210Pb Activity Research Articles

Atmospheric depositional fluxes of 210Pb in bulk precipitation at the Adriatic coast, Croatia

The atmospheric bulk depositional fluxes of 210Pb were measured at a station on the Adriatic coast, Croatia over 4 years period from March 2017 to December 2020. The monthly depositional fluxes followed oceanic deposition patterns with a lower flux between 0.0735 and 16.9 Bq m−2 month−1. The volume-weighted activities were 0.000514 and 1.35 Bq L−1 and decreased with increasing precipitation. A clear seasonal trend was observed with higher depositional flux in autumn and minimum value in the winter season. The average annual bulk depositional flux and volume-weighted activities of 210Pb were 73.8 Bq m−2 y−1 and 0.119 Bq L−1 respectively. The precipitation normalized enrichment factor (α) indicates higher depositional fluxes of 210Pb during summer and spring than desired value according to the amount of precipitation. We found that the 210Pb depositional fluxes in the coastal stations are lower due to 210Pb-depleted oceanic air masses and increase with the amount of precipitation.

Can 210Pb be used as a paleo-storm proxy?

There is increasing interest within the scientific community, as well as the public, to determine if tropical cyclones are increasing in frequency and/or magnitude because of climate change. Unfortunately, the instrumental weather record only extends over the last 100–150 years depending upon location. It is thus desirable to develop paleo-storm proxies to extend the tropical cyclone record to hundreds, if not thousands, of years. Overwash sand deposits, sediment grain size, and various geochemical parameters (e.g., δ13C, δ15N, C/N) have been applied successfully for coastal lake sediments. We present here another potential proxy candidate, the natural radionuclide 210Pb. With a 22.2-year half-life, 210Pb age dating is often used to calibrate other proxies over essentially the same period as the instrumental storm record. We hypothesize here that trends in the 210Pb profiles, in addition to providing chronological information, can provide independent records of storm deposits in some situations. To illustrate how 210Pb may serve as an additional storm proxy, we present data from sediment cores collected from the Chao Phraya Delta (Upper Gulf of Thailand), an area characterized by a rapidly retreating shoreline. Some of the 210Pb profiles mark sedimentary layers with anomalously low excess 210Pb activities interspersed between layers with significant excess activities. We suggest that these layers may result from rapid deposition offshore of older storm-eroded shoreline material. The estimated ages of these 210Pb-deficient layers match, within estimated uncertainties, years when typhoons or tropical storms are reported to have severely eroded the nearby Thai coastline. The matching of the time scales of 210Pb and recorded tropical cyclones, both about 100–150 years, allows this approach to be used to explore for storm deposits and tune geochemical and other proxies for extended study over time scales of several decades or longer.

Geochemical record of Lake Sabakty: Electrical conductivity and reconstruction of the Lateglacial and Holocene environments in the Southern Urals (Russia) steppe

Research subject. The Lake Sabakty sediments core, as a source of data on the Holocene and Lateglacial environments in the Southern Urals.Aim. To obtain a multiple regression model for quantitative reconstructions of the electrical conductivity of water based on the geochemistry of lake sediments and to reconstruct the Late Glacial and Holocene environments based on the study of the Lake Sabakty geochemical record.Materials and methods. After determination of correlations between the content of chemical elements in lake sediments and hydrochemical parameters of 107 Ural lakes, multiple regression models were obtained. Reconstructions were performed based on the results obtained by accelerator mass spectrometry (AMS 14C), 210Pb activity determination, and an analysis of chemical elements and organic matter contents in the sediment core.Results. Three multiple regression models using the concentrations of Na, Ca, Li, and Sr were obtained for electrical conductivity of water reconstruction. In the cold and dry Lateglacial (>12.0 ka cal BP), Lake Sabakty was a slightly brackish reservoir. During the transition from the Lateglacial to the Holocene (12–11.6 ka cal BP), the Lake Sabakty became more productive. In the Early (11.6–8.2 ka cal BP) and Middle (8.2–4.2 ka cal BP) Holocene, the electrical conductivity of water varied under the action of fluctuations in effective moisture. In the Late Holocene (4.2 ka cal BP – present), the Lake Sabakty became less saline due to an increase in effective moisture.Conclusions. The proposed multiple regression models enable rapid quantitative reconstructions of the electrical conductivity of water, which are particularly relevant for Lateglacial–Early Holocene sediments with a low number of microfossils. The Lake Sabakty geochemical record reflects global and regional climatic fluctuations, being more informative compared to the geochemical records of forest lakes in the Southern Urals. The decrease in the electrical conductivity of water of Lake Sabakty of approximately 7.9 and 4.2 ka cal BP coincides with similar data for several other lakes in the Urals.

