Thoron in the Environment

Thoron (²²⁰Rn), an isotope of the radon family, is produced in the earth’s crust at a rate comparable to that of common radon (²²²Rn). Thoron’s average activity concentration in soil gas and ground-level outside air is comparable to that of radon. Recent data from Europe and the United States indicate that in terms of the energy of the alpha particle decays of thoron’s progeny, its concentration in indoor air is significant, typically about half that due to radon progeny. This paper reviews current knowledge about thoron and its progeny in the outdoor and indoor environments and discusses issues involved in assessing whether or not it is a significant indoor pollutant.     

Annual and seasonal trends in chemical composition of precipitation in Japan during 1989–1998

Annual and seasonal trends were discussed for precipitation chemistry in Japan on the basis of a nationwide monitoring network by Japan Environment Agency. For this analysis, 17 sites, selected from the 23 network sites after evaluation of data completeness for the present purpose, were grouped into four areas in terms of the sea which could characterize each area: the Pacific Ocean, the Japan Sea, the Seto Inland Sea and the East China Sea areas. Major ion concentrations at each site were subjected to least-squares multiple regression analysis, and discussion was principally focused on the area-groups. Each area showed significant (p<0.05) decreasing trends in non-sea-salt sulfate (nss-SO₄²⁻) concentrations with the annual mean change rate of −3.0% yr⁻¹, whereas no significant trends were detected for NO₃⁻ at 59% of the sites. Ammonium (NH₄⁺) showed significant increasing trends for 35%, and decreasing trends for 18% of the sites; and, the maximum change rate of 3.8% yr⁻¹ was recorded in the Pacific Ocean area. Non-sea-salt calcium (nss-Ca²⁺) concentrations significantly decreased in northern and some industrialized areas. Both the annual cycle-amplitudes and effects of precipitation amounts were significant for the four ions at almost all sites. The maximum concentrations of nss-SO₄²⁻ and -Ca²⁺ occurred from winter to spring at most sites. The seasons when the maximum concentrations of NO₃⁻ and NH₄⁺ occurred, were found to differ from area to area. Furthermore, the trends in precipitation nss-SO₄²⁻, and NO₃⁻ were qualitatively consistent with those of anthropogenic emissions of SO₂, and NO_x in Japan, respectively.     

Assessment of 222Rn emanation from ore body and backfill tailings in low-grade underground uranium mine

This paper presents a comparative study of ²²²Rn emanation from the ore and backfill tailings in an underground uranium mine located at Jaduguda, India. The effects of surface area, porosity, ²²⁶Ra and moisture contents on ²²²Rn emanation rate were examined. The study revealed that the bulk porosity of backfill tailings is more than two orders of magnitude than that of the ore. The geometric mean radon emanation rates from the ore body and backfill tailings were found to be 10.01?×?10^?3 and 1.03 Bq m^?2 s^?1, respectively. Significant positive linear correlations between ²²²Rn emanation rate and the ²²⁶Ra content of ore and tailings were observed. For normalised ²²⁶Ra content, the ²²²Rn emanation rate from tailings was found to be 283 times higher than the ore due to higher bulk porosity and surface area. The relative radon emanation from the tailings with moisture fraction of 0.14 was found to be 2.4 times higher than the oven-dried tailings. The study suggested that the mill tailings used as a backfill material significantly contributes to radon emanation as compared to the ore body itself and the ²²⁶Ra content and bulk porosity are the dominant factors for radon emanation into the mine atmosphere.     

Basement Ventilation Needed to Lower Indoor Radon to Acceptable Levels

Although many remedial measures have been proposed for excessive Indoor ²²²Rn concentrations, their general effectiveness in given situations is not well established, In part because of the number and complexity of the factors that influence Indoor ²²²Rn. The strategy considered here is the use of basement ventilation to control upstairs Indoor radioactivity. A simple two-compartment model is described and used to derive ventilation rates that are needed to lower radon concentrations to specified levels. Previously published indoor radon measurements are used to derive the parameters needed for the calculations. The results of the two compartment model differ typically by a factor of two from the simpler, more often used one-compartment approximation.     

