In recent years, the North Atlantic and the Caribbean Sea have experienced unusual and unprecedented pelagic Sargassum blooms, which may adversely affect coastal ecosystems and productive ocean. Sargassum has the potential to scavenge trace elements and radionuclides from seawater, and when bioaccumulated and thus concentrated, can pose a potential threat to higher trophic organisms, including humans that consume impacted seafood. In this study, trace elements and naturally-occurring U/Th-series radionuclides were measured in Sargassum that were collected in the coastal waters of the Caribbean Sea (Antigua/Barbuda, Belize, and Barbados) to better define baseline concentrations and activities, and to assess the scavenging potential for these trace elements and radionuclides. The mean concentration of trace elements observed in Sargassum collected across these three Caribbean Sea are ranked accordingly to the following descending order: Sr > As>Fe > Mn > Zn > Ni > V > C > Cd > Se > Co > Cr > Pb > Ag > Hg. 210-Po and ²¹⁰Pb activities in Sargassum were observed to be more elevated than previously reported values.

This baseline study highlights the ²¹⁰Po and ²¹⁰Pb concentration in seven macroalgae species from the northern Gulf that are frequently washed ashore during the bloom season from February to April. The highest concentrations of ²¹⁰Po and ²¹⁰Pb were 2.947 ± 0.032 and 1.057 ± 0.145 Bq kg⁻¹ wwt, respectively, in brown algae Sargassum boveanum, and the lowest in green algae Ulva prolifera with 1.533 ± 0.058 and 0.170 ± 0.069 Bq kg⁻¹ wwt, respectively. A ²¹⁰Po enrichment was observed in both brown and green algae species, with the ²¹⁰Po/²¹⁰Pb ratio being >1 for all the samples. The mean concentration of ²¹⁰Po in all species was an order of magnitude higher than ²¹⁰Pb, and the difference in mean concentration is statistically significant (p < 0.001). At the same time, the mean concentration of dissolved ²¹⁰Po and ²¹⁰Pb in seawater was 0.28 ± 0.01 and 0.52 ± 0.01Bq m⁻³ with a ²¹⁰Po/²¹⁰Pb ratio of 0.54 ± 0.02 indicating that ²¹⁰Po was absorbed from water and more concentrated by macroalgae. The measured concentration factor (CF) for ²¹⁰Po in these macroalgae for the northern Gulf varied between 5 × 10³–1 × 10⁴, higher than the IAEA recommended value of 1 × 10³ which suggests that a revision of that value may be needed. The field derived CFs for ²¹⁰Pb vary between 3 × 10²–1.8 × 10³, comparable to the ICRP recommended value of 2 × 10³.

This baseline study highlights the 210Po and 210Pb concentration in two species of the benthic macroalgae Sargassum from northern Gulf, also known as the ROPME Sea Area (RSA). Within the marine environment, 210Po is initially absorbed from water and concentrated by phytoplankton and macroalgae, and this concentrated 210Po can then readily be passed along to the higher trophic level of the marine food web. The 210Po concentration measured in Sargassum boveanum (22.5–25.6Bqkg−1) was higher than that in Sargassum oligocystum (20.2–22.5Bqkg−1), but is not statistically significant (p>0.064), where as the difference between 210Pb concentrations in Sargassum boveanum (15.3–16.8Bqkg−1) and Sargassum oligocystum (18.4–22.0Bqkg−1) was statistically significant (p>0.019). The measured concentration factor for 210Po in Sargassum in the northern Gulf varied between 0.55 and 1.2×104, values higher to the IAEA recommended value of 1×103. The 210Po enrichment is observed in both the species of Sargassum,210Po/210Pb ratio was >1 at all the stations for all the samples.

Radionuclides levels were determined in indigenous and transplanted mussels (Mytilus galloprovincialis) collected from Turkish marine environment. Radioactivity concentrations of 137Cs, 40K, 226Ra, 228Ra, 210Po and 210Pb were determined in the soft tissues of the mussel samples collected in Bosphorus Strait, Coasts of Black Sea, Marmara Sea and Aegean Sea. Mussel transplantation was carried out by using mussel cages in Levantine Sea coast since M. galloprovincialis did not naturally adapt along the coast. The average activity concentrations of 137Cs, 40K, 226Ra, 228Ra, 210Po and 210Pb in the coastline of Turkey were found to be 0.7±0.1, 469±24, 0.9±0.1, 1.0±0.1, 122±4 and 10.9±0.9Bqkg−1 in dry weight (dw), respectively. The average of 210Po/210Pb ratio was found to be ∼14. Total annual effective 210Po dose was calculated to be in the range of 0.25–3.30 μSv due to mussel consumption. Radioactivity and dose levels were compared with those of similar studies carried out in Mediterranean countries.

The Golden Horn is an estuary located in the center of İstanbul receiving freshwater discharges from two creeks and connecting to the Bosphorus Strait. Activity concentrations of natural and artificial radionuclides were determined in mussels (Mytilus galloprovincialis) and sediments from the Golden Horn sampled in February 2012. Mean activity concentrations of 137Cs, 40K, 226Ra, 228Ra, 210Po and 210Pb in the mussels were determined at 1.03±0.23, 389±41.6, 2.61±1.23, not detected (ND), 91.96±37.88 and 11.48±4.85Bqkg−1, respectively. In sediments, it was observed that 137Cs, 40K, 226Ra, 228Ra, 210Po and 210Pb activity concentrations in<63μm particle fraction of sediment were generally higher than those determined in mussels. Po-210 and 210Po/210Pb ratios in mussels from the Golden Horn were much lower than in mussels from other coastal regions and this was related to low plankton productivity and eutrophication of the Golden Horn.

