210Po/210Pb dynamics in relation to zooplankton biomass and trophic conditions during an annual cycle in northwestern Mediterranean coastal waters

Ocean Acidification-Mediated Food Chain Transfer of Polonium between Primary Producers and Consumers

Phytoplankton and zooplankton are key marine components that play an important role in metal distribution through a food web transfer. An increased phytoplankton concentration as a result of ocean acidification and warming are well-established, along with the fact that phytoplankton biomagnify 210Po by 3−4 orders of magnitude compared to the seawater concentration. This experimental study is carried out to better understand the transfer of polonium between primary producers and consumers. The experimental produced data highlight the complex interaction between the polonium concentration in zooplankton food, i.e. phytoplankton, its excretion via defecated fecal pellets, and its bioaccumulation at ambient seawater pH and a lower pH of 7.7, typical of ocean acidification scenarios in the open ocean. The mass of copepods recovered was 11% less: 7.7 pH compared to 8.2. The effects of copepod species (n = 3), microalgae species (n = 3), pH (n = 2), and time (n = 4) on the polonium activity in the fecal pellets (expressed as % of the total activity introduced through feeding) was tested using an ANOVA 4. With the exception of time (model: F20, 215 = 176.84, p < 0.001; time: F3 = 1.76, p = 0.16), all tested parameters had an impact on the polonium activity (copepod species: F2 = 169.15, p < 0.0001; algae species: F2 = 10.21, p < 0.0001; pH: F1 = 9.85, p = 0.002) with complex interactions (copepod x algae: F2 = 19.48, p < 0.0001; copepod x pH: F2 = 10.54, p < 0.0001; algae x pH: F2 = 4.87, p = 0.009). The experimental data underpin the hypothesis that metal bioavailability and bioaccumulation will be enhanced in secondary consumers such as crustacean zooplankton due to ocean acidification.

Spatial variability in Polonium-210 and Lead-210 activity concentration in New Zealand shellfish and dose assessment

The activity concentrations of Polonium-210 (²¹⁰Po) and Lead-210 (²¹⁰Pb) were determined in shellfish (Perna canaliculus and Paphies subtriangulata) sampled bimonthly from March 2018 to February 2019 from 14 sites around New Zealand. Activity concentrations of ²¹⁰Po ranged from 4.7 ± 1.1 to 324 ± 17 Bq. kg^-1 with a mean value of 57 ± 72 Bq. kg^-1 (wet weight). The activity concentrations of ²¹⁰Pb were lower than those for ²¹⁰Po (0.1 ± 0.4 and 1.9 ± 0.4 Bq. kg^-1, with a mean value of 0.7 ± 0.4 Bq. kg^-1, wet weight). The calculated ²¹⁰Po/²¹⁰Pb activity concentration ratios were higher than unity in all samples indicating that radionuclides are not in equilibrium in shellfish and most of the ²¹⁰Po was unsupported by its grandparent ²¹⁰Pb. No significant difference was noted in ²¹⁰Po activity concentration between different seasons, species or shellfish condition index. Significant spatial variability in ²¹⁰Po activity concentration was observed with elevated ²¹⁰Po activity concentration in two sampling sites: Ninety Mile Beach (mean 257 ± 47 Bq. kg^-1) and Maunganui Bluff (mean 127 ± 22 Bq. kg^-1). Elevated ²¹⁰Po is hypothesised to be related to an increase of ²¹⁰Po accumulation through diet. Individuals who consume large quantities of shellfish (10 g per day or more) from areas affected by elevated ²¹⁰Po activity concentration may be exposed to an annual committed effective dose from ²¹⁰Po in shellfish in excess of 1 mSv.

210Po concentration in selected calanoid copepods in the northern Arabian Gulf

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.

210Po concentration in selected diatoms and dinoflagellates in the northern Arabian Gulf

