Distribution Of Radionuclides In Sediments Research Articles

Long-lived radionuclides in marine sediments from the Beibu Gulf, South China Sea: Spatial distribution, controlling factors, and proxy for transport pathway

The source and transport process of sediments are of great concern in marine sedimentology. In this study, naturally occurring radionuclides (238U, 226Ra, 228Ra, and 40K) in surface sediments and sediment cores were comprehensively analysed using high-purity germanium (HPGe) γ spectrometry in order to explore radionuclide fingerprints as novel proxies for tracking the source and transport pathway of sediments in the Beibu Gulf. We found that the radioactivity level of sediments in the Beibu Gulf was lower than that in other Chinese seas, following a comprehensive compilation and comparison of radioactivity in the region, indicating the Beibu Gulf is a high-quality marine environment. An interesting “butterfly pattern” was exhibited in the horizontal distribution of radionuclides in surface sediments from the Beibu Gulf, mainly attributable to the controlling factors of the non-linear negative regulation of sediment grain size and positive role of total organic carbon in sediment. Furthermore, the vertical distribution of radionuclides in sediment cores was affected by the redox state and a physical/biological disturbance, which were demonstrated by the simultaneous analysis of redox-sensitive element Mn and 210Pb, respectively. Additionally, the 226Ra238U endmember model and 232Th238U endmember model were proposed for quantifying local input (85%) and trans-region input (15%) of marine sediments in the Beibu Gulf in the context of the Guangdong-Qiongzhou Strait-Guangxi framework. We inferred that the Beibu Gulf was at risk of contamination by artificial radionuclides derived from nearby Guangdong Province, which has the highest number of nuclear power plants in China, through a trans-region input by ocean currents. Our study not only provided spatiotemporal distributions of radionuclides in the Beibu Gulf and their controlling factors (sediment grain size, total organic carbon, redox state, physical/biological disturbance, and ocean currents) but also indicated the radionuclide fingerprints (226Ra/238U and 232Th/238U) as potential geochemical proxies for quantifying the distinct sources of radionuclides and other associated chemicals (e.g., heavy metals, organic pollutants) in sediments.

Distribution of natural and anthropogenic radionuclides in northwest Mediterranean coastal sediments

The distribution of radionuclides in NW Mediterranean coastal sediments, and the processes controlling their abundance were investigated in three cores taken near the island of Porquerolles and one offshore Monaco. The sediments collected near Porquerolles were strongly anoxic due to diagenetic processes involved in the decomposition of organic matter, whereas they transitioned from oxic to anoxic at a depth of 4 cm beneath the seawater interface at Monaco. Organic carbon (OC) was more abundant in sediments at Porquerolles (by about a factor of 3–5) than at Monaco and elsewhere in the coastal NW Mediterranean. Sediment cores collected NE of Porquerolles also possessed elevated uranium concentrations that correlated with high OC content and strong reducing conditions. The 239,240Pu and 241Am activities in surficial sediments ranged from 1 to 5.7 Bq kg−1 and 0.3 to 1 Bq kg−1, respectively, while the 137Cs activity ranged from 0.3 to 6.2 Bq kg−1. The mean activity ratios of 241Am/239,240Pu and 238Pu/239,240Pu in Porquerolles and Monaco sediments were similar to the global fallout ratios. Sediment inventories of global fallout 239,240Pu (430–800 Bq m−2) and 241Am (150–285 Bq m−2) were by about a factor of 5–10 higher at Porquerolles, whereas the inventory of 137Cs (430–1000 Bq m−2) was substantially lower at the investigated stations than have been reported elsewhere at similar latitudes. Specific local conditions characterised by high OC sediment loads due to the growth and mortality of Posidonia oceanica have been responsible for deposition of large amounts of seagrass tissues at the NE corner of Porquerolles, which have had a profound effect on the distribution of radionuclides in the sediments.

Statistical regularities in the distribution of radionuclides in sediments of transcarpathia mountain rivers

The results of the low-background gamma-spectrometric measurements of sediments from three Western Carpathian mountain rivers during a three year term (2006–2009) are presented. These sediments are dynamic and very informative for environmental monitoring of a large watershed. Distances between the river sample points were 10–20 km and the total change of the altitude was 200–400 m. The proposed sampling scheme allows to investigate the changes of seasonal and spatial distributions of the radionuclides in sediment. The statistical correlations between the sampling points, the water level of the river and the contents of natural or anthropogenic radionuclides in sediment were studied. The effect of the intensive leaching of radionuclides from sediments during the flood season is shown and this can be considered as the principal self-purification mechanism.

Radioactive impact in sediments from an estuarine system affected by industrial wastes releases

A big fertilizer industrial complex and a vast extension of phosphogypsum piles (12 km 2), sited in the estuary formed by the Odiel and Tinto river mouths (southwest of Spain), are producing an unambiguous radioactive impact in their surrounding aquatic environment through radionuclides from the U-series. The levels and distribution of radionuclides in sediments from this estuarine system have been determined. The analyses of radionuclide concentrations and activity ratios have provided us with an interesting information to evaluate the extension, degree and routes of the radioactive impact, as well as for the knowledge of the different pathways followed for the radioactive contamination to disturb this natural system. The obtained results indicate that the main pathway of radioactive contamination of the estuary is through the dissolution in its waters of the radionuclides released by the industrial activities and their later fixation on the particulate materials. Tidal activity also plays an important role in the transport and homogenization along the estuary of the radioactivity released from the fertilizer plants.

Marine environmental radioactivity — The missing science?

In paying attention to the specific needs of radiological protection and the protection of man and the environment from ionizing radiation, insufficient attention has been paid to the identification of prime processes which control the distributions of radionuclides. A major omission has been a failure to optimize the use of cost effective direct observational data for the in situ distribution of radionuclides in sediments by autoradiographic techniques. Here I consider the distribution of alpha particle radioactivity, together with some actinides in marine/ estuarine sediments of the Cumbrian coast, England. Today, the alpha particle radioactivity from Pu, Am and Cm, orginating from authorized low level discharges of effluents into the NE Irish Sea from the British Nuclear Fuels plc plant at Sellafield, is associated with three main phases: BNFL hot particles, the minerals haematite and magnetite and hydrated iron oxide flecks which are associated with quartz grains. The receiving environment contains large quantities of industrial iron together with other elements, from haematite mining, blast furnace production of iron, coal mining and phosphogypsum wastes. These wastes have interacted with the radionuclides, but as the industrial activities have now ceased, future distributions of alpha emitters are likely to be different and existing transport-dispersion models may not be suitable. Preliminary evidence indicates that the rate of loss of stable and radioactive elements from coastal waters may have increased. This applies to most of the UK coastal waters. In order to understand the behaviour of radionuclides in marine and estuarine systems, site specific characteristics must be recognized. The use of global values and vague operational concepts in order to account for radionuclide distributions has limited scientific meaning.