Предварительные результаты исследования хронологии осадконакопления в Центральной впадине Баренцева моря

The article represents the results of the study of bottom sediment cores taken from the R/V “Dalnie Zelentsy” in the Central Depression of the Barents Sea during the 2022 expedition. The exposed stratum of bottom sediments is composed of silty-pelitic material, in some layers there is an admixture of uneven-grained sand and grains of well-rounded gravel. The chronology of sedimentation was determined by changing the specific activity of excess 210Pb, the obtained data were verified by 137Cs. The rate of sedimentation in the study area over the past 120 years has varied within 0.05–0.1 cm/year.

Atmospheric radioactive nuclide deposition on the coast of the Maowei Sea, northern Beibu Gulf, China

The natural radioisotopes 7Be, 210Pb, and 210Po, with different half-lives, are all particle-reactive and serve as natural tracers to study sources and transportation of sediments, sedimentation rates, and sediment chronology. Atmospheric deposition of these radioisotopes is the premise and foundation of their tracing application. The Maowei Sea is a semi-closed bay along the Beibu Gulf, which is an important gulf in the northwest of the South China Sea, but the atmospheric deposition of the abovementioned radioisotopes has not been systematically reported along the coast. In this research paper, the atmospheric depositional fluxes of 7Be, 210Pb, and 210Po were observed over a period from June 2018 to December 2021 on the coast of the Maowei Sea. The annual atmospheric depositional fluxes (Bq m-2 yr-1) of 7Be, 210Pb, and 210Po on the coast of the Maowei Sea were 496.80, 201.72, and 58.08, respectively. The distributions for 7Be and 210Pb depositional fluxes during a whole year (years 2019 and 2021) followed a bimodal pattern, with one peak from February to April and another peak from August to October, while the distribution for 210Po depositional flux showed only one peak during the year of 2019 and another during 2021. The deposition flux and activity of 7Be showed a strong positive correlation with the deposition flux and activity of 210Pb, respectively; the deposition flux and activity of 210Po also showed positive correlations with the deposition fluxes and activities of 210Pb and 7Be, respectively, indicating a similarly scavenging behavior from the atmosphere. A Pearson correlation matrix was used to illustrate the factors influencing the atmospheric depositions and found that precipitation, air quality index (AQI), and PM (both PM2.5 and PM10) were the major factors that influenced the deposition of these three radionuclides. Precipitation had significant positive correlations with the deposition fluxes of all three radionuclides, indicating that, for these radionuclides, rainfall was the main scavenging way from the atmosphere. The observations for specific single rainfall events and their air mass backward trajectory analyses showed that the air masses movement during the rainfall may be another important factor that impacted the depositional fluxes for 7Be, 210Pb, and 210Po.

Method of 210Pb geochronological to estimate sedimentation rate in water reservoir in the Brazilian semiarid region

Dams are important reservoirs in semiarid regions providing the needs of the population and agricultural activities in an area in which intermittent rivers predominate. These reservoirs are subject to erosion processes that can cause sedimentation and affect the quality of the water in them. The method of dating sediments using 210Pb is well known and is used to establish a precise chronology of the sediments in places where abrupt changes in sedimentation conditions do not occur. The work aims to determine the sedimentation rate in five main tributary points of the dam located in the semiarid region of the state of Pernambuco, Brazil, using the geochronologic dating of the sediments by measuring 210Pb activity. The method used was the Constant Rate of Supply (CRS) model. Dating coincides with the date of the conclusion of the construction of the dam. The sedimentation rate grew with the increase in depth and presented a decline in both the rate and flow of the sediments over time. The most recent results presented a decrease in sedimentation rates. The greatest occurrence of the sedimentation rate was identified at points located at the entrance of the dam, which could be justified by the reduction in the average speed of final drainage due to the existence of the reservoir itself.

