Vertical distributions of plutonium and 137Cs in lacustrine sediments in northwestern china: quantifying sediment accumulation rates and source identifications

Source, preservation and re-suspension of 239,240Pu in a well dated peat core collected from northwest China

Owning to the high radiotoxicity in high concentrations, as well as the irreplaceability in quantifying soil erosion rates, demarcating the Anthropocene, and dating of sediment, anthropogenic 239,240Pu have drawn high attention. However, the source in specific areas, preservation characteristics in different environment media, and re-distribution process after the cessation of atmospheric nuclear weapons tests, have not been fully understood, which obscures the exact start year, temporal variation, and deposition flux of 239,240Pu in sedimentary records, and hinders the wide application of 239,240Pu in environment study. A sediment core from the Yiwu peat bog with dominance of atmospheric deposition in the source material, simple sedimentary environment, and high dust deposition flux, was collected to examine the 239,240Pu, and explore the source, preservation, and re-distribution process. The double peaks of 239,240Pu in 1952 CE and 1963 CE, as well as 240Pu/239Pu ratios of 0.163-0.190 with an average of 0.177 ± 0.010 confirmed that the 239,240Pu source originated predominantly from global fallout. The minimal vertical migration of plutonium in the Yiwu peat core was attributed to the near-neutral pH condition. The high inventory of 128 ± 7 Bq m-2, as well as the atypical negative correlation between 239,240Pu concentrations and organic matter content (r = - 0.79, P < 0.01), was attributed to the contribution of 239,240Pu re-suspended with dust from the neighboring Gobi Desert, particularly in the cold and dry years. The total re-suspended 239,240Pu was estimated to be 77 Bq m-2, exceeding the direct fallout level of 51 Bq m-2 during 1945-2016 CE. In this study, the specified deposition pattern of 239,240Pu after the cessation of atmospheric nuclear weapons was established, providing an important standard for multiple environmental studies, and the re-suspended amount of 239,240Pu in a typical arid area was quantified for the first time.

Assessment of the depositional characteristics of the Yellow River estuary from 1960s by 239+240Pu and 137Cs

The spatial and vertical distribution of 239+240Pu and 137Cs in the sediments of the Yellow River Delta was studied to evaluate the deposition dynamics in the Yellow River estuary from 1960s. The activity of 239+240Pu and 137Cs in sediment core ranged from 0.001 to 0.212 Bq/kg and 0.52-2.53 Bq/kg, respectively. A maximum accumulation peak and two secondary accumulation peaks appeared in the sediment core YR2. The average deposition rate of 8.3 cm/y for the Yellow River estuary from 1964 to 1976 was obtained. The proportion of Pu from the Yellow River net input and direct deposition to the total inventory of Pu in the estuary was assessed, with a total inventory of Pu in the abandoned estuary of 7.4 × 1010 Bq and a net input of 2.2 × 1010 Bq from the Yellow River. Pu deposited in the estuary only accounts for 18 % of the total Pu transported by the Yellow River, and most of the Pu is injected into the Bohai Sea with the Yellow River.

Plutonium in sediments of the Eastern Guangdong coast-its sources and their contribution

The ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu atom ratios of surface sediments from the Eastern Guangdong coast (EGDC) were determined by sector field ICP-MS in order to examine the sources of plutonium (Pu) and quantify their contributions. The ^239+240Pu activities in the EGDC ranged from 0.113 to 0.451 Bq kg^-1, with an average of 0.225 ± 0.090 Bq kg^-1 (n = 17). Consistently high ²⁴⁰Pu/²³⁹Pu atom ratios, ranging from 0.218 to 0.274 (average = 0.254 ± 0.014, n = 17), indicate a non-global fallout Pu source in the EGDC. The horizontal distribution of the ²⁴⁰Pu/²³⁹Pu atom ratios in the EGDC sediment suggests the non-global fallout Pu is sourced from close-in fallout from the Pacific Proving Grounds (PPG). Using a simple two end-member mixing model, we calculated the relative proportions of Pu from the PPG and global fallout in the EGDC to be 57 ± 9 % and 43 ± 9 %, respectively. Moreover, from the well-defined relationship between ^239+240Pu activity and total organic carbon content in sediments and a two end-member mixing model using δ¹³C, we further calculated the Terr-global fallout (riverine input) and Mar-global fallout (direct atmospheric deposition) to be 11 ± 2 % and 32 ± 6 %, respectively. Finally, from the activity levels and atom ratios of Pu isotopes in the EGDC, we established a baseline for future use in environmental risk assessment related to nuclear power plant operations.

Vertical distribution of plutonium isotopes from the floodplain and lacustrine sediments in Poyang Lake, China

Anthropogenic radionuclides deposited in sediments have been used for environmental radiation risk valuation as well as source identification. In this study, we investigated the vertical distribution of plutonium (Pu) isotopes and ²⁴⁰Pu/²³⁹Pu atom ratios in both floodplain and lacustrine sediments in Poyang Lake. The ^239+240Pu activity concentrations in floodplain sediment cores were found to range from 0.002 to 0.085 Bq kg^-1, with a maximum value at the subsurface layer. The activity in lacustrine sediment cores was from 0.062 to 0.351 Bq kg^-1 with a mean of 0.138 ± 0.053 Bq kg^-1. The inventory of 43.15 Bq m^-2 in lacustrine sediment core is comparable to the average value of global fallout expected at the same latitude. The average ²⁴⁰Pu/²³⁹Pu atomic ratios (0.183 ± 0.032) for sediment cores indicated that the global fallout is the major source of Pu in the studied region. The results are of great significance to the further understanding of sources, records, and environmental impacts of regional nuclear activities in the environment.

Plutonium-based radiometric dating of rapidly accumulated sediments in the Sanyuan sinkhole, southern Chinese Loess Plateau

Radionuclides, such as ²¹⁰Pb, ¹³⁷Cs and ^239,240Pu, have been widely used for dating recent sediments in terrestrial and marine environments, while ¹²⁹I, as an important artificial radionuclide in the environment, is also a potential tracer for sediment dating and environmental process studies. However, they were not always successfully applied to sediment dating because of their different sources, half-lives, environmental behaviour and measurement techniques. The dating applicability of these nuclides in a sedimentary environment with rapid accumulation on land was investigated for sinkhole sediment from the southern Chinese Loess Plateau. Our results showed that ²¹⁰Pb and ¹³⁷Cs could not be adequately used for dating the sediments due to the difficulties in accurately measuring ¹³⁷Cs and excess ²¹⁰Pb (²¹⁰Pb_ex) signals caused by the dilution effect of rapid accumulation. ¹²⁹I is not an ideal dating tracer because of its multisource feature causing no remarkable peak value in the sediment cores. The depth distribution of ^239,240Pu in the sediment core showed a single peak corresponding to its maximum fallout in 1963 from the atmospheric nuclear weapons test, suggesting that Pu isotopes have significant advantages in dating recent sediments. The sensitive inductively coupled plasma-mass spectrometry (ICP-MS) measurement technique enables the determination of very low levels of ²³⁹Pu and ²⁴⁰Pu and makes ^239,240Pu a suitable tracer for dating the rapidly accumulated sediment. Based on the ^239,240Pu mass balance equation estimation and field observations, we proposed the water-eroded input from soil surrounding the sinkhole as another vital source of the sediments in addition to the aeolian contribution.

