symptoms as well. The use of gas stoves is qualitatively related to symptoms. Algae and other contaminants of evaporative coolers do not appear to be important in producing symptoms. More complex statistical analyses are required to determine interactions of these factors. Distinction has to be drawn between infectious episodes, allergic episodes, nonallergic but similar episodes, and asthmatic attacks. This study demonstrates the need for further investigations in this area.     

Preparation of size-selected fibers and fibrous aerosols for biological experiments

A size-selective procedure was developed for the preparation of fiber fractions of uniform size of chrysotile, crocidolite, amosite, and glass. The raw material was first ground to a suitable fineness, then suspended in liquids by ultrasonic agitation and separated by fiber diameter by means of slow sedimentation. The fractionation by fiber length was done by a vibrating sieve method. Fibrous aerosols of different size distributions could be prepared by using a vibrating bed aerosol generator.     

Effect of pollutant aerosols on spectral atmospheric transmissivity in Cairo

Spectral atmospheric transmissivity has been greatly affected by air pollutants in Cairo atmosphere. This has been studied by measuring the energy of solar radiation, selecting four bands at different wave-lenghts. Three selected bands are in the visible (blue 440 nm., green 500 nm., and red 640 nm.), while the fourth band is in the infrared region (880 nm.). The Cairo atmosphere was found to be greatly polluted by fine particulates, which were held in suspension for a longer time than coarse pollutants. The transmissivity of the spectral radiation showed a clear wavelength dependence comparable to particulate sizes found in different concentrations. The transmissivity was found to be highest for the infrared band, followed by the red and then the green bands, and the lowest was for the blue band.     

Measurement of semivolatile carbonaceous aerosols and its implications: A review

Measurement of carbonaceous aerosols is complicated by positive and negative artifacts. An organic denuder with high efficiency for removing gaseous organics is an effective approach to eliminate the positive artifact, and it is a precondition for the accurate determination of SVOC by an adsorbent backup filter. Evaluations of different configurations of the organic denuder, and SVOC determined by different denuder-based samplers, both integrated and semi-continuous, are reviewed. A new equation for determination of the denuder efficiency is estimated, considering the efficiency of removing both the gaseous organics that could be adsorbed by the quartz and the gaseous passing through the quartz that could be subsequently adsorbed by the backup adsorbent filter. The origin of OC on the backup quartz filter, behind either quartz or Teflon filter, is quantitatively evaluated by the denuder-based method based on the data published. The backup-OC is shown to be dominated by either gaseous organics passing through the front filter or the evaporated particulate organic carbon depending on the sampling environment.     

Mechanisms of desorption of 134Cs and 85Sr aerosols deposited on urban surfaces

The radioactive isotopes of cesium and strontium may be deposited on urban surfaces in the case of an accidental atmospheric discharge from a nuclear facility and thus imply a health hazard. In order to handle the decontamination of these surfaces, we have carried out experiments under controlled conditions on tiles and concrete and we have studied.the physical and chemical mechanisms at the solid-liquid interface. The deposition of radionuclides was carried out in the form of aerosols indicating an accidental source term. Their desorption by rainwater is low in all cases, of the order of 5-6% for cesium for any material and 29 and 12% for strontium on tile and concrete, respectively. The low desorption values of cesium may be explained by the strong bonding that occurs with the silicates constituting the tile due to virtually irreversible processes of exchange of ions and by the formation of insoluble complexes with the C--S-H gel of concrete. The strontium-tile bonds are weaker, while strontium precipitates with the carbonates of concrete in the form of SrCO3. In view of these characteristics, washing solutions with high concentrations of chloride and oxalate of ammonium chosen for their ion-exchanging and sequestering properties were tested on these surfaces. The desorption of cesium improved strongly since it reached 70% on tile and 90% on concrete after 24h of contact, which is consistent with our knowledge of the; bonds between this element and the surfaces. Strontium, given the greater complexity of physical and chemical forms that it may take is less well desorbed. The ammonium chloride improves the desorption (50% and 40%, for tile and concrete, respectively) but the oxalate, while it does not affect desorption on the tiles, decreases that on the concrete since by strongly etching the concrete, it causes the release of carbonate ions that precipitate with strontium.     

