Plutonium in Southern Yellow Sea sediments and its implications for the quantification of oceanic-derived mercury and zinc

Spatial distribution, source identification, and transportation paths of plutonium in the Beibu Gulf, South China Sea

To investigate the spatial distribution and source of plutonium isotopes in the Beibu Gulf, surface sediments were collected and analyzed using sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). The activities of 239+240Pu in surface sediments ranged from 0.012 to 0.451 mBq/g (mean: 0.171 ± 0.138 mBq/g, n = 36), indicating a decreasing trend in a counterclockwise direction from the southern bay mouth. The counterclockwise decreasing trend in the south of the bay mouth is similar to the current in the Beibu Gulf. The 240Pu/239Pu atom ratios in surface sediments ranged from 0.156 to 0.283 (mean: 0.236 ± 0.031, n = 36), slightly higher than that of the global fallout value of 0.18. This suggests that the Pu in the Beibu Gulf was a combination of global fallout and Pacific Proving Ground (PPG). The average contribution of the plutonium (Pu) derived from the PPG in the sediment was estimated to be 52 % ± 24 %.

Impact of the lockdown period during the COVID-19 pandemic on the metal content of the anemone Anemonia sulcata in the Canary Islands (CE Atlantic, Spain)

Anemones, specifically the species Anemonia sulcata, are cnidarians that serve as bioindicators in marine ecosystems, indicating the health of the environment and changes in environmental conditions. Monitoring anemone populations and studying their well-being and distribution provide valuable insights into marine ecosystem conditions. This study aimed to investigate the impact of the SARS-CoV-2 pandemic on the metal content of Anemonia sulcata. Over a six-year period (2017-2022), twenty specimens of Anemonia sulcata were collected in Tenerife, Spain. The results showed that in 2020, during the two-month lockdown in Spain from March to May when tourism was halted, A. sulcata exhibited the lowest concentrations of various metals studied (Al, Cd, Cu, Fe, Pb, and Zn). This finding suggests that the reduced anthropogenic pressure on the coast due to the absence of tourism significantly decreased pollution levels. Therefore, the study emphasizes the importance of promoting sustainable tourism worldwide. The research highlights that minimizing human impact on coastal areas through responsible tourism practices can effectively reduce pollution in marine ecosystems.

Short review of plutonium applications for the sediment transport studies

The transport of sediments in surface waters is a natural process involving the relocation of the sediments themselves and the nutrients, pollutants and radionuclides associated with them. Plutonium isotopes have proven to be a useful tool for studying this process over several decades. In this article, we review the characteristics of the behaviour of plutonium in the water column and the main directions of its use to study the transport of sediments at different scales. The characteristic isotopic fingerprints of the sources and their known input functions, as well as the good reactivity of the particles, favour the widespread use of plutonium for the study of the chronology of sediments and deposits and for studies of the fate and migration pathways of sediments at different scales. While other radionuclides are losing relevance due to the short half-life the ²³⁹Pu and ²⁴⁰Pu will remain useable for a long time.

Spatio-temporal distribution of 239+240Pu in sediments of the China sea and adjacent waters

Data of ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu atom ratios in surface and core sediments of the China Sea and adjacent waters were collected. We examine a dataset of ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu ratios determined from surface sediments at 516 sites and 84 core sediment mainly across the China Sea and adjacent waters. For the first time the spatial distributions of the ^239+240Pu activities, the ²⁴⁰Pu/²³⁹Pu ratios and the Pacific Proving Ground (PPG) fraction in the China Sea and adjacent waters are fully presented at the same time. Four types of typical ^239+240Pu distribution with depth are commonly summarized: non-peak, pseudo single peak, single peak and multi peaks, which are based on the comprehensive analysis of the vertical distribution of ^239+240Pu in 84 sediment cores that had been studied in the China Sea and adjacent waters. Their occurrence probability are ∼15%, ∼4%, ∼67% and ∼11%, respectively. This is the dominant Pu source in seawater which was transported by the North Equatorial Current and Kuroshio Current and its extension into the China Sea and adjacent waters first from east to west, then from south to north. A sea area to the northeast of Taiwan Island and the Okinawa Trough, shows high ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu atom ratios spatial distribution trends, which are related to the intrusion of the Kuroshio Current carrying ^239+240Pu from the PPG nuclear weapon tests. The used two end-member mixing model suggests that global fallout and PPG close-in fallout are the main sources of Pu in most of the investigate areas. As the ²⁴⁰Pu/²³⁹Pu of global fallout is relatively constant, the change of ²⁴⁰Pu/²³⁹Pu ratios in surface sediments of the China Sea and adjacent waters are mainly controlled by the PPG close-in fallout input.

Bacterial community response to chronic heavy metal contamination in marine sediments of the East China Sea

Marine sediments act as a sink for various heavy metals, which may have profound impact on sedimentary microbiota. However, our knowledge about the collaborative response of bacterial community to chronic heavy metal contamination remains little. In this study, concentrations of seven heavy metals (As, Cd, Cr, Cu, Hg, Pb, and Zn) in sediments collected from the East China Sea were analyzed and Illumina Miseq 16 S rRNA sequencing was applied to characterize the structure of bacterial community. Microbiota inhabiting sediments in the East China Sea polluted with heavy metals showed different community composition from relatively pristine sites. The response of bacterial community to heavy metal stress was further interrogated with weighted correlation network analysis (WGCNA). WGCNA revealed ten bacterial modules exhibiting distinct co-occurrence patterns and among them, five modules were related to heavy metal pollution. Three of them were positively correlated with an increase in at least one heavy metal concentration, hubs (more influential bacterial taxa) of which were previously reported to be involved in the geochemical cycling of heavy metals or possess tolerance to heavy metals, while another two modules showed opposite patterns. Our research suggested that ecological functional transition might have occurred in East China Sea sediments by shifts of community composition with sensitive modules majorly involved in the meaningful global biogeochemical cycling of carbon, sulfur, and nitrogen replaced by more tolerant groups of bacteria due to long-term exposure to low-concentration heavy metals. Hubs may serve as indicators of perturbations of benthic bacterial community caused by heavy metal pollution and support monitoring remediation of polluted sites in marine environments.