Specific accumulation of polychlorinated biphenyls and organochlorine pesticides in Japanese common squid as a bioindicator

Organochlorines (OCs) representing Persistent Organic Pollutants (POPs) such as PCBs (polychlorinated biphenyls), DDTs (DDT and its metabolites), CHLs (chlordane compounds), HCHs (hexachlorocyclohexane isomers) and HCB (hexachlorobenzene) were determined in the liver of Japanese common squid (Todarodes pacificus) collected from the waters around Japan (Japan Sea and western North Pacific Ocean). Among OCs concentrations, PCBs (upto 5600 ng/g lipid wt.) were the highest, and those of other OCs were in the order of DDT> CHLs > HCHs > HCB. Studies on growth trend and seasonal variation of OCs in this species suggest a rapid reflection of the pollution levels in seawater where and when they were collected, regardless of body-length and time of collection. These results indicate that Japanese common squid is a suitable bioindicator for monitoring OCs pollution in waters around Japan. With regard to the geographical distribution of OCs in this species collected from waters around Japan, OCs concentrations in specimens from Japan Sea were higher than those from the Pacific Ocean. This result might reflect some existing of local pollution sources of OCs around Japan Sea, and slower water exchange between Japan Sea and open ocean.     

Relationship between Sulfate Aerosol and Visibility

A PM₁₀ monitoring network was established throughout the South Coast Air Basin (SOCAB) in the greater Los Angeles region during the calendar year 1986. Annual average PM₁₀ mass concentrations within the Los Angeles metropolitan area ranged from 47.0 µg m^-3 along the coast to 87.4 µg m^-3 at Rubldoux, the furthest inland monitoring station. Measurements made at San Nicolas Island suggest that regional background aerosol contributes between 28 to 44 percent of the PM₁₀ aerosol at monitoring sites In the SOCAB over the long term average. Five major aerosol components (carbonaceous material, NO^- ₃, SO⁼ ₄, NH⁺ ₄, and soil-related material) account for greater than 80 percent of the annual average PM₁₀ mass at all on-land monitoring stations. Peak 24-h average mass concentrations of nearly 300 µg m^-3 were observed at inland locations, with lower peak values (?130–150 µg m^-3) measured along the coast. Peak-day aerosol composition was characterized by increased NO^- ₃ Ion and associated ammonium ion levels, as compared to the annual average. There appears to be only a weak dependence of PM₁₀ mass concentration on season of the year. This lack of a pronounced seasonal dependence results from the complex and contradictory seasonal variations in the major chemical components (carbonaceous material, nitrate, sulfate, ammonium ion and crustal material). At most sites within the Los Angeles metropolitan area, PM₁₀ mass concentrations exceeded both the annual and 24-h average federal and state of California PM₁₀ regulatory standards.     

Radiostrontium monitoring of bivalves from the Pacific coast of eastern Japan

In early April 2011, radiostrontium was accidentally released from the Fukushima Daiichi Nuclear Power Plant to the Pacific coast of eastern Japan. We developed a simple procedure to analyze radiostrontium levels in marine mussels (Septifer virgatus) and seawater using crown ether (Sr Resin; Eichrom). Then, we used our method to describe the spatial and temporal distribution of radiostrontium in mussels and seawater on the Pacific coast of eastern Japan from 2011 to 2013 and for 2015. Activity of ⁹⁰Sr in mussels and seawater decreased with distance from the Fukushima Daiichi Nuclear Power Plant and between 2011 and 2013 tended to be higher in areas south of the Fukushima Daiichi Nuclear Power Plant than to the north of it. Activity in mussels and seawater also tended to decrease from 2011 to 2013 and by 2015 had reached levels experienced prior to the Fukushima accident. Our results suggest that radiostrontium discharged from the Fukushima Daiichi Nuclear Power Plant was dispersed by coastal currents in a southerly direction along the Pacific coast of eastern Japan from 2011 to 2013, following which its activity decreased to background levels by 2015.     