Distribution and migration of 239,240Pu in soil profiles in North China

The source, vertical distribution and migration behavior of plutonium in five soil profiles (from forest, grassland and desert areas) in northern China were investigated. The average ²⁴⁰Pu/²³⁹Pu atomic ratio of 0.184 ± 0.022 observed in these samples is in good agreement with the reported value of global fallout, suggesting that the global fallout is the major source of plutonium in northern China. The ^239,240Pu inventories in five soil profiles ranges from 43.3 Bq/m² to 175 Bq/m², lying in the reported range for global fallout in the similar latitude band. The effective convection velocity (0.04-0.16 cm/y) and effective dispersion coefficient (0.13-0.41cm²/y) of plutonium in different soil profiles derived using the CDE model varies significantly, attributed to multi-factors including location, topography, climate and soil types. The results showed that the migration of plutonium in grassland soil is significantly slow compared to other type of soil, especially desert soil.

Insights on the distribution and environmental implications of the radio-isotope 235U in surface soils and glaciers of the Tibetan Plateau

Atom ratio between ²³⁵U and ²³⁸U is often used as an indicator of U contamination as the isotopic signature of products generated by the nuclear and military industry significantly vary from the natural isotopic ratio of U. In this study, surface soils and glaciers samples were collected in the Tibetan Plateau (TP) and its surrounding areas and analyzed for U isotopic composition. Results show that the ²³⁵U/²³⁸U atom ratios in the surface soils of the TP ranges from 0.007122 to 0.007615, with an average value of 0.007378 ± 0.00011; while in the snow/ice dust from high-altitude glaciers it ranges from 0.007254 to 0.007687, with an average value of 0.007345 ± 0.000128. These ratios are slightly higher than the typical crustal value, indicating that the TP was affected by an anthropogenic input of ²³⁵U, especially in its northeast and southwest sectors. The variability of our results suggests that the spatial distribution of this contamination is not uniform, pointing to differences in the potential sources and transmission paths of radioactive particles. Combining the knowledge of past tests and activities conducted in the geographic areas around the TP with the knowledge of prevailing winds, we hypothesize that the observed ²³⁵U contamination in the TP surface soils and glaciers may have originated mainly from the previous nuclear related activities in surrounding areas (e.g., north Gobi Desert and South Asia). In addition, the horizontal and vertical wind field around the Tibetan Plateau, as well as the atmospheric aerosol optical thickness data also demonstrated the possible transport paths of the radionuclides, that is, originated from in northern Gobi desert and South Asia and reached the TP crossing the Himalayas.

An overview of plutonium isotopes in soils, China: Distribution, spatial patterns, and sources

Plutonium (Pu) is an anthropogenic radionuclide which has drawn significant attentions due to its radiotoxicity, and the sources of plutonium linked with nuclear accidents and contaminations. The ²⁴⁰Pu/²³⁹Pu atom ratio is source dependent and can be used as a fingerprint to determine the sources of radioactive contaminant. However, the distribution and sources of plutonium in soils of China have not yet been systematically studied at a national scale up to date. The distribution, spatial patterns, and sources of plutonium in soils of China were discussed in this work. The concentrations of ^239,240Pu are in the range of 0.002-4.824 mBq/g with a large variation, and the ^239,240Pu concentrations in surface soils increase with the increasing latitude, which affects by multi-factors such as organic matter and particle size, etc. The inventories of ^239,240Pu are in the range of 7.31-554 Bq/m². The weighted average of ²⁴⁰Pu/²³⁹Pu atom ratios (0.180 ± 0.004) in all surface samples is good agreement with the ratio of global fallout (0.180 ± 0.014) of the nuclear weapons tests, this indicate that the major source of plutonium in China is global fallout. However, among some sites, distinctly lower ²⁴⁰Pu/²³⁹Pu atom ratio compared to the global fallout values were observed in the northwest China, indicating a significant contribution from other source besides the global fallout. Furthermore, the spatial clustering patterns of hot spots (high values) and cold spots (low values) for plutonium showing the clear associations with nuclear tests, especially the Chinese Lop Nor nuclear weapons tests (CNTs) and the Semipalatinsk nuclear weapons tests (STS). Radioactive material including plutonium from the STS or CNTs was transported by the prevailing westerlies to the northwest China. This review about the fingerprints and distribution of plutonium in soils of China will help researchers to establish a reference database for future radiation risk assessment and environmental radioactive management.

Sources and Variability of Plutonium in Chinese Soils: A Statistical Perspective with Moving Average

We investigated the different sources and their corresponding impact areas of Pu in Chinese surface soils to illustrate the state-of-the-art of the sources, levels and distributions of 240Pu/239Pu atom ratios as well as 239+240Pu activity concentrations in China. For the first time a moving average strategy in combination with statistical analysis was employed to partition geographic areas in China based on the reported 240Pu/239Pu atom ratio and 239+240Pu concentration data from public literature. During the partitioning, the median (MED) of the dataset was basically employed as a criteria in place of the commonly used arithmetic average (AM). Concisely, three areas were partitioned according to the different influences of Pu from the Lop Nor (LNTS) and Semipalatinsk (STS) test sites and the global fallout. The partitioned Ternary area (80° E–105° E, 35° N–50° N) was supposed to have multiple sources of Pu including the STS and LNTS besides the global fallout, which was characterized with slightly lower 240Pu/239Pu atom ratios (MED = 0.174) as well as elevated 239+240Pu concentrations (MED = 0.416 mBq/g). Meanwhile, the Binary area (35° N–45° N, 100° E–115° E) was considered to have received the extra contribution from the high-yield nuclear tests at the LNTS besides the global fallout, resulting in the highest 240Pu/239Pu atom ratios (MED = 0.200) across China. The remaining area was marked as the Unitary area, where it only received the exclusive contribution of global fallout. Furthermore, through the statistical analysis of the 240Pu/239Pu data in the Unitary area, we recommended a value of 0.186 ± 0.021 (AM ± SD) as a representative or area-specific 240Pu/239Pu atom ratio baseline to characterize the global fallout derived Pu in Chinese soils.