Excess nitrogen in the Bohai and Yellow seas, China: Distribution, trends, and source apportionment

The Bohai and Yellow seas are marginal seas of the western North Pacific, characterized by coastal eutrophication and populated coastlines. In this work, six survey datasets collected between 2011 and 2018 were used to investigate the excess of dissolved inorganic nitrogen (DIN) related to soluble reactive phosphorus (SRP), referred to as N*, in the Bohai and Yellow seas. High N* of more than 5 μmol kg^-1 occurred mostly in the Changjiang and Yellow River plumes and/or near the Jiangsu coast. Away from these river plumes and the Jiangsu coast, however, N* usually ranged from -2.5 to 1.0 μmol kg^-1. Combining our field data and previously published data, we found that N* in the Bohai and Yellow seas increased in the 1990s and 2000s, likely caused by the combined effect of atmospheric nitrogen deposition increase and the Kuroshio N* rise. In the 2010s, however, the coastal N* increases stopped. Based on a N*-budgeting approach, marine N (either from in situ decomposition of marine organic matters or from the open seas via current inputs) and non-marine N (either from riverine inputs or from local atmospheric nitrogen deposition) were distinguished. Marine N accounted for 51% ± 38% of DIN in the Bohai Sea and 67% ± 37% of DIN in the Yellow Sea. Although this is a regional study, we suggest that accumulation of atmospheric nitrogen along oceanic circulation pathways dominates the decadal evolution of coastal eutrophication. These findings and new insights may improve management of eutrophication in these two important marginal seas, and will also improve our understanding of nutrient dynamics in other marine systems.

Distributions of 239Pu and 240Pu Concentrations and 240Pu/239Pu Atom Ratios and 239+240Pu Inventories in a Water Column in the Eastern Indian Ocean: Transport of Pacific Proving Grounds-Derived Pu via the Indonesian Throughflow

The ^239+240Pu concentrations and ²⁴⁰Pu/²³⁹Pu atom ratios in seawater from the eastern Indian Ocean were determined to identify their Pu sources and to propose the transport pathway of Pacific Proving Grounds (PPG)-derived Pu into the studied area. This is the first study by anyone on these Pu atom ratios in the Indian Ocean. In the West Australia Basin, the ^239+240Pu concentration was 2.89 mBq m^-3 in the surface water and increased with depth; a subsurface maximum was identified at 200 m depth and then decreased gradually with depth; its water column inventory was 32.8 Bq m^-2. The inventory-weighted mean ²⁴⁰Pu/²³⁹Pu atom ratios were 0.208 in the South Australia Basin, 0.226 in the Perth Basin, 0.242 in the West Australia Basin, 0.232 in the Bay of Bengal, and 0.225 in the Andaman Sea. The obtained ²⁴⁰Pu/²³⁹Pu ratios were clearly greater than the mean global fallout ratio of 0.18. These high atom ratios proved the presence of close-in fallout Pu from PPG nuclear tests. The relative contribution of global and PPG fallouts was evaluated using the two-end-member mixing model. The ^239+240Pu inventories originating from the PPG fallout were calculated as 2.9-14.9 Bq m^-2, which corresponded to 20-46% of the total ^239+240Pu inventory. A significant amount of the PPG-derived Pu has been transported to the eastern Indian Ocean. The proposed transport pathway accounting for the high ²⁴⁰Pu/²³⁹Pu ratio is the transportation of PPG-derived Pu by the North Equatorial Current followed by the Mindanao Current, Indonesian Throughflow, and then spreading over the Indian Ocean by its surface circulation system.

Spatial-temporal characteristics of mercury and methylmercury in marine sediment under the combined influences of river input and coastal currents

Mercury, especially in the form of methylmercury (MeHg), is a global pollutant, and aquatic products are considered the main sources of Hg exposure to humans. The Bohai and Yellow seas are two important epicontinental seas for marine fisheries and aquaculture in China. A decreasing trend of the THg in the Yellow River Estuary toward the outer edge was reported according to 83 surface sediments (27.3 ± 15.0 ng g^-1) and 3 sediment cores from the Bohai Sea and Yellow Sea. The relatively higher THg levels in the central Yellow Sea can be primarily attributed to higher organic carbon levels and finer-grained sediment sizes and partly to the particulates from the riverine input of the Yellow River driven by the currents. An increasing trend in THg levels since industrialization in north China around the Bohai and Yellow seas, and a decreasing trend of Yellow River THg input in recent years were recorded by sediment cores. The spatial distribution pattern of surface sediments MeHg (161 ± 130 pg g^-1) was different from that of THg. A higher MeHg content and MeHg/THg ratio were found in the Bohai and Yellow seas compared to the East China Sea, and extremely high MeHg levels (714 pg g^-1) were found in the Yellow Sea Cold Water Mass (YSCWM) area, which is considered an important region for fishery and marine breeding, suggesting that more attention should be paid to the potential ecological and human health risks in the region due to mercury exposure.