A study on nighttime–daytime PM10 concentration and elemental composition in relation to atmospheric dispersion in the urban area of Milan (Italy)

In this paper, results on a PM10 daytime–nighttime measurement campaign carried out in Milan to study the evolution of PM10 concentration and composition in relation to atmospheric dispersion conditions are shown. To account for the evolution of atmospheric dispersion conditions, Radon hourly concentration measurements were performed. The significant correlation between PM10 and ²²²Rn daytime concentrations evidences the dominant role of atmospheric dispersion in determining the temporal variation of PM10 levels. Whenever ²²²Rn concentrations accumulate during the night (indicating the formation of nocturnal atmospheric stability conditions), PM10 concentrations are higher than those registered during the daytime before, despite a decrease in emissions from active sources. On the contrary, when ²²²Rn concentrations do not accumulate during night hours, PM10 levels are lower than those measured during the daytime before.As concerns the average elemental concentrations (in ng m⁻³), the nighttime–daytime variations are in the range −17% to +37%; during the night, soil-related elements (Al, Si, Ca, Ti) decrease while anthropogenic elements (Zn, Cu, Fe, Pb) increase.A case study concerning a ‘green’ Sunday (when traffic was forbidden from 8 a.m. to 8 p.m.) is also discussed. The difference of PM10 concentration and elemental composition registered during the ‘green’ Sunday daytime and the following nighttime, together with the information on atmospheric dilution power obtained by Radon measurements, allowed the characterisation of the traffic source elemental profile and increased the comprehension of the low effectiveness of some PM10 reduction strategies.     

Diurnal and seasonal variation of short-lived radon progeny concentration and atmospheric temporal variations of 210Pb and 7Be in Egypt

During a one-year period, from November 1998 upto October 1999, the atmospheric activity concentrations of the short-lived (²²²Rn)-progeny (²¹⁸Po, ²¹⁴Pb, ²¹⁴Po) were measured every 4 h in the open air, using α-spectrometry. The concentration data of short-lived radon progeny together with meteorological variables (relative humidity, air temperature, and wind speed) were used for a comprehensive regression analysis of daily time variation of radioactivity in the air. The seasonal concentration pattern of all short-lived radon progeny shows the same trend for diurnal variation with higher values at night and early morning hours compared with lower values at noon and in afternoon. The activity concentrations were observed to be higher during the winter months (November–January) than in other seasons. The mean activity concentrations of ²¹⁸Po, ²¹⁴Pb and ²¹⁴Po within the whole year were found to be 6.7±0.8, 4.9±0.5 and 4.4±0.3 Bq m⁻³, respectively.Also, within that time period, approximately 120 samples were analysed to determine the concentrations of the long-lived radon decay product ²¹⁰Pb and the cosmogenic radionuclide ⁷Be using a single-filter technique. The course of ²¹⁰Pb air concentration is characterized by higher values in autumn/winter season and lower values in spring/summer season. The seasonal concentration pattern of ⁷Be reaches regular maximum values in the spring to early summer months. The annual average concentration values of ²¹⁰Pb and ⁷Be have been found to be 0.37±0.06 and 2.0±0.09 mBq m⁻³, respectively. A mean aerosol mass concentration of 36.6±6.2 μg m⁻³ was also determined during the measurements of the long-lived radionuclides. The majority of attached ²¹⁰Pb and ⁷Be were observed at lower aerosol mass concentrations while small fractions of attached activities were found to be associated with the higher mass concentrations.     

Sea salt concentrations across the European continent

The oceans are a major source for particles that play an important role in many atmospheric processes. In Europe sea salt may contribute significantly to particulate matter concentrations. We have compiled sodium concentration data as a tracer for sea salt for 89 sites in Europe to provide more insight in the distribution of sea salt across Europe. The annual average sea salt concentrations above land were estimated to range between 0.3 and almost 13 μg m^?3. Maximum concentrations are found at the Irish coast. At coastal sites along the Atlantic and North Sea coast concentrations tend to be around 5 μg m^?3. More inland locations up to about 300 km away from the coast tend to show concentrations between 2 and 5 μg m^?3, whereas sites further away from the coast are characterized by lower concentrations. An analysis of the representativity of the data with respect to a long term average showed that the long average is associated with a standard deviation of around 15%. The compilation of observations provides an improved overview of sea salt concentrations in Europe as well as an improved basis for model validation. Verification of the results of the LOTOS-EUROS model learned that the model represents well the spatial variability of the observed sea salt concentrations very well. However, the absolute concentrations are significantly overestimated due to large uncertainties in the emission and dry deposition parameterizations. Using the high explained variability in the gradients across Europe, the bias-corrected modelled distribution serves as a best estimate of the sea salt distribution across Europe for 2005.     