Predictions of evaporative loss rates of solutes in stagnant and turbulent waters in relation to rates of reference materials

A previously published kinetic model for evaporative rates of substances into air leads to the estimation of the dependence of solute transfer coefficients on turbulence to the system. The ratios of the transfer coefficients of all solutes become insensitive to air turbulence and to water mixing either when they have comparable Henry's law constants or when their Henry's law constants are sufficiently low, but not otherwise. Confirming data are presented and methods for simplifying the estimation of transfer coefficients are discussed.     

Radionuclide transfer to animal products: revised recommended transfer coefficient values

A compilation has been undertaken of data which can be used to derive animal product transfer coefficients for radionuclides, including an extensive review of Russian language information. The resultant database has been used to provide recommended transfer coefficient values for a range of radionuclides to (i) cow, sheep and goat milk, (ii) meat (muscle) of cattle, sheep, goats, pigs and poultry and (iii) eggs. The values are used in a new IAEA handbook on transfer parameters which replaces that referred to as ‘TRS 364’. The paper outlines the approaches and procedures used to identify and collate data, and assumptions used. There are notable differences between the TRS 364 ‘expected’ values and the recommended values in the revised Handbook from the new database. Of the recommended values, three milk values are at least an order of magnitude higher than the TRS 364 values (Cr, Pu (cow) Pu (sheep)) and one milk value is lower (Ni (cow)). For meat, four values (Am, Cd, Sb (beef) I (pork)) are at least an order of magnitude higher than the TRS 364 values and eight values are at least an order of magnitude lower (Ru, Pu (beef), Ru, Sr, Zn (sheep), Ru, Sr (pork), Mn (poultry)). Many data gaps remain.     

Full-spectrum analysis of natural gamma-ray spectra

In this paper, a new system to measure natural gamma-radiation in situ will be presented. This system combines a high-efficiency BGO scintillation detector with full-spectrum data analysis (FSA). This technique uses the (nearly) full spectral shape and the so-called 'standard spectra' to calculate the activity concentrations of 40K, 232Th and 238U present in a geological matrix (sediment, rock, etc.). We describe the FSA and the determination of the standard spectra. Standard spectra are constructed for various geometries and a comparison in intensity and shape will be made. The performance of such a system has been compared to a more traditional system, consisting of a NaI detector in combination with the 'windows' analysis. For count rates typically encountered in field experiments, the same accuracy is obtained 10-20 times faster using the new system. This allows for shorter integration times and hence shorter measurements or a better spatial resolution. The applicability of such a system will be illustrated via an example of an airborne experiment in which the new system produced results comparable to those of much larger traditional systems. This paper will conclude with a discussion of the current status of the system and an outlook for future research.     

Weather-dependent change of cesium,strontium, barium and tellurium contamination deposited as aerosols on various cultures

Various types of plants (wheat, bean, lettuce, radish and grass) were contaminated by dry deposition of radioactive aerosols (¹³⁷Cs, ⁸⁵Sr, ¹³³Ba and ^123mTe) in order to supplement the radioecological data necessary for operational post-accidental codes. A few days after deposition, rainfalls were applied to these cultures to evaluate the influence of some characteristics of the rain on the contamination of the culture over time. On the other hand, for wheat and bean, the influence of the humidity condition of the foliage at the contamination time was considered. For a given plant species at a given vegetative stage, the four radionuclides were intercepted in an identical way. The interception varied from 30% for bean (young sprout) to 80% for lettuce (near maturity). The global transfer factor values were dependent on both the radionuclides and the plant species; nevertheless, a higher value was obtained for cesium, regardless of the plant and the rainfall (from 0.006 m² kg_fresh⁻¹ for wheat-grains – contaminated at the shooting stage – or for bean-pods – contaminated at the pre-flowering stage – to 0.1 m² kg_fresh⁻¹ for a whole lettuce). The analysis of the results allowed us on the one hand, to extract parameter values of the foliar transfer directly usable in operational codes, in particular those relating to barium and tellurium, unknown until then, and on the other hand, to lay the foundations of a future, more mechanistic model, taking into account the foliar processes in a finer way.     

