Recent 210Pb, 137Cs and 241Am accumulation in an ombrotrophic peatland from Amsterdam Island (Southern Indian Ocean)

A High–Resolution Accumulation Record of Arsenic and Mercury after the First Industrial Revolution from a Peatland in Zoige, Qinghai–Tibet Plateau

The impacts of human activities on Zoige peatlands are poorly documented. We determined the concentrations and accumulation rates of As and Hg in a 210Pb-dated peat profile collected from this area and analyzed the correlations between accumulation rates of both As and Hg and other physicochemical properties. To reconstruct recent conditions of As and Hg, we analyzed peat sediments of Re’er Dam peatland in Zoige using 210Pb and 137Cs dating technologies. The concentrations of total As (86.38 to 174.21 μg kg−1) and Hg (7.30 to 32.13 μg kg−1) in the peat profile clearly increased after the first industrial revolution. From AD 1824 to AD 2010, the average accumulation rates were 129.77 μg m−2 yr−1 for As and 18.24 μg m−2 yr−1 for Hg. Based on our results, anthropogenic emissions significantly affected the atmospheric fluxes of As and Hg throughout the past 200 years, and As was also likely to be affected by other factors than atmospheric deposition, which needs further identification by future studies. The historical variations in As and Hg concentrations in Re’er Dam peatland in Zoige mirror the industrial development of China.

Evaluating the effectiveness of soil conservation at the basin scale using floodplain sedimentary archives

Evaluation of the spatial and temporal composition of floodplain sediments and soils is critical in the creation of soil management strategies for impacted riverine catchments. The objective of this study was to determine the distribution, and to identify the sources, of particulate trace elements and fallout radionuclides in the catchment of the River Avon (SW England), where sedimentary processes had been altered by reservoir construction in the 1950s. The catchment was compartmentalized into its main functional units namely, cultivated land, pasture, woodland, wet moorland, and channel bank. Surface soils were collected in each unit, along with four strategically-placed cores, all of which were analyzed for particle size, fallout radionuclides and elemental concentrations. Sediment particle sizes and sediment accumulation rates were affected by the construction of the reservoir, specifically the distributions of silt and clay. The concentrations of fertilizer constituent Cr and P were highly correlated in the mid-catchment but were unrelated downstream due to elevated concentrations of Cr from geological deposits. Copper, As, Pb and Sn had variable down-core distributions, with pulses in concentrations due to mining inputs. The contributions of the end-member sources of particulate elements in the sedimentary mixtures were evaluated, quantitatively, using a Bayesian Mixing Model and the cultivated land was identified as a significant contributor to the mixtures, independent of space and time. The results contribute to advances in soil quality and conservation measures as components of a catchment management plan for the Avon, an approach maybe applicable to other small catchments in the UK and internationally.

A review of current and emerging approaches for Quaternary marine sediment dating

Dating methodologies for Quaternary marine sediments play increasingly important roles in the reconstruction of paleoenvironments and paleoclimate in (paleo)oceanography. Previous reviews or studies have focused mainly on one or two methodologies, and their applications in one specific environment. With the continuing technological and methodological advances in different methods over the past few decades, an up-to-date comparison of the pros and cons of each dating methodology is needed to clearly understand their applications in marine geoscience research. In this review, we first briefly summarized the common methods of absolute dating and relative dating. These are (1) radioisotope dating with different half-lives using natural nuclides of ²³⁴Th, ²¹⁰Pb, ²³⁰Th, and ²²⁶Ra, cosmogenic nuclides of ⁷Be, ¹⁴C, ¹⁰Be, ³²Si, ²⁶Al, ³⁶Cl and ²¹Ne, and the artificial radionuclides of ¹³⁷Cs, ^{239, 240}Pu, ²⁴¹Am and ¹²⁹I that have been induced by atmospheric nuclear tests, accidents in nuclear plants, and discharges of radioactive wastes; (2) radiation exposure dating of luminescence and electron paramagnetic resonance (ESR) dating; and (3) stratigraphic dating of δ¹⁸O and paleomagnetic sequence. Applications and limitations from the marine terraces, estuaries, to hadal trenches have been summarized to each technique in the study of Quaternary marine geoscience extending from the Anthropocene through the Pleistocene. Finally, we introduced some emerging event dating methods, namely the arrivals of microplastics, mercury isotopes, and organic pollutant deposition that all appeared after the industrial resolution in our now changing ocean influenced by acidification, global warming, and anthropogenic activities. We ended by discussing future perspectives for reliable and high-resolution chronology by interdisciplinary methods including computer programming to better understand the natural geological evolution and predict the future changes in earth science.

Atmospheric fallout of radionuclides in peat bogs in the Western Segment of the Russian Arctic

This article presents the results of studies of the activity of radionuclides in peat-bog profiles of the European subarctic of Russia. Two peat profiles were collected in different areas of the Arkhangelsk region. The peat cores were used to determine ²¹⁰Pb, ¹³⁷Cs, ²⁴¹Am, ²³⁹Pu, ²⁴⁰Pu, ²³⁸U, and ²³⁴U content. To estimate the relationship between radionuclide activity and physicochemical parameters of peat, the content of organic matter, water-soluble salts, carbonates and ash, and the pH of aqueous and salt extracts were studied. Radionuclide activity concentrations in peat samples were measured using inductively coupled plasma mass spectrometry (ICP-MS), low-background semiconductor gamma spectrometry with a high-purity germanium (HPGe) detector, and alpha spectrometry. The ²¹⁰Pb chronology of peat cores was studied using a constant flow model based on the Monte Carlo simulation method. Comparison of ²¹⁰Pb dating data showed that the position of the maximum activity peaks of anthropogenic radionuclides shifted along the peat profile. This is probably due to the relative mobility of different radionuclides in the peat massif. Measurement of the atomic ratio ²⁴⁰Pu/²³⁹Pu showed that the main sources of pollution in the peatlands of the European subarctic of Russia are global fallout from atmospheric tests from the 1950s through 1980 and fallout from the Chernobyl nuclear accident in 1986. This study shows that a complex of radioactive isotopes in peat deposits can provide valuable information on the environmental pollution loads of subarctic territories.