The Atmospheric Input of Dissolvable Pb Based on the Radioactive 210Pb Budget in the Equatorial Western Indian Ocean

To estimate the atmospheric deposition flux of 210Pb in the equatorial western Indian Ocean, we determined the dissolved (<0.45 μm) and particulate 210Pb (>0.45 μm) in the water column. In addition, we calculated the atmosphere-derived dissolvable Pb in seawater using the budget of 210Pb. The dissolved 210Pb and total 210Pb were higher in the surface layer and, overall, showed a decreasing distribution with depth. In particular, radioactive 210Pb activities in the surface-to-upper layer (<1000 m depth) were 1.5 to 2 times higher than those reported in the 1970s (in nearby regions), suggesting that there has been additional 210Pb input in recent years. Based on the mass balance of the total 210Pb budget in the water column, we estimated the atmospheric deposition flux of 210Pb and the residence time of Pb for the first time in this region. The atmospheric deposition flux of 210Pb was estimated to be 0.1–0.5 dpm cm−2 yr−1, and these values agreed with the general global estimations for the major oceans (0.1–0.7 dpm cm−2 yr−1). Considering the residence time of 210Pb (29–41 years) in the water column (estimated from the 210Pb inventory and 234Th-based Pb scavenging rate), the atmospheric input of seawater-dissolvable Pb was quantified to be 0.08–0.1 nmol cm−2 yr−1, which is about eight times higher than the estimated input in the early 1990s in the region. Therefore, these results imply that radioactive 210Pb could be a useful tracer for quantifying Pb flux in seawater.

Natural radioactivity of groundwater in Vendian deposits in St. Petersburg Region

The study is focused on the hydrogeological conditions and the chemistry of groundwater of the Vendian aquifer in the western part of the Leningrad oblast (Karelian Isthmus and the area near Sosnovy Bor town) and St. Petersburg City, where groundwater features higher radioactivity, but nevertheless it is used for drinking water supply. Data on the radiological characteristics, which have been determined in the estimation of the quality of groundwater used for drinking are generalized and analyzed. These characteristics include the gross alpha and gross beta activity and the specific activity of natural radionuclides 222Rn, 226Ra, 228Ra, 210Pb, 210Po, 238U, and 234U. The data were subjected to statistical and correlation analysis to determine the hygienic criteria for the use of groundwater of this aquifer for drinking water supply and to study the sources and the processes of formation of the natural radiological background. Groundwater quality standards were shown to be exceeded in the majority of the analyzed wells. The brackish water in the southern, deeper, part of the aquifer system was shown to have higher radioactivity and relatively high concentrations of 226Ra, 228Ra, 210Pb, and 210Po, compared with fresh water in the northern part of the territory, of which higher, though nonuniform, 222Rn activity is typical. Relationships between the radiation characteristics of groundwater are considered along with the causes of formation of groundwater radionuclide composition as a result of the higher radioactivity of the host deposits and the chemistry of groundwater; changes in the radiological and hydrochemical background groundwater characteristics from the north to the south are characterized in accordance with the subsidence of the aquifer system and an increase in the stagnation of the hydrochemical regime. The analysis of the well-known relationship between the concentrations of radium isotopes in groundwater, uranium and thorium isotopes in the host rocks, and groundwater residence time in the aquifer, along with the comparison of the available field data with calculation results, suggested the conclusion that the concentration of uranium in the water-bearing rocks in the major portion of the area under consideration is higher than its regional mean values.

The Chronology of Modern Sedimentation in the Storefjorden Strait (Svalbard Archipelago)

Periods of formation of different sedimentary lithotypes were determined using the results of the study of modern sedimentation processes in the Storefjorden Strait (West Spitsbergen). The chronology of sedimentation was established from variations in specific activity of 210Pb and 226Ra and verified by 137Cs data. Sedimentation rates have varied considerably over the last century in different parts of the sedimentation basin, ranging from 0.04 to 0.3 cm/yr. Sedimentation in the Storefjorden Strait was closely related to changing climatic conditions. Climatic factors (air temperature, atmospheric precipitation) have a different effect in morphologically different sections of the sedimentation basin. In the south of the strait, lithotypes are determined by an oceanological factor (bottom current). Despite the changes in sedimentation rate, the lithotype in the south of Storefjorden has remained stable for more than 100 years. In the north and in the central part of the strait, cooling in the period from 1970 to 1995 caused a change in the bottom sediment structure.