Investigation of the soil radon variation during the winter months in Sapporo, Japan

Soil radon was measured from late October 2000 to January 2001 at three test sites on the campus of Hokkaido University in Sapporo, Japan. Factors affecting radon concentrations were investigated with relation to meteorological data, as well as soil 226Ra content, mineral composition, water content, and pH, Eh and conductivity. Soil radon varied with time and with sampling site appreciably, in a manner unaltered by the surface geology. However, the ratio of radon isotopes (220Rn/222Rn) in the soil was constant within each sampling site, regardless of varying concentration of these nuclides during the monitoring period. Snow covering on the soil surfaces may affect the 222Rn concentration.     

Seasonal cycle and composition of background fine particles along the west coast of the US

We used aerosol data from 4 sites along the west coast of the U.S. to evaluate the role of transport, seasonal pattern, chemical composition and possible trends in the marine background aerosol for the Pacific Northwest. For the Crater Lake samples, the data have been segregated using 10 day back isentropic trajectories to evaluate the role of transport. Our analysis of the segregated data indicates that the trajectories can successfully separate “locally influenced” from “marine background” aerosol, but are not able to identify a significant difference in the mean concentrations during marine vs Asian transport pathways.The background marine aerosol has an annual mean and median concentrations of 2.0 and 1.5 μg m⁻³, respectively, for particles less than 2.5 μm diameter. There is a seasonal pattern in all components of the aerosol mass, with a summer maximum and winter minimum. This pattern is most likely due to the strong seasonal pattern in precipitation, which peaks in winter, combined with enhanced sources in summer. The Crater Lake marine aerosol composition is dominated by organics (∼40% by mass), with smaller contributions from sulfates, mineral dust and elemental carbon. Analysis of the background marine aerosol found no apparent trend since 1988. This is in contrast to results reported by Prospero et al. (J. Geophys. Res. 108 (2003) 4019) for nss-SO₄²⁻ samples from Midway Island in the North Pacific. Comparison of the mean concentrations for each site shows that the Midway samples are significantly more influenced by Asian industrial sources of sulfur, compared to Crater Lake, which implies a substantial loss of nss-SO₄²⁻ from Asian sources that occurs during transit across the Pacific to Crater Lake due to precipitation scavenging.     

Estimating contribution of precipitation scavenging of atmospheric particulate mercury to mercury wet deposition in Japan

Mercury wet deposition is dependent on both the scavenging of divalent reactive gaseous mercury (RGM) and atmospheric particulate mercury (Hg(p)) by precipitation. Estimating the contribution of precipitation scavenging of RGM and Hg(p) is important for better understanding the causes of the regional and seasonal variations in mercury wet deposition. In this study, the contribution of Hg(p) scavenging was estimated on the basis of the scavenging ratios of other trace elements (i.e., Cd, Cu, Mn, Ni, Pb and V) existing entirely in particulate form. Their wet deposition fluxes and concentrations in air, which were measured concurrently from April 2004 to March 2005 at 10 sites in Japan, were used in this estimation. The monthly wet deposition flux of mercury at each site correlated with the amount of monthly precipitation, whereas the Hg(p) concentrations in air tended to decrease during summer. There was a significant correlation (P<0.001) among the calculated monthly average scavenging ratios of trace elements, and the values in each month at each site were similar. Therefore, it is assumed the monthly scavenging ratio of Hg(p) is equivalent to the mean value of other trace elements. Using this scavenging ratio (W), the wet deposition flux (F) due to Hg(p) scavenging in each month was calculated by F=WKP, where K and P are the Hg(p) concentration and amount of precipitation, respectively. Relatively large fluxes due to Hg(p) scavenging were observed at a highly industrial site and at sites on the Japan Sea coast, which are strongly affected by the local sources and the long-range transport from the Asian continent, respectively. However, on average, at the 10 sites, the contribution of Hg(p) scavenging to the annual mercury deposition flux was 26%, suggesting that mercury wet deposition in Japan is dominated by RGM scavenging. This RGM should originate mainly from the in situ oxidation of Hg⁰ in the atmosphere.     