Marine phytoplankton is a primary producer in the ocean that forms the base of the marine food web and supports the pelagic food chain. The two dominant groups of phytoplankton observed in northern Gulf waters are diatoms and dinoflagellates. The diatoms outnumber dinoflagellates in the Gulf waters. This study presents baseline information on the concentration of ²¹⁰Po among selected phytoplankton in the northern Gulf. The concentration among diatoms varies between 6.99 and 11.4 Bq kg^-1 wwt, whereas a higher concentration range of 8.51-15.41 Bq kg^-1 wwt was observed among dinoflagellates. The diatoms analyzed includes Thalassiosira spp. - 10.2-11.4 Bq kg^-1 wwt; Chaetoceros spp. - 6.99-7.14 Bq kg^-1 wwt; Rhizosolenia spp. - 9.12-9.95 Bq kg^-1 wwt. The analyzed dinoflagellate genera include Gymnodinium spp. - 8.51-8.78 Bq kg^-1 wwt; Noctiluca spp. - 15.2-15.4 Bq kg^-1 wwt; and Karenia spp. - 14.1-14.9 Bq kg^-1 wwt. The ²¹⁰Po concentration in seawater shows a seasonal variation, with a higher concentration range of 0.70 and 0.58 mBq L^-1 during summer and autumn, whereas a lower range in concentration of 0.38 and 0.30 mBq L^-1 occurring during winter and spring. The resultant computed concentration factors vary between 2 ∗ 10⁴-5 ∗ 10⁴ demonstrating a significant ²¹⁰Po enrichment in the base of the pelagic food chain.

Naturally Occurring Radioactive Material (NORM) in seawater of the northern Arabian Gulf - Baseline measurements

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.

Accumulation of 210Po in coastal waters (Gulf of Trieste, northern Adriatic Sea)

The total activity of ²¹⁰Po was determined by alpha-spectrometry in various samples (matrices) collected in the Gulf of Trieste (northern Adriatic Sea) where fresh water inflows, especially from the Isonzo River in the northern part, affect water quality. Observed ²¹⁰Po levels were: 1) 0.56-3.75 mBq/L in the dissolved phase (<0.45 μm) in the seawater column and local rivers, 2) 0.35-3.11 mBq/L (400-2300 Bq/kg, dry weight, dw) in suspended particulate matter (SPM, 0.45-20 μm) in the seawater column and local rivers, 3) 40 (Isonzo River) -158 Bq/kg (in a surface sediment cores collected in a NS transect in the gulf and sectioned to the depth of 20 cm) and 4) 239 (autumn) - 415 to 1800 (spring) Bq/kg (dw) in meso(zoo)plankton (>200 μm). In seawater and tributaries, up to 80% (mean 49%) of total ²¹⁰Po was found in particulate form. In sediments, slightly higher levels were encountered in the Isonzo prodelta and in the central (depocenter) part of the gulf. K_D (L/kg) calculated between seawater and SPM, and seawater and sediment amounted to about 5 × 10⁶ and 6 × 10⁴, respectively. Lower autumn ²¹⁰Po levels can be a consequence of biological dilution by higher mesozooplankton biomass in the autumn compared to spring. Plankton fractionation revealed in general the highest levels in the >200 μm mesoplankton fraction (239-1800 Bq/kg) followed by 50-200 μm (388-996 Bq/kg) and 20-50 μm (318-810 Bq/kg) microplankton fractions. Obtained data show higher ²¹⁰Po levels in all matrices analyzed in the Gulf of Trieste compared to other Adriatic (central Adriatic) and western Mediterranean areas. The ²¹⁰Po/²¹⁰Pb ratios in water, plankton and sediments were mostly below or around 1, while this ratio was much higher at higher trophic levels (up to about 50), reflecting a preferential bioaccumulation of ²¹⁰Po over ²¹⁰Pb. ²¹⁰Po accumulation between seawater and SPM and seawater and mesozooplankton amounted to 3.7 × 10⁴ and 1.1 × 10⁴, respectively, similar to other Adriatic areas. Comparison of the relative importance of pelagic and benthic bioaccumulation pathways, excluding the filter feeder bivalves, suggests greater accumulation in pelagic-feeding species.

210Po bioaccumulation and trophic transfer in marine food chains in the northern Arabian Gulf