Using microcomputed tomography (μCT) to count varves in lake sediment sequences: Application to Lake Sagtjernet, Eastern Norway

Varved lake sediments are one of the most important natural archives that allow annual resolution paleoclimate reconstructions. Conventional varve counting techniques use thin sections to manually identify lamina. However, this technique is destructive, labour intensive and limited to a 2D representation of complex 3D features which may lead to misidentification of varve boundaries. This study presents the use of microcomputed tomography (μCT) scans in constructing varve chronologies, utilizing scanning resolutions of ∼50 μm (binned to ∼200 μm) for core sections up to 150 cm long. To evaluate this method, we cored and analysed Lake Sagtjernet in Eastern Norway — revealing a 593 cm-long sediment record of the past 10274 (+220/-329) years, with continuous laminations from 84 to 533 cm depth (75% of the sediments). Through limnological monitoring and microfacies analyses we demonstrate that the laminations are rare ferrogenic varves, with an annual deposition pattern comprised of seasonal changes in biogenic production superimposed on seasonal precipitates of iron and manganese hydroxides. The floating μCT-counted varve chronology presented here is the first non-glacial varve chronology in Norway and covers 4023 +113/-185 years. We find that μCT scans allow for a very fast and non-destructive way of counting varves with sufficient detail of varve boundaries. In the few sections where varve boundaries are too vague to resolve, we recommend using complimentary techniques such as thin sections in parallel. The varve chronology is in good agreement with the 95% confidence interval of the independent radiocarbon chronology based on 16 14C dates, and 210Pb and 137Cs activity peaks, indicating that the varve chronology can be equated to calendar age.

Temporal variations of 7Be and 210Pb activity concentrations in the atmospheric aerosols during 2018–2019 in Beijing, China and their correlations with meteorological parameters

In order to establish a regional database on natural radioactivity, a series of measurements of 713 atmospheric aerosol samples collected on filters over a two-year period (2018–2019) in center of Beijing, northeastern China have been performed to analyze 7Be and 210Pb activity concentrations. The mean activity concentrations of 7Be and 210Pb were found to be 7.10 ± 2.44 mBq m−3 and 2.93 ± 1.52 mBq m−3, respectively. Both the radionuclides exhibited strong seasonal variations, with maximum concentration of 7Be occurring in the spring and that of 210Pb in the winter. The concentration of both the radionuclides was minimum in the rainy summer. Higher 7Be concentration in the spring was mainly caused by the stratosphere to troposphere exchange. Higher 210Pb concentration during winter was maybe attributed to the combustion processes in heating systems and the ingression of continental air masses resulted from winds originating from northwest. The dependence of the activity concentrations of 7Be and 210Pb with meteorological parameters such as rainfall, temperature, and humidity was studied through linear correlation analysis. Statistically significant negative correlations were observed between 7Be and 210Pb activity concentrations with rainfall, respectively, which suggested that the removal mechanisms of these two radionuclides were similar. Lead-210 showed statistically significant correlations with temperature, humidity and PM10. A comparison of the data obtained in the present study for Beijing with the northern hemisphere literature values of 7Be and 210Pb in the atmospheric aerosols showed that the values were smaller than the ones observed in the present study. Overall, the study provides an improved understanding of the temporal variability and correlation of 7Be and 210Pb concentrations in the atmosphere in center of Beijing, northeastern China.

How large peak ground acceleration by large earthquakes could generate turbidity currents along the slope of northern Japan Trench

Deep-sea turbidite has been used to determine the history of occurrence of large earthquakes. Surface-sediment remobilization is a mechanism of the generation of earthquake-induced turbidity currents. However, the detailed mechanism of surface-sediment remobilization caused by earthquake ground shaking is unclear. To understand how high peak ground acceleration (PGA) caused by a large earthquake can remobilize surface sediments, we determined the age of a surface-sediment core recovered from the mid-slope terrace (MST) of the inner slope of the Japan Trench in northern Sanriku to determine turbidites generated by large historical earthquakes and calculate the PGAs of these earthquakes using an empirical attenuation relation commonly used in Japan. Small offsets in radiocarbon ages and excess 210Pb activities between turbidite and hemipelagic muds suggest that the turbidites in the core resulted from surface-sediment remobilization. 137Cs and excess 210Pb chronologies indicate that the three uppermost turbidites in the core are correlated with three large historical earthquakes, namely the 1968 common era (CE) Tokachi-oki, the 1933 CE Showa–Sanriku, and the 1896 CE Meiji–Sanriku earthquakes. Calculation of PGAs for large historical earthquakes along the northern Japan Trench indicates that a PGA of > 0.6 g is necessary for turbidite deposition in the MST basin. This threshold is larger than that reported for central Sanriku and may vary spatially. Moreover, turbidites in the MST deposits are more frequent in the northern Japan Trench than in the central Japan Trench, suggesting that the occurrence of three types of large M8-class earthquakes in the northern Japan Trench might have contributed to the frequent occurrence of large PGAs.