Plutonium isotopes in the northwestern South China Sea: Level, distribution, source and deposition

The spatial distribution of plutonium isotopes (²³⁹Pu, ²⁴⁰Pu) in the surface sediments collected from the northwestern South China Sea (SCS) in 2018 was investigated. The ^239,240Pu concentrations in surface sediments vary from 0.048 to 0.960 mBq/g (with mean of 0.282 ± 0.242 mBq/g) depending on the geographical feature of the sampling location such as the river estuary, continental shelf, slope and deep basin. Higher ²⁴⁰Pu/²³⁹Pu atomic ratios (0.24-0.31) in the surface sediment of the SCS compared to the global fallout value of 0.18 were observed, this is attributed to the input of close-in fallout of the Pacific Proving Ground (PPG) transported by the North Equatorial Current and Kuroshio Current to the northern SCS. The contribution of the PPG derived plutonium in the SCS sediment was estimated to be 39%-78% using a simple two-end member mixing model based on the measured ²⁴⁰Pu/²³⁹Pu atomic ratios in the sediment. Besides the soluble ^239,240Pu level in seawater, load of suspended particulate matter from the river runoff and biological debris, hydrographic and hydrodynamic conditions are key parameters influencing the deposition process of plutonium to the sediment.

Distribution of plutonium isotopes in soils between two nuclear test sites: Semipalatinsk and Lop Nor

Plutonium (Pu) has attracted attention as an environmental tracer due to its radiotoxicity and the possibility of sources linked with nuclear accidents in recent years. Plutonium isotopes (^239,240Pu) were detected at trace levels in soils collected from the Xinjiang region located between the Semipalatinsk nuclear test site and China's Lop Nor nuclear test site. Little is known regarding the spatial variation of ^239,240Pu in soils from this region. This study reports the use of Sector Field Inductively Coupled Plasma Mass Spectrometry (SF-ICP-MS) methods to distinguish between Pu isotopes derived from global fallout and nuclear weapon tests. We found that the ^239,240Pu activity concentrations ranged from 0.035 to 1.338 mBq/g; the ²⁴⁰Pu/²³⁹Pu atomic ratios were 0.157-0.223 with a weighted average of 0.180 ± 0.002, corresponding with the expected average global fallout ratio of 0.180 ± 0.014. This indicated that global fallout is the major source of Pu in the study region. The ^239,240Pu inventories in these soils ranged from 23.67 to 222.7 Bq/m², corresponding with those from other areas in China and other countries within the latitude range. Our Pu isotope data was supplemented with other published Pu data for soils collected in the vicinity of the Semipalatinsk nuclear test site and Lop Nor nuclear test site. Results indicate that ^239,240Pu inventories and ²⁴⁰Pu/²³⁹Pu atomic ratios in soils exhibit large variations with distance from the Semipalatinsk nuclear test site. High deposition and accumulation of Pu, and low ²⁴⁰Pu/²³⁹Pu ratios were observed in close-in fallout and downwind regions of the Semipalatinsk nuclear test site and China's Lop Nor nuclear test site.

Level, distribution and sources of plutonium in the northeast and north China

Concentrations of ²³⁹Pu and ²⁴⁰Pu in 163 surface soil samples and five soil cores collected from the northeast and north China were analyzed using the radiochemical separation combined with inductively coupled plasma mass spectrometry measurement. The average ²⁴⁰Pu/²³⁹Pu atomic ratios (0.185 ± 0.018) for all surface soil samples indicated that the global fallout is the major source of plutonium in the studied region. The ^239,240Pu concentrations of the surface soil ranged from 0.002 mBq/g to 4.82 mBq/g, lying in the range of the reported results in the areas with similar latitude, except for a few samples. The distribution of ^239,240Pu in this region is controlled by the deposition of plutonium in the atmosphere and its preservation in the soil, which were affects by multi-factors such as topography, climate, utilization of the land and vegetation coverage. The analytical results could be used as the baseline data for the assessment of the impact of nuclear activities in the past and the future.

Distinctive distribution and migration of global fallout plutonium isotopes in an alpine lake and its implications for sediment dating

This work investigated plutonium (Pu) isotopes in sediment cores collected from an alpine lake (Lake Heinongpo with 3779 m above sea level) in Southwestern China. ²⁴⁰Pu/²³⁹Pu atom ratios in all sediment samples showed the typical global fallout values of ∼0.18 without any influences from other Pu contaminant sources. ^239+240Pu activities with surface and subsurface maximums followed by exponential decline with sediment depth were respectively observed in the two sediment cores. The distinctive depth distributions of ^239,240Pu in the lake sediments was attributed to the very slow sediment deposition rate due to the lack of terrestrial sediment input, while the alpine snowmelt input was the primary source of Pu in the lake sediments in addition to the direct atmospheric deposition. The total Pu inventory was estimated to be 56.3 ± 1.4 and 63.9 ± 0.8 Bq/m² respectively in the two sediment cores. The generally higher Pu inventory in the Lake Heinongpo compared with other reported lakes in similar latitude should be mainly attributed to their different Pu input passages. The advection-diffusion equation was further applied to evaluate the downward migration of Pu isotopes in the sediment cores and predict the future evolution of Pu distribution in the sediment cores. The fitted results indicated that the diffusion effect controlled the downward migration of Pu in the sediments, but this diffusive migration will not prevent the peak of global fallout Pu in undisturbed sediment cores from being a valuable time marker for sediment dating.

The level, distribution and source of artificial radionuclides in surface soil from Inner Mongolia, China

Mid- and long-half-life artificial radioisotopes in the earth's surface environment are of great concern to the environmental radiation risk assessment. As nuclear fuel and fission products, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Am, ⁹⁰Sr and ¹³⁷Cs in soils from Inner Mongolia of China were analyzed with a modified systematic separation procedure combined with ICP-MS and LSC measurements, to study the level, distribution and source of artificial radionuclides in the region. The radioactivity and inventory of ¹³⁷Cs (0.26-28.3 Bq/kg, 0.5-5.4 kBq/m²), ^239+240Pu (0.05-1.26 Bq/kg, 20-229 Bq/m²), ²⁴¹Am (0.036-0.35 Bq/kg, 11-81 Bq/m²) and ⁹⁰Sr (1.2-7.6 Bq/kg, 0.39-1.7 kBq/m²) all lie in the range of the global fallout. Vertical distributions of these radionuclides were examined for two soil core samples SC14025 and SC14038, and great differences were observed between these two sample locations. For SC14025 where little human disturbance to soil occurred, both ¹³⁷Cs and ^239+240Pu have a subsurface activity maximum followed by an exponential decay. Fittings base on CDE model gives a small downward migration velocity of about 0.097 cm/y for both Pu and ¹³⁷Cs. Source identification for SC14025 and SC14038 soil cores with ²⁴⁰Pu/²³⁹Pu (average of 0.180 ± 0.017 and 0.164 ± 0.035, respectively), ¹³⁷Cs/^239+240Pu (average of 25.3 ± 0.6 and 25.6 ± 3.0, respectively) and ²⁴¹Am/^239+240Pu (average of 0.56 ± 0.08 and 0.60 ± 0.09, respectively) ratios consistently indicated that anthropogenic radionuclides in Xilingol region are mostly from the global fallout of atmospheric nuclear weapons tests in the last century. According to the geographical distribution of the radioactivity level, the high radioactivity level in the east of Inner Mongolia probably results from enhanced deposition by the blocking of the Great Khingan Range.