Treatment of wastewater by natural systems

Experimental results from a pilot-scale constructed wetland (CW) treatment plant have been described. The study was conducted at two different systems: continuous and batch. In the continuous system, the treatment yields were monitored in different loading conditions in 1-year period. The pilot plant consists of two serially connected tanks settled up with fillers; Cyperus was used as treatment media and wastewater between the two tanks was recycled periodically. Chemical oxygen demand (COD) and suspended solid (SS) removal efficiencies were obtained as 90% and 95%, respectively. The effluent COD concentration at an average loading of 122 g COD/m2 day was satisfactory for the Turkish Water Pollution Control Regulation. This means that a 0.8 m2 of garden area per person is required. Other removal values for the same conditions were as follows: total Kjeldahl nitrogen (TKN) was 77%, total nitrogen (TN) was 61%, and PO4(3-) -P was 39%. The batch experimental systems consist of 12 pairs of serially connected tanks, with each pair having a surface area of 1 m2. Each set was filled with sewage once a day, and the wastewater between the paired tanks was recycled periodically by the pump. Each pair of tanks was filled with materials such as gravel, peat, and perlite. Seven of them were vegetated with Phragmites, Cyperus, Rush, Iris, Lolium, Canna, and Paspalum, while the other five were not seeded. The best performances were obtained by Iris for COD (% 94), by Canna for ammonia nitrogen (% 98), and by Iris for total nitrogen (% 90) and phosphorus (% 55) removal.     

Weather-dependent change of cesium, strontium, barium and tellurium contamination deposited as aerosols on various cultures

Various types of plants (wheat, bean, lettuce, radish and grass) were contaminated by dry deposition of radioactive aerosols ((137)Cs, (85)Sr, (133)Ba and (123 m)Te) in order to supplement the radio-ecological data necessary for operational post-accidental codes. A few days after deposition, rainfalls were applied to these cultures to evaluate the influence of some characteristics of the rain on the contamination of the culture over time. On the other hand, for wheat and bean, the influence of the humidity condition of the foliage at the contamination time was considered. For a given plant species at a given vegetative stage, the four radionuclides were intercepted in an identical way. The interception varied from 30% for bean (young sprout) to 80% for lettuce (near maturity). The global transfer factor values were dependent on both the radionuclides and the plant species; nevertheless, a higher value was obtained for cesium, regardless of the plant and the rainfall (from 0.006 m(2)kg(fresh)(-1) for wheat-grains - contaminated at the shooting stage - or for bean-pods - contaminated at the pre-flowering stage - to 0.1m(2)kg(fresh)(-1) for a whole lettuce). The analysis of the results allowed us on the one hand, to extract parameter values of the foliar transfer directly usable in operational codes, in particular those relating to barium and tellurium, unknown until then, and on the other hand, to lay the foundations of a future, more mechanistic model, taking into account the foliar processes in a finer way.     

Generic approaches to transfer

A review of methods which have been used to describe and predict transfer of radionuclides in biota was undertaken. The intent was to identify approaches that might prove useful in extending predictive estimates to other organisms and environments. Empirical approaches, such as found in the use of transfer factors, were examined. Kinetic methodologies were also presented. Allometric functions, with their ability to make broad generalizations, were also discussed. Data from several earlier radioecological assessments were tested for their potential utility in developing allometric relationships, with the result implying that such an approach might prove useful.     