Climate change effects such as ocean acidification (OA) are known to affect the trace metal distribution. This experimental study provides the first data on ²⁰⁹Po uptake rates and ²¹⁰Po concentration in five microalgae species under different pH scenarios. The experiment was conducted in replicates at three pH conditions 8.2, 8.0, and 7.5, representing the current and future climate change scenario as per IPCC RCP8.5. The ²⁰⁹Po uptake in the phytoplankton was highest in Thalassiosira weissflogi, i.e. 83% of the ²⁰⁹Po tracer was taken up at 8.2 pH whereas the lowest uptake was observed in Dunaliella salina equivalent to 20% at 7.5 pH. Similar behavior was observed in ²¹⁰Po concentrations in these microalgae, where ²¹⁰Po ranged between 3.16 ± 0.03 and 11.6 ± 0.04 Bq kg⁻¹ wet weight (ww), with the highest in the Thalassioria weissflogi at 8.2 pH, and the lowest in Dunaliella salina at 7.5 pH. The difference in ²⁰⁹Po uptake and ²¹⁰Po concentration was statistically significant (p < 0.001) both among species and the pH treatments in the order: Thalassiosira weissflogi > Tetraselmis suecica > Chaetoceros muelleri > Isochrysis galbana > Dunaliella salina and 8.2 > 8.0 > 7.5. A higher concentration of ²⁰⁹Po in seawater was measured at low pH condition in all the experimental tanks. Though the data clearly show the difference in concentration and uptake of polonium at different pH conditions, it is not known if lower pH is affecting the adsorbed or absorbed fraction. A detailed investigation will be required to understand the process as it can have a significant effect on biomagnification and marine food chain transfer under changing climatic scenarios.

In this study, the activity concentrations of ²¹⁰Po and ²¹⁰Pb were determined in different types of bivalve molluscs sampled during the period of May 2014–June 2015 along the Andalusian littoral. Radioactivity concentrations of ²¹⁰Po were determined through alpha-particle spectrometry using ²⁰⁹Po as an internal tracer. Radioactivity concentrations of ²¹⁰Pb were determined through low-level gamma-ray spectrometry. The activity concentrations of ²¹⁰Po and ²¹⁰Pb varied between 40 ± 2 and 515 ± 9 Bq kg⁻¹ dry weight (d.w.), and ND (lower than limit of detection) and 73 ± 10 Bq kg⁻¹ d.w., respectively. The committed effective dose to humans was calculated to range from 39 to 477 μSv year⁻¹. Radioactivity and dose levels were compared with previous studies from other countries.

Copepods are the most abundant metazoans, forming a vital food chain link between the primary producers the phytoplankton and fish. This study presents baseline information on the concentration of ²¹⁰Po among calanoid copepods isolated from the Kuwait marine area. The concentration of ²¹⁰Po in six species of copepod, including Subeucalanus flemingeri, Parvocalanus crassirostis, Acartia pacifica, Calanopia elliptica, Acrocalanus gibber, and Euterpina acutifrons were 151.3–158.8 Bq kg⁻¹ wwt, 121.1–129.5 Bq kg⁻¹ wwt, 51.23–54.91 Bq kg⁻¹ wwt, 38.88–40.09 Bq kg⁻¹ wwt, 38.07–38.29 Bq kg⁻¹ wwt, and 33.46–36.50 Bq kg⁻¹ wwt, respectively.The ²¹⁰Po concentration in seawater shows a seasonal variation, with a higher concentration range of 0.58–0.70 mBq L⁻¹ during summer and autumn, while a lower concentration is found (0.30–0.38 mBq L⁻¹) during winter and spring. The concentration factor among the copepods varies between 8 ∗ 10⁴ and 5 ∗ 10⁵ that is an order of magnitude higher than the diatoms and dinoflagellates.

This study focuses on creating baseline for 238U, 235U, 234U, 210Pb, 210Po and 40K concentrations in the northern Arabian Gulf. The respective concentration ranges were 0.047–0.050, 0.00186–0.00198, 0.054–0.057, 0.00085–0.00092, 0.00051–0.00062 and 18.6–19.1Bql−1. These results suggest that the levels are generally comparable to other marine waters in the northern hemisphere. There were no hot spots observed from oil and gas industry. These data will serve as a baseline to gauge possible future inputs of TENORMs in the northern Gulf. A positive and linear correlation was observed between 238,234U, 40K isotopes and seawater salinity. The results also suggest significant fractionation between 210Po and 210Pb, attributed to rapid removal of 210Po by biota compared to 210Pb. The mean residence time for 210Po in the study area was 371days. The 234U/238U and 238U/235U activity ratios in seawater samples vary between 1.14–1.15, and 0.038–0.040. The 234U/238U and 235U/238U ratio is similar to the expected composition of seawater (1.148±0.002) and 0.0462.

Several species of tuna fish were analyzed for 210Po content in their edible muscle tissues. This study was carried out as a part of baseline data generation around a large nuclear power plant situated at Kudankulam, southeast coast of India. The concentration of 210Po in the muscle tissue ranged from 40.9±5.2 to 92.5±7.9Bq/kg of fresh fish, and the highest activity was recorded for the tuna Euthynnus affinis and the lowest for Auxis thazard. The committed effective dose to the local residents was calculated to be 62.7–141.8μSvyear−1.