Plutonium isotopes in Northern Xinjiang, China: Level, distribution, sources and their contributions

Plutonium in the environment has drawn significant attentions due to its radiotoxicity in high concentration and source term linked with nuclear accidents and contaminations. The isotopic ratio of plutonium is source dependent and can be used as a fingerprint to discriminate the sources of radioactive contaminant. ²³⁹Pu, ²⁴⁰Pu and ¹³⁷Cs in surface soil and soil cores collected from Northern Xinjiang were determined in this work. The concentrations of ^239,240Pu and ¹³⁷Cs are in the range of 0.06-1.20 Bq kg^-1, and <1.0-31.4 Bq kg^-1 (decay corrected to Sep. 2017), respectively, falling in the ranges of global fallout in this latitude zone. The ²⁴⁰Pu/²³⁹Pu atomic ratios of 0.118-0.209 and ^239,240Pu/¹³⁷Cs activity ratios of 0.039-0.215 were measured. Among the investigated sites, distinctly lower ²⁴⁰Pu/²³⁹Pu atomic ratios of 0.118-0.133 and higher ^239,240Pu/¹³⁷Cs activity ratios of 0.065-0.215 compared to the global fallout values were observed in the northwest part, indicating a significant contribution from other source besides the global fallout. This extra source is mainly attributed to the releases of atmospheric nuclear weapons testing at Semipalatinsk Nuclear Test Site, which was transported by the west and northwest wind through the river valley among mountains in this region. This contribution is estimated to account for 28-43% of the global fallout in the northwest part of Northern Xinjiang. The contribution from the Chinese atmospheric nuclear weapons testing to this region is negligible due to the lack of appropriate wind direction to transport the radioactive releases to this region.

First study of 237Np in Chinese soils: Source, distribution and mobility in comparison with plutonium isotopes

In this study, the distribution and migration of ²³⁷Np and ^239+240Pu in soils in the vicinity (<5 km) of Qinshan and Tianwan Nuclear Power Plants in China were studied, which is the first specific study of global fallout ²³⁷Np in Chinese soils. The ²³⁷Np and ^239+240Pu concentrations in surface soils showed large spatial inhomogeneity. A remarkable ^239+240Pu concentration (4.783 mBq/g) was observed in a surface soil near Qinshan NPP and stands for the ever reported highest value in the Chinese soils. The inventories of ^239+240Pu in two Qinshan and Tianwan soil cores were estimated to be 128.8 Bq/m² and 121.0 Bq/m², respectively; while the ²³⁷Np inventories were 0.039 Bq/m² and 0.035 Bq/m² at these sites, respectively. The ²⁴⁰Pu/²³⁹Pu atomic ratios in these soils indicated that the global fallout is the main source of Pu in these regions. However, the non-isotopic ²³⁷Np/²³⁹Pu atomic ratio in environmental soil is not a sensitive indicator for source identification. Furthermore, we conducted pilot study on the migration behaviors of ²³⁷Np and ^239+240Pu in soil core at Qinshan site with the Convection-Dispersion Equation (CDE) model. The obtained apparent dispersion coefficients of ²³⁷Np (2.82 ± 2.06 cm²/y) was 5 times higher than that of ^239+240Pu (0.57 ± 0.16 cm²/y), proving that ²³⁷Np has stronger migration ability than Pu isotopes in the Qinshan soil. Finally, we predicted that with the increase of migration time, both ²³⁷Np and ^239+240Pu concentration in the soil will gradually become more evenly distributed among different soil layers due to the dominant dispersion effects.

Characteristic of Pu from urban wetland and lacustrine sediments in Suzhou Industrial Park, China

In this study, plutonium activity concentrations in the urban wetlands and lacustrine sediment of Suzhou Industrial Park (SIP) are studied for the first time. Results show ^239+240Pu activity concentrations in the wetland surface soils of SIP range from 0.035 to 0.426 mBq/g and the ²⁴⁰Pu/²³⁹Pu atom ratio ranges from 0.171±0.024 to 0.226±0.049. Judging from the atom ratio of ²⁴⁰Pu/²³⁹Pu, the main source of Pu in the wetland is global fallout. The correlations of Pu between organic matter and heavy metals are also studied. The correlation coefficients show Pu has significant positive correlations with Cu, Sn and Pb but negative correlation with As. Unlike distributions of Pu in other places, Pu in SIP has weak correlation with organic matter content. A sediment core from Lake Yangcheng is also analyzed to investigate the historical record of Pu deposition. The atom ratios of each layer in the sediment core indicate the area is mainly influenced by global fallout. Using Pu as a discrete-time maker, the deposition rate in Lake Yangcheng is 0.396±0.019 cm/yr. The calculated inventory of ^239+240Pu is 58.5 Bq/m², which is in the range of inventories of the corresponding latitudes according to UNSCEAR.

An overview of current knowledge concerning the inventory and sources of plutonium in the China Seas

This study reviews the current understanding of the inventory and sources of plutonium (Pu) in the marine environment adjacent to China. The ^239+240Pu inventory in the China Seas was found to have large spatial variations. The quantity in sediments decreases away from the shore, generally tracing the sedimentation rate distribution. High ^239+240Pu inventories indicated that Pu in the water column was easily scavenged since Pu has a high particle affinity. Indeed, substantially higher ²⁴⁰Pu/²³⁹Pu atom ratios were observed in the sediment and seawater of the China Seas than are found in global fallout. We thus clarified that Pu sources in the China Seas were from both global fallout and the Pacific Proving Grounds (PPG) in the Pacific Marshall Islands. Plutonium from the latter source is transported into the China Seas through the North Equatorial Current (NEC) and Kuroshio. Using a two end-member mixing model, we revealed that the contribution of Pu from the PPG accounts for over 40% of the Pu in the East China Sea (ECS) and South China Sea (SCS), and less than 20% of the Pu in the Yellow Sea (YS). The distributions and isotopic composition of Pu in the China Seas indicate strong scavenging of Pu in the ECS and high Pu accumulation in the SCS. This information on the inventory and isotopic composition of Pu helps to establish a background for the future study of Pu in the China Seas.