Geochemical markers of the Anthropocene: Perspectives from temporal trends in pollutants

Determining stratigraphic markers of the Anthropocene is important for demarcating Global Stratotype Section and Point (GSSP). Heavy metals and persistent organic pollutants (POPs) are candidate geochemical markers of the Anthropocene, but no study has comprehensively evaluated temporal trends in these pollutants in sediment cores globally. 454 data points for 8 heavy metals and 8 POPs were compiled to reconstruct their temporal trends and evaluate their global consistency. The heavy metals did not increase rapidly in the 20th century, and their temporal trends were locally but not globally consistent, which are not suitable geochemical markers of the Anthropocene. POPs rapidly increased beginning in the mid-20th century but have declined in the past decade, and these data are more consistent globally. The time of the peak concentration and period of rapid increase for polychlorinated biphenyls (PCBs) occur near the boundary of the Anthropocene and are consistent globally. Forty-five percent of the studies evaluated used only ²¹⁰Pb chronology for dating, which creates definite uncertainty in the analysis. In GSSP candidate sections, PCBs could be considered candidate markers of the Anthropocene.

Comment on: "A novel approach to peatlands as archives of total cumulative spatial pollution loads from atmospheric deposition of airborne elements complementary to EMEP data: Priority pollutants (Pb, Cd, Hg)" by Ewa Miszczak, Sebastian Stefaniak, Adam Michczyński, Eiliv Steinnes and Irena Twardowska

A recent paper by Miszczak et al. (2020) examines metal contamination of mires in Poland and Norway. The authors conclude that lead (Pb) records in ombrotrophic peatlands cannot be used to reconstruct the chronological history of anthropogenic activities due to post-depositional mobility of the metal. We contest this general conclusion which stands in contrast with a significant body of literature demonstrating that Pb is largely immobile in the vast majority of ombrotrophic peatlands. Our aim is to reaffirm the crucial contribution that peat records have made to our knowledge of atmospheric Pb contamination. In addition, we reiterate the necessity of following established protocols to produce reliable records of anthropogenic Pb contamination in environmental archives.

Natural radioactivity and radiation hazard assessment of industrial wastes from the coastal phosphate treatment plants of Gabes (Tunisia, Southern Mediterranean Sea)

This work is a first contribution to the knowledge of natural radionuclides (²²⁶Ra, ²³⁸U, ⁴⁰K, and ²³²Th) activities in phosphate rock (NORM), phosphogypsum, and phosphogypsum foam (TENORM) from the coastal fertilizer plants of Gabes (Southeastern Tunisia) and the assessment of their radiation hazards on human health and the surrounding environment. In the three studied materials, activities were found to be in the range of 35.4 (⁴⁰K)-375.1 (²²⁶Ra), 10.0 (⁴⁰K)-220.2 (²²⁶Ra), and 79.2 (²³²Th)-1168.6 Bq kg^-1 (²²⁶Ra), respectively. Considering the studied radionuclides and materials, the corresponding decreasing activity orders were found to be ²²⁶Ra > ²³⁸U > ⁴⁰K > ²³²Th and PGF > PR > PG, respectively. All human health hazard indices exceeded the worldwide recommended safety limits, which show that the workers in Gabes phosphate fertilizer plants as well as the neighboring human community may potentially be exposed to significant radiation, which may cause several diseases and malformations. It is therefore recommended to avoid and/or reduce the potential fertilizer industry radioactive impact in the area.

Discussions on the driving mechanism of postdepositional migration of 241Am and 137Cs in organomineral sediments (Lake Krugloe, Tomsk region, Russia)

A core of bottom sediments from Lake Krugloe located within the 30 km influence zone of the Siberian Chemical Plant (located in the city of Seversk "Tomsk-7") was studied to determine scales and rates of migration of artificial radionuclides ¹³⁷Cs and ²⁴¹Am in organomineral sediment. It was found that the main portion of ¹³⁷Cs and ²⁴¹Am was contained in the sediment interval above 10 cm. This means that the horizon of 10 cm corresponds to 1950-the time of the start of widespread tests of nuclear weapons. The ²¹⁰Pb_ex dates also confirm that this particular horizon was formed in the 1950s. Pore waters in the core above the 10 cm horizon are in oxidizing conditions. The depth of the oxidized/reduced boundary was determined from the distribution of redox-sensitive elements Fe and U dissolved in the pore solution. The core distribution of ¹³⁷Cs is a slightly sloping step, with the lower edge at the 10 cm level. The smearing of the lower boundary of this distribution showing the scale of ¹³⁷Cs migration made it possible to estimate the diffusion mobility of ¹³⁷Cs. Its diffusion coefficient turned out to be of the order of 10^-8 cm² s^-1. As shown by measurements, the scale of migration of ²⁴¹Am and the scale of migration of ¹³⁷Cs have similar values. Theoretical analysis carried out in this work shows that the most probable mechanism of ¹³⁷Cs and ²⁴¹Am migration in the pore solution of lake sediment is the migration of colloidal particles to which these radionuclides are strongly bound. Calculation of the diameter of such particles by the Stokes-Einstein formula shows that they have submicron dimensions (d ≈ 400 nm). No evidence was found that the change in redox conditions in the sediment had an effect on migration of Am ions in pore solution.