Distribution and storage of uranium, and its decay products, in floodplain sediments

Industrialised rivers contain legacy contaminants stored in their sediments and floodplain soils which may inhibit attainment of environmental quality criteria. The River Fal catchment, SW England, is impacted by inputs from uranium mining and clay production and serves as an exemplar for understanding the consequences of medium-term process dynamics in contaminated basins. Radionuclides were determined, by gamma spectroscopy, in six cores from the river floodplain with the aim of quantifying the activities of 238U, and its decay products, and the bomb fallout radionuclides137Cs and 241Am. Activity concentrations of 238U implied inputs from mining, accentuated by flood events and historic industrial accidents, whereas 210Pb activities included a significant input of unsupported 210Pb linked to processed mine spoil. The radionuclide inventories did not decrease systematically downstream revealing evidence of attenuation of particulate radionuclides within the river floodplain sediment column. Storage of legacy contaminants in fluvial systems, at levels in excess of contemporary environmental quality guidelines, emphasises the challenges posed by changing climatic conditions. This scenario raises significant consequences for the management of uranium-contaminated, fertile riverine floodplains within Europe.

Inventories, profiles and deposition fluxes of 210Pbex in mineral and organic (peatlands) Southern Hemisphere soils

Unsupported 210Pb (210Pbex) activity profiles have been determined in both mineral soils from Argentina (La Plata region) and organic soils from Brazil (Serra do Espinhaço Meridional). For the Argentine mineral soils, no significant differences in the 210Pbex inventories are found (ranging from 2920 ± 560 to 4570 ± 460 Bq/m2). The measured activity profiles are properly fitted by the one-dimensional transport model by effective diffusion and migration developed by He and Walling and the resulting parameters were analyzed considering the soil properties. It was observed that the migration rate is inversely proportional to the illite content, that the soils with higher amounts of smectite exhibit higher migration rates, and that the higher the pH, the higher the migration rate. These results agree with the higher Pb sorption capacity of smectite than illite, at identical conditions, and the Pb speciation with pH, that gives raise to different interactions between Pb and soil components. For organic soils, 210Pbex accumulates in superficial layers (5 cm depth) and the 210Pbex inventories (ranging from undetectable value to 5100 ± 200 Bq/m2) depend on the altitude of the sampling points. The activity values of 210Pbex and 137Cs (previously reported) are not significantly correlated, probably because the 137Cs fallout occurred more than 50 years ago, allowing the 137Cs profiles to develop. Finally, the deposit fluxes were determined for both regions studied and were incorporated into the global curve elaborated in previous works, contributing to a better definition of the general trend reported for the Southern Hemisphere.

Influence of Precipitation on the Spatial Distribution of 210Pb, 7Be, 40K and 137Cs in Moss

Mosses have been widely used as biomonitors of a variety of atmospheric pollutants, including radionuclides. Here we determine the radionuclide activity concentration of 210Pb, 137Cs, 7Be, and 40K in moss tissue (Hylocomium splendens) collected from 24 sites across Ireland and assess the influence of precipitation on radionuclide spatial distribution. Lead-210 was the most abundant radionuclide (range: 226–968 Bq kg–1), followed by 7Be (range: <DL—604 Bq kg–1), 40K (range: <DL—155 Bq kg–1), and 137Cs (range: <DL—41 Bq kg–1). Albeit nearly thirty years since the Chernobyl disaster, 137Cs activity concentration was detected at 67% of the study sites; however, the spatial distribution was not fully consistent with the 1986 Chernobyl deposition pattern. Rather, 137Cs was weakly correlated with rainfall, with higher concentrations along the west coast, suggesting that the 2011 Fukushima Dai-ichi nuclear accident was also a potential source. Average annual rainfall was a significant predictor of 210Pb activity (linear regression, R2 = 0.63, p < 0.001). As such, the highest radionuclide activity was observed for 210Pb (average: 541 Bq kg–1), owing to the high levels of precipitation across the study sites (average: 1585 mm). In contrast, 7Be or 40K were not correlated with precipitation; rather, 40K and 7Be were significantly correlated to each other (rs = 0.7), suggesting that both radionuclides were transferred from the substrate or through soil re-suspension. Precipitation is widely reported as an important factor in the spatial distribution of radionuclides; however, only 210Pb activity concentrations in moss were strongly influenced by precipitation in the current study.