Distribution and Source Identification of Pu in River Basins in Southern China

The ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu atom ratios in surface sediments from the major river basins in southern China were analyzed to investigate the distribution and source of Pu. We clarified that the ^239+240Pu activities in these river basins were very similar, however, only the ^239+240Pu activities in the Jinjiang Basin were generally higher than other samples. Because of river transport function, the distribution of ^239+240Pu activities in these river basins presented an increasing trend from the upstream region to the estuary. According to the ²⁴⁰Pu/²³⁹Pu atom ratios, the Pu source in the inner river basins might be from global fallout, and the Pu in river estuaries might be from the global fallout and the Pacific Proving Grounds (PPG) in the Marshall Islands. Using a mass balance of the Pu model, we quantified in the Pearl River Estuary and the Pu contribution from the Pearl River Basin to Pu inventory was 13 ± 5%. These data not only filled in a knowledge gap of Pu in these river basins but also served as background data for Pu contamination from a nuclear reactor. Also, there are several planned and operating nuclear power plants in these river basins and these data could provide some indications for dealing with nuclear accidents in different parts of river basins in the future. In this study, we also analyzed some factors that would affect the distribution of ^239+240Pu activities; however, only total organic carbon (TOC) content and the heavy metal As had a positive correlation with the ^239+240Pu activity.

Level, distribution and sources of plutonium in the coastal areas of China

Plutonium is an important radioactive element in view of its biological toxicity and environmental impact. The two most important isotopes of plutonium, ²³⁹Pu and ²⁴⁰Pu, in the surface soil from the coastal area of China were determined using radiochemical separation combined with inductively coupled plasma mass spectrometry (ICP-MS) measurement. The average of the measured ²⁴⁰Pu/²³⁹Pu atomic ratios in all these samples is 0.186 ± 0.021, which is in good agreement with the ratio of global fallout of the nuclear weapons tests. This indicates that the major source of plutonium in this region is global fallout, and there is no measurable release of plutonium from any nuclear power plant along the coast of China. The ^239,240Pu concentrations in all 71 soil samples range from 0.002 mBq/g to 0.670 mBq/g, which fall in the range of the reported values in the background area not directly influenced by nuclear activities. The anthropogenic disturbance of sampling sites, vegetation coverage of land, precipitation rate and organic substance content and erosion of soil have significant influence on the level of plutonium in the surface soil.

The 240Pu/239Pu atom ratio in Chinese soils

The ²⁴⁰Pu/²³⁹Pu atom ratio is a very effective tool for the identification of the origin of plutonium (Pu) in the soil environment. We examine a dataset of ²⁴⁰Pu/²³⁹Pu atom ratios determined from surface and core soils at 240 sites across China. The data were compiled from 18 separate literature sources from the last 20 years. For the first time the spatial distribution (3 latitude bands and 7 natural regions) of the weighted average ²⁴⁰Pu/²³⁹Pu atom ratios in Chinese soils is investigated. An area to the West of Xining City, shows a weighted average ²⁴⁰Pu/²³⁹Pu atom ratio of 0.167 ± 0.002, lower than that of average global fallout, which likely arises from the addition of local fallout radionuclides from the Chinese nuclear weapon tests at Lop Nor between 1964 and 1980. The Yumen and Jiuquan areas of Northwest China in particular show evidence of very low ratio material from the Chinese nuclear weapon tests. Excluding the impacted area around the test site the weighted average ²⁴⁰Pu/²³⁹Pu ratio of 0.182 ± 0.002 suggests that global fallout is the main source of Pu in most Chinese soils.

Isotopic composition and source of plutonium in the Qinghai-Tibet Plateau frozen soils

The 239+240Pu activities and 240Pu/239Pu atom ratios in the frozen soils of the Yellow River Source Area (YRSA) were determined to examine the Pu source and evaluate its environmental risk. The 239+240Pu activities of surface frozen soils in the YRSA, ranging from 0.053 to 0.836 mBq g-1, are comparable to those observed in China elsewhere (0.005-1.990 mBq g-1). The 240Pu/239Pu atom ratios of surface soils in the YRSA are in the range of 0.168-0.201 (average = 0.187 ± 0.012, n = 6), comparable to the global fallout of 0.180 ± 0.014. Based on the latitudinal and spatial distribution of Pu isotopic composition, I clarified that the Pu source is mainly from global fallout at present. The activity levels of Pu in the YRSA do far not cause a Pu toxicity to the downstream drinking water even the frozen soil begins to melt and release Pu to the Yellow River. However, since close-in fallout from Lop Nor where the Chinese nuclear tests were carried out during 1964-1980, high deposition and accumulation of Pu was observed in the Chinese soil cores through synthesizing an expanded Pu dataset, which alerts us it is necessary to further monitor the Pu activity levels in the YRSA soil cores to ensure the safety of downstream drinking water. Finally, I point out that information on Pu isotopes would help in establishing a baseline for future environmental risk assessment.

Characteristics of artificial radionuclides in sedimentary soil cores from a volcanic crater lake

The distributions of ¹³⁷Cs, ²³⁷Np, and ^239+240Pu activity concentrations in sedimentary soil cores of the volcanic crater-lake have been studied. The ²⁴⁰Pu/²³⁹Pu atom ratios measured by MC-ICP-MS and mutual activity ratios were examined. These results were used to evaluate the sedimentation characteristics of the crater-lake (Baengnokdam of Mt. Halla, Korea). The ¹³⁷Cs, ²³⁷Np, and ^239+240Pu activity concentrations showed similar distribution patterns and one maximum peak was observed in each sediment core, except at St.10. For all sediment cores, the activity concentrations were in the range 1.03 × 10⁰-1.92 × 10² Bq·kg^-1 dw for ¹³⁷Cs, 7.56 × 10^-3 - 7.15 × 10⁰ mBq·kg^-1 dw for ²³⁷Np, and 5.20 × 10^-3 - 5.13 × 10⁰ Bq·kg^-1 dw for ^239+240Pu, respectively. The averaged ²⁴⁰Pu/²³⁹Pu atomic ratio (0.159) was slightly less than the global fallout ratio (0.176). The averaged inventories were estimated to be 9.21 × 10³±5.34 × 10³ Bq·m^-2 for ¹³⁷Cs, 2.27 × 10²±1.58 × 10² Bq·m^-2 for ^239+240Pu, and 3.22 × 10^-1±1.78 × 10^-1 Bq·m^-2 for ²³⁷Np. The averaged ^239+240Pu/¹³⁷Cs and ²³⁷Np/^239+240Pu activity ratios were 2.21 × 10^-2 and 2.21 × 10^-3, respectively. The mean sedimentation rates calculated using ^239+240Pu activity concentrations at the central area (St.30 - St.45) and at all stations (St.5 - St.75) were estimated to be 0.844 cm yr^-1, and 0.767 cm yr^-1, respectively. In addition, the sedimentation rates calculated using ²¹⁰Pb and ²²⁶Ra were 0.856 cm yr^-1 at depths of 0-35 cm and 0.204 cm yr^-1 at depths of 35-55 cm. These results imply that the sedimentation in Baengnokdam was relatively slow (0.204 cm yr^-1) until about 44 years ago and then became faster (0.856 cm yr^-1) to the present. The excess ²¹⁰Pb dating is consistent with the sedimentation rate calculated from the vertical ^239+240Pu profile.