Characterizing the Occurrence,Sources, and Variability of Radon in Pacific Northwest Homes

A compilation of data from earlier studies of 172 homes in the Pacific Northwest indicated that approximately 65 percent of the 46 homes tested in the Spokane River Valley/Rathdrum Prairie region of eastern Washington/northern Idaho had heating season indoor radon (²²²Rn) concentrations above the U. S. EPA guideline of 148 Bq m^?3 (4 pCi L^?1). A subset of 35 homes was selected for additional study. The primary source of indoor radon in the Spokane River Valley/Rathdrum Prairie was pressure-driven flow of soil gas containing moderate radon concentrations (geometric mean concentration of 16,000 Bq m^?3) from the highly permeable soils (geometric mean permeability of 5 × 10^?11 m²) surrounding the house substructures. Estimated soil gas entry rates ranged from 0.4 to 39 m³h^?1 and 1 percent to 21 percent of total building air infiltration. Radon from other sources, including domestic water supplies and building materials was negligible. In high radon homes, winter indoor levels averaged 13 times higher than summer concentrations, while in low radon homes winter levels averaged only 2.5 times higher. Short-term variations in indoor radon were observed to be dependent upon indoor-outdoor temperature differences, wind speed, and operation of forced-air furnace fans. Forced-air furnace operation, along with leaky return ducts and plenums, and openings between the substructure and upper floors enhanced mixing of radon-laden substructure air throughout the rest of the building.     

Chemical characteristics of cloud water over the Japan Sea and the Northwestern Pacific Ocean near the central part of Japan: airborne measurements

Cloud water was collected by aircraft over the Japan Sea and the Northwestern Pacific Ocean during the winter and early spring seasons. The concentrations of major ions in the cloud water were higher at cloud bases than at cloud tops. The equivalents based ratio of Na⁺/nssSO₄²⁻ and NO₃⁻/nssSO₄²⁻ at cloud bases was higher than that at cloud tops, whereas the nssCa²⁺/nssSO₄²⁻ ratio was higher at cloud tops. The concentrations of nssSO₄²⁻ were higher than those of NO₃⁻ over the Japan Sea. The ratio of NO₃⁻/nssSO₄²⁻ in the cloud water over the Pacific Ocean was higher than that over the Japan Sea. Especially, when the winter monsoon wind pressure pattern collapsed, the concentrations of NO₃⁻ were much higher than those of nssSO₄²⁻. The concentrations of peroxides in the cloud water ranged from below the detection limit to 6.2 μM, and were much lower than those in the fog water near the summit of Mt. Norikura during the summer season. Most of the samples showed the condition (NH₄⁺+nssCa²⁺)<(NO₃⁻+nssSO₄²⁻), which implies insufficient amounts of bases to neutralize the acids. Chloride loss in the cloud water was observed, and this may be caused by the deposition of HCl gas to the sea surface.     

Seasonal variation in the levels of organohalogen compounds in herring (Clupea harengus) from the Norwegian Sea

The Norwegian spring spawning (NSS) herring is an ecologically important fish stock in the Norwegian Sea, and with a catch volume exceeding one million tons a year it is also economically important and a valuable food source. In order to provide a baseline of the levels of contaminants in this fish stock, the levels of organohalogen compounds were determined in 800 individual herring sampled at 29 positions in the Norwegian Sea and off the coast of Norway. Due to seasonal migration, the herring were sampled where they were located during the different seasons. Concentrations of dioxins and dioxin-like PCBs, non-dioxin-like PCBs (PCB₇) and PBDEs were determined in fillet samples of individual herring, and found to be relatively low, with means (min-max) of 0.77 (0.24-3.5) ng TEQ kg⁻¹ wet weight (ww), 5.0 (1.4-24) μg kg⁻¹ ww and 0.47 (0.091-3.1) μg kg⁻¹ ww, respectively. The concentrations varied throughout the year due to the feeding- and spawning cycle: Starved, pre-spawning herring caught off the Norwegian coast in January-February had the highest levels and those caught in the Norwegian Sea in April-June, after further starvation and spawning, had the lowest levels. These results show that the concentrations of organohalogen compounds in NSS herring are relatively low and closely tied to their physiological condition, and that in the future regular monitoring of NSS herring should be made in the spawning areas off the Norwegian coast in late winter.     