Sedimentary dinoflagellate cyst records of human-induced environmental changes in Daya Bay, the northern South China Sea

High resolution dinocyst records were established in sediment core to detect human-induced environmental changes in Daya Bay, the South China Sea. The grain was homogeneous except at depths of 17–18 cm, where the clay proportion increased dramatically from ∼40% to ∼80%. The 210Pb activity varied from 25.1 Bq kg−1 to 78.5 Bq kg−1 and showed temporary interruption at depths 17–18 cm associated with 1978, while dinocysts showed no obvious hiatus. Totally 36 cyst species were identified, with the highest species richness (20) and cyst abundance (900 cysts g−1) occurring at 7-cm depth, associating with severe blooms of Scrippsiella acuminate from 1998 to 2000 in Daya Bay. Cyst assemblages showed high similarity (>70%), especially in the interrupted and upper layers, indicating similar marine-originated for these intervals. Moreover, autotrophic and heterotrophic cysts dominated alternately before and after 1978, indicating high potential of the cysts to trace human-induced environmental changes in Daya Bay.

Distribution Pattern of Dioxins in Sediment Cores from the Xiangxi River, a Tributary of Three Gorges Reservoir, China

Sediment cores were collected from the Xiangxi River, a tributary of the Three Gorges Reservoir, the deposition time in the longest sediment core (90 cm) was measured by radiometry (137Cs, 210Pb) activities and polychlorinated dibenzo-p-dioxins/furan (PCDD/F) concentrations in different depths of the sediment core were measured. The results indicated that the mean deposition rate was 1.01 cm/a. The total PCDD/F concentrations ranged from 19.28 to 70.07 pg/g d.w. with a mean of 35.06 pg/g d.w. PCDD/Fs in the 1960–1990s were higher than others, which were significantly different in the various layers and cores (p < 0.05). PCDD occupied 63.42–87.33% of PCDD/Fs, and octachlorianted debenzo-p-dioxin (OCDD) was the predominant congener. The ratio of PCDD to PCDF was 2.26–8.08. PCDD/Fs significantly correlated with total organic carbon (TOC) (p < 0.01). The toxic equivalent (TEQ) ranged from 0.15 to 0.98 pg/g d.w. No significant difference was found in TEQ (p > 0.05). It was concluded that the spatio-temporal heterogeneity determined by hydrodynamics and total organic carbon (TOC) was the distribution pattern of PCDD/Fs in the sediment cores of Xiangxi River, the concentrations of PCDD/Fs were low, with a low environmental pollution risk, and by-products of sodium pentachlorophenate might be the main source.

Bioaccumulation and retention of Po-210 and Pb-210 in two species of mosses from the zone of influence of the former radium-extracting plants.

The presented study was aimed at assessing the ability to accumulate and retain 210Po and 210Pb in two species of the mosses Sphagnum girgensohnii Russow and Pleurozium schreberi (Willd. ex Brid.) Mitt. Mosses were collected in the zone of influence of the former radium-extracting plants (Komi Republic, Russia). 210Po and 210Pb activity concentrations in S. girgensohnii varied from 131 ± 15.4 to 221 ± 18.3Bqkg-1, and from 164 ± 18.6 to 309 ± 26.1Bqkg-1 respectively. In P. schreberi corresponding activity concentrations ranged from 107 ± 18.8 to 328 ± 29.2Bqkg-1 and from 117 ± 13.2 to 399 ± 31.1Bqkg-1. Activity concentrations of 210Po and 210Pb in autumn were higher than in summer. In the young parts of the mosses, they were lower than in the old parts. To assess the ability to retain accumulated radionuclides, watersoluble (distilled H2O), exchangeable (1M CH3COONH4), and acidsoluble (0.1M H2SO4) fractions of 210Po and 210Pb were isolated from the studied mosses by the method sequential extraction. It was revealed that these fractions in total contained up to 26% of 210Po and 39% of 210Pb. The results showed that the studied moss species are a good biogeochemical barrier and long-term storage for 210Pb and 210Po.