Sedimentary record of plutonium in the North Yellow Sea and the response to catchment environmental changes of inflow rivers

Plutonium (Pu) isotopes were first determined in surface and core sediment samples collected from the northern North Yellow Sea (NYS) to elucidate their source terms and deposition process as well as the response to catchment environmental changes of inflow rivers. ²⁴⁰Pu/²³⁹Pu atom ratios in all sediments showed the typical global fallout value of ∼0.18 without any influences from the nuclear weapons tests conducted recently in the North Korea or early in the Pacific Proving Ground. The large variation of ^239+240Pu activities (0.022-0.515 mBq/g) observed in surface sediments should be mainly attributed to the re-suspension and transportation of fine sediments influenced by the Liaonan Costal Current. Based on the two ^239+249Pu depth profiles with easily observed onset fallout levels (1952) and global fallout peaks (1963), ^239+240Pu served as a valid time mark in the coastal sedimentary system. Riverine input Pu contributed only 15-27% to the total global fallout inventory (92.5-108.8 Bq/m²) in the northern NYS, much lower than that in the Yangtze River estuary (77-80%), indicating a better soil conservation in the northeast China due to higher forest coverage compared to the Yangtze River's drainage basin. The increase of riverine input Pu after 1980s reflected the more intense soil erosion degree caused by the land use and cover change due to the increment of human activities in the northeast China at the same period. Our results demonstrated that plutonium is a good indicator for studying sedimentary process and its response to the environment in the coastal area.

From floodplain to aquatic sediments: Radiogeochronological fingerprints in a sediment core from the mining impacted Sancho Reservoir (SW Spain)

The Sancho Reservoir (SW Spain) was built in 1962, about the time of maximum ¹³⁷Cs fallout, and it has been affected by acid mine drainage (AMD) particularly since the mining cease in 2001. This is a unique scenario for studying the radiogeochronological fingerprints in AMD-affected sediments deposited over the former flood plain. A sediment core sampled in 2011 was analysed for bulk density, ¹³⁷Cs, ²³⁹Pu, ²⁴⁰Pu, ²¹⁰Pb, ²²⁶Ra, ²²⁸Ra, ²³⁴Th (²³⁸U) and ⁴⁰K, and studied with various radiometric dating models. Bulk density revealed unsteady compaction and likely depositional events. The activity concentrations of ²²⁶Ra, ²²⁸Ra, ²³⁴Th (²³⁸U) and ⁴⁰K were uniform down-core, but declining overall in the upper 0-25cm, revealing changes in provenance except for ²³⁸U, which increased in the top 10cm likely due to its supply by AMD. The AMD fingerprint was also found in the ^239+240Pu/¹³⁷Cs activity ratio, which increased in the top sediment layers. The ¹³⁷Cs and ^239+240Pu profiles show well defined peaks at the same depth, with inventories being about four times higher than the expected integrated atmospheric deposition in the area. The unsupported ²¹⁰Pb (²¹⁰Pb_exc) showed a complex non-monotonic profile interrupted at several sections, particularly around the ¹³⁷Cs peak. The whole dataset cannot be interpreted in terms of continuous sedimentation processes. Based upon correlated features in the bulk density and ²¹⁰Pb_exc profiles, a series of depositional events (likely linked to peaks in the rainfall records) have been identified in the core. These events date back to the period comprised since the construction of the dam until its increase in height in 1972, which likely displaced upstream the main depositional area of riverine loads, as inferred from sediment trap data. The CRS (with a reference date) and (a piecewise) CIC models have been used for complementing and discussing the chronology.

Sources of plutonium isotopes and 137Cs in coastal seawaters of Liaodong Bay and Bohai Strait, China and its environmental implications

In order to investigate the sources of plutonium in seawaters of Liaodong Bay and Bohai Strait, China, surface seawater samples were collected and analyzed for ^239+240Pu and ¹³⁷Cs by radiochemical separation combined with ICP-MS and γ-spectrometry, respectively. A large variation of ^239+240Pu activities was observed, ranging from 1.993 to 29.677 mBq/m³ in the Liaodong Bay and from 0.932 to 10.183 mBq/m³ in the Bohai Strait. ¹³⁷Cs activities showed little variation between the investigated locations, which was attributed to the different behavior characteristics of ^239+240Pu and ¹³⁷Cs in seawaters. The ²⁴⁰Pu/²³⁹Pu atom ratios showed a significant variation between the Liaodong Bay (0.185) and Bohai Strait (0.225), indicating that Pu derived from the Pacific Proving Grounds might have been transported to the Bohai Strait but not yet to the Liaodong Bay, which could further provide valuable reference for evaluating the seawater exchange cycle between the Bohai Sea and Yellow Sea.

Spatial and vertical distribution of radiocesium in seawater of the East China Sea

The ¹³⁷Cs activity in surface water of the East China Sea (ECS) was 0.66-1.36 Bq m^-3 during May of 2011. The low activities were observed in the Changjiang Estuary and Zhejiang-Fujian coast and high activities were observed in the south offshore and Kuroshio Current pathway, suggesting that the influence from the current system in the ECS. The ¹³⁴Cs were undetectable (<0.03 Bq m^-3) and the contribution of the Fukushima accident to ECS is estimated to be below 3%; hence it is negligible during the investigation period. Using the vertical profiles of ¹³⁷Cs in the ECS, the mass balance is obtained, which suggests that the oceanic input dominates the ¹³⁷Cs source in the ECS. ¹³⁷Cs is potentially useful to trace water mass movement in the ECS. Our study provides comprehensive baseline of ¹³⁷Cs in the ECS for evaluation of the possible influence of the nuclear power plants in the future.

Sources and accumulation of plutonium in a large Western Pacific marginal sea: The South China Sea

In order to examine the sources of plutonium (Pu) and elaborate its scavenging and accumulation processes, ²⁴⁰Pu/²³⁹Pu atom ratios and ^239+240Pu activities in the water column of the South China Sea (SCS) were determined and compared with our previously reported data for the sediments. Consistently high ²⁴⁰Pu/²³⁹Pu atom ratios that ranged from 0.184-0.250 (average=0.228±0.015), indicative of non-global fallout Pu sources were observed both in the surface water and at depth during 2012-2014. The spatial distribution of the ²⁴⁰Pu/²³⁹Pu atom ratio in the SCS showed a decreasing trend away from the Luzon Strait, which was very consistent with the introduction pathway of the Kuroshio Current. The Kuroshio had an even heavier Pu isotopic ratio ranging from 0.250-0.263 (average=0.255±0.006), traceable to the non-global fallout Pu signature from the Pacific Proving Grounds (PPG). Using a simple two end-member mixing model, we further revealed that this PPG source contributed 41±17% of the Pu in the SCS water column. The ^239+240Pu activities in the SCS surface seawater varied from 1.59 to 2.94mBqm^-3, with an average of 2.34±0.38mBqm^-3. Such an activity level was ~40% higher than that in the Kuroshio. The distribution of ^239+240Pu in the surface seawater further showed a general trend of increase from the Kuroshio to the SCS basin, suggesting significant accumulation of Pu within the SCS. The ^239+240Pu inventory of the water column in the SCS basin at the SEATS station with a total depth of ~3840m was estimated to be ~29Bqm^-2, which was substantially higher than the sediment core estimates made for the SCS basin (3.75Bqm^-2) but much lower than the sediment core estimates made for the shelf of the northern SCS (365.6Bqm^-2). Such differences were determined by the lower scavenging efficiency of Pu in the SCS basin compared to the northern SCS shelf.