Influence of rainfall characteristics on elimination of aerosols of cesium, strontium, barium and tellurium deposited on grassland

This work is aimed at quantifying foliar transfer of cesium, strontium, barium and tellurium under the influence of rainfall characteristics (intensity, frequency and time elapsed between contamination and first rainfall). Grassland boxes were contaminated by dry deposition of multi-element aerosols of (137)Cs, (85)Sr, (133)Ba and (123m)Te. They were grown in a greenhouse under controlled conditions. The treatments consisted of mowing and applying rainfalls (8 and 30 mmh(-1)) at different times after the contamination. At a leaf area index of 5.9+/-1.9, interception of the aerosols was similar for the 4 radionuclides (83.8+/-5.9%). Dew produced significant radionuclide accumulation in the base of the vegetation and transfer to the soil. For moderate intensity, an early (2 days after contamination) first rainfall was as efficient, in terms of leaf wash-off, as a longer rainfall occurring later (6 days after contamination). For early rainfalls, eliminated activities were comparable because the influence of rain intensity was compensated by rain duration. However, for late rainfalls, wash-off efficiency increased with rainfall intensity. Total transfer factors (TTF) were determined on whole grass immediately after 4 rainfalls and at harvest. After 4 medium intensity rainfalls, rain frequency did not influence total transfer factors (TTF) of strontium, barium and tellurium (about 0.2, 0.3 and 0.35 Bq kg(fresh weight)(-1) by Bq m(-2), respectively). Cesium TTF value was lower in the case of a weekly rain (0.1 against 0.2 Bq kg(fresh weight)(-1) by Bqm(-2)). TTF values were similar for twice-a-week rainfalls, whatever their intensity. They were higher for weekly rains of high intensity (between 0.3 and 0.75 Bq kg(fresh weight)(-1) by Bqm(-2) against 0.1-0.35 Bq kg(fresh weight)(-1) by Bq m(-2), depending on the radionuclides). TTF values attested that wash-off was more efficient when rainfalls lasted longer. Field loss on the top of the leaves was well described by an offset exponential model. The half-lives varied with rainfall characteristics from 4 days for cesium, strontium and barium to 20 days for tellurium. The offset value varied between 0% for tellurium (high intensity rainfalls) and 14% for cesium (medium intensity rainfalls).     

Measurements of major ion concentration in settled coarse particles and aerosols at a semiarid rural site in India

Deposition rates and deposition velocities of water-soluble ions (F, Cl, NO3, SO4, NH4, Ca, Mg, Na and K) were measured at a rural site (Gopalpura, Agra). Dry deposition samples were collected throughout the year from December 1995 to August 1997, while the aerosol samples were collected only during the winter season of 1996. Surrogate technique was used to collect the dry deposition samples, while aerosol samples were collected on PTFE membrane filter. Deposition velocities (Vd) of SO4 and NO3 are < or = 0.01 m s(-1) while Ca, Mg, Na, K, NH4, F and Cl exhibit greater than 0.01 m s(-1) Equivalent concentration ratios of K/Na, Ca/Na and Mg/Na conform with the corresponding ratios of local soil, indicating the dominant contribution of local sources. Deposition rates are maximum in winter, followed by summer and monsoon. No significant differences are found in dry deposition rates of all ions or in atmospheric concentrations of soil-derived elements with respect to wind direction. However, in aerosols, concentrations of F, Cl, NO3 and SO4 are higher with winds from southwesterly and westerly directions corresponding to pollution sources located in these directions. Deposition data have been used to calculate the critical load of S and N for soil with respect to Triticum vulgaris. The critical load of actual acidity was found to be 622.4 eq ha(-1) year(-1) within the range of 500-1,000 eq ha(-1) year(-1) as assessed by the RAINS-Asia model for this region. The present load of S and N (77.4 and 86.4 eq ha(-1) year(-1)) was much lower than the critical load of S and N (622.4 and 2,000 eq ha(-1) year(-1)), indicating that at present there is no harmful effect on ecosystem structure and function.