The tendency of ²¹⁰Po to concentrate in body tissue poses a serious concern of radiological safety. This study compiles available information and presents recent ²¹⁰Po data for the marine food web in the northern Gulf waters. Since ²¹⁰Po is concentrated in marine biota, a large number of samples of various marine organisms covering several trophic levels, from microalgae to sharks, were analyzed. ²¹⁰Po was found to be highly concentrated in several marine species with the highest ²¹⁰Po concentrations found in yellowfin tuna, i.e. 37.3-44.9, 451-548, and 1511-1693 Bq kg^-1 wwt in muscle, digestive system and liver, respectively. In most dissected fish samples, ²¹⁰Po showed increasing concentrations in the following order: edible tissue, gills, digestive system, liver and fecal matter. Fish feces had ²¹⁰Po concentrations several orders of magnitude higher than that in seawater, fish muscle, and the fishes' ingested food. The high ²¹⁰Po concentration in fish fecal matter suggests that the bulk of ²¹⁰Po content in fish is eventually excreted back into the environment as fecal pellets. In most fish high concentrations were noted in liver, with the highest ²¹⁰Po concentration recorded in yellowfin tuna liver. Moreover, ²¹⁰Po concentration in the soft tissue of tunicate and bryozoan samples were 872-1012 and 402-527 Bq kg^-1 wwt, respectively, far higher than that in fish muscle (0.04-44.9 Bq kg^-1 wwt). It was observed that the maximum ²¹⁰Po concentration in edible fish tissue among the fish in trophic level 2 was an order of magnitude lower than those in trophic level 3 and two orders of magnitude lower compared to fish in trophic level 4. The highest concentrations in the muscle tissue were observed in the following order: tunicate > bryozoan > mollusc > crustacean > algae > fish. Among all the biota analyzed, the highest overall concentration of ²¹⁰Po was noted in yellowfin tuna (Thunnus albacores) indicating a potential biomagnification of ²¹⁰Po in this particular top predator species. In general, ²¹⁰Po concentrations found in the commercially important fish from Kuwaiti waters were comparable to levels that have been reported for similar fish species from several other marine areas worldwide.

Modelling the relationship between zooplankton biomass and environmental variations in the distribution of 210Po during a one year cycle in northwestern Mediterranean coastal waters

To clarify the relationship between zooplankton biomass and the environmental kinetics of the natural radionuclide ²¹⁰Po during a one-year period (October 1995 to November 1996) in northwestern Mediterranean coastal waters, a modelling analysis was applied. Using ²¹⁰Po concentrations in seawater and zooplankton, the ²¹⁰Po uptake rate constant from food for zooplankton was evaluated using a biokinetics calculation involving the uptake and the excretion rate constants between seawater and zooplankton. Using the transfer constants obtained, the ²¹⁰Po concentrations in zooplankton were reconstructed and validated by observed concentrations. The simulation results were in good agreement with the measured ²¹⁰Po concentrations in zooplankton. Assuming that ²¹⁰Po fecal excretion represents the majority of the excretion of ²¹⁰Po from zooplankton, the fecal matter associated ²¹⁰Po vertical flux was calculated, and compared with the observed vertical fluxes of ²¹⁰Po measured in sediment traps. The modelling evaluation showed that fecal pellet vertical transport could not fully explain the observed sinking fluxes of particulate organic matter at 150 m depth, suggesting that other sinking biodetrital aggregates are also important components of the plankton-derived vertical flux of ²¹⁰Po. The relationship between ²¹⁰Po concentration in seawater and that in rain and dry fallout and their potential effect on ²¹⁰Po concentrations in zooplankton at this location were also examined. A similar, but diphased trend between ²¹⁰Po in zooplankton and ²¹⁰Po in rain and dry fallout deposition rate was demonstrated. ²¹⁰Po concentrations in the dissolved phase of seawater tended to diminish as mean daily rainfall increased suggesting that rain inputs serve as a ²¹⁰Po dilution mechanism in seawater at this location.

Linking the distribution of (210)Po and (210)Pb with plankton community along Line P, Northeast Subarctic Pacific

Depth profiles of (210)Po and (210)Pb activity and phytoplankton and zooplankton abundance were collected during two cruises along the Canadian time-series Line P in the Northeast Subarctic Pacific (ranging from 48o39 N to 50o00 N and 126o40 W to 145o00 W) in August 2010 and February 2011 to evaluate connections between the planktonic community and distributions of these radionuclides in the upper 500 m of the water column. Statistical analysis indicates that (210)Po is more effectively removed from the surface ocean when large (>0.1 mg ind(-1) dry wt) zooplankton dominate, and is less effectively scavenged when the picoplankton Synechococcus is present at high concentrations (>1 × 10(5) cells ml(-1)). While the zooplankton field data are consistent with previous lab studies and field observations, the phytoplankton results seem to conflict with recent evidence that small cells may contribute significantly to export in other oligotrophic regions. Differences in ecosystem mechanisms between the Subarctic Pacific and other oligotrophic systems that limit the contribution of small cells to sinking flux remain to be identified.