Vertical distributions and source identification of the radionuclides 239Pu and 240Pu in the sediments of the Liao River estuary, China

Activity concentration of plutonium (Pu) and its isotopic compositions are extensively used for measuring transport processes of Pu and identifying its source. We investigated the spatial distribution characteristics of ^239+240Pu activity concentrations and ²⁴⁰Pu/²³⁹Pu atom ratio in several sediment cores collected from the Liao River coastal zone. Additionally, we calculated the ^239+240Pu inventories and based on the ²⁴⁰Pu/²³⁹Pu atom ratio to trace Pu source. The activity concentrations of ^239+240Pu in surface sediments of the Liao River estuary ranged between 0.103 ± 0.008 and 0.978 ± 0.035 mBq/g, with an average of 0.294 ± 0.024 mBq/g. The ²⁴⁰Pu/²³⁹Pu atom ratios, ranging from 0.173 ± 0.047 to 0.215 ± 0.061 (mean: 0.188 ± 0.049 (1σ)), were consistent with global fallout value, which indicates the global atmospheric fallout is the main source of Pu in sediment cores from the both sides of Liao River estuary. As for the tidal flat core LT-2, the mean ²⁴⁰Pu/²³⁹Pu atom ratio, slightly higher than that of the global fallout value, was 0.217 ± 0.050. Such pattern of Pu isotopic compositions indicated that Pu on the tidal flat in the Liao River estuary is sourced from a combination of global fallout and close-in fallout from the PPG by ocean currents transporting. And by using a two end-member mixing model, the results indicate the relative contribution of the PPG close-in fallout to core LT-2 is round 27% and 73% can be attributed to global fallout and river input. Therefore, these results clearly indicate that the direct global fallout is the main source of Pu in the Liao River estuary.

(129)I record of nuclear activities in marine sediment core from Jiaozhou Bay in China

Iodine-129 has been used as a powerful tool for environmental tracing of human nuclear activities. In this work, a sediment core collected from Jiaozhou Bay, the east coast of China, in 2002 was analyzed for (129)I to investigate the influence of human nuclear activities in this region. Significantly enhanced (129)I level was observed in upper 70 cm of the sediment core, with peak values in the layer corresponding to 1957, 1964, 1974, 1986, and after 1990. The sources of (129)I and corresponding transport processes in this region are discussed, including nuclear weapons testing at the Pacific Proving Grounds, global fallout from a large numbers of nuclear weapon tests in 1963, the climax of Chinese nuclear weapons testing in the early 1970s, the Chernobyl accident in 1986, and long-distance dispersion of European reprocessing derived (129)I. The very well (129)I records of different human nuclear activities in the sediment core illustrate the potential application of (129)I in constraining ages and sedimentation rates of the recent sediment. The releases of (129)I from the European nuclear fuel reprocessing plants at La Hague (France) and Sellafield (UK) were found to dominate the inventory of (129)I in the Chinese sediments after 1990, not only the directly atmospheric releases of these reprocessing plants, but also re-emission of marine discharged (129)I of these reprocessing plants in the highly contaminated European seas.

Pu isotopes in soils collected downwind from Lop Nor: regional fallout vs. global fallout

For the first time, soil core samples from the Jiuquan region have been analyzed for Pu isotopes for radioactive source identification and radiological assessment. The Jiuquan region is in downwind from the Lop Nor Chinese nuclear test (CNT) site. The high Pu inventories (13 to 546 Bq/m²) in most of the sampling locations revealed that this region was heterogeneously contaminated by the regional fallout Pu from the CNTs. The contributions of the CNTs to the total Pu in soils were estimated to be more than 40% in most cases. The ²⁴⁰Pu/²³⁹Pu atom ratios in the soils ranged from 0.059 to 0.186 with an inventory-weighted average of 0.158, slightly lower than that of global fallout. This atom ratio could be considered as a mixed fingerprint of Pu from the CNTs. In addition, Pu in soils of Jiuquan region had a faster downward migration rate compared with other investigated places in China.

Plutonium as a tracer for soil erosion assessment in northeast China

Soil erosion is one of the most serious environmental and agricultural problems faced by human society. Assessing intensity is an important issue for controlling soil erosion and improving eco-environmental quality. The suitability of the application of plutonium (Pu) as a tracer for soil erosion assessment in northeast China was investigated by comparing with that of 137Cs. Here we build on preliminary work, in which we investigated the potential of Pu as a soil erosion tracer by sampling additional reference sites and potential erosive sites, along the Liaodong Bay region in northeast China, for Pu isotopes and 137Cs. 240Pu/239Pu atomic ratios in all samples were approximately 0.18, which indicated that the dominant source of Pu was the global fallout. Pu showed very similar distribution patterns to those of 137Cs at both uncultivated and cultivated sites. 239+240Pu concentrations in all uncultivated soil cores followed an exponential decline with soil depth, whereas at cultivated sites, Pu was homogenously distributed in plow horizons. Factors such as planted crop types, as well as methods and frequencies of irrigation and tillage were suggested to influence the distribution of radionuclides in cultivated land. The baseline inventories of 239+240Pu and 137Cs were 88.4 and 1688 Bq m(-2) respectively. Soil erosion rates estimated by 239+240Pu tracing method were consistent with those obtained by the 137Cs method, confirming that Pu is an effective tracer with a similar tracing behavior to that of 137Cs for soil erosion assessment.