210Po and 210Pb as tracers for particle cycling in a shallow semi-enclosed bay of Taiwan Strait

Naturally-occurring 210Po and 210Pb are good tracers for particle cycling in the estuarine and coastal environment. Activities of 210Po and 210Pb were measured in samples of bulk (wet + dry) atmospheric deposition, river water and surface seawater collected in the Zhangjiang Estuary-Dongshan Bay to investigate the geochemical scavenging rates (or residence times) of these particle-reactive nuclides. The spatial distribution of 210Po and 210Pb were strongly influenced by suspended particulate matter (SPM) concentrations and in almost all stations, 210Po and 210Pb were mainly in particulate form (51.7%–92.2% of the total for 210Po and from 44.3% to 90.3% for 210Pb). Due to the very high SPM concentration, enhanced scavenging of 210Po and 210Pb was observed in the maximum turbidity zone of Zhangjiang River, with a marked decrease of dissolved nuclides’ activities. We built a mass balance model and we found out that atmospheric inputs are the major source of these radionuclides comparing with other sources (e.g., river inputs or ingrowth production) in the study area. Residence times of 210Pb were calculated to be 2.2–9.8 and 0.5–8.9 days for dissolved and particulate 210Pb, respectively. And residence times of dissolved and particulate 210Po were 6.3–31.7 and 2.2–13.9 days, respectively. In the turbidity zone, we found an unexpected result that particulate 210Po and 210Pb had the longest residence times (about two weeks), suggesting that SPMs in the turbidity zone would not be easy to sink to the sea floor. We also found that different SPMs showed significantly different 210Po/210Pb activity ratios, which increased in the following order: atmospheric deposition in dry season < SPMs in river < SPMs in the Zhangjiang Eastuary-Dongshan Bay < biogenic particles (including detritus, fecal pellets, cells of phytoplankton and zooplankton). This phenomenon implied that 210Po/210Pb activity ratio in the particles has the potential application in distinguishing SPM sources in the coastal seas.

Spatial-temporal occurrence and sources of organochlorine pesticides in the sediments of the largest deep lake (Lake Fuxian) in China.

Compared with shallow lakes, less attention has been paid on pollutions in deep lakes. Lake Fuxian is the largest deep lake and an important water resource in China. The knowledge on organochlorine pesticides (OCPs) in sediments of Lake Fuxian was rare. Fifteen surface sediments and one sediment core were collected from Lake Fuxian. Sediment chronology was dated with the activities of 137Cs and 210Pb. Twenty-one OCPs in the surface sediments and sediment core were analyzed by a GC-MS. Spatial and temporal occurrences of OCPs in the sediments of this lake were studied. Correlations, isomer ratios, and principal component analysis (PCA) were applied to apportion the sources of OCPs in the sediments of this lake. The OCPs in the sediments of Lake Fuxian were dominated by p,p'-DDT (4,4'-dichlorodiphenyltrichloroethane) and HCHs (hexachlorocyclohexane). The concentration of ΣOCPs in the surface sediments ranged from 0.42 to 67.5ngg-1, with an average of 42.3 ± 23.5ngg-1 (mean ± SD, n = 15). The concentration of ΣOCPs in the sediment core varied from 3.5 to 707.9ngg-1 in the period from 1950 to 2010, with an average of 167.7 ± 203.7ngg-1 (n = 24). The highest concentrations and fluxes of α-HCH, γ-HCH, and p,p'-DDT were found in the years of 1964 and 1967, respectively. The fluxes of HCH isomers in the sediment core decreased in the orders as γ-HCH > β-HCH > α-HCH in the period from 1950 to 2010. The concentrations of HCHs and p,p'-DDT in the sediments of Lake Fuxian were higher than those of most shallow and deep lakes in the world. HCHs and p,p'-DDT were derived from both the technical HCH and DDT and the usage of lindane and dicofol. Technical DDT and technical HCH may be used simultaneously, but technical DDT and lindane were not applied simultaneously in the catchment. Lindane was used not only in the period from 2002 to 2010 but also in the period from 1950 to 1964 in the catchment.