Radon exhalation and ultrafine fraction of radon progeny in closed room air

The influence of ²²²Rn exhalation from walls and air exchange (low ventilation rates ν<0.3 h^-1) upon its concentration in room air has been considered. It was found that the radon concentration reachs 84 Bq m^-3 at exhalation and ventilation rates of 66 Bq hm^-2 and 0.28 h^-1, respectively. The radon concentration and the ultrafine fraction f_p of potential α energy concentration as well as the equilibrium factor F of the short-lived radon progeny were also determined in three different completely closed rooms. An electroprecipitation method was applied for determining the ²²²Rn concentration while a single wire-screen technique was used for the determination of ultrafine radon progeny. During the measurements, the radon concentrations were varied between 33 and 134 with a mean value 89 Bq m^-3. A mean ultrafine fraction (f_p) of 0.16 was obtained at a mean aerosol particle concentration (Z) of 1700 cm^-3 and a mean equilibrium factor (F) of 0.33. The obtained mean value of f_p was found to be about five times higher than the value reported in the ICRP publication (f_p=0.03). The attachment rate (X), the deposition rate (q^f) and the deposition velocity (v^f_d) of the ultrafine radionuclide ²¹⁸Po were calculated. A mean value of X was found to be 49 h^-1 at a mean q^f of 46 h^-1 and a mean v^f_d of 4.6 m h^-1. The attachment coefficient β of ²¹⁸Po was found to vary between 0.016 and 0.047 with a mean value 0.028 cm³ h^-1.     

Measurement of the 210Po/210Pb activity ratio in size fractionated aerosols from the coast of the Japan sea

The seasonal variation of the ²¹⁰Po/²¹⁰Pb activity ratio in aerosols, as a function of particle size, have been studied at Kamo, on the west coast of Japan from July 1995 to June 1996. It was shown that 70% of ²¹⁰Po and 77% of ²¹⁰Pb activities were measured in aerosols with a diameter smaller than 0.7 μm. On the other hand, the abundances of ²¹⁰Po and ²¹⁰Pb in aerosols with a diameter larger than 10.9 μm were 3 and 1%, respectively. In general, the maxima of the ²¹⁰Po/²¹⁰Pb ratio were observed in aerosols of 5.4–10.9 μm, but the maxima in January and April 1996 appeared in the largest and the smallest size fractions, respectively. The results suggest that the size distribution of the ²¹⁰Po/²¹⁰Pb activity ratio may be modified by changes in the nature and intensity of aerosol sources.     

Heavy metals and Pb isotopic composition of aerosols in urban and suburban areas of Hong Kong and Guangzhou,South China—Evidence of the long-range transport of air contaminants

Rapid urbanization and industrialization in South China has placed great strain on the environment and on human health. In the present study, the total suspended particulate matter (TSP) in the urban and suburban areas of Hong Kong and Guangzhou, the two largest urban centres in South China, was sampled from December 2003 to January 2005. The samples were analysed for the concentrations of major elements (Al, Fe, Mg and Mn) and trace metals (Cd, Cr, Cu, Pb, V and Zn), and for Pb isotopic composition. Elevated concentrations of metals, especially Cd, Pb, V and Zn, were observed in the urban and suburban areas of Guangzhou, showing significant atmospheric trace element pollution. Distinct seasonal patterns were observed in the heavy metal concentrations of aerosols in Hong Kong, with higher metal concentrations during the winter monsoon period, and lower concentrations during summertime. The seasonal variations in the metal concentrations of the aerosols in Guangzhou were less distinct, suggesting the dominance of local sources of pollution around the city. The Pb isotopic composition in the aerosols of Hong Kong had higher ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb ratios in winter, showing the influence of Pb from the northern inland areas of China and the Pearl River Delta (PRD) region, and lower ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb ratios in summer, indicating the influence of Pb from the South Asian region and from marine sources. The back trajectory analysis showed that the enrichment of heavy metals in Hong Kong and Guangzhou was closely associated with the air mass from the north and northeast that originated from northern China, reflecting the long-range transport of heavy metal contaminants from the northern inland areas of China to the South China coast.