Vertical distributions of radionuclides ((239+240)Pu, (240)Pu/(239)Pu, and (137)Cs) in sediment cores of Lake Bosten in Northwestern China

Artificial radionuclides ((137)Cs, (239+240)Pu, (241)Pu, (241)Am) deposited in lacustrine sediments have been used for dating as well as radionuclide source identification. In the present work, we investigated the vertical distributions of (239+240)Pu and (137)Cs activities, (240)Pu/(239)Pu atom ratios, and (239+240)Pu/(137)Cs activity ratios in sediment cores collected from Lake Bosten, which is the lake closest to the Lop Nor Chinese Nuclear Weapon Test site in northwestern China. Uniformly high concentrations of (239+240)Pu and (137)Cs were found in the upper layers deposited since 1964 in the sediment cores, and these were controlled by the resuspension of soil containing radionuclides from the nearby land surface. As the Chinese nuclear tests varied remarkably in yield, the mixing of the tropospheric deposition from these tests and the stratospheric deposition of global fallout has led to a (240)Pu/(239)Pu atom ratio that is similar to that of global fallout and to a (239+240)Pu/(137)Cs activity ratio that is slightly higher than that of global fallout. However, a low (240)Pu/(239)Pu atom ratio of 0.080 and high (239+240)Pu/(137)Cs activity ratio of 0.087, significantly different from the global fallout values, were observed in one sediment core (07BS10-2), indicating the inhomogenous tropospheric deposition from the Chinese nuclear tests in Lake Bosten during 1967-1973. These results are important to understand the influence of the CNTs on the radionuclide contamination in Lake Bosten.

Plutonium in soils from northeast China and its potential application for evaluation of soil erosion

Surface and soil core samples from northeast China were analyzed for Pu isotopes. The measured (240)Pu/(239)Pu atomic ratios and (239 + 240)Pu/(137)Cs activity ratios revealed that the global fallout is the dominant source of Pu and (137)Cs at these sites. Migration behavior of Pu varying with land type and human activities resulted in different distribution of Pu in surface soils. A sub-surface maximum followed by exponential decline of (239 + 240)Pu concentrations was observed in an undisturbed soil core, with a total (239 + 240)Pu inventory of 86.9 Bq/m(2) and more than 85% accumulated in 0 ~ 20 cm layers. While only half inventory of Pu was obtained in another soil core and no sub-surface maximum value occurred. Erosion of topsoil in the site should be the most possible reason for the significantly lower Pu inventory, which is also supported by the reported (137)Cs profiles. These results demonstrated that Pu could be applied as an ideal substitute of (137)Cs for soil erosion study in the future.

Polybrominated diphenyl ethers and decabromodiphenylethane in sediments from twelve lakes in China

Sediment cores from 12 Chinese lakes were analyzed to investigate the historical inputs of polybrominated diphenyl ethers (PBDEs) and decabromodiphenylethane (DBDPE) during the past few decades. Concentrations of ΣPBDE(1) (sum of tri- to hepta-BDEs), ΣPBDE(2) (sum of nona- to deca-BDEs) and DBDPE in the surface sediments were 0.02-0.29 ng g(-1), 0.46-46.6 ng g(-1) and 1.02-3.64 ng g(-1), respectively. The temporal trends of PBDEs and DBDPE followed a general increase from the bottom to the surface. The calculated fluxes for ΣPBDE(1), ΣPBDE(2) and DBDPE were 0.001-0.09, 0.03-4.24, and 0.05-0.31 ng cm(-2) yr(-1), and the inventories were 0.09-7.86, 0.91-461, and 3.83-24.6 ng cm(-2), respectively. The urbanization and industrialization are highly related to the contamination of PBDEs and DBDPE in sediments. The DBDPE input in recent years was still lower than ΣPBDE(2) but the temporal trends indicated that the contamination would increase with the increasing usage of DBDPE in the future.

Reconstruction of metal pollution and recent sedimentation processes in Havana Bay (Cuba): a tool for coastal ecosystem management

Since 1998 the highly polluted Havana Bay ecosystem has been the subject of a mitigation program. In order to determine whether pollution-reduction strategies were effective, we have evaluated the historical trends of pollution recorded in sediments of the Bay. A sediment core was dated radiometrically using natural and artificial fallout radionuclides. An irregularity in the (210)Pb record was caused by an episode of accelerated sedimentation. This episode was dated to occur in 1982, a year coincident with the heaviest rains reported in Havana over the XX century. Peaks of mass accumulation rates (MAR) were associated with hurricanes and intensive rains. In the past 60 years, these maxima are related to strong El Niño periods, which are known to increase rainfall in the north Caribbean region. We observed a steady increase of pollution (mainly Pb, Zn, Sn, and Hg) since the beginning of the century to the mid 90 s, with enrichment factors as high as 6. MAR and pollution decreased rapidly after the mid 90 s, although some trace metal levels remain high. This reduction was due to the integrated coastal zone management program introduced in the late 90 s, which dismissed catchment erosion and pollution.

Anomalous plutonium isotopic ratios in sediments of Lake Qinghai from the Qinghai-Tibetan Plateau, China

The vertical profiles of (239+240)Pu and (137)Cs activities and (240)Pu/(239)Pu isotopic ratios are determined for three sediment cores of Lake Qinghai from the Qinghai-Tibetan Plateau, China, and compared with those in sediments of another three lakes (Lakes Bosten, Sugan, and Shuangta), the only existing ones closest to Lop Nor area, China's nuclear weapons test site in the northwestern part of the country. The mean inventory of 47.7 ± 18.7 MBq km(-2) for (239+240)Pu activity in Lake Qinghai is comparable to the average value of global fallout expected at the same latitude, yet the mean inventory of 1112.0 ± 78.0 MBq km(-2) for (137)Cs is slightly lower than that of global fallout. Anomalously low (240)Pu/(239)Pu isotopic ratios (0.038-0.125) were found in the 3-6.5 cm deep sediment layers, indicating the trace Pu input from early nuclear weapons research activities at Atomic City in the lake's watershed during the 1950-60s. Model calculation indicated that the Pu input accounted for approximately 5-16% of the total Pu inventory. The observation of low (240)Pu/(239)Pu ratio in the deep sediment layer provided a new time marker for recent sediment dating in the lake and around the area. The results are of great significance to the further understanding of sources, records, and environmental impacts of global and regional nuclear activities in the environment and provide important chronological information for further studies on the water eutrophication process and climatic change, and reconstruction of pollution history of organic contaminants and heavy metals in the watershed of Lake Qinghai.

Distribution of artificial radionuclides in lacustrine sediments in China

Establishing accurate historical records of the distribution, inventory and source of artificial radionuclides in the environment is important for environmental monitoring and radiological health protection due to their potential toxicity, and is also useful for identification and risk assessment of possible future environmental inputs of radionuclides from nuclear weapons tests and accidental release from the nuclear fuel reprocessing facilities or nuclear power reactors. A sector-field inductively coupled plasma mass spectrometer was used to study the recent sedimentation of Pu isotopes in 11 lakes in China. The distribution of (137)Cs was investigated using the conventional radiometric analytical methods. Based on the isotopic compositions of Pu and the activity ratio of (137)Cs/(239+240)Pu, the sources of artificial radionuclides were identified. The potential applications of Pu isotopes for sediment dating and for regional and global environmental change studies were discussed.